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Been doing a little thinking while I’m trying to source some of ph2t’s uber fets 🙂
Unfortunately Its left me with a few questions …
ph2t – is there a reason you havn’t stacked the fets on Nelly? I know it would put the cost up, but wouldn’t you further reduce the resistance and increase the max current? (ok weight and cost go up, but would it work and would it bring any noticeable performance differance?)
No reason why I haven’t stacked them. I want to get the best possible fets first. It’s an intrinsic thing…:smiley2: There would be a performance difference, there always is. How much? Only real world tests would possibly show.
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Could someone correct me if I’m wrong but doesnt the mini-z/iwaver regulate speed by pulsing power to the motor … more pulses = more frequently the motor is reciving power = car goes faster, has anyone experimented with putting a cap (larger than the 104 or 103’s for reducing interference) to smooth out power going to the motor? (to large a Cap will make speed changes sluggish I think but the right size might help. Any attempts / info.
The speed control used is nothing different from traditional methods. PWM = Pulse Width Modulation. It’s more about the width of the pulse and for how long within one cycle is it on for. This is also known as duty cylce. 10% duty cyle means the pulse is on for 10% of the time in one cylce. Once cylce could easily be 1/1000th of a second long. 90% duty means the pulse is high almost all of the time. Obviously the greater the duty cycle, the greater the average power delivered to the motor. Hence, speed control.
Putting a capacitor across the output terminals will have a negative effect. This is because the cap will sink current when the motor should be. Since this is a cylce, the cap will always be reset and therefore always sinking current to fill it up again.
Putting a cap across the battery though should improve acceleration BUT at this scale people have stated that the effects are minimal. Personally I’m yet to try this, I believe with the right capacitor it could work. You would want a capacitor that had a really low ESR value. (Equivalent Series Resistance, avail on cap datasheets…) A low ESR is like a set of punchy ni-cd’s. The low ESR allows the capacitor to discharge a high current. This is the goal in increasing performance though using a capacitor across the battery terminals….
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Thanks
ph2t – seeing as you’ve managed to source these awesome fets would you be willing to resell/spill the beans on where you’re getting them?
http://www.digikey.com – Shipping is a bitch, but beggars can’t be choosers(spelling?)…..
cheers,
ph2t.
