Motor just buzzing with Dual Motor TinyShield

[arturoservin]

Hi

I am trying to use a motor with the Dual Motor TinyShield but the motor just buzzes.

The code (I took the simple example) looks ok as I measure the voltage and it increases as it supposes.

The battery that I am using also looks that gives the correct amount of current as if I connect the motor directly it rotates without any problem.

It looks that the board is not providing the enough current to the motors but I do not understand why.

Any ideas?

Thanks
as

[Ben Rose]

Sounds like it could be the short circuit protection of the motor drivers kicking in- what sort of motors and batteries are you using? Can you measure the resistance of the motors?

[arturoservin]

Ben

I am using motors that I took from a small/medium drone, like these ones.

http://www.newegg.com/Product/Product.aspx?Item=9SIA4P03S81810&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC-_-pla-_-App+Enabled+Products-_-9SIA4P03S81810&gclid=CjwKEAiAmNW2BRDL4KqS3vmqgUESJABiiwDTM9LoUN2OgXk1lfwQvdLXSVVC-nU6wCx4VshNR3U10xoClYXw_wcB&gclsrc=aw.ds

The battery is the same that came with the drone, it is a Li-Po 500mA and 3.7v .

The resistance of the motors is 1.7 - 1.8 ohms.

thanks

[Ben Rose]

<2 ohms is pretty low resistance compared to the average small brushed motor, and would probably trigger the overcurrent protection in the DRV8837, see: https://e2e.ti.com/support/applications/motor_drivers/f/38/t/331431

The solution suggested there is to put an inductor in series with the motor. This might not be great for your application. Are you able to try any other motors? I've successfully driven 7mm motors from a Crazyflie and 6mm motors from some cheap quadcopter. They seem to be over 2 ohms according to a cheesy multimeter on my desk.

I had a similar problem with toy helicopter motors which measured under 1 ohm- I thought it was a unique case and the motors might have been damaged, but it looks like we'll need to put some sort of warning on our website after we've found a solution for you.

Ben

[arturoservin]

Ben

Thanks for the reply, it makes a lot of sense.

About the motors, yes, I could try to get some new ones with more inductance.

As a workaround meanwhile, do you think that dropping a resistance of 2 ohms in series with the motor would do the trick?

Regards

[Ben Rose]

I think it would allow use of the motors, while of course wasting a lot of power. Do post your findings if you have a chance.

Ben

[arturoservin]

Hi

I added a 5 ohm resistor and it work very well.

I tried a 1.5 ohm but the current was still to high.

Now my issues is to use 2 Dual-motors board, but I will start another thread.

[arturoservin]

Another question.

How do I get the maximum current/voltage to the motors?

If I use 65535 the power goes to -1 as it seems that the int maxPWM variable is signed, then the maximum that I can get is 32768 or -32768.

I tried to change maxPWM to be a longint but the result is the same.

Any ideas of how I can get more current to my motors?

.as

[Ben Rose]

maxPWM is used to assign the PWM period, and other value sets the duty cycle(direction is set by the sign). So if maxPWM is 2000, setting the motor to 2000 or -2000 is 100% power. Same with maxPWM=32000 and setting the motor to 32000 or -32000.

Not sure how familiar you are with PWM stuff- the intros of https://www.arduino.cc/en/Tutorial/PWM and https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM may be helpful.

Ben

[arturoservin]

That's why I imagined.

I will check out the links, thanks.
as