PRS Alpha Motor Cable Severed

[kenkelsey]

Just finished building our PRS Alpha 48X96 router and we screwed up while testing the machine. After we cable-tied all of the wiring, we found that we did not leave enough slack in the X motor lead. When we did a c3 on the Control Software to home the router, it pulled the wire right out of the motor (right where the wires enter the motor). The motor is a model ASM98AA-T7.2 from Oriental Motor Co, Japan. It is available from the manufacturer for $399. Shopbot sells it for $800. Does anyone know if Shopbot does anything with the wiring configuration or the connector. If it is a standard motor and a standard connector I'd rather pay $399 than $800. And/or does anyone know of a motor repair service that could open the motor and reconnect the 8 wires. Thanks

[Mark Farris]

Ken, as long as nothing changed you can buy the $399 motor and it bolts right on and plugs in. I replaced one on my 2010 PRS Alpha a couple months ago per Brady and everything matched up perfectly.
Mark

[Brady Watson]

Bummer Ken. As Mark mentioned you can get a replacement motor - plug & play - for $399. Go for it. PM me if you want to sell your damaged one. I doubt it can be rewired without ruining the magnetic charge of the motor, but I can probably salvage the gearbox off of it.

-Brady

[kenkelsey]

Thank Brady and Mark. Shopbot cut me a break since I had just bought the machine Dec 27. I have a new motor on the way. The Tech Support from Shopbot has been outstanding. I'm getting to know many of the guys by first name. Thanks again for your advice here on the forum. It saved me $400.

[blackhawk]

Ken - This motor can most likely be repaired. Do you have a pic of the damaged motor and cable? Post it up or PM it to me.

I am a design engineer for a servo and stepper motor manufacturer. I haven't been inside an Oriental Motor, but we fill our motor windings with epoxy and then the leadwires exit from the epoxy. As long as there is enough slack in the wires inside the motor above the epoxy, they can be spliced back together.

[Brady Watson]

Brad,
I'm not so sure about that. I took one apart when I first saw this thread & realized that if the wires are severed @ the strain relief, there is no practical way to repair it. In order to access the wires, you have to disassemble the whole motor - not just the dust cap for the encoder. Once the dust cap is off there is only an 8-10mm hole for the encoder wires. You have to remove the 4 screws that hold the entire motor together to get at the coil wires...this is of course after you desolder the encoder board from the encoder wires as there isn't enough slack to enable soldering extensions on the coil wires.

I am uncertain whether the shaft (because of metal encoder ring held on by epoxy) has to be removed to get access to those wires - but I didn't want to risk a new ASM98AA to find out. I'm pretty sure if you pull the shaft out you mess up the magnetism (on a stepper anyway).

This is why I suggested a new one...

-B

[blackhawk]

Brady - No doubt that it was a good idea to buy a new one. I still think it is worth a shot trying to repair this motor. At this point Ken has nothing to lose. I would be really surprised if you had to remove the shaft and rotor in order to access the wires. I have never seen a motor built that way. It appears that once you remove the 4 front screws that the rear endbell along with the feedback stator and circuit board would be able to be removed. The shaft should be able to stay in place. Once this endbell is removed you should be able to get access to the motor leadwires. I would not try to de-solder the feedback wires as long as there is some amount of wire left on there. I would just do a proper splice job and tuck the splices into the rear cover area. There is plenty of empty space for this.

I deal with servo motors exclusively in my job. The steppers are built in another building a couple of miles from my plant. So, there maybe something I am missing with the stepper, but I have a couple of stepper experts that I can get to take a look at the motor.

You are right about de-magnetizing the rotor if it is made from Alnico magnets. Removing the rotor would probably knock out 50% of your charge and that would be no good. Some manufacturers, including us, use neodymium magnets. With neo magnets, you don't have the de-mag problem.

Ken - If you want to send the motor to me, I will take a stab at getting this repaired for you. It would be a great spare for you to have on hand. If it is impractical to repair it, I will send it back to you. Either way you won't owe me anything. Like Brady said, I wouldn't want to experiment on my own working motor. But, yours is no good as-is. We may all learn something even if the repair bombs.