How To Upgrade A Chinese CNC Machine

Looking to add a small CNC machine to your garage or hackerspace’s arsenal of tools? Like any tools — China has you covered for the cheap options — but the question is, is it worth it? Typically it depends on the tool, but when you can upgrade your 3040 CNC router to use USB instead of a parallel port with the TinyG motion controller… most definitely!

The 3040 or 3020 CNC router is a popular Chinese machine used by many hobbyists — and for good reason. A rigid all-aluminum frame, decent stepper motors and pretty good resolution? It’s not a bad deal for around $1000USD. We’ve covered it many times before.┬áProblem is, the electronics are a bit out-dated. Particularly in the fact that it uses Mach3 with a parallel port… Come on, who has a parallel port these days?

[John Lauer] set out to fix this. The TinyG is a motor controller we’ve covered a few times before as well — it was just waiting to be fitted into a 3040 CNC in order to run a better control system, like ChiliPeppr!

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Pulse Density Modulation

[esot.eric] was trying to drive a motor and naturally thought of using pulse width modulation (PWM) to control the motor speed. However, he found that even with a large capacitor, his underpowered power supply would droop before the PWM cycles were complete. So instead of PWM he decided to experiment with pulse density modulation.

The idea is to use smaller pulses over a longer period of time and make the average power equal to the percentage motor speed desired. With a PWM system, for example, if the time period is T, a 50% PWM drive would have the ┬ádrive high for T/2 and low for the other half of the cycle. With pulse density, each pulse might be T/10 (as an example) and then the output would be on for 1/10, off for 1/10, on for 1/10 and so on, until by time T you’d still get to 50%. The advantage is the output capacitor gets a kick more often and has less opportunity to droop.

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