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Post by cubdad on Jan 16, 2011 22:04:52 GMT -6
Hey everyone,
I am attempting something new for our pack derby. I have cut a design that will allow me to run three wheels in the back and one in the front with a tab. I am only trying this to get people to think outside the box, but would like to have a good showing. Our rules require four wheels and all four must touch. That is what got me thinking this way. Has anyone played with sucha design? What kind of alignment issues am I facing. I have done a lot of work on my wheels and axles using all the derbyworx tools. Just not sure if I should make this car an rail rider and what kind of cant should I have on the wheel. Any help would be greatly appreciated.
Cubdad
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Post by nmanhipot on Jan 17, 2011 16:04:49 GMT -6
I've CAD'd an offset wheel design but never built one. I've seen some good "zig-zag" designs work, as well. If you're familiar with the triangle theory with the two rear wheels and the front dominant, that will guide you. Namely, the COM needs to be inside of the triangle between the two rear and the dominant front wheel. Not all the weight has to be inside the triangle, just the COM, in order to keep it from tipping forward and down and off the opposite rear wheel. Realistically, your COM would have to be almost half-way forward in order for this to happen.
A real challenge would be to put three wheels on the one side with only one on the other in the rear.
In all reality, I think it will turn out like a three wheel design with a second, in-line rear wheel like on a tractor trailer. I don't think you've got too much to worry about.
A mechanical engineer I once knew said that nearly everything really only balances on three points.
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Art Racing
Pine Head
Life's a hole dig it!
Posts: 57
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Post by Art Racing on Jan 17, 2011 20:56:51 GMT -6
YES it has been done make your rear wheels 2.5 cant and rail ride on the third wheel in the back what ever side you put it on make it so it just barley touch the track by bend the axle so it does not turn all the time.That is one of the ways to make an all four wheel touch car its fastest in my opinion if your rules allow that.Hope this helps.
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derbydominator
Head in the Pine
"Zero Gravity" PWDR Pro Modified
Posts: 146
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Post by derbydominator on Jan 18, 2011 18:49:22 GMT -6
Cubdad, Great post and great to get your pack to think out of the box! I have attached a picture of a couple of league cars I built in 2008 and 2009. Is this the wheel setup you are talking about? In each one of these, I had the rail rider set to drift left to right but the middle wheel on the left side was off the track. I did not try it for the middle wheel touching the track but with a bent axle, it is fairly easy to get the alignment such that both the left rear and the left middle wheels are in sync. Alas, if you are using the KHouse groove method on the axles, it is even easier. If you could get the middle wheel to just barely touch and still be legal, that would help as well. We used a thin piece of plastic for our tab on the right front and wrapped it in teflon tape. You can rub graphite into the tape as well to make it super slick. The advantage of the one wheel in front of the other was for reduced air flow similar to drafting in nascar. Fun design though! Nmanhipot is dead on with the triangle theory by the way. What we did was draw a triangle from the three points on the body where the axle holes are drilled. Then another line 3/4" (COM line) in front of the rear axle. Find the point on that line that intersects with the lateral center of the triangle and that is where your COM should be balanced. In this case, it was about 1/8" left of center. Dazed and Confused Purple People Eater Darryl dhuntley@DerbyDominator.com
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Post by cubdad on Jan 24, 2011 21:19:11 GMT -6
Well I didn't take a trophy but I did raise some eyebrows. I heard several people asking how many wheels does that car have? I also turned in a decent finish at 5th overall out of 45 cars. The best thing was consistency. I only saw .0111 seconds deviation over 4 runs. I have tried to attach a picture and hopefully it will show. Cubdad Attachments:
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derbydominator
Head in the Pine
"Zero Gravity" PWDR Pro Modified
Posts: 146
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Post by derbydominator on Jan 24, 2011 22:42:09 GMT -6
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Art Racing
Pine Head
Life's a hole dig it!
Posts: 57
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Post by Art Racing on Jan 26, 2011 20:52:35 GMT -6
nice looking car cubdad
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