6x4 Propeller

thingiverse

This is completely experimental. Props spin at very high speeds and can be extremely dangerous. So to test props I have printed one of my motor mounts and screwed it to a block of woord. I put the props in a push orientation with a 2200kv motor and attached the wood block to a old scale. I zero out the scale and run the prop to see how much force it exerts down in lbs. I also did a control test with a 6x4 store bought prop. This prop exerted 1.8lbs at max rpms. Part of this adventure has been getting the print quality perfect. It took about 5 or 6 attempts but I finally can print the prop with minimal cleanup required, as seen in the photos. The second to last prop I printed only registered 0.8lbs, but also had an issue where the center hole for the shaft was a little too large and the blades did not stay aligned causing the whole thing to become unbalanced. Here's where things get interesting. The last prop I printed came out very nice, and it had a snug fit on the shaft. The issue was I did not initially test the prop on my scale rig. Instead I wanted to "feel" how powerful the prop was compared to what I have felt on my model planes. This was stupid and dangerous, but I held onto the wood block making sure the motor was in front of me with the prop parallel to my body so if a blade snapped it in theroy would not hit me... probably.. Unfortuently since I was holding the rig and a controller I did not record the results, but this is what I experienced. I fired up the motor and gradually increasd the throttle feeling if anything was off balance. Then once I felt it was "safe", I maxed the throttle (I should have continued to gradually increease the throttle). As soon as it hit full thottle the entire rig pulled extremely hard in my hand exerting significant force. Unfortunetly at this point I dont know what exactly happeded. One of the blades may have snapped, though I dont recall any abnormal vibration even for a moment. Reguardless the result was that the entire motor with mount and screws ripped out of the wood board and the entire thing smasshed into the floor shattering the prop. Luckilly I wasnt hit by any shards. Though I did find a sharp across the yard. (I should have also used larger and longer screws.) I really wish I had gotten a reading for that last prop. I feel it was good as far as force exherted and I will be printing a new one to test properly on the scale. However I may try to configure some kind of plexyglass walls around it, just in case one of the blades do let go. I know the scale rig I am using is not the most scienntifgic way to test, nor am I trying to get values for complex calculations. At the moment my goal is simply to print props and compare them against the store bought prop, as well as test their strength. Feel free to download and experiment. But be safe if you do. Note: I model knowing the limitations of my 3D printer. Its old and has a few minor quirks. In general its accurate but holes especially tend to print out smaller than they are sized in the model. As such I model holes slightly larger to accommodate this. Test print any part and make sure any attached hardware like wire or skewers fit properly before bulk printing.