Quote:
Originally Posted by Lil' Lavery
Secondly, what prompted you to go with the dropping center omni wheel set-up, instead of just having the four articulating drive pods with mecanum wheels?
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We refer to the 5-omni setup as something called a "Slide Drive". When you combine a slide drive with 4 drop down traction wheels you get what we're calling "Nonadrive" (not Nano Drive as Mike Copioli seems to think...)
Why do we use a slide drive?
Here is the quantitative part:
1. This drive allows for the front and rear wheels to be "linked" without needing a ball differential or anything like that. If one wheel comes off the ground, you still have the full power available on the other wheel.
2. We have 4 motors worth of power pointing forward/backward at all times. With a Mecanum drive, you only get part of this. (The mecanum drive has better side-side power than our 1-CIM, but we don't care.
3. The "slide drive" part of the Nonadrive is 100% intuitive to control, with ZERO programming. This is not meant to discount the efforts of our incredible programmers (148 and 217 have some GREAT ones), but the slide drive can be fully utilized with default code, and its control would be identical to Halo, Call of Duty or any other FPS videogame.
Here is the "not so quantitative" part:
This will be a controversial statement...
In all of my competition robotics experience I have never encountered any drivetrain (swerve, mecanum, or omni) that drives as well as our slide drives. Maybe it has something to do with a lack of programming. Maybe it has something to do with a driver's mental block. I don't know. What I do know is that you put a slide drive in the hands of a good FRC driver, and they'll be almost immediately doing maneuvers that make your head spin.
Before you knee-jerk and reply, remember who you're talking to. We understand design tradeoffs. We understand your value propositions may be different than ours.
Honestly, I expected more people to ask us "Why the heck did you do
THAT instead of just doing a swerve or mecanum drive?" My answer is... "If you built one and drove it, you'd understand."
Quote:
Originally Posted by Lil' Lavery
Also, are you using any sort of closed-loop control to try and account for uneven forces between the forward/reverse (where you have four motors operating) and lateral directions (where you only have one)?
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Nope. The slide wheel is positioned near enough to the CG that she moves sideways almost straight as an arrow. The same can be said for forward and reverse, even without the traction wheels down. No complicated control needed. For testing (before we had any of the other electronics wired up) I took a VEX PIC Microcontroller from inventory, hooked the Victors up and we drove it with default code. Really.
-John