Weak voltage outputs on M1 and M2

General discussion of using Roboclaw motor controllers
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robocrane
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Joined: Sun Aug 07, 2016 11:43 pm
Weak voltage outputs on M1 and M2

Post by robocrane »

I have a roboclaw 2x15A. Connected via RC (mode 1) and it receives the signal. Before putting in my brushless high powered motor wheels on it I tested the output voltages on a 12.7V deep cycle 75Ah battery and I get rages of 6.x volts to 11.x volts when the RC control levels are pushed to max. What's the best way to troubleshoot this?

I also want to put a reset able circuit breaker to protect the 15A on the motor controller because these little boards are cheap... what's the best way to do this? I also read that the max power decreases when temperature increases? Really means you want a fan on these?

Thanks.
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Basicmicro Support
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Joined: Thu Feb 26, 2015 9:45 pm
Re: Weak voltage outputs on M1 and M2

Post by Basicmicro Support »

1. The Roboclaw is a brushed DC motor driver. It will not work with Brushless motors. Was that a typo on your part?

2. The maximum output voltage will never be 100% of the battery input voltage. Close to a 1v difference in input versus output would not be unexpected. The motor PWM will never get all the way to 100% duty because the motor driver must spend some time off so the boost cap for the high side mosfet can charge plus there is some deadtime between switching mosfets to prevent shootthrough.

If you want to compare the output of the RC with a known full power output use the IonMotion software to control the board. In PWM Settings move the motor slider to max and take a voltage reading. If it is the same as the RC reading then everything is working correctly. If it is slightly more then it is possible your RC receiver outputs a slightly smaller pulse at max than our default max range. This may be adjustable in your radio.

3. A fuse/breaker is not what should be used to control max current. Fuses arent anywhere near fast enough ot protect a motor controller and when they break they leave no path back to the motor so regen energy will end up eating the controller anyway. If you want to use a breaker for safety reasons then you should put the breaker on the + side of the battery and put a power diode across the breaker(this provides a path back to the battery for regen energy from the motor). The breaker should be speced for around the peak current rating of the Roboclaw(30a in this case). If the roboclaw is damaged and causes a dead short this will trip the breaker.

For current limiting you should use the IonMotion software to set your maximum current.

However if you are trying to use oversized motors(something with stall current signifcantly more than the peak current spec'd for the board) then your motors are probably going to have too low an inductance to safely use with the 15A roboclaw. Inductance determines the ripple current in the filter caps(ripple current is not the same as motor current) of the Roboclaw. If your motor inductance is too low(lower than about 250 microHenries) the filter caps can be damaged and if that happens large voltage spikes will occur which will damage the rest of the board.

Any motor with a stall current more than 60a is not recommended for use with the Roboclaw 15A.
robocrane
Posts: 2
Joined: Sun Aug 07, 2016 11:43 pm
Re: Weak voltage outputs on M1 and M2

Post by robocrane »

Awesome! Yes, brushed motors. The motors are brushed motors. Yes, that was a type. They are 3.9 Amp, I don't expect them to stall. The way the motors control the robocrane is to apply rubber wheel pressure on a metal wheel so I expect the wheel slippage before seeing any power go to the stall. Thanks for the warning.

I decide on the 15 amp because of cost and it can peak to 30 amp per motor.

Do you know of any youtube videos showing ionmotion software in action?
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Basicmicro Support
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Re: Weak voltage outputs on M1 and M2

Post by Basicmicro Support »

We havent done any videos yet though we are planning on it. The Ion Motion software once you get into it is fairly simple. If you have any questions just let us know(call or post or email). Using encoders for speed or position control is about the most complex thing and its fairly easy to setup most times(using autotune).

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