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Electronic Speed Controller

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Steve Withnell23/08/2011 22:44:33
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858 forum posts
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I'm just re-furbishing a model jeep, can't remember what it's called, it was a popular build constructed from a sheet of 8x4 ply and powered by a windscreen wiper motor.
 
My Dad built this one for my kids, but he made a number of "upgrades". One is that the drive is a Sinclair C5 motor driving one rear wheel via a commercial reduction box + chain.
 
Full speed is about walking speed and at the minute power is switched to the motor by a micro switch under the "accelerator". (Hi current relay near the motor).
 
I did think about adding a speed controller so that the power is applied in a more controlled way, but given the low top speed it seems overkill.
 
Is there some simple electronics available that would simply ramp up the power when the accelerator is pressed, as I see no need for manual speed control?
 
TIA
 
Steve
Andrew Johnston24/08/2011 09:58:46
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7061 forum posts
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As far as I'm aware the C5 motor is a permanent magnet DC motor, so speed control is just a case of varying the amature voltage. Two quick ways spring to mind.
 
One just use a large power device, a MOSFET is probably better than an IGBT at low voltage, and turn it on slowly. While turning on there will be quite a lot of dissipation in the power device; put it on a bigger heatsink! It would be simple enough to generate a linear ramp to drive the power device. However since the turn on characteristics of the device are not linear you may not get a linear increase in voltage at the output.
 
The second method uses a PWM signal increasing linearly from 0% to 100% to turn the power device on and off. To a first approximation this takes the switching characteristics of the power device out of the equation, as it is either on or off. The output voltage then becomes solely a function of the PWM.
 
Regards,
 
Andrew
Gordon W24/08/2011 10:09:53
2011 forum posts
I know you asked about electronic devices, but a simple resister switched in will do for that sort of job, use 2 or 3 for finer control. Works ok on elect bike (old type)
Steve Withnell24/08/2011 18:34:37
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858 forum posts
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Hmmm a combination could be interesting.
 
 
Pseudo gear stick, each "gear" a fixed resistor driving the mark -space on the PWM. Accelerator is "power on" so like a dead mans handle.
 
The PWM would avoid me having to bring high current to the front and back again, but then again it's only about 30 inches!
 
Steve
john fletcher 124/08/2011 19:59:13
893 forum posts
I have made quite a few speed controllers for various similar motors using PWM and MosFets, a small pcb from RS together with a 555 timer. Please send me a PM together your phone number I will tell how to make one, not expensive.Ted

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