I’ve been using a Rotozip for my build since it was available and didn’t cost me anything.
Last night I tried to wire up a dimmer switch to help regulate RPMs when I don’t need all 30K. Hopefully this will also extend the life of my bits.
Since some of the other post here suggested a cheap Walmart dimmer that’s what I tried (GE 18021).
Unfortunately, it seems like I’m either getting the full 30K RPMs or nothing at all. My thought is that the Rotozip is the problem. Can there be internal circuity that cuts power when the waveform isn’t complete?
Otherwise, why would the dimmer, which was only tested with a lamp (planning on trying with my shop vac tonight), not cut the waveform correctly?
FYI the dimmers power “limit” is 600 Watts but I imagine it was set conservatively.
I’m playing around with the idea of either taking the Rotozip apart and trying to bypass this “circuit” or switching over to a 660.
Any advice or past experience would be greatly appreciated!
Maybe not the lowest cost solution but I’ve been using a HF router speed controller with a 660 and it seems to work well and I haven’t had any issues. It’s currently shown as a clearance item for $14.97 so who knows how long it will last?
I think @B-26 is referring to an add-on speed control, not a router with a built-in speed control.
Motors and other inductive loads work differently than resistive loads like incandescent light bulbs and (other) heater coils. Simple dimmer switches are designed to work on resistive loads. They add a variable resistance inside the switch which redirects energy that would go to the lightbulb and converts it to heat instead. These work with old incandescent bulbs, but not on newer LED bulbs that use much less current. The resistive load inside the dimmer means power flows through even at very low/off settings, and this low current is often enough to cause LED’s to glow even when the dimmer is turned off.
The sort of control that @B-26 is talking about uses a Silicon Controlled Rectifier (SCR) called a triac to turn the power completely on and off several dozen times a second. These are sometimes referred to as “chopper” controllers. This allows motors to run at variable speed, but can have a negative impact on the power (torque) the tool can actually put to use, since it’s generally the higher power portions of the energy wave that get “cut off.” This means that below a certain power setting/RPM, the tool becomes very easy to “stall.” Newer LED-compatible dimmers probably also use a triac (I’m not certain), but I wouldn’t expect it to be robust enough to handle the current for running a spindle.
The controllers built into routers generally start with the triac and add a PID feedback mechanism so that if the motor slows down, power is added back in to the circuit. This keeps the bit spinning at close to a constant speed even as the load on the tool varies (starting and stopping a cut, or hitting a knot in a piece of wood).
If you’re comfortable playing around with mains voltages and some programming, @vicious1 has a PWM AC Dimmer board in the shop that can form the basis of a PID-loop controller as documented in the (very long) PID - Hardware Solution Needed for a Software Fix. Note that this is not a turn-key solution - it requires an additional Arduino Nano on a daughter PC board and several components to be added to your spindle. I don’t know the rotozip well enough to know whether there’s space for the sensor in there somewhere. Having said that, I’ve got it working on the DW660 and I like it a lot.
Another commercial solution available is the Super-PID, but this is aimed more at high-end routers. It requires the addition of similar components to the @V1 kit be added to the spindle, but all the other circuit assembly and programming is done (and not user modifiable).
To clarify, or maybe add to the confusion, I’m not really sure: I checked HF’s site and it shows both a trim router labeled as a Drillmaster as well as the separate speed controller I’ve been using being labeled as a Drillmaster.
At any rate, I can’t say it’s had heavy daily use but so far the speed controller has worked well for me in conjunction with the 660.
“Drillmaster” is one of the Harbor Freight brands, like Chicago Electric and Bauer. It tends to be on the lower-quality end of their scale, based on comments I’ve seen on other forums.
This is the speed control I’m thinking of. It wouldn’t surprise me if they’re on clearance because they’ll release a new “version” of the control under one of their “better” brands at a slightly higher price soon. Woodcraft, Rockler and other woodworking stores have similar controllers available at higher price points, but I think they all work the same way. Probably all come from the same factory with different stickers applied.
Traditional dimmers use triacs, not resistive loads (which would very quickly start a fire).
They switch on “late” in the AC cycle (based on a voltage threshold) and switch off when current crosses zero, so they don’t create voltage spikes from switching off inductive loads.
They should work fine on “universal” motors which are a rectifier and a brushed DC motor. I use one for my shop vac. A fluorescent ballast or a switching power supply (or whatever is in an LED bulb) is a different story and triac dimmers don’t work.
As a general principle, voltage determines speed of a motor and current determines torque. A motor with no load will spin fast and produce back emf that nearly matches the input voltage, and almost no current will flow. If the input power is chopped up and the current is intermittent, while the full voltage is provided, you might get nearly the same speed. But under load the router might slow down a lot more as a result of the dimmer.
You could have a look at katsu router on amazon, it‘s a makita clone with variable speed built in. It exists in few other brand name but they are the same.
Yeah, I use the Bauer from HF which is a Makita clone as well, it’s done well for me. It’s FAR superior to the DrillMaster crap and the variable speed works well.
Yeah, that’s the one I’m using. Hasn’t gone kerblamo! so far so I guess I’ll continue until it does. Wouldn’t surprise at all if the same units are sold with different stickers attached.
Thank you all especially @ttraband. I ended up on your linked page to the PID thread and time kind of disappeared.
My initial thought in my first post was that I would manually adjust the RPMs using the dimmer and not worry about any decrease under load. However, after drooling over the use of PID to control speed I decided to first take apart the RotoZip and try to find a place for an led/diode.
Once the router housing was apart I noticed that the motor has a commutator. From my limited knowledge of motors I assume that it runs on DC. Additionally, the internal circuit board had some sort of rectifier which I guess is converting AC to DC (black and red wire to motor). Are all these router motors usually DC driven? Maybe I’m wrong in my assumption/knowledge.
Regardless, it seems like there are products available to control voltage i.e. speed.
The RotoZip voltage to the motors was in the 36-40V range.
Is it unwise to bypass the circuit and wire directly to DC voltage?
BTW I do have a DC motor speed controller that I’ve yet to mess around with. KBIC-120 (9429A)
I also have a KBMG-212D but that may be overkill. Both of these, I think, could wire directly to the PWM of an Arduino output!
Line in (black and white on left). Rectifier dead center (neg/black and pos/red wires to motor). Bottom wires to switch (white and blue). Bottom triac (btb16-600bw). The back has a IC that I can post if anyone has any interest.
The combination of a rectifier and a DC motor is by far the most common configuration on relatively inexpensive tools.
Dimmers do work, but limiting power and limiting RPM are not the same, so a controller with feedback is necessary if you truly want to reduce RPM (and presumably maintain RPM under load).
I don’t know what a variac would do. It might reduce RPM and increase available torque, but I’m not sure. It might also burn up the motor.
