Side of Drives Giving Out

[LeelandS]

Our robot has been having a bit of a problem as we have been practicing for the Rah Cha Cha Ruckus in a few weeks. We will go to drive up the bridge, get up a little ways, and a side of the drives (commonly the left, occasionally the right, sometimes both) will just give out. They stop working and the robot spins backwards with only one side of the drives working. I'm looking for possible causes, as we have not clue where to look.

Here is the set-up. Each side of the drive is powered by 1 CIM motor, through a CIMple box. We have a wide orientation robot with two wheels on each side, so this set-up is chained to both wheels. My hitch with giving details is that I did not help design or build this robot. This is the 2012 robot of a team I joined in July, so I wasn't part of the design process.

I speculate (and I am by no means a mechanical engineer or an expect on motors) that the CIMs can't handle the load of going up the bridge and just shut off temporarily. We maintain communication with the robot, and after a few seconds can continue driving around. I am lead to this conclusion by that fact, and that the robot has no issue driving around on flat group. Since there is only one CIM per side, it's a hefty load, even for such a tough motor.

If there are any details that might be pertinent to the discussion, let me know. I know this has been a persistent problem (it occured during testing over the Summer). The next time I will be able to see the robot work will be Thursday morning, so I will be able to gather data and look for anything else based on feedback.

Any help would be appreciated. Due to lack of mechanical mentor support, I don't think any changes can be made. But I would like to know what the issue is. It will certainly influence how we play at Ruckus. Thank you in advance to any who are willing to offer advice.

-Leeland

[Chris is me]

I speculate (and I am by no means a mechanical engineer or an expect on motors) that the CIMs can't handle the load of going up the bridge and just shut off temporarily. We maintain communication with the robot, and after a few seconds can continue driving around. I am lead to this conclusion by that fact, and that the robot has no issue driving around on flat group. Since there is only one CIM per side, it's a hefty load, even for such a tough motor.

This is probably what's happening. You should be able to confirm this by listening to the PDB for a tripping breaker. Is there any reason you can't add 2 more CIMs to the drive?

[LeelandS]

Originally Posted by Chris is me

This is probably what's happening. You should be able to confirm this by listening to the PDB for a tripping breaker. Is there any reason you can't add 2 more CIMs to the drive?

The other two CIMs are currently being used in the shooter and bridge arm. Definitely wouldn't have been my choice, but that's what we're working with now. We were originally going to make the necessary changes to move all the CIMs to the drives and put different motors in the other parts of the robot (we have already recieved the new motors and everything), but I have been told by my team leader that due to lack of support by Mechanical mentors, all mechanical upgrades are off.

If this really is the issue, I'm going to try and make a second push to make the necessary mechanical upgrades.

[Chris is me]

If your team is hesitant about replacing both CIMs, you should be able to stick some FPs through AM Planetaries for a bit of a boost in your drive. A bit pricey if you don't have the parts lying around though.

Other factors to consider with this: Where is your CG? If it's too high or off to one side this problem might present itself, but you'd probably notice the robot being quite tippy already.

[billbo911]

CIMs don't have internal breakers, so they will keep going until they are dead. Once dead, they are DEAD. They can be worn from hard use and simply swaping in a fresh pair might help, but not likely.

It sounds like you are either tripping the breaker, or resetting a Jag. You didn't mention which speed controllers you were using, but by the sound of it, I'm guessing they are Jags. Either way, you are over currenting your drive.

Check for binding in your drive train. Check for chain misalignment. Lubricate your transmissions and chains. Possibly, change your output sprocket to a smaller one to gain more torque out of the transmission. If all else fails, swap the Jags for Victors.

[bardd]

I fully agree with Chris. To check whether that's the reason, check if the CIMs heat-up more than they usually do. If they don't heat up, it won't say much for or against the theory (because from what I understand the situation only lasts a few seconds), but If they do, overload is almost definitely your problem. I want to say definitely, but I've seen enough strange things to not commit to it

Also, if the CG is a bit closer to the left (and the overload theory is correct), it might explain why the left gives out more often than the right.
A related long-shot: do you have a turret?

[BobbyVanNess]

FRC motor controllers can easily deliver current well above 40 amps, which in short bursts wont trip the pdb breaker immediately, but if your cims are sitting stalled on the bridge, it is likely that this is your problem. This could be due to the gearing ratio also, and the motors not having enough torque to keep driving up the bridge. Maybe consider a change in your gearing ratio.

[roystur44]

If you are using Jags/PWN switch the jags and see if the stall is opposite. Could be you are resetting your Jags dues to improper gearing and stalling the CIM. Makes sure your firmware on your jags are up to date.

If you can switch to Victors try that.

[kevin.li.rit]

Leeland, I also agree with chris that you probably don't have the torque. If you don't want to run the ruckus with 6 CIMS, I would suggest you swap out the CIMple box with the tougbox from the previous years. There is a larger reduction in that gearbox for more torque and shouldn't be too hard to make this change.

It would also help if you know what the reduction is after the cimple box.

[whcirobotics]

It sure sounds like an overload tripping the breakers.

Also check the gear ratio in the gear boxes. If you have the 4?? to 1 it would cause the problem you are having.

[FrankJ]

Was the robot ever able to climb the ramp? If this is new then look for something wrong. Cims are very reliable, but they can be burned at by extended use at high loads. (Which is beyond their design spec)

Otherwise it sounds like you do not have enough torque. If adding motors in not an option, you can lower the drive ratio by changing the chain sprockets on the wheels. You will lose speed but gain acceleration, turning & pushing ability along with climbing ability. Sprockets are available from AndyMark.

Our locomotion chassis is geared for about 10 ft/s & has no problem climbing the bridge. (long chassis, 6 wheel drive, Simple boxes, 8 in wheels, 1 cim per side.)

[LeelandS]

I appreciate the advice everyone has given so far.

My first course of action is going to be to try and rally the mechanical mentors on the team and make the motor changes we had planned on earlier, including moving 2 CIMs to the drive base.

If that doesn't work or I can't get enough support, we will try changing the sprockets on the wheel to larger ones to lower the ratio. Since that seems like a substantially less time consuming job, this seems like a likely route if I can't find the support to change the motors.

Again, thank you everyone for all the help. I will be doing more research Thursday, as well as talking with mentors about getting things in gear for upgrades.

Originally Posted by FrankJ

Was the robot ever able to climb the ramp? If this is new then look for something wrong. Cims are very reliable, but they can be burned at by extended use at high loads. (Which is beyond their design spec)

The robot used to be able to climb the bridge reliably. It can still climb it on occasions, but the failure is more frequent.

Originally Posted by bardd

Also, if the CG is a bit closer to the left (and the overload theory is correct), it might explain why the left gives out more often than the right.
A related long-shot: do you have a turret?

We do not have a turret. Part of the issue I think we are having is that the shooter is largely integrated with the body of the robot (see picture), and most of the shooter hardware is over the left side. I don't really think it's a coincidence.

[AlexH]

are you running jags? you might be popping the over current protection when you climb the ramp.

[LeelandS]

Originally Posted by AlexH

are you running jags? you might be popping the over current protection when you climb the ramp.

We are indeed using jaguars on our robot.

[jwfoss]

I would never advocate doing this in-season, however it's an offseason, why not just run the 6 CIMS? A number of teams did this in the offseason after the whole BB775 case short issues. I'd just contact the Ruckus planning people to double check.

I'll even come over and help you out in the morning when I get there if you need it.