Hello everyone!
For this year’s game, we are looking into custom pulleys. We were wondering your experience with 3D printed pulleys vs custom manufacturing like CNC or etc.
Do you have any experience with any of them and if you do, do you have advices to make custom pulleys?
We printed ours on Ultimakers in shop. We have not had any issues so far. A big pro for us is that printing pulleys saves us a lot of money buying these things. Definitely make sure you adjust your 3D model’s bore size (by expanding the hole say a couple thou) so that it will slide onto a hex shaft before you print. Otherwise, it takes a while to file the bore down.
We’ve been testing with printed pulleys and found the opposite is the problem. We’ve been running them on our Mark 2 and have found that adding in a few thou, maybe .005, is the perfect fit for us. You can run a hex broach through the center to clean it out if you’re worried about it being too tight of a fit.
Thanks to both of your replies @alex.richards48 and @Katthecat . Did you guys run your pulleys at high rpms? We are planning to use them on our hopper and even though it won’t be that high in RPM, we are concerned about the durability.
We’ve lathed our own pulleys in the past, since they were weird sizes that we couldn’t buy. It was a steep learning curve, but definitely feasible, even on a manual lathe.
I always make design the CAD to be nominal, 0.5", and scale the print to compensate for the shrinkage.
0.495 / 0.5 = .99 which means I scale up to 101%. This has been very effective for us.
Wasn’t directed towards me, but we’ve used 3D printed pulleys on our robot for 3 years now. It depends what you’re using it for. Given that youre using It on the hopper, you should be fine. We recently 3D printed a prototype for some 1/4in polychord belts, and it wasn’t until there was a difference in tension in the belts (we had 3 belts on one pulley) that the thing became lopsided and dug through the plastic. This was also at 10% infill. Something we’re currently trying out is adding mounting holes for a hex hub. This is to take some of the strain from the rotating axle off the pulley itself, so that it doesn’t break like I previously mentioned.
As long as your belts aren’t too small and cause a lot of pressure, you should definitely be fine. I recommend 75%+ infill to ensure it doesn’t break though.
Also just a side note that we make our hex extrusion +.026in to compensate for shrinkage and this works perfectly for us.
We made some custom hubs out of Delrin. We made them on a lathe, then used a hex broach (normally used for a Rotary Broach) and pushed it through with pressure, using the lathe’s tailstock
They turned out really well. We might make some pulleys like this
If you’re driving urethane belts with 3D printed pulleys and those belts jam up, then the belts will weld themselves to the pulleys. Just saying.
Yeah we added 10 thou(5 thou on either side) although they don’t fit right of the printer. I tried them at both 80 and 50mm/s but we still had to file down the inside corners because the printer whipped around those corners and decided to round the inside just enough so it doesn’t quite fit. It wasn’t too much work though, it only took us about 15-20 minutes to file down the 18 pulleys we printed.
Excuse my lack of info about belts 
I am not sure what urethane belts are. We are using regular HTD belts from Andymark. Are urethane ones like the orange ones used in FUN RI3D 2020 or are they something I am missing on?
There are enough COTS HTD pulleys available that many teams, even those with the ability to print/machine their own will use COTS.
And not that I’ll have the answer, but to better inform those who may: What would your custom pulleys be doing? That is, how much tension/torque/shock load? What width belt are you using, or is that TBD?
There are actually enough COTS pulleys available for us to purchase, however we are a team in Turkey and we can’t afford shipping pulleys all the way from the US both financially and time-wise.
We will probably be using 9mm wide HTD belts.
We will be using it in our hopper which will be pushing the balls to the feeder. It does not need much torque nor RPM, but we want to make sure it is fast enough to transfer the balls for rapid shooting. My only concern is them wearing out over use in two regionals.
Any recommendations about which filament to use would be nice as well. We have PLA in house but we can try to get our hands on different filaments.
Using it as a conveyor, most of the stuff said above about urethane pulleys will also apply. Normally I would not advocate using HTD belts for conveyors because they don’t grip as well as urethane, but it sounds like the power cells are grippy enough to make up for it.
I have printed and machined pulleys before. Honestly, both work fine, but printing is easier, and is usually plenty strong enough for most applications.
My bad, I did not provide enough info. We are running compliant wheels in the hopper. We will be running the wheels off pulleys with HTD belts rather than having the belts as a conveyor.
Then CoF is not an issue. For a conveyor, you should be good with most materials provided they fit and you aren’t running a pulley seriously smaller (a third or less diameter) than your feed wheels and you aren’t running a lot of compression on your conveyor.
Our team has been heavily experimenting with 3D printed parts this year. We found that 3D printing them is actually super awesome! You might want to make sure that when you print them, you print them solid instead of webbed on the inside. Then again this all depends on what you are using the pulleys for 
We put a couple AM14U-origin belts into the intake arms of our disassembled 2018 cube grabber. Absolutely zero issue sliding power cells around. We plan to use a bunch of them on this robot.
We had our at around 7000 rpm and they seemed to be holding up fine. We will eventually try to run them faster.