3D printed hub

A "new fashioned" televisor, using an Arduino to drive the motor and display.

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3D printed hub

Postby Andrew Davie » Wed Apr 12, 2017 10:28 pm

I printed a new disc for the drive mechanism to step-down the motor rotation a bit more. It came out well, and just a push-fit on the disc shaft it hardly wobbles at all. Very happy with the result. I also came up with a neat idea to spread the changes in PWM values to fractional amounts by writing the motor duty cycle in the 22050Hz interrupt that's playing the video. Then I could have rapid integer values representing fractionals... So, 44 44 44 45 44 44 44 45 44 44 44 45 in other words 44.25. The code is incredibly simple but my first test didn't work. I'll come back to this because it's really elegant. I just wonder if/when I rewrite the duty cycle, if that changes the NEXT square wave's duty, or if it zaps the current one straight away. I need the former, not the latter.


youtu.be/Tnc_aaySTPs

I replaced the PID with some more robust code, and although it's working and more responsive, it also has many problems. I haven't tuned the one seen in the video at all - I just confirmed that it was holding and moved on. Good that I'm learning a lot about PIDs and tuning, though! In the end I may very well abandon the PID concept and put a bit of homebrew algorithm in that has specific knowledge about how to sync a disc (for example, do it like a human would). How would a human do it? Yes, I need to build a mechanical finger to push against the disc to slow it down! ;)
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Andrew Davie
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Re: 3D printed hub

Postby Andrew Davie » Fri Jun 09, 2017 5:03 pm

The toothed drive belts I ordered arrived today, so I 3D-printed some replacement pulleys. The small one goes on the motor, and it has 16 teeth. The larger one has 96 teeth, so a 6:1 ratio there. With the Nipkow disk spinning at a nominal 750 rpm that would make the motor spinning at 4500 rpm which I think might be a reasonable value. Anyway, the pulleys have walled sides to help keep the belt in place, and they're just just a push-fit over the motor/hub shafts. Hopefully the teeth will help "lock" the disc to the motor better than the rubber o-ring I'm using now. Very curious to see if it's better or worse!

pulley.jpg
pulley.jpg (268.27 KiB) Viewed 2018 times
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Andrew Davie
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Re: 3D printed hub

Postby Andrew Davie » Fri Jun 09, 2017 10:26 pm

Back to the drawing board... literally!

Well, that was a complete failure. Perhaps not a waste of time, because I learned something. That is; toothed belts running at speed are extremely noisy! I'd say 10 times louder than the O-ring that I was using before. I only had it going for a minute and realised it just wasn't going to work at all. So, there's that idea down the drain. On the plus-side, when I re-installed the O-ring system, it was significantly quieter than it used to be. Clearly the tension on the pulleys and O-ring make a huge difference. It has been suggested already that I need some fine-adjustment for the position of the motor (to adjust belt tension) and I totally agree. Starting to think about how I can 3D-print a mount that has fine precision adjustment capabilities.
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Andrew Davie
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Re: 3D printed hub

Postby Andrew Davie » Sun Sep 10, 2017 4:12 pm

I bought myself a fairly capable (but incredibly cheap) 3D printer. I though I'd have a stab at printing stuff for other people, so here's the first advertisment for my services. It will be fun to see if I get any business :)

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Re: 3D printed hub

Postby Robonz » Sun Sep 10, 2017 5:15 pm

Its interesting that you are doing this right now. I will be attempting some laser cut hub and pulley ideas soon. The trick I am planning to do, is get some large bearings and use them not as bearings but as precision spacers to make things run true. When my new belt drive motor arrives I will see.

I think you would be better off running smooth pulleys and your toothed belt inside out. Its not like you need to keep the motor timed. Once at speed it wont slip. 3D printed toothed pulleys and gears are always noisy. All good experiments though. You can never learn too much haha.

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