| Electronics > Projects, Designs, and Technical Stuff |
| Strain gauge Joystick - Could something like this work? |
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| richard.cs:
I have tried printed strain gauges on PCBs before, they weren't great. In my case I was comparing tracks on one side with others at 90 degrees on the other side of the PCB and my main problem was that the two identical geometries ended up 30% different in resistance giving large offsets. I suspect this was mostly plating rather than etching. On mine the major killer was the resistance delta meant that the self-heating didn't cancel so it wasn't as simple as removing a fixed offset. Your sketch suggests you're comparing two areas on the same side of the board which should be bent in opposing directions, they will probably be better matched than mine. You may still find the low impedance problematic though. |
| fcb:
--- Quote from: skylar on January 23, 2020, 04:04:16 pm --- --- Quote from: fcb on January 22, 2020, 11:58:35 pm ---Yeah. It’s going to be super low impedance. Commercial strain gauges are typically 120/350/1Kohms, very thin metal printed/etched onto polyamide. Principle is the same though - you’ll just have to be creative with your circuitry to cope with the low Z. --- End quote --- Not to be annoying, but would not it be easier to glue commercial strain gauges to the PCB cutout originally shown? Then you could use the standard circuit to measure it, no moving parts though there is more assembly than the project seems to aim for. --- End quote --- Sure - but then you have a $20 thing, I think the OP wants to make a low cost thing. Also, a standard strain gauge setup might still need an instrumentation amp with a gain of 100-1000, ADC etc.. Handling the low-Z is the first headache, compensating for thermal drift will be a big deal also. But then thats 90% of the fun with electronics. |
| Leo Bodnar:
Typical strain gauge has 1-2microstrains limit before deformation becomes plastic and irreversible. Have you done stress-strain analysis on it? Self-heating is usually prevented by gating the excitation voltage. Leo |
| PeterFW:
Thank you everybody for your ideas and feedback, i want it to be a cheap solution because i would like at least... 44 or 88 of them. But after a lot more thinking an research i ended up with a FSR matrix from Sensitronics, at least i ordered one. I think i can get the desired effect if i glue on suitable rubber feet with considerations of the matrix pitch. That should get me where i want. |
| jfitter:
Electrically the design is simple whether you use strain gauges, optical rotation sensors, etc. What really needs to be considered is whether the mechanical design is practical. Real joysticks used for machine control have a mechanical arrangement that provides for a centering force. What this means is that a certain critical force (torque) must be exerted before there is any output from the sensor, after which the output is linear with deflection. Check out radio control joysticks, especially the high end ones, aircraft side-sticks, joysticks for cranes and hoists, coal mining machines, etc. The problem with simple force sensors on fixed sticks is that there is an output for any force. A tiny force yields a tiny output and the practical reality of this is that it is almost impossible to control anything with it. This is why non-gymbal joysticks are NOT used for machine control. |
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