Pen Lift servo failures

[Tirki]

I have an Axidraw V3 and I seem to be burning through pen lift servos at an alarming rate.

My original servo failed about a year ago. The second has been in service until a few days ago and the third servo that I just received only responded to the raise command once then stopped working all together.

Any suggestions as to how to trouble shoot this?

[Windell Oskay]

If it’s DOA, please contact customer support for a replacement. (They should definitely not die immediately.)

Generally, though, the pen-lift servo is the one component that you should expect to wear out over time.

The primary limit to the lifetime of the servo motors is that the tiny DC motors inside them wear out. Once a servo starts buzzing, that means that it’s moving its motor constantly, and will die very soon after. (Buzzing means that the motor is moving constantly.) Heat seems to be a factor, so reducing the stroke or the amount of weight to be lifted can help extend the life. Applications where the servo has to move more weight (including rubber bands, weights, etc) tend to reduce life further. If your pen-lift stage doesn’t glide smoothly up and down, then we should address that, as it’s one of the biggest factors that can give you a reduced servo life time.

One other concern is that the motor may still jitter while the machine is not otherwise in use. We made a change in the most recent version of the EBB control board, adding a MOSFET to control servo power. (This version is distinguished by using a micro-USB connector, rather than a mini-USB connector.) This allows you to turn off servo power, and (by default) does so automatically after 15 minutes. From the age of the machine, I’m guessing that you have the mini-USB connector, not the micro-USB connector. Accordingly, it’s a great idea to unplug the AxiDraw from power when it’s not in use.

[Tirki]

Good information Windall, thank you very much.

[Tirki]

I have received and installed the new servo (Evil Mad Scientists have GREAT customer service!) but I get the same symptoms.

Using the axidraw extensions in Inkscape, I try to use setup to do the pen up/pen down test.

The pen up test works to move the pen up then the pen lift servo stops moving. No up, no down, no motion.

I can manually move the servo to the down position and it will lift again, just once, then nothing.

Seems to me like this is more likely a EBB control board problem rather than a servo problem.

Can you post a link to order a new circuit board?

If my Axidraw V3 is compatible with the new EBB control board I would prefer to use that. Otherwise I will just replace the existing board.

Thanks for all your time and effort!

[Lenore Edman]

This has been resolved through further testing.

Note that in general, if you can keep the up and down positions in the middle of the range, it will decrease the wear and tear on the servo. Settings such as 60 up and 40 down are preferable to 80 up and 60 down.

If you’re testing to see if a servo works, 60 and 40 are good starting positions, with a wide enough range to see the motion.

[Tirki]

Problem resolved!

I had the pen up/ pen down settings too high in Inkscape. Resetting pen height to 60 up and 40 down resolved the pen lift problem.

My thanks for your help and support!

[Windell Oskay]

If I understand the issue, it may be that the pen-up and pen-down positions were set too close to one another (almost the same) rather than either necessarily being too high.

[Tirki]

That is correct.

I had the pen up setting at 89% and the pen down setting at 90%.

Thanks!

[Author]

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