ok so im going to be making a mini go kart for a 3 yo kid. i have a treadmill motor its rated at 21 amps 130 volt dc. i dont want it to have to much power to it since its just alittle kid. im wondering what a good controller and voltage rating for it would be. so what would be a good amp and voltage for it? what would be a good controller for it as well?

 

Curtis makes a line of controls for DC motors--I would investigate a 24V version as this will provide 0.67HP and will run on (2) automotive batteries in series. Gear for desired max speed.

 

My neighbor had a Barbie car for his little girl. My point is, a little reverse engineering could go a long way. I'd look into how the commercial kid cars are built and go from there. Maybe find one used and fix it up. You just need to find the kiddy car junk yard.

 

Voltage = speed, generally this variable is chosen to be an adjustable/scale-able type. So daddy can "test it".

Attach a tach, or pulse counter and spin up the motor unloaded. You can hand start the flywheel if your supply is on the weak side. Assuming the supply has enough current to accelerate the motor, take the Amp Voltage and RPM readings.

You now have rpmV, and Amin. Loaded rpm will vary, but not above this number, and loaded Amin will vary but not below this number, excluding electro-braking and hills.

Stall current, torque, and fwd/rev timing. Testing this is a fine art of not breaking things. The theory goes. Bolt the motor down to a large plate with the commuters in a known location, such that the output shaft and an attached lever press parallel to the plate at a known distance onto a measuring device(bathroom scale) also setting on the plate.

Now you have a rig to test with. Align the brushes center of the pads of the shaft and attach the lever. Apply a low fixed voltage and high current source and measure the amp and torque.

Doing the same in reverse current and mechanical layout, such that the motor spins the other direction and presses on the scale. One direction will exert more pressure and or draw less current, if the brushes have been advanced.

With stall torque and current. You now have to decide how fast do you want to go, how fast do you want to get there, what you want to spend along the way, and if you wait or learn anything along the way.

You may break an off the self controller or be unhappy with it, without a solid understanding of your motors abilities. A golf cart type controller may leave you wanting an adjustable power curve for more "fun" also.

As a final note plan ahead. If you are in the north that three year old is going to be alot bigger by the time the get to ride this in the sun.