Minimum voltage needed to drive motors?

powersupply
gopigo3

#1

Couldn’t find it in another post, or in docs…

Thanks!


#2

For GoPiGo3, the battery voltage should be at least 7v (9-12v is recommended). The motors will automatically stop running when the batteries get down to 6 - 6.8v (the exact cut-off voltage depends on the RPi power requirements).


#3

Many thanks - Am seeing weird behavior when I get close to 9v. turn_degrees() starts to hang (both blocking and non-blocking). Recharging batteries seems to help; but it could be due to recharging == reboot.


#4

Please ignore previous comment - running gdb on the stuck process shows it’s hanging in some of my code… not the GPG3 code.


#5

I dont want to open a new topic so I affiliate my question to this … . I want to connect a car-batteriy 12V 45Ah is this possible?


#6

Hi @dev.td,

Yes, you can use a 12V car battery.

Though I’d be extremely careful because the car’s battery has very big discharge currents - all after all that battery is used for firing up the engine, and that requires tremendous amounts of current.

In order to avoid a short on your GoPiGo, I’d use a 10 amp fuse for it. It will keep you away from any accident.

Thank you!


#7

Could that be clarified. Can you get hurt from a car battery?
Safety First, GoPiGo safety last.


#8

@dev.td if you have any pictures . . . we would love to see them. :grinning:


#9

Hi @graykevinb, @dev.td,

No one can get electrocuted from a 12V power source.
This includes a car battery.
Just don’t connect the terminals to your tongue.


The danger is in shorting the wires. If you short the wires, here’s what happens:

  • If the wire’s resistance is low enough, the short won’t break and the battery will continue to get really hot. The battery might as well explode, therefore releasing sulfuric acid everywhere.

  • If the wire’s resistance is very low, the short will become super hot and then break. It’s sort of a short-fuse between the battery’s terminals. Nothing else happens.


Thank you!


#10

Hi Matt
I hope you do not mind me troubling you with a follow-up question:

I have just set up my GoPiGo 2 using a Raspberry Pi 3.

Weirdly enough, although the instructions say that the motors won’t work powering the setup only through the RPis microUSB-connector (I am using the official 5V/2A RaspberryPi wall outlet) and although you confirmed that for the GoPiGo 3 (energy-thirstier motors maybe?), they work just fine in wall outlet mode with the battery pack disconnected and power switch set to off.

Why is that? And does this setup present any danger to the components or is it just potentially unreliable?

I am asking because it would of course be really neat to be able to replace the battery pack (currently using alkaline batteries, contemplating buying accumulators and charger) with a regular 5V power bank.


#11

The problem with powering the GPG robot with running motors (any version) with only USB power, is that the motors can cause dips or “brown-outs” on the 5v power supply rail. If the Raspberry Pi doesn’t have a well-regulated 5v power supply, it can crash and/or corrupt the SD card.

To prevent people from running the GPG without batteries, there is a software safety that prevents the GPG3 motors from running when there is inadequate power (batteries not connected). The GPG2 and GPG3 use very similar motors (with a much-improved encoder design on the GPG3).

To run motors without batteries, I recommend that you use a 9-12V DC regulated power supply (center positive), and plug it into the battery input barrel jack. Ideally it should be rated for 2A, but 1-1.5A might still work okay. I have extensively used 12V power supplies for developing with the GPG3.