Some might remember I did a Worm Gear Setup a while back and it “kinda” worked. Well it failed due to it jamming and destroying bearings and stuff. I overlooked the fact that if you use a worm gear the way I was and hang 150lb from it - well the 150 lb transfer from the Worm gear to the worm and even though the rotational torque needed to turn it is little - according to ratio and friction but the Worm gear still works as a lever and the Worm holds and transfers the torque- caused by the 150 lb (in that case about 1/2 of it due to the way levers work) to the case and the only thing holding it was a 688 bearing which died under the thrust of 75lb vertical to its rotation plane
So a thing that should be able to be fixed with a thrust bearing protecting the 688 in that direction.
So Ali Express delivered some thrust bearings. In the meanwhile My filament tester prototype died - as I pasted previously - due to stripping out 5/16 bolts and nuts I used to break the plastic test pieces. Before it broke it showed a 50 mm2 cross section PETG piece broke at about 230lb average and I don’t want to go lighter on the test pieces as 5x10 or 7x7 are dimensions often used by themselves or in multiples in my designs so I want to test close to real world use conditions. And I want to do stronger stuff too so I am shooting for 450-500 lb (or 3 robots or a whole alliance buddy climb - lol)
The core will be a 40 tooth Worm gear (yeah I could go other ways like planetary etc too) but I did planetaries successfully and I Worm gear is still waiting for success. So I just printed the Worm Gear with 2 HTD 5 30 tooth pulleys attached
The reason for 2 pulleys are 2 fold. First to keep it centered and 2nd HTD-5 15mm Belts according to Gates can be trusted up to 275 lb
The Gear has 40 teeth with a 2.8mm Modulus. I arrived at that from Hints of previous tests. Based on the area of this print I would expect a tooth to pull at a load of somewhere between 120-150lb. At 40 teeth at least 4 teeth are engaged to some point between the worm and the gear and I am using 2 worms also the bigger the gear the bigger the lever in comparison to the .94 in lever of the 30 tooth pulley reducing the load on the thrust bearings. The pulley has a 1/2 in square axle hole to allow a steel 1/2in square stock or tubing to be inserted the axle will have some adapters to 6805 bearings (4) Which should easily hold the load as they are statically rated at about 650 lbf and 4 bearings as I intend to extend the axle to connect external loads like the rack and pinion prototype I posted about earlier.
For the last 2 days I have been working on the bottom half of the case
W450lb_Case (Master).pdf (1.6 MB)
(3d Pdf viewable in Adobe Acrobat)
Its about 90 % done. RN I am working on the input gears . A 19 tooth Mounted to the CIM Motor, A 2nd 19 Tooth as a reversing gear and 2 59 tooth gears that will hold the worms. So overall a (59 * 40 * 1.06)/19 = 131 : 1 reduction. The Cim will be controlled by an Arduino and a BTS7960 so limited to <40ish amps at 12 Volts which translates to about 5 in/lb at the shaft max or theoretically about 650 lb lifting at the output. But I expect a loss of up to 30 % along the way especially due to friction at the Worm/gear area - even with lubrication. Hence this ratio to get close to the target 450 lb.
The max speed at max load will be probably 30 rpm translating into something a little shore of 3 in/sec. Which is good for testing tensile strength and deflection and such. If one would want to go faster - well add some motors and drop the reduction.
If it is at least somewhat successful - I will make a folder on grabcad for it and share the files. Either way I will publish the results.
So its time to comment below to put down what part will fail or not and at what weight load it will fail. The test intended is to hang my scale from a static place and connect the other end to the 2 belts and then give the motor as many Volts and Amps necessary to get the weight desired up to a max of about 36 Amps and then hold it for a little while.
Things still to do: Design and print rest of gears, 2nd and 3rd part of the enclosure, mount steel and aluminum tubing, connect arduino to BTS 7960, write code, and most likely add a touch screen to control the whole thing.
