Originally Posted by Guy Smiley Yes it does. Actually, I've wired and mechanically attached an automobile wiper (Honda Civic's) to run the x-axis on my Enco type bench mill. I used 2 DPDT toggle switches to handle direction and speed (fast & slow). I also machined a brass sleeve to connect the motor shaft to the mill's drive shaft. I have been milling aluminium on it for my CNC Router project (documented in the DIY project log thread) but have kept to just max feeding of 0.5mm passes with a 3/8" 4-flute end mill. Works comfortably at that or less feed setting.
Now what I'm thinking of, is if, until I get the Gecko's. Can I get a Xylotex stepper driver board to control relays that will control these bigger wiper motors using a 20A regulated power supply (for the motor) or is there a better way? Using this board, do I need a certain circuitry to accurately control the voltage (cut-off/vent to another load the residual voltage if there's such a thing) from the relay to the motor? Or forget it and just use the Geckos.
I, as most here, am just trying to find an alternative way of doing homebrew CNC with readily available components and surplus wiper motors are sure abundant in auto parts recycling facilities. Thank you for responding.
EC |
Xylotex are bipolar microstepping stepper drivers rated at 30VDC (Max) and 2.5A per phase (Max). General DC motors cannot be used on any stepper system. Stepper motors have multiple coils and "poles" so they "step" to the next pole when you pulse the correct coil. The faster you pulse the faster they spin. They are current devices. meaning you control the current as you charge the coil. PM DC motors have a single winding and just spin when you apply DC volts. The more volts the faster they spin. No pulsing or coil switching is used.
The DC motors used in cars are often high current intermittent duty with sleave bushings instead of bearings. If gears are involved there will most certainly be hugh amounts of backlash making them unusable for any type of postional control. Modern servo controllers (Gecko's) close the loop inside the control. They will "dither" one or two encoder counts. If the encoder is not on the primary motor shaft then any system backlash is inserted into the loop equation. It's like driving a car at 60MPH with a really loose steering box and trying to stay within 1 " of the center line!
If you just want to build a machine that moves under computer control than using low precison parts is an option. If you want the machine to be useful beyond showing your friends, then you need to realize that some parts need to be of higher quality.
There are good DC motors that can be used with encoders as servos. They typically are rated for the continuous duty under load you will subject them to and have the torque and RPM that work with good CNC designs. Almost all servos need some form of speed reduction since they spin faster than steppers. Most designs use the toothed belt- pulley approach. The smaller the amount of backlash you can have in a system the better. Using rack and pinion drive a direct coupled servo will produce astounding rapids at really low torque. Leadscrews can help since they act as reduction at the TPI of the screw but can also introduce addtional errors and backlash.
Just hooking up some DC motors and a direction relay to control motor direction would not get you close to anything that would provide positional control.
Do a little more investigation into the Hobby CNC controls and read this list and look at some of the projects and how they were done. There is no substitute for experience (:-)