how much power is needed?

Submitted by Diarmuidmoloney... on Sun, 04/02/2017 - 15:27

Forums:

Hi,

I picked up a KS2 at yesterday's piwars. My KS1 was never recognised with the pi zero so I decided I would just bite the bullet and get a Ks2 at the event

I am trying to drive to small motors, the yellow ones you see sold by many retailers in this space. I can drive one at a time, but once I try to drive two the zeroborg resets. Heres a small code snippet

works -->
ZB.SetMotor1(-0.7)

resets-->
ZB.SetMotor1(-0.7)
ZB.SetMotor2(-0.7)

I am running it off of the single 9v batter underneath the Ks2.

However when I connect the pi to my pc, while keeping the 9v in place I have no issue (other than being tied to the desk)

So my question is why do I need the 2nd power source? Is one 9v not enough to drive two small motors?

Thanks

piborg's picture

piborg

Mon, 04/03/2017 - 10:34

We have had a few people with this sort of trouble, it usually turns out to be an issue with the batteries.

If you are using a non-rechargeable 9V battery (alkaline) that is likely to be causing problems. Typical alkaline batteries actually seem have less "grunt" than the rechargeables. I would suggest trying a rechargeable 9V battery and see if things work better.

If you are already using a rechargeable then it might be that it is getting a bit flat. Try charging the battery fully and then see if the same problem persists. If that does not fix the issue you may have one of the older 7.2V rechargeable "9V" batteries. Most newer ones are rated for 8.4V, which should be fine, the old 7.2V ones are really a bit too low to run the Pi and the motors.

The batteries we use and would recommend are the Powerex 8.4V 300mAh. These have proven very reliable for us during our first Formula Pi season which has robots based on ZeroBorg KS2 running four motors at full speed.

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