Quote:
Originally Posted by Chris is me
Not exactly - all other things equal, assuming a rigid frame, 6 wheel no drop drives of the same wheelbase length will turn about 1/3 better than a 4 wheel drive of the same wheelbase length. 25's drivetrains aren't magic - they just combined a nearly square wheelbase with the benefits of weight being supported by middle wheels. In the era of 28x28 frames, you might not need any drop at all. Of course, it's easy to put a little drop in and just be safe about it, so unless you really need the resistance to turning and can spare the current of more turning resistance, there's no reason not to drop your 6WD center. But I think at this point honestly teams are dropping the middle wheel out of habit / "we know it works" when the practice is to a small extent a relic of the 38x28 era.
I'll pull up the link to the old CD whitepaper in a bit, but the section on tracked drivetrains / statically indeterminate drivetrains applies to this six wheel no drop case.
|
This.
The big change that happened in (2013?) was the new frame perimeter rules. Prior that we had max dimensions in each direction and it meant you were either building a wide bot that was unstable front to back or a long bot that had a longer wheel base[1]. With the change to a 112" perimeter we were able to optimize differently. Example - 125 ran a 6 wheel flat drive in 2014[3] and had no issues turning because we were effectively 28x28, and when looking at actual points of contact, much wider than we were long.
2015 allowed teams to do whatever they wanted.
Personally, I hope to see a return to frame perimeter rules as it is both easier to inspect than transporting a box[2] and allows teams more flexibility to optimize their chassis shape.
[1] 25 Addendum - No secret sauce, their large wheels usually ended up with contact points roughly square (or close to it) as folks have said in this thread.
[2] That isn't square or always spec'd right
[3] Correction - We started w/ .125 drop, shaved to .09 and then by end of the season we were effectively flat but our frame was also bent to heck because New England.