Voltage Drop issues

[mypie4050]

When testing our robot recently, we encountered an issue where we received a significant drop in battery voltage, and therefore a drop in performance and a loss of control. This occurred whenever driving the robot on carpeted floor, particularly when turning and when crossing defenses. We experienced the problem on two particular occasions. The first was after a prolonged period of driving (over defenses and on carpeted floor). The victors controlling our drive train were rather warm. We assumed they had overheated.
The second occured on our first test after enabling the braking function on the Victors. To sum it up:

The Robot:
6 pneumatic wheels from AndyMark on the AM14U3 chassis
4 CIM motors, 2 on each of 2 toughbox minis with a 10.71:1 gear ratio
1 Victor SP controlling each pair of CIMs.
2 other motors each controlled by one Talon SRX via CAN
Weighs roughly 80 pounds

The problem:
Major power drop when turning or driving over defenses
Drop from 12 to approximately 6-8 volts

Potential Causes:
Pneumatic wheels don't have enough air
Braking feature of Victors eating up a ton of power
Victors being power hogs
Victors overheating
Faulty Wiring
Faulty Victors
Extreme friction caused by pneumatic wheels
[Edit] Two motors on one Victor

We know it isn't:
The batteries; did the same thing to 3 of them, at least one is new this year
The CIMs spinning in opposite directions; There is no power drop when the wheels are off the ground.

Any ideas as to what the problem might be? We try removing the braking feature on Monday to see if that is the issue.

Edit: Found out it's actually illegal to run two motors into one controller. Will be fixing the problem shortly

[MrForbes]

How much air pressure is in the tires? and could you provide a few pictures of your robot?

and...sounds dumb but I have to ask....the batteries are all properly charged, right? 13.5 volts before you install the battery in the robot?

[Joe Johnson]

Originally Posted by mypie4050

<snip>


Potential Causes:
Pneumatic wheels don't have enough air
Braking feature of Victors eating up a ton of power
Victors being power hogs
Victors overheating
Faulty Wiring
Faulty Victors
Extreme friction caused by pneumatic wheels
<snip>

The Victors getting hot are much more likely the symptom than the cause.

How much rock do you have on the middle wheels? If you can't clearly see that the front tires are in the air when the robot rocks to the back and vice versa, I am going with extreme friction due to grippy wheels theory.

Also, JVN spreadsheet* says that you're top speed is 17.4fps (14.1fps adjusted). That's a little bit on the high side for a one speed transmission and these grippy wheels (imho). You'd probably have a much better day if you can get more ratio betwixt those CIMs and your 8" pneumatic wheels.

Good luck.

Joe J.

*honestly, checking a box saying that your team promises to use this spreadsheet ought to be required before AndyMark or Vex sells a gearbox and/or a especially grippy tires.

[PayneTrain]

You're running two CIMs to one Victor?

Don't.

[Ether]

Originally Posted by mypie4050

1 Victor SP controlling each pair of CIMs.

Victors overheating.

Those two statements may be related.

[wireties]

Originally Posted by mypie4050

1 Victor SP controlling each pair of CIMs.

Is that legal? I thought you had to have one motor controller per motor (R52). You can drive the 2 Victors from a single PWM output but not two motors from one Victor.

[Joe Johnson]

Originally Posted by wireties

Is that legal? I thought you had to have one motor controller per motor (R52). You can drive the 2 Victors from a single PWM output but not two motors from one Victor.

Wow, I totally missed that they were driving 2 CIMs with 1 Victor. Yes, that is a problem. And No that is not legal.

There are only a handful of motors that let you have 1 Speed Controller and 2 motors, and the CIM is definitely not on that list.

See "Table 4-4: Legal Power Regulating Device Use" in R53.

Only the following motors can have 2 motors on one speed controllers:

• Automotive Window/Door/Windshield
• Wiper/Seat/Throttle Motors
• AndyMark PG
• Snow-Blower Motor

Dr. Joe J.

[dubiousSwain]

We are having the same problem. We are running one motor controller for each motor controller. We are having a voltage drop when we move and turn. We have gone through the log files and noticed that our current draw is spiking as the voltage drops. We have spikes up to 50a. Our robot is almost undriveable, please help.

[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