Mecanum Drive Killing Battery

[DinerKid]

I think what it really boils down to is how you are running for CIMs. obviously if you are stalling 4 CIMs you are at something like 428 amps, WAY over the breaker. If you can run all four at 15 amps each then you should fine from the graph we were looking at earlier.

I am still interested in hearing about other teams experiences with running 4 CIMs on drive preferably on a mecanum chassis but if not that is fine as well.

[EricH]

Originally Posted by DinerKid

I think what it really boils down to is how you are running for CIMs. obviously if you are stalling 4 CIMs you are at something like 428 amps, WAY over the breaker. If you can run all four at 15 amps each then you should fine from the graph we were looking at earlier.

I am still interested in hearing about other teams experiences with running 4 CIMs on drive preferably on a mecanum chassis but if not that is fine as well.

Pretty much right on. I don't remember exactly where on the curve you want to design for with CIMs, but you do want to design them right.

330 ran a 4-CIM drive between 2005 and 2008; I'm not sure about last year. No issues whatsoever with batteries (other than keeping them all charged during hours-long practice sessions in '07 and '08). All the robots were 6WD.

But, in 2005, the competition robot was designed to accept a mecanum drive. The Kitbot was equipped with that system for testing purposes; it didn't make it onto the competition robot. There were no battery issues on that robot.

[DinerKid]

Originally Posted by EricH

Pretty much right on. I don't remember exactly where on the curve you want to design for with CIMs, but you do want to design them right.

330 ran a 4-CIM drive between 2005 and 2008; I'm not sure about last year. No issues whatsoever with batteries (other than keeping them all charged during hours-long practice sessions in '07 and '08). All the robots were 6WD.

But, in 2005, the competition robot was designed to accept a mecanum drive. The Kitbot was equipped with that system for testing purposes; it didn't make it onto the competition robot. There were no battery issues on that robot.

With that being said... did it work out in your situation that you were running the CIMs with the desired current and still running at a decent speed? obviously you can design the CIM's to run at any current but if doing that means you are going to drive at a snails pace then it is kind of pointless. Was the robot that you are talking about able to drive with average speed without drawing too much current or was it slow?

[EricH]

Originally Posted by DinerKid

With that being said... did it work out in your situation that you were running the CIMs with the desired current and still running at a decent speed? obviously you can design the CIM's to run at any current but if doing that means you are going to drive at a snails pace then it is kind of pointless. Was the robot that you are talking about able to drive with average speed without drawing too much current or was it slow?

The mecanum robot was normal speed. The others were easily normal speed or fast. No breakers tripping, that I remember.

[DiehardCybercard]

as an off season project my team built a t-shirt cannon. the cannon and assembly is mounted on a mechanism drive base. we have driven the drive base over 30 minutes on one charged battery. We've never had issues with battery life with 4 CIMS

[J_Beth]

My former team (team 935) has made many robots that use a mecanum drive, and we have never ran into any problems with running out of power. during testing of our robots before competition we could run our robot for a good 5 minutes at full speed before we started having power loss issues. One charged battery should easily last one round, and be able to run your mecanum drive along with your other motors as well.

[Jon Stratis]

As others have said, running 4 CIM's shouldn't be a problem for a battery. The key is to monitor your current draw in testing, and any areas where it looks high at full speed you need to take a second look at - It means you probably have some unnecessary friction in your drive train somewhere (aka something is out of alignment).

Last year, we used two CIM's for a shooter. After the initial test and some adjustments, the current draw for those CIM's was cut in half!

[Al Skierkiewicz]

Diner,
The are a variety of reasons that can cause high current in a mecanum drive.
1. The gear ratio you have chosen is too low and so the motors are not developing enough torque to drive. That puts the motor in near stall conditions.
2. Something is binding in the drive system. You may have left out a required spacer or something else is causing the wheels to bind.
3. Your design produces a lot of side load on the CIM motor shafts. These motors cannot handle side loads so any loading will cause high friction on the output shaft and eventual wearing of the motor bearings.
4. One or two of the motors are running in the wrong direction. This is especially evident if everything (current and speed) seems normal if you lift the robot off the floor. While it is off the floor note the direction each wheel is turning. If coupled in a two motor transmission, try disconnecting one motor on each side and see if the current is still high.
Without seeing your design it is hard to determine exactly what might be the problem.