Jeremy Leach
Senior Member
Hi, just after any comments/ ideas ...
On an old topic I mentioned I was thinking of making a simple chart recorder to go with my PicAxe weather station - just starting to think about it more now regarding the servo to drive the pen arm.
Been wondering about making a simple servo rather than just get a ready-built one. For the purpose of just moving a pen arm a ready-built servo seems a bit extreme and power hungry.
All (!) I think I need is:
- Cheap 'toy' motor
- Slotted disk with two (cheap) IR LED/Sensor pairs to detect rotation of the motor.
- L293D motor driver chip
- PicAxe 08M to control L293D chip plus read sensors. Would hold counter of motor revolutions and copare this to desired count and control motor accordingly.
- Worm gear on the motor shaft driving a bigger gear.
Although quite a list I think this could be a lot cheaper than ready-built servo/ or Stepper motor solution and I can design it for my purpose.
One issue I can see though is that the pen arm would need to be 'zeroed' on power-up unlike a ready-built servo that uses a Pot for feedback. Plus there might be issues with detecting revolutions at high speed - may need to gear down the slotted disk. Plus of course it's all complicated compared to a self-contained ready-built unit !
Still might be woth trying though .
On an old topic I mentioned I was thinking of making a simple chart recorder to go with my PicAxe weather station - just starting to think about it more now regarding the servo to drive the pen arm.
Been wondering about making a simple servo rather than just get a ready-built one. For the purpose of just moving a pen arm a ready-built servo seems a bit extreme and power hungry.
All (!) I think I need is:
- Cheap 'toy' motor
- Slotted disk with two (cheap) IR LED/Sensor pairs to detect rotation of the motor.
- L293D motor driver chip
- PicAxe 08M to control L293D chip plus read sensors. Would hold counter of motor revolutions and copare this to desired count and control motor accordingly.
- Worm gear on the motor shaft driving a bigger gear.
Although quite a list I think this could be a lot cheaper than ready-built servo/ or Stepper motor solution and I can design it for my purpose.
One issue I can see though is that the pen arm would need to be 'zeroed' on power-up unlike a ready-built servo that uses a Pot for feedback. Plus there might be issues with detecting revolutions at high speed - may need to gear down the slotted disk. Plus of course it's all complicated compared to a self-contained ready-built unit !
Still might be woth trying though .