X & Y axis driven by DC motors with encoders

[sgraber]

Watch what happens when he manually moves the motors out of alignment during a print!



More info:

www.youmagine.com/designs/dc-motor-closed-loop-control-software#!design-information

www.aliexpress.com/item/New-boutique-12V-DC-motor-385-servo-motors-speed-encoder-888-line-AB-phase-encoder-For/1345460690.html

[BeeAmaker]

You can't pull the X and Y axis when using steppers. So the only way it will get out of alignment is is you force it to skip a tooth on the belt or skip a step or two. This happening during a print usually means something else is majorly wrong (Fluffy is sitting on the print bed).

In either case, using DC motors or steppers, if something forces it to move out of alignment during a print, the print is still F'ed unless it is a real quick interruption like your hand got in the way. In which case steppers will probably smash your hand and keep on printing. Anything prolonged will screw up the print in either case.

And frankly there is really no reason this can't be done using steppers. The primary difference is that the DC motor with encoder knows exactly where it is at, or where is should be. Steppers only count rotations, meaning that if it need to move 3 inches and it is 1 rotation per inch in rotates 3 times, but can't tell you where on the X/Y table it is. You can add encoders to a stepper motor and have the best of both worlds, in fact I have a few at my shop.
Example
www.ebay.com/itm/TAMAGAWA-STEPPER-STEP-MOTOR-WITH-OPTICAL-ENCODER-/260292053378?_trksid=p2054897.l4275

[jimustanguitar]

I think the bigger picture is that you can use any sort of motion/movement and be accurate with closed loop feedback. Not a new idea, but new-ish to RepRap and DIY CNC. You could use cheaper motors too, perhaps even more compact (less magnet poles).

I agree that skipped steps don't happen easily, but it would be interesting to use true feedback on something that can skip steps like the extruder. (one more thing to hang with bungees right?)

[sgraber]

FYI if you look at that aliexpress link, they are $5.98/motor with encoder.

[BeeAmaker]

Jan 3, 2015 21:44:52 GMT -5 sgraber said:

FYI if you look at that aliexpress link, they are $5.98/motor with encoder.

The price difference really isn't that big. Without any "real" advantage, it's just another way to do the same thing.