Convert a unipolar stepper motor to bipolar
I have two stepper motors MINEBEA Type 17PM-M041-P1, and I am planning to use them on a "Self Balancing Robot" project. These motors are unipolar with 5 cables. I am planning to use the A4988 driver which as known is suitable for bipolar motors (four cables). So, after I have identified the coil cables on my motors, I have now to disconnect the common cable in order to convert my unipolar stppers to bipolar...
Every coil has a 20 Ω (Ohm) resistance, so in between the coils edges and the common edge (cablae) I am measuring 10 (Ω)Ohms. Since I don't know how exactly the connection of the coils are made on the backplate of the motor, the question is:
If I Identify the points on the motor backplate (where all coil connection are realized) with an "almost zero" resistance between the common cable (one edge) and the various points on the back plate of the motor (the second edge) and then if I interrupt these connections, is it true that I will neutralize the common connection of the coils?
If you can access the wires you could try to separate the common turning a 5-wire effectively into 6-wire.
Since I don't know how to insert an image at the present position of my reply, I write the following link where two images of the stepper back plate and relative comments are shown...
Hope this explaining better what I am trying do describe....
I'm not sure the images help to explain what you are trying to do or not. They didn't help me as all I saw was two images that looked almost identical to me, with no additional information.
Sorry that I'm not able to be of much help.
If you zoom on the second foto you will read the comments...
In any case, thanks for your answer
I'll take another shot at this after looking at your picture. You have 8 large solder pads that are numbered 1 through 8. What I am going to suppose (to be verified by resistance measurements) is that each pad is tied to each end of a "coil pair". Look at the 6-wire diagram I put above. There is a pair on left and another on bottom. If each coil pair's center tap were separated in the picture then there would be 8 connections one for each pad.
Now you have already identified two points that are 10 ohms. Are those on the large pads, if so which numbers? It seems to me that this is the connection that needs to be broken. You don't need to turn this into a "8-wire" just a "6-wire." Can you measure resistance and see if you can get each large pad to correspond to the picture. A pad pair should measure ~20 Ohms, ~10 Ohms or close to zero Ohms. Measuring between two different coil pairs should be very high resistance.
Assuming this works out I said measuring between different coil pairs should be high resistance. But the exception is measuring between the 2 10-ohm points. They are on different coil pairs but tied together and should be close to 0 Ohms across.