[uptoolateman]

I have a Sherline CNC rotary table with the stand alone controller that I want to adapt to my new CNC mill. The stepper motor on the rotary table is a 6 lead 2.5 amp motor that has the 2 center tap wires connected together inside the DIN connector. I do not want to modify it so I can use it in either way. My driver box uses gecko 202's and which only accept a 4 wire setup. so do I just make an adapter cable with a DIN connector that matches the one on the rotary table with the the military connector that I need on the other end to connect to the mill with just the 4 field wires? Does that mean I need to change the resistor on the Gecko from a 3 amp drive to a 1 amp drive since this will be full winding setup?

Thanks for any help

[SCzEngrgGroup]

You're better off running the motor in biplolar parallel mode, which means connecting the two end-wires of each phase together, and using that for one connection, and the center tap for the other.

Regards,
Ray L.

[Heinz Reimer]

I don't think you can do it without changing the connector, because even with the full winding configuration you are shorting the two windings together, which I don't think you can do on a bipolar drive. Secondly, "parallel" configuration doesn't work on six wire motors because the two halves of each winding will run in opposite directions to each other. Your options are to use either half winding or full winding. If you haven't already done so, look at the excellent "stepmotor basics" article on the geckodrive website for pros and cons of each.

My solution to a very similar problem (converting from Sherline's P/N 8760 driver to Gecko 251's) was to change the five pin DIN connectors to six pin connectors, (they're about 1$ each at digikey) separating the two center tap wires on the male motor connector, but leaving them connected on the female end from the Sherline controller. The female connector from the Gecko drive simply uses four of the six pins to give the desired (half winding for me) configuration.

Regards
HR

[uptoolateman]

Unfortunately the 2 center taps are already tied together inside the 5 pin DIN connector thats molded onto the motor cable so I can't easily change it plus I don't want to modify the connector because I still want to be able to hook it up to the sherline controller for use on my sherline mill. So I gues I'm kind of stuck with a full winding setup and just ignoring the center tap connection on the connector and just use the 4 field wires, but does this mean I have to drive the motor at half its current rating.

[uptoolateman]

Thanks, I guess I may end up having to go to a 6 pin DIN connector and just tying the center taps together on the controller side. really like having the stand alone controller for my rotary table and since I already have the CNC table it makes no sense to buy another one for my CNC mill.

[Heinz Reimer]

All of the instructions I've seen for using six wire motors with bipolar drives emphasize taping off the unused ends to prevent shorts. A brief google search turned up one manufacturer who explicitly stated that the center taps should never be connected when used with their bipolar drive. The 201s have no short circuit protection; I think you risk damaging them if you leave the center taps connected.

If using the full winding configuration the current should be set at half of the unipolar rating.

Regards
HR

[jalessi]

It should be very simple to connect to the Gecko, here is the wiring diagram.

[uptoolateman]

For the motor side cable I'll convert the 5 pin DIN to a 6 pin DIN so I can seperate the center taps and probably use the center taps for half winding mode so I can leave it full current for the CNC mill but I'll either have to change my sherline controller plug to a 6 pin with the center taps tied together inside the sherline controller side of the plug or make a short adapter cable with a 6 to 5 pin DIN with the center tap tied together which is the it's wired right now so I can connect it back to the sherline controller, I want to be able to use it with either the sherline controller for my manual milling machine or my milling machine with the geckos by simply removing the adapter plug. I'm not sure why Sherline has the center taps hooked together on their setup and still has the 4 field wires as well in the 5 pin connector, what kind of setup is that? see this link http://www.sherline.com/67127pg.htm and then click on the spec sheet tab below the connector diagram to see the wire colors on the motor.

[Heinz Reimer]

You're on the right track. The Sherline driver is unipolar, Geckos are bipolar. See figures 3.3 and 3.9 in the following link for an electrical diagram http://www.cs.uiowa.edu/~jones/step/circuits.html

With unipolar drives, the center taps are both connected to the power supply positive (usually), and the ends of the coils are switched in sequence to produce motion. For a given winding, energizing one side of the coil vs the other produces magnetic fields in opposite directions, as the current path is clockwise for one and counterclockwise for the other.

Bipolar drives function by not only turning coils on and off, but also by switching the direction of current flow in the windings.

Because the switching in a unipolar drive is just on/off with no direction change, they are electrically "simpler", and easier to make. They will only function with center tapped motors, as this provides the mechanism for reversal of the magnetic field. In 5 wire motors, which only function with unipolar drives, the two center taps are actually connected inside the motor. Bipolar drives have no need for center taps, and should be wired as if none existed.

Regards
HR

[uptoolateman]

Thanks for all the help everybody, I'm just a noob with these drives and didn't want to burn up a gecko, a motor, or my sherline controller. Looks like I also need to change the resistor on the gecko because it's setup for a 3 amp drive and the motor on the rotary table is 2 amp and I'll run it in half winding configuration.

[jalessi]

The six pin din is very cost effective and is a simple solution.

These connectors are also an inexpensive alternative.

http://tinyurl.com/9ohq3h

Jeff...

[uptoolateman]

Ok I got my Sherline rotary table conversion done, but now I need to know what I do to configure MACH3 to move it the correct distance. the stepper is 1.8 deg per step and the worm is 72:1. I made it so I can swap the rotary table between the mill which runs bipolar and my sherline pendant controller which runs unipolar with the use of an adapter plug I made.

[Heinz Reimer]

With a 72:1 worm ratio the table moves 5 degrees per turn of the motor, or 1/5 of a turn per degree. A 1.8 degree step motor has 200 steps/turn, so 40 full steps per degree are needed for the table. The 202 is a 10-microstep drive so your control software has to be set for 400 steps/degree of motion.

Regards
HR

[uptoolateman]

Thanks' for the reply, so if I have the A axis set to angular Iwould put in 400 in the MACH motor config?

[uptoolateman]

Ok I put in 400 in the motor config in MACH and 360 for the velocity and ran the table around and checked it every 30 degrees against the marks on the table and it's dead on. The original velocity setting in MACH was 49 which was really slow. What are you all running for velocity on your 4th, 360 doesn't look any faster than what I can do manually and the motor shaft doesn't appear to be flying so I think I could go higher.