In the past I have run Nylon (Taulman 910) gears successfully and also some HIPS In most cases in a mixed environment Nylon at >1000rpm Hips <1000 rpm. and Most of the time at a 1.5mm modulus (aprox 3/16 pitch) involute double helical (herring bone).
I set up a test rig that initially will be used to help me design and build and program a low cost (< $10) Motor controller that should have most the functionality of a Talon SRX with a max current of 43 Amps at 12 Volt with limit switche, encoders, current feedback etc. So well enough suited to run a CIM or weaker brushed motor (mini CIM, Bag, Gearmotors automotives etc.) And instead of CAN I2C.
I designed this 4 stage gearbox.
This gearbox has 2 motors CIM1 will drive it and initially will be just connected to a battery with some current sensing to provide data, CIM 2 will be in “Break” mode that means its power leads shorted and as such working at a predictable load.
The overall ratio of the gearbox can be adjusted -by swapping gears - from a max of 22:1 to 1:22 and pretty much anywhere in between in steps where at least 1 of thegears of each interacting pair has a tooth count that is prime. In the config in the pic you have at each stage a 19 tooth interacting with a 53. I could go 17/55 on each stage and get to around 30 but I start to dislike the undercut necessary at a 14.5 pressure angle at gears with a count of <19
This device can also be used to answer some questions and I am willing to answer some that will be suggested here Maybe some already know the answer.
1.) Nylon is expensive and HIPS not always available - The whole rig in the PIC including the gears are PETG. Anyone ever ran PETG gears? Should I try to run them Dry (no lube) ATM I intend to run them lubed.
2.) Other Materials - maybe except PLA because I know PLA gears even with lube in the past last less than 2 min at 4000-5000 rpm under load. Which materials should we test dry/lubed? (Don’t say peek I currently dont have a printer and the $$$ to print that lol)
3.) Any interest in lower modules. I guess with a .4 nozzle you could print decent involute gears with a sensible fillet at the crown down to about 1mm module. Even tough my guess at 1mm is that non Nylons might pull teeth at some stage in that setup but that would be valuable data maybe too.
4.) How long is a successful test. Under current rules If you print a gearbox then next year you cant reuse it. So figuring on 2 min matches and some practicing I feel it is unlikely that a gearbox runs for more than 12 hours a year except maybe on drive trains. And a 12 hour test is doable. After all the intent here is hardly to make a gearbox that.
I intend to load the system up to about 35-37 Amps on the input which should create a max of about 6 in/lb torque at the input. Torque at the output will be depending on the overall ratio of the gearing. Once the controller is finished I also could provide reverse current to the “Load CIM” to adjust the current apropriately on the input motor. The CIMs graphs can then provide info on torque as the relation between current and torque of the CIM are known and so are the relation at 12 V between current and RPM.
As for the cost of a sample gearbox above:
You have roughly 300 g in gears at PETG/HIPS (volume) prices of < $10/kg its about 3 bucks. If you use taulman 910 at about $80/kg its $24. The housing is about 400 g so about $4 So in filament between $7 and $30 depending on the filament you use. Then there are 6ea 688 Bearings and 2 ea 3.5 in 5/16 bolts as axles with 2 Nuts and of course 2 CIM Motors - but bearings and bolts/nuts and motors can legally be reused.
As for reusing… as I design/print the gears etc with bearing press fit I had trouble removing some bearings I solved that like that
I make a 2.5x2.5mm cutout on each side of the bearing that is camfered on top and bottom so you can stick a 2mm key in on each side like shown in the pic and pry the bearing out and recover it easily.
Once all is working all Cad will be shared on my grabcad. Willing to share some sooner privately in case someone wants to collaborate or “print along”. The parts on this particular rig should fit any printer with a build volume of equal or greater than 200x200x200mm