12 volt ride in Toy Car potentiometer

[alwest197]

Just wondered if anyone could help. I recently bought a toy ride in car for my Grand Daughter. Its 12 volt with two very powerful 35 watt wheel motors.
My problem is its too powerful with only a foot switch pedal, which is either off or on..no slow power take up. So when she puts her foot on the pedal it takes off like a rocket (lifting the front end) . Now I guess I can do one of two things (three I suppose if I send it back) I could disconnect one of the motors or I could fit (I think) a potentiometer between the battery and the motors. I was thinking of a dial type potentiometer in the cab of the car.
This would allow me to lower the power somewhat as she gets used to the car.

Is this a) possible and b) feasible


Grateful for any help on this

Thanks

 

[flameport]

Possible yes.
Feasible NO - because the pot would have to be rated to at least the rating of the motors, and as that is over 6 amps, any pot rated to that will be very large and expensive (assuming you can actually get one).

The other issue with using any kind of resistor (fixed or variable) is the substantial amount of heat which will be given off.

 

[alwest197]

Thanks for that. Am I likely to cause any damage by disconnecting one of the motors do you think..?

 

[flameport]

Unlikely to damage anything, however is it one motor per wheel, one on each side?
If so, removing one of them will mean the car goes round in a circle.

 

[alwest197]

I think its ok from that point of view.

I had a previous ride in car which was only 6 volt (1 motor driving just the one wheel) but it could not pull the skin off..etc.

I was worried about damaging the motor but looking at the wiring I think it was designed for one or two motors...

Thanks for your help..I'll try just the one motor tomorrow... if its stopped raining that is.

 

[FDJ]

Try wiring the two motors in series.

 

[ericmark]

Is the armature and field wound separate. I had a trolley to travel down a 42 inch pipe which was powered by a dynamo. By putting a Lincoln welding set resistor in the field we were able to control the torque. However it also controlled the speed and as the field current was decreased the thing went faster although with less torque.

 

[alwest197]

Thanks guys...

but you are not talking to someone who knows very much about electrics/electronics.

Fitting a potentiometer in between the wires from the battery to the motors is about as technical as I get.

I suppose it might also be an idea to find a pedal switch which has this functionality built in... I'll try a google search and see what comes up...

thanks again.

 

[alwest197]

Just noticed on a couple of ride in car adverts (argos) that some have two speeds.. 2.5mph and 5.0mph..

Any idea how they achieve that...? because that would suffice for me..

 

[big-all]

as said above wired in series gives both half volts and no extra heat generated or extra wasted energy through resistance

 

[alwest197]

ok thanks...I'll give it a try..

 

[big-all]

just check the wheel rotation whilst they are off the ground otherwise it may turn into a mini roundabout

 

[GarethW]

What about an Electronic Speed Controller ?

http://cgi.ebay.co.uk/36V-30A-DC-Mo...al_Components_Supplies_ET&hash=item43a62c6956

You could have a "dash board" mounted potentiometer wired in series with the foot switch.

 

[Astra99]

Another possibility would be to get two heater motor resitors and one heater motor switch. Wire the switch/resistors up to each motor in a similar way to that used for the heater motor and you are away. Best of all, these parts can be obtained from a local scrapyard. Oh! Sorry, they are now called auto recyling merchants or something like that!

 

[bernardgreen]

The PWM ( pulse width modulated ) control of the motor is a good idea. But the one above is 32 volt and might not work well at 12 volt. Later I may have a source of a 12 volt unit.

You need one that is fail safe and does not rely only on a potentiometer in the "throttle" control. If the device fails the motors could be given full power.

Taking the foot of the pedal must open a switch that cuts all power to the motors

Another simple option would be to replace the 12 volt battery with a 6 volt one.