Has anyone placed diodes between the stepper motors and the controller to isolate motor current when manually moving X and Y gantry axis?
I’ve been tinkering with Arduinos and and have built several motor experiments using diodes to isolate motor kickback. I’m also looking for a good, free schematic utility to draw circuits so that I can build a small pcb with the diodes and terminal blocks.
Try Eagle, it’s free for single page schematics and boards up to 100mm x 80mm.
How could I forget Altium Circuitmaker? Free but cloud based.
you cannot put diodes between the motors and drivers.
The motor’s won’t work with diodes because they are bipolar -> current needs to be able to flow in both directions.
Thanks Geoff and Christian,
Figured there must have been a reason no one else had tried it. Kinda weird, some of my friends have said that bipolar thing about me 
Patrick
http://www.123dapp.com/circuits
All the 123dapp.com apps are free - Autodesk gets it!
Could just wire in a triple pole single throw switch?
Fritzing is free too… I’ve used it a few times and it’s easier to deal with than Eagle, but not as powerful.
Pros: easy to use if you stick to the built in components, good enough for what I need to do, and free.
Cons: making new components is painful, and it’s a bit buggy (it’s technically still in beta).
If you’re planning on sticking stuff to Arduinos, it seems to be basically custom made for that.
I’ve cut two boards on my X-Carve now using the tool chain Fritzing → FlatCAM → Chilipeppr. There was a bit of a learning curve, but the first board turned out great. Of course I had some parts clearance issues with some external components and had to recut - but I was able to turn the recut board that day… I’d still be waiting if I had to send it back out 
Since the diodes wouldn’t work I was also wondering about adding gates.
I guess maybe the bigger question is = “Is reverse current going back to the controller really an issue?”
Thanks all for the info.
Have seen lots of new cnc users worry about this for 15 years, but I don’t remember anyone who ever reported they had problems with commercial stepper drivers. If you can manually move an axis fast enough to create an issue, I think you will be far more likely to create a mechanical issue with your machine rather than electrical. Still, the advice to manually move slowly is good advice in either case.
John
Great to hear John. Thank you for your input. Sometimes we get stuck in finding a problem for our solution.
I don’t see it being an issue as long as the machine is not moved rapidly creating higher voltages. I have very little experience with stepper motors but you could look into what is called snubber diode setup or do google search about stepper free wheel circuit. Look for things related to back emf from steppers. Hope this helps. But for the most part I move mine with the controls in the software till I am close then move manually.
Don’t do this.
Most drivers (all I know of) don’t mind current being fed back from the motors - but some are very picky when it comes to disconnecting them under power and will be destroyed.
This. I connected a relay block in the circuit to isolate the motors but found the controller goes out of calibration with no load and must be power cycled to get it operational again.
Without power to the stepper motors it is likely that your spindle will not be in exactly the same position as it was when you removed power.
If you have homing switches you can just re-home the machine when you turn the power back on to the steppers to synchronize the machine with grbl.
If you don’t have homing switches you can move the machine to the place that you want to be Machine Zero and then reset the Arduino (requires adding a momentary switch to take the RST pin to ground) after re-applying power.
If you could place diodes on the control board at the actual H-bridge then it could be done but you would need 4 diodes per motor drive and know exactly where to solder in. I have looked at schematics for TB6600 (I think this is used on the x-controller) and I do not see a decent picture of the layout. Older, less sophisticated H-bridges used to allow this.
see picture of this at: http://i.imgur.com/QZbIC.jpg
I think you are correct it looks like a standard bi directional h bridge
You are correct. That is not a driver for a stepper motor. It is a circuit that is used with regular DC motors.
I opened up my x-controller to verify it does use a Toshiba TB6600HG chip and here is the link to Mouser’s description:
http://www.mouser.com/ProductDetail/Toshiba/TB6600HGO/?qs=vnbNJPHmPnOJoMWCV9C7tA%3D%3D
I am rusty on this but if you place two H-bridges (inside of one chip) you then have a stepper motor driver. So what looks like a DC motor driver then can be used for a stepper.
Sure you can use two DC motor control circuits to run one stepper motor. It is possible.
Then you have to take care of all the issues that stepper motors have, that have been solved by the stepper motor driver chips, on your own.
Things like when to activate each coil, what direction and sequence, acceleration/de-acceleration etc.
You can also implement a computer using SPST switches, but transistors make it much easier.
