Servo running rough

[matthewsx]

After reading another thread I may stock up on them....

 

[fitterman1]

Finally got all my bits and pieces together along with my act and assembled this for my grinder motor controller.
As per Roberts schematic further back I knocked this up using the suggested resistors, with one change. I used a simple 102 trimpot instead of the C1K potentiometer he used. I adjusted the pot until my preset full speed came up on the fascia tacho and it ran.
Works great.
Resistors are sized 2 watt, the switch is a household light switch fitted to a small box from a local electronics store.

 

[fitterman1]

More pix.

 

[fitterman1]

Hopefully it will not get too hot in the box as its a sealed box.
And here it is mounted.right under the front for easy access.

 

[fitterman1]

So I hooked up the belt and have the same issue, vibration above ~1500 rpm. I'm starting to think it may be an alignment issue or something to do with the mounting, it runs smooth as silk to ~2500 rpm without the belt and only vibrates a little at max 3000rpm.

I'm using the cast pot metal mount that came with the motor and when I play around with alignment it seems to move the vibration up and down in the rpm range. It's probably worth the effort to build a better mount with fine adjustment.

I'm also using a timing belt arrangement, maybe switching to v-pulleys with a round belt would be better?

John

John, i think your vibration is due to the timing belt itself. This type of belt really requires an idler pulley to tame it. My G0602 lathe came with one standard and I had the same problem which was causing a dirty surface finish. When I changed the motor to a dc treadmill version i machined the pulley teeth off and machined it to take a ribbed belt where the grooves run the length of the belt. I used the treadmill pulley on the motor.
Like a car belt. All vibration and chatter disappeared.
Cogged belts are fine for timing applications but I don't understand why the Chinese use them on lathes.
You should be ok with the original bracket. For driving a spindle go with a Vee or ribbed belt.
Cheers Alby.