Our team has been so excited to try out a mecanum drive this year. However, a reality check has set in that we will likely have extreme difficulty with this due to the fact that there are no four identical (or close to identical) motors. Does anyone know a way to get a mecanum drive working with the given motors mechanically, or will it just require some fairly intense programming :mad: ?
You can purchase 2 additional 2.5" CIM motors to use on your robot.
<R59> says you can have up to four 2.5" CIMs, but of course you’ll have to purchase the extra two.
first you have to ask yourself what you want to be able to do,
do you want a drive system that is truly holonomic
(ie you need 4 motors)
or is merely strafing enough
(can be done with 2 motors and 2 fwd/rev transmissions)
or do you want a strafing and diagonal drive system.
(can be done with 2 motors, 2 fwd/rev transmissions, and 4 on/off transmission)
use encoders or the KOP gyro
Team 401 used mecanum last year to some success. Using encoders on them isn’t very reliable as mecanum its self slips a lot and your feedback will be off.
Using 4 CIM motors with banebot gear boxes is the way to go, just keep the robot balanced.
We had a mecanum drive last year with great success. Balance is the key. Our drive only drifted a little and we had no encoders. We are using the same drive system this year with encoders. The mecanum wheels we purchased last year from AndyMark required a lot of work to assemble and modify. We did not find AndyMark wheels to be precisie enough, holes didn’t line up, rollers were not perpendicular to their mounting plate sections. Where else, besides AndyMark, can we get 8" mecanum wheels?
I’ve heard the 6in ones are much better because it’s a whole plate, no tabs like the 8in ones.
You can’t, the only place that sells mecanums for FIRST robots is andymark. There are other companies that use mecanums but for the most part they simply use them in their own vehicles and don’t sell the wheel separate. In addition these compainies make things like forlifts and you aren’t going to find a small enough wheel.
For the actuall control I would strongly suggest using a gyro instead of encoders, the code is easier and it isn’t suseptible to slipping. I have done a holonomic for the past 3 years and last year ours was a rock, it didn’t drift, it went in a perfectly straight line and overall just ran extremely well and we didn’t use encoders, just a gyro.
I’m curious - if you did not use encoders, how did you measure distance driven?
You could use a linear accelerometer and integrate it over time to get distance. However if you want distance you probably want to use an encoder, but for the basic control of a mecaum bot you don’t need distance traveled. What usually makes a mecanum uncontrollable is drifts in rotation because this can cause the bot to swerve to one side or drift in the wrong direction, for this you can integrate a gyro. While this may sound dificult it is easier than programing in interupts (or at least that is what I have always found).
That is technically wrong and right at the same time.
Yes, it looks like Andymark is the only place to buy a Mecanum wheel off the shelf… but… as with other things you COULD actually buy something that uses a Mecanum wheel and strip it off of it to use.
Nothing in the rules says you have to use the whole item that you buy, but it does say you have to account for it in your budget.
Hypothetical Situation: You buy a Remote controlled car with Mecanum wheels already on it and strip them off for use on your robot.
You must include the whole price of that Remote controlled car (which may be outrageous yes, this is true but this is just an example) in your final Bill Of Materials.
The Wheels would go in your Bill of Materials for your robot.
The whole cost of the Remote controlled car would need to be listed in the price portion of your data to prove you came in under budget.
All I’m saying is that you don’t have to limit yourself to something just because it’s “not available anywhere else” as a singular entity.
If you find a shopping cart has cool wheels you want to use, but can’t find those exact wheels for sale anywhere else, just buy the whole shopping cart, strip the wheels off, put the wheels in your Bill Of Materials, and write down how much you paid for the shopping cart (even if you did get it for “free” from a store… (as a legitimate donation of course…) 
I have a question…what is needed to really program the mecanum wheels… Is there a special code to use in programming or is it in the basic language?
private message me.
last year we set it up so you could change the power each motor gave out using a knob for each motor. That way you can fine tune the power of the motors till they are equal