3 ms·

What is the best way to increase accuracy of such servo motor ?

bronz 7y ago
harmonic gearbox
Tepix 7y ago
Buy higher quality servos, use a sturdier material for the arms instead of cardboard. Personally I like the fact that it's somewhat sloppy. The pictures have a distinct style.
pp19dd 7y ago
Better motor control. Timing: assuming rigidity of linear position is crappy, allow more time for it to bounce back. Speed: ramp-up speed in one direction may be different from the opposite direction. Position: accuracy of RC servos is almost not worth measuring, so many companies haven't. But you can hack it (via contact switch and something that juts out) to add a simple shaft rotation encoding and correct when needed. Software correction: draw a grid of straight lines and adjust drift in software until it looks like a grid.
- DanieleProcida 7y ago
  Also it's hard to defeat hysteresis in the system, both in the servo motors (they have significant dead bands) and the mechanical arrangement of the arm/pen.
MisterTea 7y ago
You could get a lot more precise with stepper motors paired with a micro stepping drive. Since a stepper does not necessarily need feedback the software doesn't have to close a loop but spit out position and velocity commands. Integrated stepper chips exist on breakout boards which keeps the design simple as it will handle the complex microstepping current control. The entire design would not increase much in complexity at all and gain a massive amount of precision.
cr0sh 7y ago
I wouldn't even bother trying. Instead, look for inexpensive small bipolar stepper motors with a small angle per step, or invest in microstepping drivers. A couple of these coupled to an Arduino GRBL CAD shield (cheap as well), with appropriate drivers, would be much more accurate. Use rigid aluminum extrusion for the arms, and only use a servo on the end to lift and place the pen on the paper. At a certain point in complexity (and cost) you could go with a cartesian plotting system run with the same board, too. If you don't want open-ended stepper control, adding on an encoder to the stepper isn't too difficult (probably the easiest and cheapest and long-lasting would be to get hall-effect encoder breakout boards and dual-shaft steppers, and mount the boards on brackets to the opposite end of the stepper, and mount the magnet on the shaft with a drop of super glue or epoxy). You can do all of this easily for well under $100 USD.

harmonic gearbox

Buy higher quality servos, use a sturdier material for the arms instead of cardboard. Personally I like the fact that it's somewhat sloppy. The pictures have a distinct style.

pp19dd 7y ago

Better motor control. Timing: assuming rigidity of linear position is crappy, allow more time for it to bounce back. Speed: ramp-up speed in one direction may be different from the opposite direction. Position: accuracy of RC servos is almost not worth measuring, so many companies haven't. But you can hack it (via contact switch and something that juts out) to add a simple shaft rotation encoding and correct when needed. Software correction: draw a grid of straight lines and adjust drift in software until it looks like a grid.

DanieleProcida 7y ago
Also it's hard to defeat hysteresis in the system, both in the servo motors (they have significant dead bands) and the mechanical arrangement of the arm/pen.

MisterTea 7y ago

You could get a lot more precise with stepper motors paired with a micro stepping drive. Since a stepper does not necessarily need feedback the software doesn't have to close a loop but spit out position and velocity commands. Integrated stepper chips exist on breakout boards which keeps the design simple as it will handle the complex microstepping current control. The entire design would not increase much in complexity at all and gain a massive amount of precision.

cr0sh 7y ago

I wouldn't even bother trying. Instead, look for inexpensive small bipolar stepper motors with a small angle per step, or invest in microstepping drivers. A couple of these coupled to an Arduino GRBL CAD shield (cheap as well), with appropriate drivers, would be much more accurate. Use rigid aluminum extrusion for the arms, and only use a servo on the end to lift and place the pen on the paper. At a certain point in complexity (and cost) you could go with a cartesian plotting system run with the same board, too. If you don't want open-ended stepper control, adding on an encoder to the stepper isn't too difficult (probably the easiest and cheapest and long-lasting would be to get hall-effect encoder breakout boards and dual-shaft steppers, and mount the boards on brackets to the opposite end of the stepper, and mount the magnet on the shaft with a drop of super glue or epoxy). You can do all of this easily for well under $100 USD.