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Unread 28-05-2014, 17:07
RRLedford RRLedford is offline
FTC 3507 Robo Theosis -- FRC 3135
AKA: Dick Ledford
FRC #3135 (Robotic Colonels)
Team Role: Mentor
 
Join Date: Jan 2010
Rookie Year: 2009
Location: Chicago, IL USA
Posts: 286
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Re: Swerve Drive vs Mecanum Wheel drive?

After reading through most of this thread, I am posting ONLY in regard to the question of whether the performance level of a poorly designed/build mecanum drive is very much different from an excellently designed and built mecanum drive.

My teams mecanum drive experience is limited to this year's 2014 FTC competition (we do both FRC: 3135 & FTC: 3507). After evaluating VEX 4" mecanum wheel, we made a last minute decision to switch to mecanum midway through our FTC bot tank build (but completed the tank too in case mecanum was a bust).

The PICS below show the basic concept of our design. This was a more robust implementation of a mecanum drive than what your typical FTC mecanum efforts are like. Twice when a slightly errant autonomous route had us collide with the scoring buckets' balance beam, we became wedged under it, going back on our rear wheels only, and totally lifting one entire side of the hanging bridge, while doing a wheelie, as we pushet it across the field, yet no damage to drive train resulted.

We were not pushed around very much by tank drive bots and could play decent defense. Granted that at FTC level, not as much drive train differences can be seen between drive type designs (compared to at FRC level). However, the point I make is that, compared to the other mecanum drive bots we saw, there was a lot of difference between a good design and a weak design.

Our "H" frame had just enough flex to help keep all wheels down most of the time, yet stiff enough to deal with high stress situations. We were able to position accurately on the sloped bridge and were stable once locations were reached. The soft urethane of VEX wheels was very grippy and gave excellent traction, better than Andy Mark 4" mecanum wheels. Our weight was fairly evenly balanced. We won a design innovation award at our 2nd regional qualifier and were first seeded team captaining the winning alliance at 1st regional. We were 2nd seed in state after qualifying rounds.

Bottom line is there was a significant range of performance difference between the weaker mecanum designs/builds of bots (not very many though) compared to ours. We plan to add field oriented gyro control, improve our speed, and do an independent wheel suspension scheme for our next year's FTC mecanum build, unless the game design makes mecanum an inappropriate option. Our first FRC mecanum drive could also be happening later in 2014.





-Dick Ledford
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FTC 3507 RoboTheosis
FRC 3135 Robotic Colonels

Last edited by RRLedford : 28-05-2014 at 17:09.
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