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I'm trying to use a linear actuator (sample electric cylinder) for a soil penetration device. Originally, I thought of using a pressure sensor to know when/if I hit a rock. However, I am not seeing many linear actuators with integrated pressure sensors but they do come with potentiometers. So I am thinking, would it be possible to use the potentiometer as a rough way to know if I hit something?

Basically, my program would check if its position does not change for a small time interval. If the position has not changed before it extends the maximum length, then the actuator must have hit something it cannot penetrate well.

Anyone have any ideas?

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  • $\begingroup$ mount the actuator on a spring ... similarly to the way a strut assembly is attached on a front wheel drive car ... here is a picture ... schmiddy.de/vw1302ig/p03/vaxl02.jpg ... remove the shock absorber assembly from the picture ... put in the linear actuator under the spring ... put a switch above the actuator assembly .... if the probe hits a rock, then the spring will compress and close the switch $\endgroup$ – jsotola Mar 13 '18 at 0:38
  • $\begingroup$ This sounds like the mechanical version of other solutions proposed here. I am trying to simplify my project, but if needed this sounds like the way to go. $\endgroup$ – Yevheniya Kupchyk Mar 14 '18 at 17:26
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Yes, you'll see the position become fairly stable when you've hit a rock (assuming that your bot is heavy enough to stall your actuator).

Measuring current will also tell you if you've stalled/are stalling. I have used a Pololu controller which apparently has current feedback over USB but I have not used that feature. I suggest that you use something like this rather than building your own H-bridge and current sensor. It will make it easy to experiment with different approaches.

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  • $\begingroup$ Ok, perfect just wanted to confirm that. I will see if I need the current feedback idea as well. Thanks! $\endgroup$ – Yevheniya Kupchyk Mar 14 '18 at 17:22
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Pressure: First of I would prefer to use piezo pressure sensors. But you can use pressure sensitive resistor films like velostat: https://www.adafruit.com/product/1361

Proximity: Alternatively, You can use sensors such as capacitive or inductive proximity sensors. It is used quite frequently in the industry to detect touch and contact or measure temparature or distance. For example:

https://playground.arduino.cc/main/capacitivesensor?from=main.caps France

https://www.sick.com/ag/en/proximity-sensors/capacitive-proximity-sensors/c/g201659

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  • $\begingroup$ Thanks, but I am trying to see if I can use built-in sensors before resorting to buying more supplies. $\endgroup$ – Yevheniya Kupchyk Mar 14 '18 at 17:24
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Using a pot, or a linear encoder, could let you know when the actuator is no longer moving. But I would not call that a pressure sensor. If you want to know the actual pressure for a dirt-penetrating device, you could use a piezo crystal, or another tip device that responds to pressures (see haptic sensors). Alternately, you could sense the current into the actuator to determine the impedance of the environment.

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  • $\begingroup$ I understand that it is technically not a pressure sensor but I wanted to see if I could replicate the effect. I am trying to avoid the piezo crystal idea, but the current idea is interesting. $\endgroup$ – Yevheniya Kupchyk Mar 14 '18 at 17:23

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