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### Topic: Need Some Help on a Project (Read 745 times)previous topic - next topic

#### aromond

##### Sep 12, 2011, 07:02 am
Hello everyone,

I'm new to arduino, new to electronics, and new to this forum. I'm starting a project of controlling a toy with an arduino uno. I could use some help understanding the motors in the toy. Any information on how to measure the power requirements of a motor would be great. The ones in it are pretty generic looking, I'm assuming they are dc motors, although that is a guess. I think they spin one way and to spin the other the current is just reversed, but again kind of a hunch. Any assistance or suggestions of what I'm attempting would be great. To see more about the toy and the project check out the blog I made for the project. http://aromond.blogspot.com/

--aromond

#### scottyjr

#1
##### Sep 12, 2011, 01:55 pm
Your assumptions on the motors being DC and the voltage being reversed to control direction are correct. Motors need alot of power. I would suspect that the batteries are wired in series to provide a hefty 6 volts to the motors. To determine the power requirements, install some new batteries  and take voltage and current readings at the motors. With the multimeter on the next highest dc voltage setting above 6V(e.g. 10VDC), measure the voltage at the motor with the motor running. Disconnect one wire going to a motor. With the meter on the highest DC current(A) setting, put the leads of the multimeter between the motor and the disconnected wire to the motor. Run the motor and read the current to the motor. Put a load on the motor (e.g. try to stop a wheel) and read the current. It is possible that the motors have some identification markings that you can google. There is no way an Arduino can power a motor like yours directly. Too much power is required. you will need transistor-transistor, transistor-relay, or mosfet circuitry to power the motors via Arduino. - Scotty

#### MarkT

#2
##### Sep 12, 2011, 08:30 pm
You can determine the stall-current of a motor by measuring the resistance across the windings, then using I = V/R

The no-load current is usually a lot less, and is best measured since it depends on the mechanical resistance and motor efficiency.

The power supply needs to supply enough current to overcome any mechanical load the motor is likely to see - this is likely to be somewhere between the no-load and stall currents.

If the power supply can supply the stall current then its voltage is unlikely to dip when the motor is under load - this is important if several devices run from the same supply.

Running the motor at full stall current for more than a short time will cause it to overheat, note.
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