Battery Voltage problem

[j801642]

We are having a problem where the voltage is dropping down to the scary range of 7-9V while just driving around. Sometimes we will not being manipulating the robot at all and the power will drop from 12V to 9V. We have a 4 CIM 8 inch Pneumatic wheel AM14U3 drive train. We have two CIMs working our lift. These are all hooked up to 40 amp breakers on the PDP. We have a window motor hooked up to a 20 amp breaker on the PDP. There's also a compressor, camera, wireless, and two servos all hooked up in their respective ports as well. This is the most power we've had on the robot in the four years I've been doing FIRST and I don't know if this is normal usage with this type of setup or is it a problem with connections? We've tested with multiple batteries all reporting 130% and a condition of "Good" on the battery beak. After using one of the battery for ~10 minutes the battery beak reported a charge of 96%. I'm worried we will go to play a full match and the robot will brownout. What troubleshooting steps should I be taking to try to fix my problem.

Thanks,
Isiah L.
Team 128 Electrical/Programming Team

[mathking]

Isiah, it might well be that the configuration of your wheels along with the pneumatic tires is causing the robot to draw a lot of current when it tries to turn. We have had this problem a few times in the past (our initial configuration in 2014 springs to mind). One suggesting is to check the inflation on your tires. We are using six pneumatic wheels with a drop center configuration. At the PAST Foundation practice session we tried running them at lower pressure so the robot would not bounce as much over defenses. That made the robot have to work a lot harder in order to turn. Have you checked how hot the motors are after driving? If they get really hot it is a good indication of a potential problem. You can try fans or CIM coolers.

That said, if you are driving for ten minutes on one battery you are probably going to be OK for a 2:15 match. My advice from past experience is to bring a few extra batteries with you to competition, because if you are draining them a lot in a match it will take longer to power them back up. I believe you are going to the Greater Pittsburgh Regional if I am not mistaken. 128 has been around a long time, so you probably have plenty of batteries. But if you needed to borrow any extras we (1014) would be happy to lend you a few since we don't have a competition that weekend. (We also have some extra CIM coolers if you want them.)

[Joe Johnson]

All closely related threads:

Power draw issues


Battery Voltage problem

Voltage Drop issues


Robot loses communication while going over obstacles


Router browns out with multiple CIMS driving WCD

[17lbrannan]

Originally Posted by mathking

Isiah, it might well be that the configuration of your wheels along with the pneumatic tires is causing the robot to draw a lot of current when it tries to turn. We have had this problem a few times in the past (our initial configuration in 2014 springs to mind). One suggesting is to check the inflation on your tires. We are using six pneumatic wheels with a drop center configuration. At the PAST Foundation practice session we tried running them at lower pressure so the robot would not bounce as much over defenses. That made the robot have to work a lot harder in order to turn. Have you checked how hot the motors are after driving? If they get really hot it is a good indication of a potential problem. You can try fans or CIM coolers.

That said, if you are driving for ten minutes on one battery you are probably going to be OK for a 2:15 match. My advice from past experience is to bring a few extra batteries with you to competition, because if you are draining them a lot in a match it will take longer to power them back up. I believe you are going to the Greater Pittsburgh Regional if I am not mistaken. 128 has been around a long time, so you probably have plenty of batteries. But if you needed to borrow any extras we (1014) would be happy to lend you a few since we don't have a competition that weekend. (We also have some extra CIM coolers if you want them.)

Thanks for your reply Greg! We seem to have this problem not only when driving but also when using our two CIMs for the lift. Our robot has the same configuration for pneumatic wheels. All the wheels are filled to their maximum pressure. I touched the CIMs on the drive train after driving for a little and they were warm but not too hot to touch. And yes you are right, we are going to Pittsburgh and we do have a lot of battery's haha!

EDIT: We did some tested and we noticed that our voltage drops drastically when we are at stall current on the ramp. We are exploring options to get around this problem. Anyone have any input?

[Ether]

Originally Posted by 17lbrannan

Anyone have any input?

Read the threads linked in Dr Joe's post:

http://www.chiefdelphi.com/forums/sh...67&postcount=3

[MetaEngineer]

Double check all connections between battery and PDP. It raises a red flag for me when you say the voltage dips low even when the bot is idle and that the CIMs are not burning hot after 10 minutes of driving with them "stalling" as much as you describe.

Loose nuts or crimps at connectors, breaker, or PDP can cause brownouts like that, even with fully charged batteries. Likewise check the connections at the battery terminals, though I suspect the problem is on the bot since it happens with multiple batteries.

That said, you should also look at the threads Dr. Joe posted and think about the gear ratio of your drivetrain and your lift. The kit chassis you have comes with a 10.71 to 1 gear ratio, which is a little weak for grippy 8-inch wheels. The 12.75 to 1 gear ratio option may help you a bit at the cost of some top speed.

[MrRoboSteve]

FWIW, on Saturday we ran ToughBox Minis in the 5.95:1 configuration with a six wheel center drop, configured with 8" pneumatic wheels.

Notes:

1. We paid close attention to chassis balance
2. Center tires inflated to 40psi, outside tires to 10psi
3. The tires are the AM-3351 ribbed tire (no longer shown on their site, similar to these

I agree with MetaEngineer that you should have some pretty hot motors on the drivetrain if you're dissipating that much current during a match. After running for a bit, you could carefully touch the things in MetaEngineer's list to see if any of them are hot.

[gpetilli]

I didnt go through all of Joe's threads, but one item we have seen is the bolts at the battery terminals coming loose. This is directly related to people (students and mentors) picking up batteries by the cables, which then twist and loosen the nuts. Just don't.

[Cam_Team 2619]

While I am not an electrically savvy student, my team the past year has conducted an extensive study of how the condition of batteries can affect robot and systems performance. This was after we placed seemingly healthy battery in the robot, and suffered many systems problems during a match due to the poor condition of said battery. The study can be found here on our website. This also includes descriptions of the tests we did and the information we found. http://the-charge.com/uploads/3/3/5/...atteries.p df

I hope this helps.

[Ether]

Originally Posted by MrRoboSteve

ToughBox Minis in the 5.95:1 configuration with a six wheel center drop, configured with 8" pneumatic wheels.

Do you have further sprocket/pulley speed reduction, or are you really geared for 31 ft/sec free speed?

[MrRoboSteve]

Originally Posted by Ether

Do you have further sprocket/pulley speed reduction, or are you really geared for 31 ft/sec free speed?

There's no further reduction in the drivetrain. Relative to the KOP chassis, the only drivetrain differences are:

8" wheels
swapping the gears

[Ether]

Originally Posted by MrRoboSteve

There's no further reduction in the drivetrain. Relative to the KOP chassis, the only drivetrain differences are:

8" wheels
swapping the gears

What was your motivation for changing the gear ratio from 10.7 to 5.95?

[17lbrannan]

Yesterday we added Gorilla Tape to the 4 outer wheels to reduce friction, this was suggested in some of the other threads. We also went through and re-soldered a lot of our Anderson connector to battery connections. This helped our battery voltage a lot and we are no longer experiencing the large drops we were before. Our driver also said that he thought the tape caused the robot to drive better than it did before as well!
Thank you all so much for your help,
Laura B.
Team 128 Electrical/Programming Team

[MrRoboSteve]

Originally Posted by Ether

What was your motivation for changing the gear ratio from 10.7 to 5.95?

Team decided they wanted a faster robot. We'll see how they like it after they've been pushed around a bit.