PWM control for single AC motor?

Hi all,
Currently putting together the Root 3 machine from Thingiverse. I’m planning to control it with a RAMPS1.4 board (designed for 3D printers but more powerful than OpenSource CNC motherboards). Now, I got myself a Moss 710W router for it. It seems to be based on the Makita router.

So I opened this thing up, pretty standard inners with 1 phase AC motor, smoothing capacitor and thyristor speed control.

I want to control the spindle speed remotely from my RAMPS1.4 board, which would do so via PWM.

So how do I control such an AC motor via PWM? Figured someone on here must have experience with this!

Many thanks :)

I'm assuming that in a router it will be a Universal Electric Motor, assuming so it depends on your router's internal controller, you will either have to set the internal control to full speed or eliminate it in order to use an external controller.

Quote:

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Originally Posted by AcrimoniousMirth

So how do I control such an AC motor via PWM? Figured someone on here must have experience with this!

Many thanks :)

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With a Super PID. But it's really not worth it for a cheap router. For a little more money, you can get a chinese spindle and VFD.

Hi,
Yes, I did some more digging last night, it’s a universal motor so what I can do is rectify the current to DC upon which PWM control is a million times easier.
The internal controller at full speed just shorts out the potentiometer by using an inbuilt switch, so what I’m going to do is remove everything from inside the body (except the smoothing capacitor) and relocate them remotely.
Then I switch out the power button for a solid state relay and implement a design similar to this: www.thingiverse.com/id/AC-PWM-Dimmer-for-Arduino
In the end realising it was a universal motor simplified things immensely, though the initial problem is still an interesting one to solve someday. :)

Looked that thing up before, looks pretty awesome! But yeah, this is just an entry level machine and I’m working my way up as budget/use allows.
I considered a spindle but they’re about 300W for the same price as the 710W router and the VFD is a lot more of the cheap ones just use a potentiometer, so manual control.
As I plan to allow the motherboard to handle speed I needed to do t somewhat differently but as in my other reply I think I have the solution.
An interesting investigation for me to do would be to check the possibility of integrating a speed sensor to PID control it.

If going the Arduino route you're better off with grbl and a uno/cncshield combo, they're super cheap I paid <£10 for mine on ebay from UK seller.

https://blog.protoneer.co.nz/grbls-p...speed-spindle/

You could also use a variac to control the speed.

Good luck with your build.

Quote:

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Originally Posted by Desertboy

If going the Arduino route you're better off with grbl and a uno/cncshield combo, they're super cheap I paid <£10 for mine on ebay from UK seller.

https://blog.protoneer.co.nz/grbls-p...speed-spindle/

You could also use a variac to control the speed.

Good luck with your build.

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I've actually already got one of those for about £4. It seems very... lacking. With the RAMPS1.4 I can add LCD and SD control, better processing and a tonne more peripheral pins if I need them. As Marlin is based on grbl it holds a lot of the functionality and holds a CNC configuration option anyway. So overall it looks like the better option.
Yes, a variac, but see, I'm trying to control the speed automatically. If I wanted to manually control it I'd just move the existing control box to a remote location. I've since solved this issue (run motor as DC via bridge rectifier).
Nevertheless, thanks and thanks again for the good wishes, I'm sure I'll come across a few issues along the way :)