Let's Make Robots!

Stupid question on ampere and motors

Probably a stupid question: if i have a motor driver that can handle at most say 1 A per motor, and two motors that consume say 2 A when stalled, what will happend when they stall? Will the robot simply underpower, or the motor controller burn, or what else ?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
BaseOverApex's picture
You could whack a big series resistor in the power line just to make sure the controller never over-currents. Terrible waste of energy, though and your motors won't be running as fast as they might.
CaptainTuna's picture
what is stalling?
BaseOverApex's picture

Stalling is when stuff stops. I'm not being funny.

For our purposes, the "stall current" is the amount of current the motor will try to draw if the shaft is physically blocked. With the shaft stopped, stalled, blocked or whatever, that's the maximum amount of current your motor will try to draw.

You probably don't want to stall a motor just to find this out. Fortunately, in most cases you can approximate it by measuring the resistance of your motor and applying the formula I=V/R, R being your resistance, V being your drive voltage and I being the max current.

* I say approximate because properties of inductive loads change when you squirt electrons through them.

 

you can increase the continuous and peak amperage it can handle by attatching a heatsink 

robologist's picture

This depends upon which motor controller is being used and how long the stall is. Several drivers I know of will go through "thermal" or over-current shut down if the current is close enough to their rated loads, and simply cease operating till they cool down.

I had a robot using a sn754410  driver board, with a series pair of 7.2 volt RC racing packs, 14.4 volts total. The motors being driven were Faulhaber 2842-012C which are 12 volt motors stalling at 2.2 A. The higher voltage meant that a stall was probably closer to 2.5 to 2.7 A. In just running the robot to a wall, the wheels would slip and the h-bridge never "smoked". In forcing a stall by holding down the robot to force the wheels to stop, the h-bridge had a pretty spectacular "flame-failure". It had to be forced in to that mode though.   The 754410 is rated at 1.1 A continuous and 2 A peak, so it was definately beyond spec when it flamed.

Nicola's picture
thank you guys :)
jka's picture

The motor controller will probably burn.

 

fritsl's picture
I can cornfirm that, from real life experience.