X axis problem

[Mike Windsor]

I just finished hooking up my new 4 g board to my old shopbot . I've had the board for quite a while , but it took me quite a while to get around to doing the modifications that I wanted to the board . I mounted the geckos on heat sinks with cpu cooling fans ,and built a 65 volt power supply . I finally got everything hooked up today , figured out the vu settings . Y and Z axis work fine but the 2nd X motor does not work . The light comes on on the gecko , but it doesn't seem to glow as brightly as the rest , and the motor is not holding or moving . ---If the driver is blown would the light still come on ? ---is there a setting or axis selection in the software set up that I might have missed ? --just looking for ideas . Thanks

[Gary Campbell]

Mike...
Swap motors to see if it is the motor or driver

[Dusty Knobel]

Mike,

I'm not qualified to answer your electronics question, but recommend you check out this entire thread:http://www.mechmate.com/forums/showthread.php?p=47818&highlight=shopbot#post47818. There is an extensive discussion on power supplies/motors and geckos, and some mention of a 50 volt limit under some circumstances. Maybe way off track, but it's a possibility that you went too high with the 65 voltage supply?
Dusty
Olympia

[Mike Windsor]

It turned out to be a bad stepper . ---Strange because it was running fine with the old PRT control box . --I wound up changing all of my X and Y motors with 4a amp 2.2 v 280 oz/in steppers . ---I notice now that the motors are getting quite hot . I set the current on the drivers to 3 a . --is there a current reduction at standby setting on the gecko 202 ?

[Mike Windsor]

did a bit of reading and am winding down the power supply to 40 v ---I'm hoping that will keep the motors running cooler .

[br928]

The 50V limit is for the G540. The G202 can take voltages up to 80V. The 65V you had was fine. I am not sure what motors you have but you might want to reduce the current to 2A.

The auto current reduction can be enabled in the G202 by moving the internal jumper from pins 1,5 to 2,6. Unfortunately, you will have to remove the Gecko's from the heatsink to get the case off. I think it comes enabled.

[Mike Windsor]

I read on the Gecko website that the power supply should not be greater than 25 times the stepper voltage . --So the 65 volts was too much for the 2.2v motors ---the machine went like stink on 65 volts though . I happened to have a smaller transformer and changed it down to 45 volts and the motors arent getting hot now . I may try to find some higher voltage steppers and put the 65 volt back in at some time in the future . --Right now I'm on to figuring out my " comm issues "

[ken_rychlik]

Mike, do a search on the forum for comm issues and you will get plenty of info on that. lol

[richards]

At one time Gecko advised not more than 25X the motor's rated voltage as the maximum. They've changed that. Now they use the formula:

32 X SQRT( Inductance ) = Maximum voltage.

The Gecko G201, G201x, G202 and G203v can handle voltages up to 80VDC. (The G540 module is limited to 50V and 3.5A per motor.)

At the maximum computed voltage, the motors will run very hot - about 80-degrees C. That's hot enough to blister a finger.

I run my motors at about 75% of the maximum voltage. That still produces good torque and the top speed is still over 750 RPM, which is the 'magic' number that I look for. 750 RPM on a belted motor will still let that axis jog at 12 to 15 ips, which is as fast I like to go with a geared/belted motor.

At the moment, I'm running a heat test on some motors that were sent to me for evaluation. One of the motors has an inductance of 2.2 mH, which means that it can be used with power supplies of up to about 48V. I ran a test for two hours with the motor connected to a 37VDC power supply. With the motor wired half-coil and the duty cycle at 50%, the motor's temperature stabilized at 44-degrees C. With a 47VDC power supply, the temperature is starting to climb a little. I don't expect it to go much over 60-degrees C before it stabilizes; however, when I wire it bipolar parallel and change the current limit resistor to let it pull 6A, I'm expecting that it will hit 80-degrees C.