Rethinking the ground reaction sensor

A project log for Quadruped Robot

A quadruped robot using cheap servos closed-loop control and force-sensing resistors for ground force feedback. Uses Teensy and PCT.

YannisYannis 07/27/2018 at 09:442 Comments

In a project that comprises multiple identical parts (four legs in this case) it is always best to sort out any issues while designing the single part, before moving on to figuring out how the parts will come together. With this in mind I tried to connect and calibrate the load cells that I would be using on each leg, to the leg prototype that I built last week.

Unfortunately the deviations on the load cells were so high that it proved impossible to obtain a consistent behavior with the setup I am using, which includes an op-amp to read the strain from the load cell whetstone bridge. An alternative would be to use the HX711 ADC that is commonly in use with load cells, but that comes with it's own sets of issues (e.g. low sampling rate, drift etc.).

Instead I considered giving Force Sensitive Resistors a try. I had done an elementary test way back with an FSR and a volt meter and was not really satisfied. But yesterday I did a proper measurement circuit and got satisfactory results. So now I'm back to the drawing board to design a new FSR bracket to be located at the root of the leg. 


Yannis wrote 08/05/2018 at 16:46 point

not as far as I tried. Some cells would only be sensitive at more than 100grams which is way too much already. Maybe with a better setup using an instrumentation amp instead of an op amp. But I haven’t tried that, because the fsr alternative seems to work better so far.

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Paul Crouch wrote 07/27/2018 at 10:18 point

Could you not compensate for the load cell offsets in software?

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