Tool Change with Stall Detection

[Red Sand Robot]

In theory, if one were to try to implement a tool changer similar to E3D but use a stepper instead of a servo for the locking mechanism, would stall detection be able to be implemented to pick up a tool? For example, when the gantry goes to pick up a tool, the mechanism would turn the pin enough to lock it in place and then when the stepper stalls it would know the it has picked up the tool and as applied enough torque to hold the tool in place.

[Phaedrux]

E3D themselves have in fact switched from a servo to a small stepper for just this. However, the stall wasn't able to be detected because the motor was to shall to produce any appreciable back emf.

I think they've gotten around adding an endstop by just reducing current so that it just stalls against the physical stop for a bit before assuming it's locked.

[Red Sand Robot]

@phaedrux Basically, I want to try to emulate this method: https://www.thingiverse.com/thing:3365456/files and I believe the stepper they are using would be an appropriate size to use stall detection. Would the stall detection be used in one of the tool change macros as part of the tool change process?

[dc42]

@red-sand-robot said in Tool Change with Stall Detection:

@phaedrux Basically, I want to try to emulate this method: https://www.thingiverse.com/thing:3365456/files and I believe the stepper they are using would be an appropriate size to use stall detection. Would the stall detection be used in one of the tool change macros as part of the tool change process?

Yes, you would configure the additional motor as an extra axis with stall detection endstops, and then use G1 S1 moves to operate it.

It should be possible to get stall detection working for this purpose if you choose an appropriate motor and operate it at appropriate speeds. I spoke to E3D about this a few days ago and gave them a few suggestions.

[Red Sand Robot]

@dc42 My plan is to use a Duex5 for the additional tools, would it be possible to map the driver for E1 on the main board to control the additional motor?

[dc42]

@red-sand-robot said in Tool Change with Stall Detection:

@dc42 My plan is to use a Duex5 for the additional tools, would it be possible to map the driver for E1 on the main board to control the additional motor?

Yes. You would configure it as a new axis (say U) in M584, hide that axis normally, and un-hide it when you need to run that motor.

[Red Sand Robot]

@dc42 Thanks for the help!