Hi everyone! I developed a brushed motor controller for a ~120 pound desktop milling machine build. I feelt hat steppers are not well suited for some machines past a certain point. Nema23 steppers output power is kinda low, as is its maximum speed, and bigger steppers are quite heavy and not cheap at all. They have the advantage of not needing a position feedback sensor to work, but if one wants to use one anyway, that advantage is gone. That's why I decided to use some brushed motors, and I was not dissapointed. Now, after finishing the machine, I made some improvements to the controller, and I'm soon launching a crowd funding campaing for the board Tarocco: Open Source Closed Loop Motor Controller I believe this controller is a good choice for machine builders that want to get away from steppers, so please consider backing the campaign if you feel you have a use for the controller. Any questions/comments are more than welcome!
As a little bit of background information, closed-loop position detection systems with DC (brushed) motors are commonly used in printers. As you have noticed, printers are now very inexpensive, but very precise. Unlike with stepper motors, the system "knows" where the inkjet (or in our case the spindle) is at all times. The sensors are simple and inexpensive, consisting of printed lines on a transparent disk, or on a long transparent strip. There is a light source and photo detector array to read the optical pattern of the disc's position. In that system, the motors are driven until they reach the desired position, (not x number of steps). Stepper motors are also precise, but there is no position feedback. If they become out of position (rarely I think), they do not correct themselves. There is an amusing video of an Austrian builder, complete with a thick accent, who built a very ugly CNC with an optical feedback sensor. Send that guy some C-beams, plates, and wheels and see what he can do with optical sensors and DC motors. "I want your clothes, your boots, and your motorcycle"
Hi Terry! I've done some testing with salvaged inkjet printer hardware. The motion is indeed precise, but the drawback is that the motors are very small. They are good for 3d printers or pen plotters, but they don't really work for machines that use cutting tools, like mills, as they dont have enough power to push things hard enough. My controller was designed to supply nearly 1/2 hp of output power to a motor. It is useful for the larger machines, though it may as well be used with printer brushed motors. I tried to use an atmega328 to decode the quadrature output from an encoder, and to handle a PID control loop, but it was kinda slow, so I decided to change the AVR for a PSoC4. It makes handling high resolution encoders at high speeds so much easier. For example, I can drive a 4000 rpm motor with a 1600 count per revolution encoder without breaking a sweat. There's more info about the motor controllers on Tarocco and Brushed DC Servo Drive Now, if you'll excuse me I need to get to da choppa
