July 23rd, 2014

Go Kart Suspension Systems: How Do I Build One?

Again, I hate say this, but every time anyone of us sees a go kart and we see

Other Articles/Videos on Go Kart Suspensions:
Video 1 On Go Kart Suspension
Video 2 On Go Kart Suspension

Developing Calcs For A Suspension
one of these fancy ones with suspension on it, we look at it and we are like: 

“Whoa!  That looks expensive!  It it really necessary?  Man how would I actually build that?”
Well suspension systems by their nature can be complicated because of how the wheels hit the ground, that is the most complicated part of it.    

The second complication is the linkages, for instance the steering linkages, the center lines so that are not out of sink and cause the wheels to move when the suspension is flexed.  

And thirdly you have the drive components which you are trying to convey the drive power through the suspension component.

 

Fourthly, how do you actually get the suspension to be springy? 

And I hate to keep going on , but Fifthly, How do I actually configure my suspension system?

All of these questions need to be addressed when you are dealing with suspension.  I am not trying to make it sound complicated, but it can be, were trying to get a lot done, make  a lot happen in a small area.  That really is what a suspension is.

So you need to take great care in your design, to make sure the suspension is not faultily designed, in other words, the angle of the incidence and all of the other five criteria are fulfilled, otherwise you are going to have some sort of problem.

What Does a Suspension Do?

We should explain what a suspension does, so you will get a better direction where you are going when you decide to make a suspension.

First of all suspension is designed to take impacts.  A vehicle is flying down the road, and when you hit a bump, it is designed to flex so that you don’t have to make the thing super stout to handle the stress.

Secondly, it is designed to absorb impacts so that the rider is not jostled around.  You can actually damage someone if you are going over a rough road.  You can jar them around so sufficiently that they can become sick, or they can become disoriented, or actually brake bones, or  even rip loose organs inside.  You have to be very cognizant of the fact that suspension systems have their place especially if you are in bumpy territory.

For the most part, the go karts found on this web site are designed for flat pavement.   For instance a semi smooth driveway.

Suspension Types

Now the basic suspension systems out there are:  rhomboid style suspension (really all that is saying is that you have a parallelogram that each wheel runs in.  That is a four wheel independent suspension.)  

A compromise is to have the front wheels have the suspension components and the back to be one system that bounces around.  That would be similar to a two wheel drive suburban.  The suburban has a live axel and the front wheel are actually suspended by the parallelogram system.

A third system is where it is a trailing arm style system.  And that is used on the front primarily and in the back you have your conventional suspension component where actually the whole engine system moves.  It is hinged.

There are variance on all three of those.  The most prominent ones you will see on dune buggy style is a four wheel suspension system.

Successfull Systems

The most successful that I have seen, which is the simplest,  which is actually a trailing arm system.  Which is very similar to the rear suspension on an old Volkswagen bug or a porche 944.      The component of the suspension hinges forward and bounces up and down in one plane. 

You will see that a lot on foreign cars these days, where they have a three point suspension.  There are two points that hinge for below and then there is one point for above.  That is basically the strut.   Those are perfectly acceptable systems.

Handling Problems With Suspensions

The biggest problem that you are going to run into with the suspension, is that when you do a corner the body will shift.  It will roll.  And when it rolls over towards the curve it tends to make the wheels go on their sides.   And in doing so  you will actually put yourself in an instability situation where the vehicle wants to roll more. 

Now you are not going to be able to do everything that you want to with a  four wheel independent suspension.  You are not going to get it corner exactly the way you want.  But what I have seen is that people is that people will put their wheels at angles, so that when it wants to go into a roll that at least the tire is not going over on its side and it tends to push it back over and handle the corner much better. 

So you need to keep that in mind, when the suspension goes down, what is the final angle of the wheel when it is in full up position, or at least in a corner position: what is the angle of the wheel?    You would like to have a vector type angle, where it actually leans like a motor cycle into the curve when you are turning.    You get better use of your tire that way. 

Trailing Arm System

I wanted to talk about the trailing arm system, and I did not talk about it really well.  There are two different types.  In the front you can have a trailing arm that goes with the body, or you can have a trailing arm that goes across the body.  Either way is acceptable. 

Again, when you have a suspension system, you want to make sure (especially on the steering) that the steering is taken care of because that will be the most complex part of your front.  Make sure that your steering rods, your tie rods,  have  place to go and are in the center, or at least don’t change in their position relative to the steering wheel.  

Now I suppose you could make a suspension system where the steering wheel and the whole steering system moved together then you would eliminate that problem.  But it might get  a little disconcerting, get a little distracting if your steering wheel is constantly moving around.  The idea is that you are not moving as much as the frame work is moving around.   

Platform Engine Suspension Problems

Now the suspension that you will see out there where the engine moves on a platform, the weakest point actually is at the hinge.  It have seen it many times where the hinge point is not designed for the amount of flexation that was occurring on the  gokart.  It was used over the summer, and by the time the summer had  ended the whole engine rear end ripped off.  Needless to say it had to be rewelded and gusseted.  So you want to make sure that if you are making that style of go kart that it actually can handle the stress.  Put ample attention into the hinge and how the hinge is mounted to the frame work. 

You don’t want to over build it, because you do not want it to be too heavy.   But at the same time you don’t want to under build it either.

Trailing Arm System Never Tried...


Now, on the web site, I have been working more with trailing arm systems, where the frame sits still and the axel itself is free to move up and down.  It is not fixed in one plane.  It is a unique design.  It  is more unique than even a four wheeler system because you do not have to keep the whole rear axel stiff.  You can actually allow it to flex up and down.  There is a trailing link device that prevents it from moving side to side.

I have not experimented much farther that on paper with it, but I do know that it would work because of my mechanical experience in many areas is would be a pretty sound system it would just be made complicated more in the chain area.   Because one of my first ideas was to use a flex chain.  And after careful thought and working in the chain area for a couple of years, flex chain is probably not going to happen.  Chain manufacturers do not have much like that, and plus that is a lot to ask of a chain and not have it derail.

So the best thing would be to have an arm that goes forward.  It works on a universal joint system.  And the only purpose of its is to make sure that the driven gear actually has a place to sit and maintain a position with the rear axel.  You would have a universal joint that would go to that particular part of it.  And then you would drive that.  Basically it would be a little jack shaft with a universal joint on the end of it.    It would have to be held in a housing so that the universal joint wouldn’t flop all over the place.

Basically it would be a sound suspension and relatively cheap because you would have spherical bearing that you would be basically bolting onto some plates and then you would have some trailing arms that would go forward. 

One of the considerations that you need to look at is the axel shaft.  How much pounding are you actually going to put on this thing?   And your hubs when you mount them, make sure they can handle the stresses of pounding up and down.   That goes for all the hubs, including the hubs up front. 

Four Wheel Drive Go Karts...

Now one of the more exciting things, and I have not actually seen this, I have seen it on college campuses where they have done it with hydraulics,  is to have a four wheel drive go kart.  Now you are going to add a lot of weight, and you are going to need a lot of horsepower.   (We talked before about how much horsepower you are going to need) you are going to need at least 25 horsepower to get a four wheel drive go kart to do what you want. 

One of the things that is going to happen is that you are going to have driveline complexity.  It is doable,  but you are going to have driveline complexity where are going to have chains that would actually go underneath you  and you need to have the chains shielded very well,  tracked very well and lubricated very well.  Once the chain comes up to the front area to run it, then you need to get the spinning shafts all protected because you are going to have your feet and your pants up there.  And if you have your pants leg hanging down, they would just get twisted up in the shafting.

A Word On Saftey...Well Worth The Effort


Believe you me a drive shaft is very unmerciful.  Any spinning device even an axel shaft is very unmerciful.  It will just grab and go.  It does not care what is in its way.  It will not stop.  Trust me on that.  I have seen farmers in my area lost both arms because of augers and corn pickers and trust me, it does not care.  The machine does not know the difference.  There is not enough sensitivity in the machine to bog down and stop.  Because it is designed hog through loads. 

So if you are dealing with some sort of spinning shaft and it is going to be near the proximity of someone at all, it needs to be covered and protected.  So as a general rule, spinning devices need to be protected, covered.  It is just good engineering sense.  And a guard is not that big a deal to make.  It protects the devices underneath anyway.  Keeps the oil from flying around and protects from dirt getting in there as well. 

In Conclusion...


So to sum up, suspension systems (this is more an introduction to suspension systems) rhomboid suspensions systems require special geometry.  (We go over this in greater details in the Go Kart Building coarses.)  It has to do with roll centers.  Any suspension system you need to keep a good eye on,  but in particular if you are trying to do some performance suspension you need to keep in mind the orientation of the suspension, especially during rolls (turns).  

I have seen, at college, senior design projects where they did take that into account and when they turned that cart the suspension system angled over badly.  And it was an embarrassment. Well if they had designed the suspension correctly and had gotten the roll center where it needed to be then it would actually turn the opposite direction.  Or if you are ingenious enough, you can get the whole suspension to lean into the curve. 

So suspension systems can be complicated. I would not say don’t do it. It can be a good challenge for you.   

 


 
 

Great Birthday Present:  The Father and Son Wood Go Kart Project

Wood Go Kart Project


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