Author Topic: Sabertooth 2x10 R/C Overamping Motors????  (Read 3192 times)

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Offline JBotTopic starter

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Sabertooth 2x10 R/C Overamping Motors????
« on: May 24, 2008, 06:47:22 PM »
I've just completed the mechanical build on my first R/C robot - working towards autonomous. I have a Sabertooth 2x10 R/C motor controller wired to two surplus windshield wiper motors for drive motors. Using a Futaba 6 channel controller, I have connected the Sabertooth but I'm having trouble driving the wheels correctly. The motors tested at about 2.5 amps under full load. When I operate them through the motor controller / transmitter - FWD/REV, they move forward / reverse (both wheels turning is same direction) at a very slow pace and pull about 12-15 amps and quickly overamp the controller. Activating the TURN stick on the transmitter is no problem as they turn in reverse directions and pull about 2.5 amps each. I tried changing the dip switches on the controller to no avail unless Im missing the right combination. Any ideas?

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #1 on: May 25, 2008, 04:11:12 PM »
Quote
The motors tested at about 2.5 amps under full load.

and
Quote
at a very slow pace and pull about 12-15 amps and quickly overamp the controller


Wait . . . I'm confused . . . are you sure both are measured correctly? When they go slow, do they also seem weak? Does it overheat?

Are you using 0V for the battery ground? (because if you do, that will break it!)
http://www.dimensionengineering.com/datasheets/Sabertooth2X10QuickStart.pdf

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #2 on: May 25, 2008, 06:30:51 PM »
Thanks for the reply. For clarification, I'm using the 2X10 R/C model of the Sabertooth which wires slightly different then the 2X10. The battery is connected to the B+ and B- terminals of the controller. The two motors are wired to the respective M1 and M2 terminals of the controller. Yes I feel confident both are measured correctly. I disconnected the motor lead from my terminal strip and connected the ammeter leads to the motor lead and to the terminal strip - completing the circuit. So both 12-15 A and 2.5 A readings are measured using the same method. Yes in the "overamped" situation, the motors / wheels turn very slow and seem weak and the controller gets hot. After a few seconds, the overload LED on the controller lights.

Thanks again for any advice.

Kirk

http://www.dimensionengineering.com/Sabertooth2X10RC.htm

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #3 on: May 25, 2008, 06:54:03 PM »
What battery are you using and what voltage? What are your switch settings?

for reference:
http://www.dimensionengineering.com/datasheets/Sabertooth2X10RCQuickStart.pdf

Offline JBotTopic starter

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #4 on: May 25, 2008, 07:34:34 PM »
The battery is a 12V 7Ah sealed lead acid battery (sold as power supply for electric fences). I'm hoping you're on to something with the switch settings. It came from the factory with all in the ON position. I've tried other combinations but not fully understanding all of the option criteria, I may be missing an important setting. My goal is to have the right joystick on the R/C controller drive and steer the robot. It does this now but as mentioned previously, overamps when moving the joystick up/down to make the robot go FWD/REV. So I guess in answer to your question, the switch settings are currently all in the ON / "UP" position.

Offline jman571

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #5 on: May 25, 2008, 10:21:02 PM »
Not sure if this will help, but try disabling switch 1, which will switch from mixed mode (controlling turning and FWD/BACKWARDS with one stick) to independent mode, where you will need to use both sticks. I'm just grasping at straws here, but perhaps it has something to do with that. Also check to see what your Auto-Calibrate switch is set to, perhaps try turning it off. I own a Sabertooth 2X5 R/C but didn't have a problem anything like yours.

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #6 on: May 26, 2008, 06:51:19 AM »
Something just doesn't sound right . . .

Without commanding the motors to do anything, how much current is being drained from the battery?

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #7 on: May 28, 2008, 07:45:36 PM »
I've talked to Dimension Engineering the last two days and they too are baffled by the problem. They say it might be a bad board but asked me to check other possibilities first...which has raised more questions...or answers depending on your understanding of grounded motors! With the controller completely detached, I have continuity just about everywhere. It started when I disconnected one of the motor leads and when operating the other still connected motor, the motor with one lead continued to slowly rotate. I have now found I have continuity between the motor leads, the robot frame and the motor case. I'm going to try insulating the motor from the frame but not sure what this will do. But since I don't have any other ideas at this point I'll give it  a try. For what it's worth, I also have continuity between the motor terminals of each respective motor on the controller.

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #8 on: May 28, 2008, 08:09:05 PM »
Hmmmm I'm having trouble understanding your setup . . . it really really really sounds like you are shorting something somewhere . . .

Without commanding the motors to do anything, how much current is being drained from the battery?

Have you tried other motors? And motors not physically attached to anything else (such as the robot frame)?

Try swapping M1A and M1B connections with each other.

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Re: Sabertooth 2x10 R/C Overamping Motors????
« Reply #9 on: May 29, 2008, 07:04:49 PM »
I think I found the problem. I detached one motor from the frame and they both operated at normal amps and speed. Apparently the motor frame is grounded to the negative lead and thus shorts across to the other motor causing the low speed and high amperage. I'm now working on insulating the motor bracket mount from the main part of the frame. By all indications are that this should fix the problem. Thanks for the advice.

 


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