Did I blow my motor?

[waynec]

Another story in my PR upgrade saga.

I bought a new Z axis motor from Tormach. Its a 4 wire motor with over 600 Oz/In of torque.

I connected it to my Ascension and it turns correctly- that is page up turns one direction, page down goes the other.

The problem is that the torque is very low. I can stop the turning motion with my fingers easily. No way is this enough to lift my Z axis with the router mounted.

I'm confident that I wired the motor correctly, and no smoke escaped. Its a 4 wire motor, and I had the color code and checked with a meter before I connected it. The motor gets warm to the touch while connected, but there is no smell of burning insulation or the like.

Is this motor defective, or is there some way to wire a 4 wire bipolar motor that will give more torque?

Sorry to ask so many questions. I'm trying to determine if I need to buy a new motor.

Thanks all

Wayne from White Salmon

[Brady Watson]

Wayne,
2 things - 1) You will need to change the resistor in terminals 11 & 12 to one appropriate for the amperage rating on the motor. 2) You will need to open up the Gecko cover & change the jumper from 'Reduced Current Range'. This limits amperage to 2A. If in doubt, read the instructions: http://www.geckodrive.com/photos/G202_MANUAL.pdf

This is something that the Ascension people should be able to help you with. It's a shame that you didn't just go with a 4G setup - you'd have a lot more support than you are getting.

-B

[waynec]

Does this mean I didn't fry the motor?
I'll read the instructions on the Gecko and get a resistor installed no sweat.

I bought the Ascension back before the 4G was available, and had to put the box on the shelf for various reasons. I just got around to connecting it this week.

Technically the Ascension is out of warranty, but Alan was good enough to get me going with connection info. Maybe I should purse him for more info, but I often get quicker response here, and I still feel like part of the Shopbot community with my modified PR.

I do appreciate your help over quite a long time this project has taken, Brady. And again today!

[Brady Watson]

Wayne,
You'd have a difficult time frying a stepper motor. They usually don't go bad unless they are really abused...and that is not an easy thing to do with DC current and voltage. In my experience, Geckos sometimes 'flake out'...I have 2 at the moment that work fine until they get a little warm and then they shut down. They aren't Oriental drivers...that's for sure.

-B

[richards]

Wayne,
A Gecko G202/G203 without a current limiting resistor defaults to maximum current (7A) going to the motor. Most motors will not handle 7A without frying, but usually they'll start to stink long before they fry. A motor that has more than just a whiff of electrical stink needs to be checked. (Most electronics 'smell' hot when they're run close to their maximum rated current, so, if smell something, start checking around.)

Torque is more related to the current being drawn by the motor and speed is more related to the voltage furnished to the motor. Of course, both current and voltage are inter-related, but if a motor is rated at 600 oz*in, I wouldn't be able to turn the shaft with my fingers.

I can't find any specs on the Tormach stepper motor on the Tormach web site. If you post the information on the motor's spec plate someone might be able to make some specific recommendations.

Edited: Brady, you posted while I was searching the Tormach web site. I agree that stepper motors don't easily burn up. Of the dozens that I've installed over more than a decade, not one motor has ever failed. The only time that I've had trouble with a Gecko shutting down is when I've used it either without a heat sink or with a heat sink that is too small. I've never used a G201, but the G202 and the G203 models both have been very forgiving of my mistakes. However, if either one faults, I have to turn the power off until the capacitors on the power supply have drained in order to reset the Geckos.

[waynec]

The forumula in the Gecko instructions is'
R (in kilo-ohms) = 47 * I / (7 – I) .

Just so I don't miss the the obvious, 'I' stands for inductance, which the motor plate shows inductance as millihenries or MH, correct?

Its good to hear I probably didn't fry the motor. I didn't smell anything, and certainly no burned insulation smell. That's good.

Another question if I may. My Shopbot steppers are geared motors. When I crank up the speed in Mach 3 to over 300 ipm the motor will begin skipping even when disengaged from the rack. It just stops spinning even though you can hear the motor running and the gears spinning.

Is it likely this is from a worn motor, or is this characteristic of geared motors in general?

What sort of speed can I expect from a PKxxx3.6 geared motor from a Shopbot PR?

Thanks for all the help, Mike.

Wayne

[richards]

Wayne,
The 'I' in the Gecko formula is for current (Amps). "H" is the common variable used for inductance (Millihenry). So, if the motor is rated at 2 Amps, the forumla would be 47 * 2 / (7 - 2) = 18.8K, which means that you would use the closest standard value resistor to 18.8K - for a 2A motor.

The geared motors that I use are the PK296B2A-SG3.6 model. I believe that the motors that Shopbot uses are very similar to the PK296A1A-SG3.6 model. I wire mine using the half-coil configuration which gives me speeds on the test-bench upto the 500 RPM maximum rating of the gearbox. That means that the stepper is turning at 1,800 RPM. That also means that I'm sending the motor 60,000 pulses (steps) per second. Obviously, that requires the Gecko G100 pulse generator, but it also means that the motor can turn as fast as the specs say that it will.

With proper ramping and (perhaps) half-coil connections rather than the Bipolar series connections, you should be able to run your motors at a jog speed of about 480 IPM or faster.

[richards]

Wayne,
I've been trying to contact the Ascension people via their forum, but their forum page times out before connecting. Their web site (www.custom-cnc.com (http://www.custom-cnc.com)) just returns the default Apache page. Would you email me one of their email addresses. I would like to verify with them some of the recommendations that I've been posting - just to make sure that I'm not recommending something that would cause you problems somewhere down the line. My email address is miker@xmission.com (mailto:miker@xmission.com).