current drive for motor robot

[garg29]

dear friends
m making a four wheel car in form of a robot. i have used two motor on the back side wheels. the motor is running on 12 v and has 200 rpm each. how can i calculate the current drawn from each motor so that i can make its control using power transistors. i actually want to make the car form robot turn on the either sides when needed.
can anybody please help me
with best regards
amit

 

[bloody-orc]

mesure those amps with a multimeter or something like that. or when there is power marked on it then you can calculate it from there. i dont know if you can calculate using ohms law... you can try. mesure ohms betwean two pins of the motor.

 

[Nigel Goodwin]

mesure those amps with a multimeter or something like that. or when there is power marked on it then you can calculate it from there. i dont know if you can calculate using ohms law... you can try. mesure ohms betwean two pins of the motor.

No you can't, the amount of current drawn will vary greatly according to the load - the stall current is going to be massively greater than the off-load running current, expect between 10 and 100 times greater!.

 

[bloody-orc]

the best way is to mesure. copnnect your meter and then hold the rotor in place (create an auful lot of force) so that the motor will draw as much current as possible.

 

[slurp]

the best way is to mesure. copnnect your meter and then hold the rotor in place (create an auful lot of force) so that the motor will draw as much current as possible.

be careful if you've got a small gearbox on the end of your motor... if there's no torque limiting there might be a chance that you'll damage a gear tooth or two.

think about your motor/gearbox shaft too, you probably don't want to damage the surface either.

In the past I've fitted the wheels I've planned to use to the output shaft and gripped this with a view to stalling the motor & measuring the current. Similarly you could put your 'bot up against the wall and start to load up with a bit of extra weight before making your current readings.

regards,
colin

 

[Oznog]

The stalled current is going to be the resistance, nothing more. This is not really relevant though. You will probably want to use some sort of current limiting in case the motor gets jammed rather than leaving full battery voltage across a stuck motor.

The motor has a rated power level. It can usually be used to produce more. What you need to know is how much current it will need for your app, which varies based on incline, weight, tire type, surface (carpet is slow for example), and of course how fast you want to run it.

There's also a point where your tires will slip. Using more current than the tires could possibly use without slipping on the best of surfaces would only happen if an object had jammed the tire or something wrapped around the drive shaft. Those are things you want to shut down for, rather than building a driver that could keep providing it.