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Power management & limit switches

Started by mcduff on in TinyG Support. 2 replies, last activity Sep 24, 2012.

mcduff #3518

I have a tinyg hooked up to a zen toolworks 12x12x6, and have made some first cuts.  I've run into a couple issues:

1) power management

The ZTW leadscrews are fairly aggressive (8mm per turn), and it turns out that I need to use the always-on power management (x and y deviate only a little, z axis with an upcut bit in wood and a heavy spindle = bad news bears).  If I have the ${x}pm settings all on 1, then switch them all to 0, they don't actually put current to the motors.  I have to make a move that engages the motors (a move on all axis--if I only move one axis then only that motor is turned on continuously) for current to start flowing continuously.  The same behavior exists for switching the power management mode back to 1.  Especially for the latter, it would be nice if the change would take effect immediately, rather than needing a move.  Also if I move only slightly (1 mm in each direction), sometimes the motors will not pick up the new setting.

2) limit switches

I initially had trouble with EMI tripping the limit switches.  Turning on the spindle always tripped them, although putting a switch between the spindle power supply and the spindle (and keeping the spindle power supply always on), and putting some ferrite chokes between the power supply and the spindle helped.  But then turning on the vacuum would trip the limit switches.  So I tore out all the old wiring, replaced the motor and spindle wires with coax and the limit switch wires with telephone wire (hoping that twisted pairs would help), and kept the new wires as short as possible.  It's better, but about 25% of turning spindle/vacuum on/off still trip the limit switches.  I have some ferrite chokes coming, which I plan to place on everything, but I'm not sure how well that will work.  Has anyone battled this problem and won?  Should I be using coax for the limit switches?  I am worried that a large part of the problem is that the ancient house I'm in has crappy wiring without a proper ground.  For now I have the limit switches mode as homing-only.

3) Disconnecting the motors?

If I have the tinyg turned off and twist motors by hand, I noticed that the green motor light turns on (obviously due to the current generated by turning the motor).  Since then I've been unplugging the motors if I need to turn the motors by hand.  Is this necessary (i.e. is it possible to damage the tinyg by feeding some current back into the board)?

aldenSynthetos #3519

Thanks for your interest. Here's some status on your points.

1) Power management. To summarize (if I got this right): you would prefer that power management settings take effect immediately instead of at the end of the next move. This has been requested before, and has been added to the issues list on the github https://github.com/synthetos/TinyG/issues

We are planning to roll up a set of changes in preparation for the 1.0 release planned for October and will include this.

2) Limit switches / noise. Are you using the switches as limits, or just for homing?  If just for homing then set switch mode for homing only, and this will take them out of the loop during cutting operations. However, I imagine you already considered this and are actually using them for limits. Progress has been made on Issue #16 - Noise on limit switches. I have coded the switch ports to use normally closed switches as a switch mode option - which is probably the preferred way to do this. This has not been tested yet, but is one of the items for the 1.0 release.

Before then, however, you can try putting a strong pullup on the hi-side of the switch. Since I can't draw here I'll have to describe. On the input side of the switch lines on GPIO2 - which are the even numbered pins on the switch connector - run a 2.7K resistor to the 3.3volts on the GPIO2  connector. See https://www.synthetos.com/wiki/index.php?title=Projects:TinyG-Hardware-Info:#Interface_Pinouts

The TinyG v7's have these pullups on board but the earlier revisions do not.

3) Disconnecting the motors for hand operation. I do not believe it is necessary to disconnect the motors before turning by hand. But you raise an interesting point. There are 2 cases - one when the board is powered up and one where the board is not. Presumably you would want to know it's OK in either case. We have not had any of the TI's blow out on us, and we have been doing this (turning motors by hand) for 2+ years. That said, I will torture test one of my boards and report back to this forum. I believe it is OK, but don't want to steer you wrong.

- Alden

mcduff #3521

Sorry, I now realize my last sentence on #2 was confusing.  I used to have the limit switch in mode 2 (limit & homing), where they caused problems.  After unsuccessfully trying to solve the issues I put them in mode 1 (homing only).

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