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 Post subject: RoboClaw 2x60 Error LED blinking & no motor movement
PostPosted: Sat May 03, 2014 7:35 am 
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Joined: Sat May 03, 2014 7:13 am
Posts: 1
I have an issue with my new 2x60 controller. I have been testing out the balancing scooter code with pretty reasonable first results & have been able to ride the scooter forwards & backwards in the workshop. All of a sudden the motors stopped turning and the error LED on the controller began blinking continuously.
The setup is as follows:
2 x 500W motors (limited in the code to 1/3 pwm output for initial testing)
8 x LiFePo batteries fully charged (approx 26.6V)
Arduino Nano sending packet serial commands to RoboClaw
BEC source is LB-MB
Arduino Nano powered by RoboClaw 5V pin
AMT102 encoders powered by RoboClaw 5V pin (10mA each)
All cables are shielded.
Arduino serial monitor shows gyros are working as expected.

Cycling power with the Nano connected has the LEDs go out for 2 seconds then the error light comes back on. The software has a 2 second startup delay for the RoboClaw to initialise.
Next, I turned power off, unplugged the Nano & connected a USB cable straight the RoboClaw. Connected RoboClaw to notebook, turned on power & started the new IonMotion software.
I can connect OK & see the overall status but that is all I can do.
Status 1 LED is on as expected but as soon as I try & move the motors via PWM or Velocity (I have encoders fitted too), the Status 2 LED flashes ever so briefly and the error LED starts blinking with no movement at all from the motors.
Status 1 LED remains on solid.
Cycling the power stops the error LED from blinking but it will start again as soon as I try & send any sort of motor movement command from the IonMotion software.
Before this error LED , I was able to control either motor with either PWM or Velocity from the IonMotion .
Seems like the RoboClaw has developed a fault with only 1/2 hour of use.

 Post subject: Re: RoboClaw 2x60 Error LED blinking & no motor movement
PostPosted: Thu May 08, 2014 3:28 am 
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Joined: Thu Mar 01, 2001 7:00 pm
Posts: 1316
Location: Temecula, CA
I've been working with you in email I think but for other peoples info I'll post the problem here and potential solutions.

The motors are MY1020Z 500w, 26amp rated current. Stall is probably 6 times more than that. Unknown inductance(mh) but I suspect it is too low for the regular 60a. The error indicates a mosfet driver failed. This can happen if a voltage spike larger than 50v gets to it. The voltage spike can be generated by a motor with too low an inductance. Motor inductance dictates the nexecssary filtering cap ripple current required. The 2x60a can handle ripple current of about 7amps. This equates to a motor with around a .5mh inductance or higher. Anything lower than that will cause the ripple current to go over the capability of the built in filter caps to handle it. When that happens a voltage spike can be generated which feeds back through the boost circuit on the mosfet driver. If that spike hits above 50v(even 50.1 will do it) the chip will fail.

Note that PWM percentage has no effect on with the motor will generate ripple current that is too high. If the inductance is too low even 1/3 PWM rates could generate voltage spieks that kill the mosfet driver.

There are a couple potential work arounds for this case. Add more filter caps at the battery inputs or add a coil in series with the motor to increase the systems total inductance. There are special coils specifically for this though I've not used them.

Also you should keep your battery wires as short as possible. Make sure the battery wire gauge is large enough. If you are using two motors your battery wire gauge should be around double the size of the motor wires(eg cross sectional area of the wire). All the current that has to get to the motor has to come from the battery so having undersized wires will slow down how fast the batteries can source/sink current. If they cant do that fast enough to keep the motors happy the current to/from the motor will be forced to slow down(if it exceeds the ripple current of the filter caps). If it slows down voltage will go up. The more it slows down the worse the voltage spike gets. When current is force to stop it theoretically will cause the voltage to go infinite. In reality that doesnt happen. Instead the joice finds(or makes) a path for the flow to continue. This is when the mosfet drivers get killed.

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