Originally Posted by chuckinnc
I have a junkbox full of motor,prop and esc's, now I am trying come up with
some working setups. I have a wattmeter and scales but need a diy setup to measure thrust so I can come up with something that I hope will fly when I get to the field.
I've picked up a scale from Harbor Freight that measures 0 to 50 pounds. To use it, I just tie a rope around the tail of the model airplane, set it on a concrete driveway and run up the motor. Might be that this is not as exact as a real fancy reading, but it works.
Just a reminder though, thrust is not the only factor here. You can have a LOT of thrust with a propeller with a very low blade pitch. And once the model is moving, that very low blade pitch might not have enough prop blast in MPH to fly the model.
One good way to help out in this is one of those computer spreadsheets such as www.motocalc.com
. Free for 30 days, then $39.
With this, and an unknown motor, you can "design" a phony motor that will turn over your propeller at the RPM you measure. Just put in the LiPo battery pack, a few numbers for the motor weight, zero load current, motor winding resistance and KV. You can juggle the KV rating to get the RPM your motor turns the propeller. From that, motocalc will let you know how well the model airplane will fly. I've even designed phony motors to represent a glow engines performance.