Can I Make a Small Engine Power My Go Kart?
Posted on April 30th, 2014 by GKG... (GoKartGuru)
Often the question arises “Can I make this 3.5 hp engine make my go kart run?” The answer is, as Archimedes said “If you give me a long enough lever I can move the world.” And he was right, the longer the lever, the easier it is to move an object.
The same goes for drive systems. The steeper the ratio, the easier the engine has to work, and the more likely the go kart will move. The down side is the slower the go kart will go.
That is why in cars they have what is called “Grandma gear” or “1st gear” because the car will go real slow, but be able to pull stumps out of the ground.
On a go kart the way to get the ratio steeper is to increase the driven gear on the drive system. There becomes an obstacle in that the driven gear on the rear axle can become larger than the rear wheel and then actually become a “wheel” itself digging into the ground.
The way to get around this is to break up the rear sprocket into multiple sprockets. We call that a jackshaft. Jackshaft arrangements are used frequently on go karts that are either under powered or are extra heavy.
The go kart plans sold on the GoKartGuru.com web page do not require a jackshaft for normal flat surface driving, however, if the go kart needs to climb hills frequently a jackshaft is required for hills over 10 degrees in slope.
The Go Kart Building 203 Course goes into extensive detail about how to maximize your drive train so that you can get the maximum performance out of the engine size that you have selected for your gokart. In this course charts are first used to demonstrate the overall performance curves for the weight/hp selection that you have selected.
If you want quick answers there is a program that is included with the e-book package, that gives suggestions about what you can do to change the overall performance of your go kart drive line.
Bottom line is that there is an optimum drive system that will work for your go kart, despite the small horsepower that you might have available to you. You make the sprocket large enough, or the ratio steep enough a small engine can move a large load.
The Best Kept Secret About How to Use Tractor Wheels On Your Go Kart
Posted on April 5th, 2014 by GKG... (GoKartGuru)
A riding lawnmower tractor is one of the best resources or goldmines for sourcing parts for a homemade go kart. There are so many goodies on the riding lawnmower that it just makes it the best bargain around for fabricating your own go kart. Typically a riding lawnmower can be had for 50 dollars because the owner just wants to be rid of it.
However, and this is a big however, there are some secrets about how to use the parts that just aren’t discussed because most don’t know what the solutions are.
This article is about taking a riding lawnmower rear wheel and mounting it to a “live-axle” on a standard go kart. You might be inclined to just close your laptop and stop reading this article because “This is just a no-brainer right? I mean, anybody with half a brain knows you just slip the go kart axle into the hub of the riding lawnmower wheel and walla…. (viola actually)…you have an instant cheap go kart wheel.”
Uh….No. Have fun with that…
As I said this article is about mounting that rear axle to the riding lawnmower wheel, so let’s get to it.
There are two types of axles on garden tractors: the splined versions and the ¾ shaft keyed versions. The lower cost riding lawnmowers invariably have the “¾ shaft keyed versions.” We will call them the TQSV (Three Quarter Shaft Versions) for short from now on. Just as an FYI, the splined versions are more difficult to use and require custom parts. That’s where 3d printer and a friend who can do casting comes in….but that for another article.
The conundrum with the TQSV hub is that it is ¾” in diameter and gokart shafts are 1 inch in diameter. There is a reason why the axles on a go kart are 1” and in some cases larger, it is because they will bend if they are any thinner. For example we have a “Will our go kart shaft bend page” on our web site that helps calculate the amount of distance from the frame a wheel can be before it will bend the axle on the go kart. A shaft will bend like a diving board if hanging out too far from the frame.
The reason I say it is a conundrum is that the wheel/hub will not fit neatly onto the go kart shaft.
The axle will just spin in the hub, because the key-way is in the one inch section of the go kart axle. The problem is how to connect the axle to the riding lawnmower wheel?
The wheel can be slipped over the threaded section of the axle, but there is nothing to make the axle and hub connected, or solid.
There are three issues with the wheel and axle assembly that the rear wheel hub will have:
1. Locking the hub to the axle in a rotation (translation: making the axle transmit power to the wheel, otherwise it will just spin.)
2. Locking the hub on to the shaft in a horizontal or along the shaft (in plain English, keeping the hub on the shaft so the wheel doesn’t fall off)
3. Removability: the wheel should be able to be removed for service.
The quick and easy solution would be to weld the rear wheel onto the axle; however that poses some very significant maintenance issues:
1. Removing the axle,
2. Placing chain on the sprockets,
3. Placing bearings on the shaft,
4. Placing the assembly into the go kart….just to name a few.
Welding the axle to the wheel hub is possible for one side, but not for the other side of the axle.
The answer lies in a weld on coupler. The coupler will provide the keyway necessary for transmitting torque to the wheel and then a cross bolt across the coupler will keep the wheel on the axle.
To accomplish this, place the coupler and the wheel onto the axle. The axle will act as a “weld fixture” holding the coupler in place. Prepare the surfaces of the hub and the coupler and then weld the hub and coupler together.
To keep the coupler from sliding off of the axle, a cross bolt will need to be drilled across the coupler. The size of ¼ -20 grade 5 or grade 8 bolt should be used (do not use grade 2!). Do not make the mistake of having the bolt transmit torque. The axle can deliver enough power to shear off the bolt, so the keyway must be used to transmit torque. The cross bolt is only designed to keep the wheel on the axle; this same concept is used on riding lawnmowers frequently.
The importance of the keyed coupler cannot be stressed enough, because this is where the power can be transmitted to the rear wheel. The shear area is much greater on a key than on a cross bolt. A cross bolt has its uses, but more for keeping nuts from turning, or for applications where side loads are minimal, such as retaining a pivot pin.
So to recap, the riding lawnmower rear hub can be retained using a weld on coupler that transmits the torque through the keyway and is retained in place with a cross bolt.
The Coupler is welded to the rear drive hub and then a cross bolt is used to keep the wheel from falling off the axle. A grade 5 bolt or greater is used.
As a side note if there is enough shaft exposed outside of the hub of the riding tractor wheel, then a nut can be used. If using a nut it is essential that the nut cannot loosen. Don’t make the mistake that a large ¾” nut is not going to loosen. It will loosen, with acceleration and braking, the axle hub transmits tightening and loosening torque on the nut and it will follow Murphy’s law and loosen. To keep the nut from loosening (lock-tight WILL NOT WORK), either double nut (jamming a nut on the tightening nut), or castle nut (a special nut that has openings for a cotter pin) the axle hub mount.
A double nut application to keep the wheel from falling off. A double nut acts likes jam nut that can be loosened when needed. It has superior holding power over conventional jam or nylock nuts.
Limitation of Liability Statement:
The Go Kart Guru assumes that you have a full working knowledge of mechanics, and are at least 18 years of age, or accompanied by adult supervision to aid in the project development.
Under no circumstances, including, but not limited to negligence, shall the Go Kart Guru (Gamble Industries LLC) or its affiliates be liable for any direct, indirect, incidental, special or consequential damages that result from the use of, or the inability to use, materials presented here. You specifically acknowledge and agree that the Go Kart Guru is not liable for any improper, welding, material selection, tubing selection, mechanical layouts suggested in any correspondence whether emails, or materials such as plans or web site materials.
The Solidoodle 3-D Printer Go Kart Guru Product Review: Best Bang For Your Buck!
Posted on November 13th, 2013 by GKG... (GoKartGuru)
I have been actively shopping for a low cost 3-d printer for almost 2 years now. At first when I was looking all that was available were wooden versions and semi plastic versions. I have been looking at reviews and examining the best possible values out there.
My consensus: a Solidoodle. My concern when looking at the lowest cost versions out there were they are made out of wood, and had an x-y mechanisms that to me was not solid enough for good consistent parts. The reviews on-line tallied that up too.
I will admit that when we opened the box and started trying to make parts, that I went to bed upset and a little disappointed. The problem was two fold:
- First we couldn’t get parts to stick to the bed
- Second the machine was not making round parts, and they were not even to scale properly.
After about a week of futzing, my boys and I figured out the sweet spot for making parts. It really is simple:
1.) Take off the special Kapton tape and use a slurry of ABS and Acetone. Basically you make your own bed that is as thin as you want it to be and adheres magnificiently to the aluminum bed. Also it does not appear you need to run the heated bed, but it doesn’t hurt.
2.) Run the parts on a lower setting per layer. The unit automatically slows down and that takes care of the out of round parts. Also we reset the y axis, but we are not sure if that was needed.
Now the machine is fantastic. I love the way it is made, the durable nature of it makes it stay in line (or square). We have run the machine for about 10 to 15 hours now and it still is making good parts.
The biggest problem that I can see with the 3-d printers out there is that the parts won’t stick to the platform, due to the adhesion issues. Typically a raft will be put down, but that too comes up because it is relying on a thermal/mechanical adhesion.
The problem is fundamental. When ever you use glues on two opposing surfaces to get the best adhesion they recommend roughing the surface up. The reason for this is to give the glue something to bite into. Glue relies on micro-valleys in the material to make a mechanical bond.
The same applies with 3-d printer bases. A liquid will penetrate better into a surface, than a piece of hot gooey plastic. In fact, the thinner ABS-Acetone material acts like a paint and uses capillary action to suck the mixture into the surface of 3-d printer base. We had such a good adhesion at first that the Kapton tape came up. I think also that the Kapton tape probably dissolves eventually in the acetone as well. Not sure the rationale behind the Kapton tape, because we could not get anything to stick to it.
The ABS-Acetone mixture however, is just the answer. It acts like a micro layer of plastic that gives the part something to melt to. Essentially the whole plate when coated with the ABS-slurry becomes a raft and holds the parts down and keeps it from lifting. (You will discover a third problem with parts is that they want to peal up due to the shrinkage of the material. I am not sure if the ABS-Slurry will entirely cure this, especially with larger platforms, but it will definitely keep the part bonded to the base better.)
The software for the Solidoodle actually works quite well. I am a techy type guy so it took a little playing with it to discover what it can do. Any program really just requires working with it. They have on line videos and those were helpful. So be sure to avail yourself of their videos right away. If I were to make a comment about improving the Solidoodle it would be that the instructions should be a little bit more full. Not that they were insufficient, but to use the software perhaps a video link or something.
A 3-d printer opens up a whole new dimension that was not possible with our CNC mill. The CNC mill requires a lot of thought on how you are going to place the part, what tools you are going to use to rough out the part and so on. It also makes a ton of noise and eats up a lot of motor electricity. When I am working on getting a rough idea about a prototype and whether it works, the 3-d printer will get it done in a few hours at a click of a mouse.
The other day, I woke up and started the Solidoodle. Let the unit warm up and had breakfast. Came down after breakfast, and loaded up a model and went to work. The kids later that day took the model off and gave me a report one what happened with the part.
The other day for example we designed a potential product in one day. Outside our house is a ground post that the house is hooked too. It is first off an eyesore and two a potential hazard. I asked my 13 year old son to model it up on our 3-d software (Alibre) and then show it to me. We sat together on the couch and refined the model. Then we ran it just before bed. By 11:00 the model was done.
The next morning we tried it out, painted it and put it in place. Now we can refine the model to make it stronger if need be. We designed and developed a product in two days. Without a 3-d printer prototyping it could potentially have cost thousands of dollars, with little tweaking available.
So needless to say, I am pleased with the printer and most especially how much value I received. The Solidoodle is a 500 dollar unit (plus shipping). We opted for the unit with the heated table. In retrospect I still would get the heated table, I think it does help keep parts on the table, even with the ABS-Slurry.
If you are a family with kids who love to tinker, a good investment would be some 3-d software and a 3-d printer. Oh and by the way I was going to make my own unit, but after looking at the Solidoodle and the complexity of it, I would suggest just buying a unit, the headaches you will save might be worth the 500 dollars after all. To me the object is making parts….so that’s what we are doing. Maybe we will print out parts for our next machine….hmmmm.
Don’t Spend an Arm and a Leg on Nuts and Bolts!
Posted on October 27th, 2013 by GKG... (GoKartGuru)
I will be honest, the last thing I think about for the Go Kart is nuts and bolts. Nuts and bolts are cheap and really should not be something to worry about…right?! Uh….Wrong!
I almost fainted the other day when I was putting together our wood gokart. We needed some nuts and bolts and I thought we could just run to the local hardware store, use my 5 dollar off coupon and end up with some free hardware.
Wow, by the time I walked out the door, even with the coupon the cost for the bolts, nuts and washers was almost 20 dollars!
I was having a hard time coughing up the money, even then, but I thought I could use this as an opportunity to compare. We were out, so I thought I would shop elsewhere and see how much different if at all the prices for nuts, bolts and washers was going to end up being.
First of all nuts, bolts and washers are not all the same grade. These are the types of grades that you can get at hardware stores:
Okay, what do these grades mean? Quite simply the higher the number the better. However, for sake of clarity I will spell out the differences:
- Grade 2
Grade 2 bolts are basically as step above construction grade steel rated at 55000 psi. You will find that grade 2 bolts are very prone to stripping threads, bending and shearing off.
- Grade 5
Grade 5 bolts are rated at approximately 85000 psi strength. They are what I would call the minimum grade that would be acceptable for any type of equipment, whether it be lawnmowers, snowthrowers, tractors and go karts. It is pretty tough to strip the threads on a grade 5 bolt.
- Grade 8
Grade 8 bolts are rated at 120,000 psi strength. These style bolts would be on the upper end of strength, and if given the chance and the price comparison, I will choose a grade 8 over a grade 5 depending on the application.
Where to use grade 5 versus grade 8 bolts:
- -.625 axel spindles for steering mechanisms: grade 8
- -Steering hardware: grade 8 (rod end bolts and steering assembly mount bolts)
- -Engine mount bolts: grade 5 or grade 8
- - Manifold mount bolts: grade 5 or grade 8
- -Bearing retention bolts: grade 5 or grade 8
- -Chain Tensioner – grade 5 or grade 8
- - Brake Mount bolts –grade 5 or grade 8
- -Steering Wheel mount bolts – grade 8
Shopping for bolts should not be a spurt of the moment thing, where you have to run off the hardware store just to assemble the go kart. A pretty comprehensive list should be put together so that you can get the project going, plus you can always over buy and return later. Keep your bolts in the bag you bought them in, plus keep the receipt handy so that returning is not so painful.
By the way, the washers, nuts and bolts that I bought at the hardware store, I returned because I was able to find them at almost 1/3 the cost at a different store that sold their hardware by weight versus by cost per bolt and nut.
You will always get a better deal if you can buy them by weight. Sometimes the one store may be closer than the other and that may be the convenience factor, that my cause you to spend 10 bucks more. I try to save money, because I can always use it somewhere else on the go kart.
Be very leery of preassembled hardware kits, because typically they will not have the quantity you need and also they will be of low, low quality grade 2 bolts not really useful for any dependable project.
Be aware also, that the higher the grade, the higher the cost. The best value, is the grade 5 bolts because they can be pretty much used anywhere on the go kart. They have high strength and comparable cost to even a grade 2 bolt. It is well worth it to spend the extra money on grade 5.
To sum it all up, buy grade 8 if cost is no option. Buy grade 5 if you are on a limited budget. Also, buy your nuts, bolts and washers in bulk or by weight not by per piece unit pricing. You will be amazed at how much you can save just by buying them in bulk or by weight.
10 Things You Wish You Knew Before You Started Your Go Kart Project
Posted on October 19th, 2013 by GKG... (GoKartGuru)
In my adventures over the years I have fallen into the trap of putting pressure on myself to make go karts out of junk, out of old tractors, old vertical engines, out of wood….this list goes on. I am a little special in that I try to put myself into the shoes of the guy who has nothing, but wants to have some fun with the junk he has sitting around.
There is a two prong approach to this effort in my mind. I want to get that gokart running and for cheap, but I also want to teach and help others understand the principals behind mechanisms, engines, and vehicle dynamics.
That being said, there are ten things that I had to discover for myself and as hindsight is always 20/20 I am relaying them to you here….
To start the list off, the drive line is so important. Not having the right driveline is like having a Porsche 911 that is pedal powered. It can be the most exasperating and exhausting elements of the gokart if not designed properly. You may have an awesome running engine but a gokart that just smokes the clutch and doesn’t go anywhere.
If I were to tally up the complaints on go karts it would be the drive system. For example on our Wooden GoKart, the Phi Alpha 20 we did our due diligence in the beginning on the drive line. We had limited components, but with the calculations program included in with How To Build A Go Kart 203 book we designed our driveline exactly as the program told us, and came up with an awesome accelerating machine that can climb hills and bop around yards.
The vertical engine drive system falls into the same category, though it is a bit different, it too can be tuned to fit optimum hill climbing conditions. That is why we include our vertical engines drive course (Go Kart Building 202) with all our bundles, because we know the importance of getting the drive line right.
I’ll let you in a little secret, there is no ONE SIZE fits all drive line, each one needs to be tailored to your go kart, and the Go Kart Building 201, 202, and 203 courses explain how drive lines work and how to get the optimum out of it.
Often I am stuck with time constraints and the balance between what I can scrounge, what I can make , and what I should buy. The answer to that question is first what do you have that you can use on a gokart? You may have a 30000 foot level understanding. For example you have a riding lawnmower and you know you could probably use the wheels, the steering wheel, the engine etc.. But the hard question to ask yourself is: How can you use the wheel and hub on a go kart?
Another prime example of using stuff off of a lawnmower is using the rear wheels and tires. They are fantastically huge and have plenty of wear left. But the conundrum comes into mating that wheel with an axel. How is it possible to get a 1 inch live axel to drive a .750 inch diameter hub? If you study our blog article on hub-axel transformation you can get that answer. The point I am making is, do you know how to do it? If you do not, or you have come to the conclusion it is not possible to do, then that answers your purchasing question: you will have to buy rims and tires.
There are a host of other items on the go kart that require that decision, can I use it? Or do I need to buy it. I have developed whole go karts and in the end I have come to the conclusion, perhaps I should have bought that part.
This is a small list of parts that if you are not mechanically inclined or don’t have the ambition to fabricate stuff that you should buy:
- Front Steering Knuckle Assemblies
- Rod Ends and Rod Stock for the steering
- Rear Axel
- Rear Bearings
- Brake Caliper
- Brake Disc
- Steering Wheel (yes I said steering wheel, unless you know how to mate a tractor steering wheel to a splined shaft system….stay clear and buy a simple steering wheel.)
- Rear Drive Sprocket
After you have made that list of stuff to buy, then you will complain, “Well golly that is expensive! I was hoping to spend less.” That is where you need to have tallied up that list before you start buying stuff.
That’s right; I said make a list. Tally up the list, and here is the hard part…walk away and think about it for a day or two. Then come back and start weighing the list. Do you have some of the things in the list above that you could perhaps not buy, like rear wheels and hubs? How much could you save by not buying that stuff?
In my opinion, you can make a seat, you can make a frame, you can make a decent steering system. Are you willing to make it, or are you stuck on buying it?
Stopping a go kart is actually quite important, especially when the chain link fence is showing its mean acing existence. Stopping the go kart there is not enough that can be said about it. So if stopping the go kart is so important then why is it the last thing we think about when we design and built our go kart?
The best and most sure stopping power is to have both rear wheels have brakes. The simplest system is the live axel, where a brake disc can be mounted easily and the brake caliper mounted to the frame.
When turning the steering wheel the last thing you want to have happen is that the front wheels continue to go straight. We call that severe understeer. You want good steering response, and the center of gravity is the answer to this problem. Getting enough weight on the front wheels is the problem and positioning of the front wheels is the key to solving this problem. We offer as a free download the center of gravity spreadsheet which allows you to calculate the center of gravity before you develop your gokart design. We used the spreadsheet on all of our go kart designs with success.
When you have the go kart all completed and it drives like a dream, it is tough to share it, because it only has one rider. Because the go kart that was developed for a larger person, such as an adult, the smaller “eager-to-have-a-thrill-rider” misses out because the go kart only seats one person safely.
So the bottom line is consider the number of riders as one of your top priorities when you develop a go kart. This decision will affect the drive system drastically, because now the 5 horsepower engine may now need to be an 8 horsepower, or at least the drive line will need to be tailored to a 5 horsepower so that you still get the thrills.
Also the brake system needs to be upgraded to handle the extra load.
If you haven’t guessed yet but are now figuring it out, it takes some thought when building a go kart and not wanting to bust your budget.
Tip # 7
The glossy eyed go kart lover may want to cut corners and try to use anything available like bike tires or solid style tires used on push mowers. Stop! No you cannot use these wheels safely, the power and the demands of go karting will destroy them. Likewise don’t be fooled into thinking that the Chinese knock- off- 5-dollar wheels and rims are going to last. They might last an outing, but the bearings might be toast after that. Also the rubber specked out in these tires is so totally cheap that they will wear through in minutes. A high quality rubber tire and rim is needed.
I have run into this brick wall a couple of times: bearings. More specifically, front wheel bearings. The wheel bearings (or even bushings) that are on tractor tires or cheap rims will have ¾” diameter bearings. These cheap bearings cannot take a large amount of load before they literally eat through the casing and then fall apart.
Be very leery of these cheap pressed bearings. You need industrial grade radial sealed bearings. The problem is that the inside of the hub will only mate up with a 5/8” roller bearing. To remedy this problem either the steering knuckles that you just purchased need to be modified so that they can take 5/8” bearings, or you need to fabricate your own.
Careful purchasing of steering knuckles with the 5/8” diameter shafts is required, or you will need to modify the steering knuckles that you just purchased and weld on a grade 8 bolt to replace the steering knuckle bolt.
When constructing a steering system it is important to take into account the amount of steering effort that may be required to turn the steering wheel. You may be surprised when you start putting camber and castor into your system the amount of effort required to turn the steering wheel. The reason for this is that the camber and caster put the front wheels at angles which in effect cause the steering to leverage or lift the gokart into the air. This added amount of leverage can be quite a problem when trying to turn the wheels. Be aware of these consequences.
For simplicities sake and for the sake of steering ease, you may want to nix the camber and caster, seeing it is just a go kart, not a Ferrari and a Lamborghini. If you are not willing to nix the camber and caster you may have to make a ratio reduction into your steering system to make the steering easier to turn.
Additionally, when making a two seater gokart the steering forces increase because of the weight. Make sure all the steering linkages move well when a load is applied. What can fool you is when you have the go kart on the stand and all appears to turn and move well, but when the go kart is put on the ground all the tire and friction forces come to bear.
To minimize friction make sure all surfaces are lubed well and that the contact surface between the steering knuckles and the channel housing are not binding but have minimal slippage.
Don’t be surprise with all you busy schedules if the go kart does not get completed in a summer. You really have to have a game plan or as I call it a Realistic Gokart Building Schedule. We offer as a free download the building schedule in our download section.
Realistically if you have your act together you should be able to get a ready and running go kart in 7 weekends.
These Ten tips are by no means exhausting but they do help with the major road blocks to go kart building.
Be sure to stop by our downloads page or sign up for our free newsletter to get access to our downloads page. The downloads have products that are a great help for accessing your center of gravity and basic stress calculations.
Suspensions and Unsprung Wieght
Posted on March 10th, 2012 by GKG... (GoKartGuru)
I watched a couple of your youtube videos on suspensions and have a question.
I completed a clutch driven go kart with stub axles and no suspension, but would like to add a torque converter. So I’ll need a live axle, and i thought I I’d add a suspension while I’m at it. The easiest way would be to put the whole rear part of the kart (engine and everything) on a hinge. But I’d heard that a good suspension system minimizes unsprung weight. Having the engine unsprung would seem to be a bad idea. But as you show in your “pitfall ” video, the independent rear whepel suspension looks pretty complex and expensive. I plan to use it mostly off road. It has an 8 hp engine.
The unsprung weight issue becomes more of a problem if you are looking for high performance applications such as Baha racing and so forth.
The purpose of having a low inertia suspension is to have it return to its relaxed position quickly, so that it is not bottomed out and essentially becoming useless.
The suspension is designed to absorb the impacts that an irregular road surface exhibits. The trouble is if you are driving along at 50 mph on a road surface in car and then you encounter a corner with a ton of bumps in it, you want the tires in contact with the ground so that the vehicle will react in turning the car around the corner instead of having intermittent road contact and essentially going straight and off the curve.
The suspension weight or mass dictates how fast the suspension is going to react. The lighter the quicker the suspension will react. The reaction is for two purposes:
1. Good road contact for optimum directional response
2. Bump absorbtion
We mentioned the good road contact previously, but the bump absorption can be equally important in that the vehicle needs to be able to continue to absorb impacts. If the suspension is bottomed out, and wont return it essentially is now a solid brick and what hits it now will damage and bend elements in the vehicles such as drive shafts and rims.
On a go kart, the MPH on a rough road situation is not going to be much more than 10 mph. Suspension response may not be as critical in this situation. Having the suspension respond quickly is really the question here. Is it essential on a go kart?
Depends on how much money you are willing to spend. If money is an issue, then the compromise of using the total flex rear is acceptable.
On thing of note on the flexible rear suspension is that the engine should be kept as close as possible to the hinge point as possible, this will lessen the Inertial moment that is require to be rotated. The nice thing about making the whole rear move together is that the drive line is much, much simpler and durable.
The chain does not need to be worried about, because the engine and the drive axel relationship doesn’t change, and so the chain will not lengthen and shorten as the suspension moves up and down. This is a big plus.
So to recap,
The suspension mass is critical for:
1. Suspension response and tire contact for good vehicle performance
2. Suspension response is important for the next bump, will the suspension be ready, or will it be bottomed out.
Low suspension mass is important for fast moving vehicles that encounter large bumps and repeated hammerings. Baha vehicles for example are designed for speed, vehicle cornering performance, and bump absorption.
How Does the Rear Sprocket To Tire Size Affect Overall Speed and Performance?
Posted on January 29th, 2012 by GKG... (GoKartGuru)
Question: Does increasing the rear sprocket size to be the same size (or nearly the same size of the tire) cause the go kart to loose speed, especially as the tire gets bigger?
The question is a peculiar one especially for those that are making their own go kart and are wondering what ratio would work best on the go kart.
The question is this again, broken down into pieces:
The rear sprocket is the same size as the tire. If the tire gets bigger (and the rear sprocket correspondingly grows with the tire), what happens to the performance of the go kart?
Actually, nothing. The speed does not change, and the acceleration does not change.
I thought the answer I gave was preposterous myself, until I did the math. The following chart shows the corresponding Drive Wheel/Sprocket Sizes versus the overall top speed and acceleration (based on a 5 horsepower engine and a 300 pound gokart):
As the wheel diameter changes (the sprocket diameter changing proportionally with it) the top speed (MPH) and the acceleration (FT/S^2) does not change; they remain constant.
It is hard to grasp that as the sprocket and wheel grow together in size, that the overall performance would not suffer, but it does not.
So what does that mean for the go kart drive line enthusiast? The rule of thumb stands, keep your rear sprocket as large as possible (as close the wheel diameter as possible) and you will have a decent go kart performer.
As you notice, the ratios in the list all change starting from 6:1; 8:1, 9:1, 14:1 17:1. So the ratio does not tell the whole story, but is a start.
So how does this knowledge practically apply to a go kart?
If you for example are building a wood go kart, and the rule of thumb is being applied to have the rear sprocket (or pulley) as large us the rear tire, then what if you upgrade to a larger tire, from your small 7 inchers that you currently have? The rule of thumb still applies; you will have to make a larger pulley (or sprocket) to make the gokart perform like it did before.
Just in case you are thinking that you do not need to increase the sprocket diameter, because you increased the tire diameter, then you are going to run into stalling smoking clutches, and burning belts.
For more information about drive lines and computer program to help trouble shoot your drive line problems, go to the http://gokartguru.com/go_kart_building_203.php. In this course you will learn how to calculate and make your own drive line system that will allow your go kart to climb hills without smoking the clutch.
Don’t be caught making a go kart and then have the drive line be the major headache. And you don’t have to spend a lot of money on drive systems, such as a fancy clutch, just to get what you want.
Again, the go kart drive line course has a computer program that helps maximize your drive line for optimum acceleration and hill climbing performance. Stop scratching your head, and get the answers explained and at your finger tips.
Wood Go Kart Steering Basics
Posted on January 3rd, 2012 by GKG... (GoKartGuru)
The wood go kart steering is based off a bogie mechanism where the front wheels are mounted to one axle and the main axle on the front pivots at a center point. The bogie concept is based on basically a wagon geometry however it is very efficient as far as vehicle dynamics are concerned, because it has a true arc path.
In order for the bogie system to maintain stability it must be constrained in the z-axis. What I mean by the z-axis is that the up and down motions of the axle system are not allowed to move. The side to side motions the x-y motions are allowed however the up and down motions are not allowed.
The reason for the constraint of the axle system is to keep it from suddenly jumping up in the air and causing an imbalance situation.
The main constraint with a bogie system is trying to get it to connect to the steering mechanism, such as a steering wheel. The basic way to make a bogie system move is through a cable system, where the steering wheel is turned and the cables are pulled in and retracted on one side and extended on the other side.
The rule of thumb is that when the steering system is set up, the ropes are wrapping when the steering wheel is turned to the left. The left bogie is pulling in in other words and so the steering drum is rotating counterclockwise and is pulling the rope in from the left side. The right side is correspondingly extending the same amount of rope that the left side is.
- Angle of Steering Wheel Vs Angle of Bogie System. This graph is important for choosing the diamter of the pulley diameter for the main steering system. Additionally, it gives you an idea of how much steering resistance to expect. As you can see the bogie system has this main issue when designing a wood go kart.
The relationship between the steering pulley diameter and the amount of steering wheel rotation is shown in the following graph. When you have a 2 inch diameter drum it takes approximately one full turn to get the full angling of the steering bogie system. This angling is approximately 26° to 30°. To get a 180° wrap or turn on the steering wheel the steering drum needs to be around 4 inches in diameter.
The downside to making the drum larger is that the forces double. So that at a 2 inch diameter drum the amount of force required to move one side of the steering wheel is 12 pounds. When the steering drum is increased to 4 inches the amount of force required to move the steering wheel is approximately 20 pounds or more.
If a larger steering drum is desired to restrict the steering wheel movement then friction reducing materials are required to make the bogie system not bind up.
In order to make the bogie system not bind the bogie can be lubricated with grease on the bottom rails of the frame. This will allow the bogies to slide back and forth with greased surface. If for whatever reason the grease is not working out as well as it could, the bottom frame rails can be coated with either a plastic material such as a polyethylene strip, or a stainless steel plate, or a copper sheet, or a galvanized piece of steel sheeting. It is important not to have any fasteners in the sliding surface areas otherwise the fasteners will catch and bind up the steering mechanism, more specifically the bogie mechanism will get bound up.
The bogie system itself needs to be coated with plastic or a steel material as well to reduce the friction between the two surfaces. Grease should still be used regardless of whether or not you use steel or plastic so that the surfaces will slide easily.
Use of steel cables is appropriate, however, roller surfaces will be required to make the cables not bind up or cut through the wood frame work. Ropes can be used however a very strong expensive nylon style rope is recommended so that the rubbing action does not deteriorate the rope quickly.
It is recommended that the ropes be replaced every year.
Additionally the rope should be greased on every rubbing surface to make sure that the friction is reduced.
A rule of thumb about friction is that if any of these mechanisms are making noise such as squeaking noises then the surfaces should be greased so that the noises go away. Additionally the amount of force should be noticeably reduced when the surfaces are greased.
Tightening The Ropes
Tightening the ropes is accomplished by tensioning one side with a wrench. What essentially occurs is that the retention bolt becomes a mini tensioner device. The rope will be wrapped as the bolt is twisted. The compressive action of the bolt against the tube-washers will cause the rope to become blocked or bound in a tight position.
To tighten the ropes the steering mechanism is turned full to one side. Then the other side is tightened with the ratchet bolt mechanism until the slop in the mechanism is gone.
The actual diagrams for the rope layouts and the steering assembly are provided in the Wood Go Kart Building Series; and is explained in further details in the Wood Go Kart Video.
A DIY Home or School Project Well Worth Looking Into….
Posted on August 13th, 2011 by GKG... (GoKartGuru)
One thing I like about projects is that they are mini building programs. Ever onward, ever upward, step by step, plug along until you finally see the fantastic results.
Go Karts as you know are those types of projects, but as you well know too, once the go kart is done, then what? Well of course another go kart, or tweaks on the existing go kart. But today I am going to seek to expand your horizons into other areas.
One thing that go karts do is teach you mostly physics, mechanics and some minor electrical. I remember growing up and my Dad was saying that electronics was the next wave. In fact I had my choice, I could have gone into Mechanical Engineering or Electrical Engineering, or even become a Doctor…but I chose what I was comfortable with: Mechanical Engineering.
I chose Mechanical Engineering because it was something I could touch and feel. To be quite honest I never was introduced well to the field of Electrical Engineering, other than by those who said “It is really hard, very math based.”
Needless to say, by the time I was half way through college I could see I could probably do Electrical Engineering, but I probably would not be as happy there, so I stuck with the mechanical world.
But this article is about opening up new horizons. DIY Home School Projects are an excellent format for exposure to many high tech fields. The downside to conventional education is the 8 hour day restriction. Additionally, the restriction on free thinking or stepping outside the box is generally discouraged. With many public schools shrinking their budgets in the tech areas and deferring their tech courses to colleges, the actual ability to get your hands dirty and do some tech stuff will not come until it is time to get a full time paying job.
And that is the Catch Twenty Two (or bite in the rear you did not expect) the business owners are looking for experience, especially in these tech jobs.
So let’s be real where to you get tech experience? Where do you get your hands dirty?
Projects are the backbone to any career choice. Or more specifically can show people what you can do with your own two hands, or your two brain halves.
The go kart project when done right gives you an edge in a world of mechanical design. Also fundamental to go karts is engine repair and upgrade. (We don’t go much into that on this site, but I am planning on releasing a book on engine diagnostics. Whether it will exhaustive remains to be seen. )
The project I am proposing involves multiple disciplines, mechanical, computer, and electrical. The nice thing about the times we live in is that pioneers, ones that I went to school with, developed software and wrote programs that are extremely useful to a mechanical engineer. Additionally, the electrical engineers for the most part service the mechanical world providing electrical plug-in solutions to a complicated mechanical problem.
For example an electrical engineer may provide a cam actuation package that involves servo motors and other electronic goodies versus a complicate cam profile that is fixed. You may not understand that last comment, “fixed cam profile.” But the best a mechanical world can muster is a one stab approximated solution, whereas the electrical world applied to the mechanical world opens the world of variables to the engineer.
With a push of the button a cam profile on a starving engine can be changed with a network of electrical sensors and computer mapping programs, or even better yet get real time data and give the best solution to the combustion problem at that moment.
What does that mean to the mechanical world? More Power! More speed for less weight. Moooore!
Okay just what is this project? The project involves like I said is multidiscipline but is yet in the young person’s grasp.
Okay what is it?
Well I can tell you what it isn’t…
It isn’t boring, it isn’t going to sit in the corner and never be used. It isn’t a go kart, but it could make go kart parts, perhaps….
Alright I almost let the cat out of the bag right there…
It is a Do It Yourself 3d-printer. There are about three different manufacturers of ready to build 3-d printers. They can be either ready built or they can be assembled by yourself.
A 3-D printer is a printer that instead of just printing a sheet of paper with a .0001 inch of material (such as ink on the paper) prints over and over again and starts building off of the paper and makes a stack of ink. Typically a 3d printer uses a nozzle or syringe to dispense material down and then build upon that material to make a 3d object such as a human skull or a carburetor intake for a go kart, or better yet supercharger component for the racing enthusiast.
Another way to look at 3-d printer is that they are the inverse of CNC machines. Instead of starting with a chunk of material and wittling it into a shape like a CNC machine, the 3d printer builds up material and makes the shape at the first.
These projects are not for the timid, or those that give up easily. These printers are projects that tax the mechanical genius to be efficient, the computer geek to use his skills and the electrical guru to come up with something better.
I have been watching this DIY 3d Printer field for a while now. What has spurned this urgency for this field is that though CNC machining is powerful, I believe 3d Printing has more power to it.
From a set up stand point there really is none, other than turning the printing on. With a CNC mill you have to be very careful and have everything homed in and placed carefully. Additionally the CNC mill is noisy and messy, the 3d printer is much, much quieter and there is less dust and waste.
So our project is going to be Project 3d Printer and we will see where it leads us.
You may be wondering why the change in focus? This is a go kart site. Unless you think I have lost focus fret not….remember what you can do to go karts? Supercharge them? Fuel inject them…the 3d printer can get us closer to that goal in less time that a CNC machine, because we can make mistakes without fretting. Do a redo overnight….
The next article will be comparing the different types of 3-d Printers and the directions that a DIY 3-D printer enthusiast can go with relatively low cost….
Making a Free Wheeling Coaster Brake Drive For a Pedal Go Kart
Posted on June 25th, 2011 by GKG... (GoKartGuru)
I have been racking my brain on how to develop a rear coaster brake system for a pedal go kart for a while now and it dawned on me the other day that I was making it too complicated.
It does however require two bicycle rear ends to complete the task but in reality it is quite simple.
The way it works is that the coaster brake rear end from one bicycle is made to drive a solid drive axel.
Coaster Brake Assembly with spokes removed
The wheel hub will need to be de-spoked. A sprocket will then need to be welded onto the wheel hub. This sprocket then will drive the rear axle.
The lower rear section of the bicycle should be retained and mounted into the framework the go kart. It is important to maintain a workable drive ratio, and typically 1 to 1 drive will work best for the weight involved on the cart.
Ideally the most robust drive uses the bike frame work (cut back of course) because it has metal frame work. If you cannot afford to use the bike frame work, then metal plates are the next best option. The metal plates are fixed into the frame work using sheet metal screws or lag screws.
Free Wheel System Put Into Pedal Go Kart System. The rear (grey system) sprocket is fixed to the main drive shaft.
When using a bike coaster system, a basic understanding is needed. The way it works is that the hub drives the wheel and the inside of the hub acts as brake. So in action (as many of us grew up with) the pedals cause the bike hub to turn in one direction, coast in the other and then brake when the pedals are reversed.
The important note in all this is that there is a brake arm that hangs off the opposite end of the drive hub. This brake arm needs to be fixed to the frame work; otherwise the brake will not work. What will occur if the brake arm is not fixed is that the brake arm will tend to rotate when the brake is applied. So fixing it is important.
As you have been guessing, at least two bike systems are needed to make this drive system work. The reason I say that, is because the drive ratio of 1 to 1 is needed, and in order to attain this a large sprocket in the rear is needed. This large sprocket will be removed from a pedal system off of another similar bike. Then this sprocket will be attached to the smaller drive sprocket on the coaster brake system. Because of the forces associated with the pedal go kart (mainly how heavy it is) a ratio of 1 to 1 or even higher is needed.