Peter McCloudI'm doing some planning before getting back into doing some more testing with Goliath and trying to get everything setup to measure the thrust that Goliath is producing. I was hoping to get some feedback on how I should tackle the wiring for the load cell electronics.
For those who aren't aware, I'm following a tutorial on using a load cell to an Arduino. It's pretty straight forward, with the load cell connected to an instrumentation amplifier which boosts the very low voltage signal to something in the range the ADC on the Arduino can pick up. I'll be using 4 load cells, and it's a matter of just summing up the measurements from all the load cells to get the total weight. The only other change is that I'm using a Pro Trinket instead of the vanilla Arduino board
The complication is that the load cells only have 2 feet of cable and some sort of wire extension is needed to get the signals from all the load cells to the Pro Trinket. I'd need at least one or two of the sensors to have 6-8 feet of cable to reach the micro-controller. My two options are: 1) add a extension between the load cell and the instrumentation amplifier and co-locate all the amplifiers on the same board, or 2) connect the load cells to the instrumentation amplifiers as is and run cables from the instrumentation amplifiers and the micro-controller.
I'd like to have all the chips on a single board to make life easier, but I'm concerned about running extensions with the mV level signals from the load cell. I'd love to hear from anyone who has some experience with this or has another idea.
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No experience with load sensors what-so-ever, just rambling;
Maybe to obvious to suggest, but i would just test it, take something you know the weight off (heck, maybe even some basic rc heli taped too the sensor?) and 2 load sensors, add an extension cable to one of the sensors, then measure the weight of your object with both sensors (one with and one without extension cable) If there is a difference, try determine how much different, once you know that add extension cords to the remaining sensors (so all have the same length cable again) and calculate the difference into your weight measurements.
That said, im actually wondering if you will see any difference, its not like you add yards of cable, if you add say 3 feet of extension cable to each sensor you should have enough room to wire stuff up and place the sensors below each prop, pro trinket in the middle below the quad copter, a usb cable from trinket to a laptop to read out the sensors. (or if your feeling fancy, attach a basic screen to the test stand in a place where u can safely read it while Goliath is running, and wire that up too the trinket)
I understand that you are perhaps slightly worried about the quality/resolution of the sensor output because you want to have spot on perfectly divided lift across the 4 props, but im guessing that the sheer size and weight of Goliath means small differences in lift shouldn't be much of an issue, the slight pitch it may cause will go so slow that your gyros etc and the code controlling rotor speed should have no problem compensating, that said i do understand your quest for perfection ofc, nothing wrong with that.
Also, good to see you back, hope the new place is everything you wished for & will help you succeed in your great goal :)
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Good thoughts. It makes sense to just push forward and learn by experience. Thanks for the feedback!
And thanks for the kind words. The place is great, it'll just take a while to get all settled.
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