Stepper kill ideas?

Im getting close to having my test rig finished. The purpose is to test various steppers and a couple different ball screw leads all while throwing around ballast on a linear rail at potentially very high speeds.I will be hand writing g-code to put the system through various cycles of speed and accelerations using different amounts of ballast.My concern is safety for myself and the components. If something doesnt go right and the carriage slams into the bearing blocks at 2-300mm/s it aint gonna be pretty. I need ideas on how to kill the thing instantaneously if thats even possible. if I put a switch at either end to kill the power it will take some time for the electronics to dicharge so that wont work. If I kill the power going from the stepper to the driver that might smoke the driver. Maybe thats the only way and that will have to be the result of an unexpected event. Any ideas?? Using Duet Ethernet to drive the whole thing on 24v

If you are not driving a bed heater from 24V then you can use a small 24V PSU, in which case the stepper motors will only move a small amount after you kill the power. Another possibility is to wire an external reset button to the expansion connector.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

You put high Amp limit switches that will open the circuit to the motor coils and short circuit them (eventually through a low value resistor). The switches will suffer but braking effect guaranteed.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

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dc42
If you are not driving a bed heater from 24V then you can use a small 24V PSU, in which case the stepper motors will only move a small amount after you kill the power. Another possibility is to wire an external reset button to the expansion connector.

David, I have one of these power supplies. [www.ebay.com] Can I use that for testing? I would set the current limit to just above the set current for the single stepper?

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MKSA
You put high Amp limit switches that will open the circuit to the motor coils and short circuit them (eventually through a low value resistor). The switches will suffer but braking effect guaranteed.

"Braking" Damn good idea I do remember though reading in the Duet documentation that disconnecting the steppers while the board is under power could damage it. Is there a solution? whats the resistor for?

Yes you can use that PSU for testing, but keep the voltage output to 25V or below.

Disconnecting stepper motors while they are powered produces high voltages that arc across the contacts you are breaking, producing transients that are likely to damage the stepper drivers. In fact the modern Duets are fairly tolerant of it (see [m.youtube.com]) but we still advise against it.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Why not use a tennisball at the end of the rail?
If you only use Duet drivers the harm will be pretty small. External drivers with like 50V/10A, I'd be afraid off.

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Bill Clark

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dc42
If you are not driving a bed heater from 24V then you can use a small 24V PSU, in which case the stepper motors will only move a small amount after you kill the power. Another possibility is to wire an external reset button to the expansion connector.

David, I have one of these power supplies. [www.ebay.com] Can I use that for testing? I would set the current limit to just above the set current for the single stepper?

Quote
MKSA
You put high Amp limit switches that will open the circuit to the motor coils and short circuit them (eventually through a low value resistor). The switches will suffer but braking effect guaranteed.

"Braking" Damn good idea I do remember though reading in the Duet documentation that disconnecting the steppers while the board is under power could damage it. Is there a solution? whats the resistor for?

A low value resistor to dissipate the energy and limit the current.
A running motor is an alternator plus when you open the circuit, its inductance lead to high voltage spikes.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

It's a faulty design if you can crash at high speeds. I'd put a limit switch in before your carriage can hit the end of its travel. You can test the distance it needs in the middle of the travel instead of the end.

Thanks guys. All great solutions. I'll post an action video once its operational

Quote
etfrench
It's a faulty design if you can crash at high speeds. I'd put a limit switch in before your carriage can hit the end of its travel. You can test the distance it needs in the middle of the travel instead of the end.

its just a mechanism for testing. we are designing it now. lots of manual g-code input. wont be able engineer out my ability to potentially input something wrong