motors working unreliably

[jvanick]

... I have a hobbycnc pro rev1 board attached to my pc via a 3 foot cable...

between the hobby cnc card and the steppers, I have 2 2-pair cables for each stepper... they're about 20 feet long between the card and the steppers...

on each stepper, I have the cabling configured as follows:

Cable 1:
Pair 1: A + common
Pair 2: a + common

Cable2:
Pair1: B + common
Pair2: b + common

the commons on each pair are connected together at the motor side as well as at the board side.

the board is powered by a 24v, 10a transformer, attached to a bridge rectifier with a 31,000uf 65vdc cap.

I'm seeing 33.5vdc at the input to the hobbycnc board.

I'm using the 23-305-DS8A steppers from Hobbycnc...

the supposed max output of the board is 3a (assuming the voltage trimmer is turned all the way up).

What I'm seeing is what I think is an overload condition.

if I have the voltage turned up for 3A, I get a few steps out of each of the motors, then they turn off... after I power cycle the card, I can step them again for a few steps.

if I set the voltage trim lower, I am not getting enough torque out of the motor to turn the leadscrews.

the motors worked fine when they were connected to the card directly, with no load on them.

My thoughts are:

1. is the twisted pair cabling causing the motors to freak out? should I change to have A and a on one pair, and the commons on the other pair?

2. is my power supply just not big enough to handle these motors?

or... am I missing something else?

Any help would be greatly appreciated!

Thanks!
-J

[jvanick]

ok, so my long wires were the problem. i moved things around in my shop and now the PC is right next to the machine... and it's working pretty good.

I'm still getting a bit of wierd behavior where it sounds like the motors are just not having enough torque to move the gantry, but I think that might be due to EMC.

does anybody have a good EMC configuration file that i can use? with 1/4 microstepping enabled, I'm using 8000 pulses per unit. I've got 1/2" acme 10pitch leadscrews, so the unit = 1 inch.

I think the problem is due to EMC going from 0 to whatever inches per minute... if I keep the feed rate slow (like 10 or 15 ipm) it seems fine. If I increase to 100 sometimes it 'locks up'.. when the machine is moving properly tho, 100 ipm is fine, and it seems like there's room for more speed.

I'll probably post over in the EMC forum too...

-J

[jvanick]

Heads up...

the Hobby CNC cards don't like twisted pair cabling.

I had some 18ga 2-pair twisted cable that I was using for my stepper wires.
(it's usually used for alarm and home-theater signalling lines).

with that connected between the steppers and the controller, I was having the drivers go into protect mode.

I changed out all the twisted cable to non-twisted cctv power leads (it's 18ga, 2 conductor, non twisted)

everything works nearly perfectly now.

-J