I am starting my 80100 direct drive build and would like to test motor and ESC (especially the ESC) beforehand under roughly realistic conditions. In particular I want to apply some varying loads on the motor (without emptying my bathtub) and test different cooling options for the ESC and measure how effective they are. I am looking for a simple, cheap and dry solution.
I thought of spinning a metal disc with the motor and brake it with an old bicycle brake.
Other option would be an electrical generator, but I don’t have one.
Will this draw current similar to a prop in water? Also it would be nice to be able to vary the load.
I mean, it is not very practical if a single blade fills my printer and I have to print 3 sizes or so.
The ideas above are good but they would not supply a measurement of the motor torque which with the RPM and electrical current measurement would give the efficiency which would be valuable information.
take a look at:
I would suggest to build a simple dynamometer and plot RPM vs. Torque
take a look at:
for the basic calculations.
I think this experiment will generate very valuable data as to what speed the motor should work at in order to get the best efficiency and torque. this will also aid in choosing the right propeller that will work in these conditions.
@hovav That is the best solution for sure, but it is a pretty involved project on it’s own (at least for me). And my main interest is testing ESC cooling, so I’ll probably do this at a later point.
My current favorite is something similar to what @sunrise305 suggested: a bike rollerbrake (drum brake) from Shimano, it is less expensive than a kart brake, said to have no wear and is designed for air cooling through airflow from riding, so some forced airflow by PC fans could do the job I guess. Through the rope I can apply different brake forces and draw different kinds of current.
For my initial tests with a frankenstein Vesc I used my lathe. I‘m not sure if this would work with other ESCs. I did drive the motor with the lathe and charged the battery by braking the motor with the vesc. Torque mesure ment is also easy then, as the motor mount can affect a scale. This is however pretty unnecessary if you know the motor current.
I‘m looking forward to your results with the disc brake.
What do you think about this (different from my initial requirements, because it is wet):
Putting the motor with prop down facing in a (relatively large) bucket of water, running the cables through a plate on top of the bucket that seals it. Cable holes in the plate sealed with silicone. The whole bucket is filled with as much water as possible, leaving not much air. Then I could run the motor in realistic conditions without making everything wet, as long as everything stays tight. The question if the vortex that will likely be created greatly affects the current draw.
I think you will need a really big bucket! The amount of water move is enormus
During my test the vortex created a air pocket in front the propeller , but it was not deep enough and i could not hold it full throttle any way …
I think the static bench gives information but not really what happens when you start to fly , for me same rpm but a lot more speed , less load and propeller slip …
Back when I designed my hydrid drivetrain for my boat I made a simple dyno by converting a ac-motor to a generator. Something similar could be used here. I used a 240V ac motor that was spun at a rpm that made it produce 200-300V Ac. I added some capacitors and the load consisted of a heater and a couple of light bulbs.
You can find the info regarding capacitor sizes on the net.
