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Balanced suspension design

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Eveslage

Eveslage

Automotive
Joined
Jun 29, 2004
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4
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US
I am a member of the Purdue Mini-baja team and I recently began working on our suspension setup for the coming year. I was looking through Carroll Smith’s latest book, Racing chassis and suspension design and found a very interesting paper from Erik Zapetal SAE # 2000-01-3572
This design allows the four suspension modes to be independently varied and I believe this would be very useful for an off road vehicle such as ours. I am currently thinking about using a damper at each wheel hydraulically connected to four other pistons on the balance plate similar to what is shown here.


I am hoping that such a design would decrease the weight compared to our current coil over shocks that each use two large springs stacked on top of each other.
Our mini-baja vehicles typically weigh about 450lbs and have about 12” of suspension travel using fully independent A-arm suspension. WE are also limited to 10 horsepower.

So I am looking for a more experienced persons thoughts on such a design or any additional information you may have about this system. I think this system would work well but I’m afraid it might end up being either to heavy, complicated, or expensive when compared to coil overs.

Here is a link I have found that is also related to the topic.

Thank you for your help
Eric Eveslage
 
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Great stuff. Don't worry about patents, you can't get into trouble if it is a one-off for non-commercial applications.

What sort of modelling software do you have? Could you build a full dynamic model and simulate its performance over 'typical' events?

I have a hard job believing that a 10 hp 220 kg machine with such short wheelbase and narrowish track needs to worry about warp, but then I don't know what you expect to be able to do, and how refined current designs are.

As a practical observation KISS has a lot going for it in off road applications.

Cheers

Greg Locock
 
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We use Adams for modeling. I am going to try to build a full model this year even if it only helps the next year’s team. Unfortunately I don’t know a whole lot about Adams because the people that learned it previous years graduate without passing much down.

A rock crawling event was added two years ago and all the teams struggle with it. Our solution last year was to use four-wheel drive. 4wd added about 50 pounds and 8” to the length though. So I am hoping to get better articulation with the balanced suspension and get rid of the 4wd.

A month ago my plan was to just keep a similar setup but refine suspension points and find better shocks. Some of the other guys wanted to use inboard suspension but I don’t see any real advantages to it.

I think your last line pretty well sums it up.

Thanks
Eric
 
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4wd is very hard to beat in that sort of application.

If you are using ADAMS/View it should be easy to design your complex spring system from scratch. If you are using Car then it might be rather difficult, as you'll need to modify the template.

If you are using View look at the example for cable controls - it includes a god summary of how to write equation based linkages, which will be easier than modelling the linkage piece by piece.





Cheers

Greg Locock
 
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Wonderful news! I have played with a similar system, so far only at 1/10th scale on a radio controlled model, and with mechanical linkages. I started on the basis that a rock crawler needs to maintain as close as possible to equal load on all four wheels. My model has no spring element at all, and simply allows free warp between the axles. There is no way to overcome load transfer resulting from body angle (i.e. CG shift), but it does prevent load changes due to spring rates. The system allows the use of open diffs at all times. The model has the ability to allow the axles to articulate until they are at almost 90° to one another, giving some impressive obstacle crawling. The scary thing is what happens when you try to manouvre the vehicle at high speeds. It effectively has four 'roll centre' axes forming a diamond shape in plan view. Hrad cornering can cause it to lift an inside front wheel, whereupon it continues to corner, but as a tricycle with the front axle stood on end! Needs some refinement!
 
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Zapetal has an interesting idea here, and I can see the use in something that is for off-road use. His initial paper was for a road race car, though. After reading the paper and listening to his presentation, I could only think one thing. How the hell are you supposed to tune the roll couple distribution on the damn thing? For it's originally intended use, it's completely useless.
 
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