servo gears

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Spaceman
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servo gears

Post by Spaceman » Tue Oct 23, 2018 6:39 am

Another question.

gear trains with servos.

Im sure at AWS57 I saw someone using a servo with a custom head that was a cog driving a pincer.

I wondered how feesible it is to print such a thing? and if so how to simulate all the little grippy teath that the output of a servo has. or is there a far simpler way to do it?
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Isioviel
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Re: servo gears

Post by Isioviel » Tue Oct 23, 2018 9:14 am

The servo pincer was me - there's a cut down servo horn glued inside the cog to make it stay put! I started modelling the grippy teeth for inside but quickly got bored counting teeth and decided to take the easier route. It's not pretty but it works :).

I've been having issues with the (ABS) teeth on the cogs wearing down anyway, so am not convinced that tiny inside spokes would hold up for long. I'd love to hear anyone else's experiences though, if it's worth the hassle then I'll put more effort in haha.

I tried to go without the horn on my flipper this time (which essentially works the same way as the pincer, lack of imagination, I know!) by printing it too small and pushing it on whilst warm, hoping it would scratch its own teeth in on the way. It didn't work. Not sure if it scratched no teeth, or if they just wore away over the day, I haven't taken it apart yet. I plan to just cover it in superglue for now, and make sure to add room for the horn in the next iteration.

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MarkR
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Re: servo gears

Post by MarkR » Tue Oct 23, 2018 10:39 am

if it's one of the servos with the brass knurled type of output, can you 3d-print the hole slightly small, then (gently) heat the output shaft of the servo, push the PLA part on, then when it cools it should be welded?

I have used this approach on small nuts welded into PLA parts.

One problem would be that it could be tricky to replace the part, the old part would be welded on and tough to remove.

I used a soldering hot air gun with small nozzle - be careful, they get very hot, very quickly. (NB: I haven't actually used this technique with a servo, it might damage it if too much heat is used)
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?
Stacie - tidy flipper; 4wd driven by hair bands

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Spaceman
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Re: servo gears

Post by Spaceman » Wed Oct 24, 2018 10:24 am

Intresting. Thanks for the responses.

I was considering counting teath and making a keyed bit but that sounds like much more bother than its worth.

I think the embedded horn is the way to go by the sound of it. What measures did you take to get the gear running concentric?
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Isioviel
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Re: servo gears

Post by Isioviel » Thu Oct 25, 2018 2:46 pm

What measures did you take to get the gear running concentric?
I wasn’t that scientific – printed the cog to the same height as the horn, stuck some superglue inside and pushed the horn in, then used a flat bit of scrap to push it down to keep it level. Because it’s so small any variance is unnoticeable.

But… my gears are not very well mated. I had to slightly bevel them to get a 90 degree connection, but couldn’t make a full bevel gear because I had two sides to the gripper. It was my first attempt at designing/using gears (and I’m pretty new to CAD) so it’s a bit of a bodge job. I will be redesigning at some point, now I’ve got slightly better at CAD and have seen how it works in action :) .

So it’s possible that the variance only doesn’t matter because it’s all a bit dodgy in the first place!

I’m happy to share the stls if it’s useful to you (given what I said above…).

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Spaceman
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Re: servo gears

Post by Spaceman » Fri Oct 26, 2018 6:30 am

Isioviel wrote:
Thu Oct 25, 2018 2:46 pm
What measures did you take to get the gear running concentric?
I wasn’t that scientific – printed the cog to the same height as the horn, stuck some superglue inside and pushed the horn in, then used a flat bit of scrap to push it down to keep it level. Because it’s so small any variance is unnoticeable.

But… my gears are not very well mated. I had to slightly bevel them to get a 90 degree connection, but couldn’t make a full bevel gear because I had two sides to the gripper. It was my first attempt at designing/using gears (and I’m pretty new to CAD) so it’s a bit of a bodge job. I will be redesigning at some point, now I’ve got slightly better at CAD and have seen how it works in action :) .

So it’s possible that the variance only doesn’t matter because it’s all a bit dodgy in the first place!

I’m happy to share the stls if it’s useful to you (given what I said above…).
That would be cool thank you.

Crabulon was my first stab at a gear train in a robot so its all learning at the moment. After the horizontal fight i realized the gear train was also missing several teeth.

What CAD package are you using?
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Isioviel
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Re: servo gears

Post by Isioviel » Sun Oct 28, 2018 6:43 pm

Files here: https://www.thingiverse.com/thing:3200932

Crabulon was so cool to watch - I regret not coming to take a proper look, will make a point of it at the next event! Did your gear train loose teeth during the battle? What did you print it out of?

I use Fusion360 for CAD - it's been a steep learning curve! There are add-ins for spur and bevel gears which is nice, but I couldn't find anything that really did what I wanted, so I've been mostly making it up as I go a