RepRap: Blog

It works now...

After Simon published the debugging protocol in the wiki I decided that I had better regularise my handling of connections to the stepper motor. To that end I installed two screw terminals to handle the connections rather than the direct to motor soldering that I had done earlier.

I was a good boy and walked through Simon's test series for voltages before trying to run a stepper motor. Everything checked out perfectly with ~10.75v being sent to the stepper motor.

Just for luck I hooked up a different NEMA 17 than I had used earlier for the test. That stepper motor turned quite nicely. That SN754410 chip doesn't get half hot! You could cook breakfast on it! :-o

I tested the board for speed and direction and it seemed to respond perfectly.

After satisfying myself that the board worked properly, I swapped stepper motors for the old one. After doing that the whole system froze. It stayed frozen when I disconnected the stepper motor and restarted the exerciser programme. At that point I decided that hot swapping the stepper motors was a bad idea and that I must have fried the board doing that.

I disconnected the stepper board and hot wired the token ring on the comms board and still not even that worked. Hyperterminal wouldn't even echo. It struck me that I couldn't have fried the comms board too so I crawled under my worktable and checked the serial connector and discovered that the pin 3 comms line had broken free.

I resoldered that and resolved to put a housing on the connector in the morning and then went back and checked out both the first and second stepper motors on the comms board after extablishing that both comms board and the stepper board weren't misbehaving in any way.

Both ran nicely.

As hot as that SN754410 chip got I wonder about the sense of stacking them. It also strikes me that on a practical board they need to be spaced out away from the PIC16F628 and from each other and good heat sinks glued to them if we are going to run steppers driving a reprap for long periods of time.

Those are details, though. That's just tweaking, something that I am in a good position to do now that I have a working design. Many thanks go to Simon and Vik for the design and realisation of the bipolar stepper controller board and associated firmware. Well done, guys!