 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : STEP-DIR decoder for picomite PIO
  Page 3 of 3 |
|||||
| Author | Message | ||||
Bryan1 Guru  Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Hi Phill thanks heaps mate that code tweak worked a treat and on doing several runs the average is 432 pulses to move 0.098" so the resolution is 0.00268" a step. I will continue this in my cnc thread. Regards Bryan |
||||
| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 857 |
My buddy has a CNC plasma and man, talk about a rapid ROI (return on investment). He fabricates log-grabbing attachments for JCB-type backhoes. He simply lists them on eBay. It's a sideline business but he pocketed £35K from it last year. Now he has designed and built a log splitter and the market also looks good. He has something like £15K into the CNC Plasma. Anyway, he called me yesterday, totally puzzled and fearing a fault developing. During cutting, the PSU cooling fans only switch on occasionally but when standing still, the PSU fan is on full-time AND the stepper-driver fans now kick-in. "How can this be right?" Well I explained that stepper-motors receive the most current when standing still because there's no back EMF. If the motors were disabled, then you risk an axis being disturbed by some external force. This doesn't sit right with him and so here was my opportunity to tell him about this development  Kinda wish I hadn't because he's more excited than I expected and I am up to my ears Anyway, there's my future test-bed. I'll start by driving free-standing motors and when happy, swap-out all three drives and motors. He's happy to spend the money because he just wants his machine to not consume power when standing still  |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4223 |
Phenix, Most stepper motor drivers use PWM to control the coil current of the stepper motor. I am not sure if you can control the current limit of this particular stepper motor driver IC, but if you can, you could reduce the current when there is no activity. This will limit the heat build up in the coils, while maintaining the (even in microstepping) position. You will however loose torque. It is depening the application if that is acceptable. For a robot arm it is not acceptable to loose torque, but for a CNC machine in "waiting" position it might. Volhout PicomiteVGA PETSCII ROBOTS |
||||
| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 857 |
Sure but drop the torque and the machine is vulnerable to being knocked out of position and the controller will be totally unaware...next part becomes scrap. With servo-motors, we have options: -Disable the motor completely and position continues to be updated via the encoder -Just let the motors hold position which typically requires milliamps (thanks to PID) -Let the motors hold position but with a user-defined dead-band: Deadband=1mm (in encoder counts) do If abs(command_position - encoder_position) > Deadband then Enable_motor_and_or_PID 'bring the motor back to command_position else Disable_motor_and_or_PID 'we are within the deadband so kill the power end if loop |
||||
| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Well guy's if you at my thread on my cnc you will see this is only a small one. Now when I did have it going it was rock solid in milling pcb's also I used to cut signs in red gum using it with a round cutter. OK I only took 0.5mm cuts but at no time did any axis wander. For large machines yes servo's are the go but back in 2011 when I built this cnc I did have a few years prior building and re building to make it solid as. |
||||
| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 857 |
When referencing another thread, it's always helpful to provide a link I had to search and it's in "Other Stuff". I never go there. However, I see you just posted: The same issue as my buddy's plasma. Yup |
||||
| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
When I do get started on the code I will start a CMM2 CNC thread in this forum so you can find it mate Yesterday arvo started on making the isolation board and as I do have 10 off 4n35's all of them are going on the perf board. Now I have looked at that PIO code heaps of times and for the step movement I do think it's just a case of doing a pulse then have a count setup to control the distance traveled. But first baby steps and those limits and E-Stop need to be setup so the CMM2 can see and act when one is hit. |
||||
| Page 3 of 3 |
|||||
 Print this page |
