That's great! I've 3D printed loads of planetary gearboxes, the best results are the ones you print with the gears in place but they still ground down quickly & are noisy. I hope you release this open source with your arm I'm excited to print it and have a play!
The problem seems to be the tolerance between the idlers and outer ring, or the lack of adjustment of said. If that could be snugged up, basically capturing the belt between them, then it could take a lot of torque. Loose and it will skip as the belt is tensioned to the wrong side, away from the ring-gear teeth. Add adjustment to the idler wheel position... maybe a rotating cam-plate (with 4 ramps) that pushes out the idler wheel studs, maybe mount the idler studs on some kind of flexure arms. Only need a couple mm, and that adjustment would ease assembly too. I don't expect there's much side to side force on the idler wheels as the belt is taking that force. A flexure that only bends inwards shouldn't be that hard to design. The cam to push outwards against said and locks in position is just 1 more printed part. Cheap. Some kind of adjustment to get that tension right and this could be a pretty slick system.
Wow! This is awesome! May I please know how many teeth the belt has? Cheers for showing! After having seen so many printed gear boxes (mine as well) this is outstanding!
curious geometry. these pulleys would have to be in precise locations so the timing belt going *straight* lines up exactly with the teeth of the outer gear
Hi Christoph, you have good eye ;) indeed you are totally right those pulleys are not in random position. They must be on those precise positions, otherwise the timing belt wouldn’t fit perfect into the profile. Thanks for your comment!
Good idea 👍. Instead of plastic rollers why not just put more smaller bearings? I believe will have more contact. Inner:Outer as gear ratio? Thanks for sharing ❤
Hi, it is very clever solution!! How high the gear ratio? How it is wear the load? Coud i get the cad file on grabcad or someting else platform? Thank you for your answear!
Really low. It’s basic prototype. This design needs to improve a lot, more number of teeth engaged and increase the pressure contact between the crown and the belt. Then we can start talking about interesting torque values 😉
Nice to look at but will fail under torque as the friction is how high enough and the heat will warp the belt. If you can glue two belts back to back so that the timing notches can be used on both sides, then that will work. I would also do an in-line stitch with nylon (fishing line) so make sure that under heat and friction the stitching will hold to a degree. 👍😁 My Two Cents.
Both th loaded inner and outer gears engage with the belt teeth; only the unloaded idlers run against the smooth side of the belt. No need whatsoever to glue two belts back to back. Main weak spot of this design seems to be the number of effective tooth enegatgements on the large high torque gear. Its a relatively small number; certainly with this flexy an output gear it will skip quickly, though i suppose it will go into some kind of rigid bearing. Still, its not a huge number of teeth engaging compared to a gear with exterior teeth.
gluing two belts together back-to-back sounds like a recipe for disaster. those things individually bend so a line _internal_ to the belt maintains its length. if you glue two together, you will either not be able to bend them anymore, or you'll apply forces that'll wear them out in no time at all.
