Motor don't start or only in one direction

Submitted by Diodote on Wed, 03/27/2019 - 12:29

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Hello,

I use a ZeroBorg with 3 smalls motors (Opitec) and 1 quite big motor (Conrad D919 148:1 motorreductor).

The input voltage is 10,8 V from a power supply capable to fournish up du 30 V DC in 10 Amp.

The 3 Opitec run OK in 2 directions with a usage a SetMotorX(0.2). With a smaller value, the do a noise but don't start. I need they rotate not to quickly. But It's OK.

But the big motor doesn't run OK. It a quite "big" motor but the problem occurs even without any load on it.

It starts and is capable to rotate in both directions for a few seconds, then it rotates only in one direction and do a noise in the other direction.

I've change the "condensator" of 100 micro-farad to another one of 470 micro-farads because of spikes that reboot the Raspberry. Today, I've separated the Raspberry power supply from the supply of the ZeroBorg (I inactived pins 2 and 4 of GPIO 5 V to do this).

What's the matter ? Are the "condensator" to high ? Why the Conrad 4,5-15 V DC don't spin up well ?

I've a competition robots in 3 days, Saturday so I'm a little in a hurry (:-((

Thanks for any advice.

Harvey.

piborg's picture

piborg

Wed, 03/27/2019 - 13:19

Usually a high pitch "whine" from the ZeroBorg indicates that the over-current or thermal protection is limiting the output to protect the board.

Given that it works for a few seconds I suspect that the motor is drawing a bit too much current and causing the board to warm up. Once warm the thermal protection is then limiting the output below what is needed to operate the motor correctly.

Do you have a link to the motor specifications?

Diodote

Thu, 03/28/2019 - 12:27

Hello,

Thanks for your reply. Yes, I have. Here is the link to the large motor : https://www.conrad.fr/p/moteur-a-entrainement-12-vdc-mfa-919d1481-1-222366

Finaly, the problem has changed a little since I've mounted the motors on the robot.

The large one succeed to spin up, slowly, but sufficiently in both directions. The change seems to occur because I put in SetMotor4(1), 100 % of the 10,8 V the board accept. One thing has to be mounted on this motor but this one seems to be OK.

BUT 2 of the 3 smalls motors don't succeed to spin up because there is a little mechanical resistance. They seem to be too weak to start and are noisy like a little buzzer, even with 7 to 10.8 V. These motors are OK with a 4,5 V commercial battery (alcaline) and powerfull.

Is the PWM the fault ?
Why can I do ?
Do I have to put a "condensator" to "smooth" the power entry ?

Thanks for your help.

piborg's picture

piborg

Thu, 03/28/2019 - 15:26

Your large motor exceeds the 1.5 A specification for the ZeroBorg. Looking at the datasheet it has an 8.24 A stall current when operating at 6 V. It will use even more current running at 10.8 V. This is why it is behaving so poorly and it may damage the ZeroBorg in the worst case :(

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