I make a lot of my own printed circuit boards and etching was always a bit of a chore since you really need to keep the acid moving over the copper. My left arm muscle is now testament to the number of boards I have made over the years by manually agitating the acid bath.
I was watching a agitator built by TechBuilder on YouTube and decided I needed one.DemonstrationHardware
The unit is built around a Jiffy Box (157x95x53mm). The motor is a 100RPM geared 12V brushless motor from eBay. The hinge was one I had found in my toolbox (I think I got from Bunnings but can't really remember. Anyway it's a Black Nylon Hinge (48mm length x 48mm (open) x 9mm thick). The 3D printed Cam is held on to the motor shaft using a M3 grub screw and M3 nut. The bar incorporates two 3x8x3 bearings to reduce the friction.
100RPM geared 12V brushless motor
The motor speed is controlled using a PWM signal generated from a 555 timer via a N-Channel MOSFET. I used the same circuit that I designed for my Ender 5 light bar. Instead of driving an array of LEDs, it drives the motor. The other side of the motor is connected to VCC or 12V. You need to add a diode across the motor to stop back EMF from the motor destroying the MOSFET. (Anode to the MOSFET, Cathode to VCC). Also you need to replace R2 with a 0 ohm resistor.
Schematic of motor controller
The PCB was designed to fit a 45mm slide potentiometer with a 35mm travel. I used surface mount components because that what I had around the workshop.
The PCB is designed to be solder to a 45mm slide potentiometer.
Assembled controller mounted to side of box (Note diode soldered across connections to motor)
I used a DC Panel connector and a 12V 2A power brick to provide the power.
DC Panel connector and final wiring
To secure the tray that holds the acid, I decided to use fridge magnets. Trade people tend to leave a lot of these in letterboxes here in Sydney so now I finally have a use for them. Glue some to the top plate of the agitator and to the bottom of your etching trays.
Fridge magnets make a great way to attach/deattach the etching trays
I found its best to agitate along the longest axis of the tray. To much liquid when the top is over to one side will place a lot of load on the motor especially when that liquid is further away from the fulcrum. You don't want a lot of movement, just enough to have the acid slowly go back and forth across the copper.