So the rumors are true!
MOE is developing a swerve drive this off season and if you were at Ramp Riot you may have seen our hex shaft based prototype.
This it the CAD for the final (round shaft based) module.
Designed to be powered by either a CIM or a CIM+MiniCIM
Weight: 10.5lb in this configuration 8lb if no MiniCIM
Theoretical speed: 10-20 fps depending of final stage sprocket
2in wide 4in dia blue nitrile wheel
As we have limited machining resources this module was designed to be made with as few custom/complex parts as possible.
Big thanks to 1640 for letting us borrow one of their modules and for all the resources on Swerve Central - DEW Robotics
and an additional thanks to all the teams who have posted designs and code to give us a place to start.
The prototype used chain and we have not had any problems with that. The belt can be tensioned by sliding the CIM. If we do run into problems with the wrap we can very easily switch to chain.
I was actually wondering about how much belt engagement you are getting. In the pic it looks like you only have around 90* of belt engagment on the driveshaft.
Is it a fair assumption that you will be using 8 CIM drive with this.
If so, how are you planning to keep from popping your main breaker?
Are you using current monitoring to keep yourself in a safe zone?
I would consider changing the location of your digital encoder for a couple reasons.
First, as you tension the belt by moving your cim, it will change the engagement on the Digital encoder.
Secondly, generally speaking those things don’t appreciate a lot of side-loading.
Third, if your belt slips, your wheel will no longer be aligned with the encoder reading.
I’d consider a small lightweight bracket that places it directly over the primary shaft of the module itself, so you’ll always know the true position of the module. This also relieves any side-pressure on it, and it can be coupled with something as simple as surgical tubing. It will probably be a wash weight-wise.
4 CIM + 4 MiniCIM (assuming the motor count rules stay the same) but yes, current monitoring is the plan, I know there are a few teams this year who had this many CIMs on the drive without problem, but they did not have the additional draw of the 4 rotation motors so we may be forced down to 4 CIMs. We will be testing with 4 CIMs to start then if we can scrounge up enough Jags, all 8. The new control system should make this much easier. We are also concerned about weight, so no guarantees but we wanted to include all 8 mounting positions to cover our bases.
I am not sure if you can tell but the encoder is also on a slot so we can adjust it along with the CIM and make it just kiss the belt so there is almost no side loading. If the belt skips im pretty sure we are just gonna go to chain, we had enough headaches dealing with skipping belts this year
We did consider a bracket like you describe but it was just another part to manufacture and would also put the encoder in a more vulnerable location. If there is some unforeseen mechanical problem with it’s current location we may go this route.
Team 2587 ran 4 CIMs + 4 Mini-CIMs all year for around 70 matches + lots of practice time. Here are details about our drive system.
We did not experience breaker issues while also running an intake motor & compressor.
We also did not perform any type of current sensing.
Good to know, depending on the final speed we pick I suspect it will be fine, we shouldn’t be trying to pivot the module while stalling the CIMs anyway. Also, nice video, I’m surprised more teams didn’t use a pneumatic shooter like you guys, looks quite effective. I couldn’t help but notice in the close ups, are you guys using Churros for drive axles? Did you have any problems with that?
I don’t think your encoder position will yield good values because it isn’t properly engaged with the belt. With the encoder pulley tangent to the belt I don’t think the encoder will rotate in perfect relation to the belt. When you have a belt wrapped around a pulley, there is always at least one tooth that is fully engaged with the pulley. This ensures smooth movement. When a pulley is placed tangent to the belt you don’t have a tooth constantly engaged with the pulley, because of this there will be some sliding action as the pulley rotates and your encoder values will not reflect the true motion of the belt. This effect is exaggerated when you decrees the size of the pulley.
This is all conjecture, but I highly recommend testing this type of encoder setup or it could come back and bite you.
+1. That kind of reduction will result in an extremely low speed, around 5 fps according to JVN design calc. Not really worth a 4 cim 4 minicim drive IMO, as even in high gear mecanum you’re only running 12fps…
