Duty Cycle Mod, version 2

[codesuidae]

I've got the preliminary version of the DCModV2 working on the test stand. This does pretty much the same thing as the original DCMod, but its a little fancier.

For anyone who doesn't already know, the DCMod is a microcontroller that intercepts the signal sent from the ZipZap SE MCU to the forward leg of the car's main drive motor H-bridge. It can perform some modifications to the waveform to improve (double) performance.

DCModV2 has four modes of operation:
Mode 0 : Passthru, same duty cycle, same PWM frequency
Mode 1 : PWMPass, same duty cycle, 8khz PWM frequency
Mode 2 : PWMFast, scaled duty cycle (max 100%), 8khz PWM frequency
Mode 3 : PWMSlow, scaled duty cycle (max 15%), 8khz PWM frequency

I've still got some tweaking to do to get the output duty cycles right, and I'll probably cut the PWM frequency down to 4 or 2khz. The audio frequency it generates is about twice the pwm frequency, so it sounds like a seriously pissed off mosquito at 16khz.

The main goal with this project was to bring the PWM frequency up from 100hz to something that would deliver smoother power. While I've achieved that, at the moment its only installed on my test stand, so I can't really drive it yet to say if it is an improvement.

This project has also been a learning project as a base for a dual ESC project for nasphere. The requirements for the two applications are essentially the same, read an input waveform and control a PWM output in proportion to it. Adding a second channel should be fairly straightforward, although I may have to move up to a slightly more powerful MCU.

[crazydave]

So mode 1 does not modify the duty cycle, only the PWM frequency?

And the modes will be selectable after installation, like with a dipswitch?

If so, that should be interesting. I actually found the 100% duty cycle to almost be too much with the 2.4v power source for controlled racing in smaller areas. I like how the newer Zip Zaps perform. This would be the DC Mod I'd want to put in a newer car because it'd be nice to be able to switch to between stock, and various degrees of more speed when needed.

[codesuidae]

Yep, thats right. I'm not sure mode 1 is useful, but it's interesting to see how just changing the PWM frequency changes the car.

The DCModV1 actually has three modes of operation, Passthru, 1st Gen and 2nd Gen. You can unset (ground) the passthru pin to run in stock mode.

The PWMSlow version will probably be special order with the regular version substituting a PWMMedium mode where it provides a 75% max.

[ph2t]

Yep, thats right. I'm not sure mode 1 is useful, but it's interesting to see how just changing the PWM frequency changes the car.

Very nice work suidae, if I can remember anything from my esc doco, higher frequency drive work better on lower turn motors. Lower freq is better for high turn motors and more torque off the line....