I use the Rockler controller. It looks a lot like an HT unit. But it seems to work better. My HT one died after about 10 hours of use.I know there's the normal cheap router speed controllers like the HF controller.
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And then there's the Super PID controller that's used on CNC machines.
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I've also seen several DIY web sites that show how to make Arduino based controllers, But that's a little out of my skill level unless it was something I could follow a diagram & downloading the codes.
I seen this Dart 55AC15C that states it's a full wave controller, So you wouldn't get that half-wave clipping assonated with the cheaper controllers. However at $126 it's almost the cost of the Super PID controller?
Is there anything in-between the lower cost controllers & the higher priced ones?
I must be honest. The first Rockler one didn't work right out of the box. One e-mail to Rockler and I had a new one in a week. Didn't have to send the old one in nor take it to one of their stores. Great customer service. But beware none of these less expensive ones will work with Soft Start tools.