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Sep 26, 2019, 07:35 PM
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Griphin's Avatar
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3D printing a motor pinion (Tamiya Hornet)

To test out an FPV pan and tilt setup for my aircraft models I wanted my first RC car. For giggles I got a Tamiya Hornet kit I always wanted as a kid and had zero intention of building it stock and wanted to use spare plane parts on hand and 3S 2200 lipo batteries which I have plenty of. Brushless of course. The motor is a 3536 1800kv which fits fine but the shaft is 4mm which is a problem. I could have just drilled out the pinion bore but decided to design a pinion in CAD and see if to would work.

So several versions later I have a 18T M0.8 pinion with 20 pitch teeth which fits my motor perfectly and is spaced 16mm long as required by the Hornet. The pinion is tightly press fitted on the shaft with a locking grub on a flat I ground on the motor shaft myself. I can modify the pinion size and shape in anyway. More or less teeth, change the pitch or module.

Printed in PLA it wasn't strong enough for the grub but in the stronger PLA+ it seems good. On the ABS gears in the diff will it work? Should I be particular aware of anything going wrong? 20mins to print out a new pinion so I'm not worried about the pinion wearing out.

I'm not after top performance it's a test model and some fun. I'm also giving WD-40 Specialist 150g Anti Friction Dry PTFE Lubricant a go rather than the grease that came with the kit.
I'm going to go back to building the car which I've only just finished the diff.
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Sep 27, 2019, 07:27 AM
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Lynxman's Avatar
PLA works well as gears if you grease them. They usually break because of friction which makes them overheat, which happens at very low temps with PLA. You can make the teeth the whole length of the pinion. That will provide extra strength tot he part of the teeth that's in contact.
Sep 27, 2019, 02:48 PM
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Pinions are kind of easier as you can adjust the mesh but diff gears have to be a really perfect fit , I've used the Fusion 360 gear making tool extensively and have found that different materials shrink different amounts so you then need to scale them up or down 1 or 2% till its a good fit ,i do the scaling in Fusion so the axle holes can also be adjusted as well , if you scale it in the slicer the axle holes will change and there's nothing you can do except drill them out .
printing gears on a raft is good as well to avoid elephants foot on the bottom of the gear .
The best material I've found so far is Carbon Fibre fill Nylon , it prints as easy as PLA but you do need an all metal hot end as it prints at 260+ C .
If you lube PLA gears really well they can work for some time , it might be worth a try to get some CF PLA ,you can get CF PLA quite cheaply and it might hold up better .
Sep 28, 2019, 08:06 PM
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Griphin's Avatar
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Polytetrafluoroethylene (PTFE) is the best anti friction coating I can reasonably expect to get. Good bit better than silicon.

Yesterday I soldered the connections on to the the 35A brushless ESC I got and calibrated it using my Spectrum DX9 aircraft TX. Took much longer and was more frustrating than expected as I didn't know the ESC wouldn't arm until the ESC was calibrated. Fortunately I got the programming card for the ESC so it all set and working now. I have steering and axel spin! Set the forward throttle to 70% and the acceleration to weakest as I'd rather not break anything in the first run.

I'm going to give your suggestion a try dadio and increase the length of the teeth. Also I might just get some CF PLA if the PLA+ pinion breaks. From my reading it wears brass 3D printing nozzles out very quickly but it's only a small part and nozzles are cheap. CF material might be good to use for any replacement parts on the model too.
Thanks for your ideas gentleman
Sep 28, 2019, 10:12 PM
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You should get 1/4 to 1/5 a kilo of CF filament printed before you need a new nozzle , that's a lot of pinions and steel nozzles are not very expensive either .
Sep 29, 2019, 03:46 AM
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Griphin's Avatar
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Just finished putting the chassis together and gave it a run in the grass in the dying light of the evening. On the 3S 1800 pack which is more then half depleted with the throttle set to 70% it went pretty well. Nothing broken. I'm going to set the throttle to 50% and charge up a 3S 2200 which is what I intended from the start and test it later this week.

I'll order a roll of CF tonight. That was a good suggestion. I like brass nozzles as they heat quickly so I'll just get a lot of spares.
The rear wing set seems pretty flimsy so I might make a little mod for that. Spray painting the shell and cosmetic stuff is going to have to wait until next weekend.
Sep 29, 2019, 04:47 AM
Registered User
Brass nozzles are cheap so yeah just have a go . I designed and printed a simple wing in TPU , just 2 layers thick and its held up really well , you need a reasonable extruder for TPU but if you print slowly then with the cheap unbranded eBay stuff will print on an ender 3 if you keep to Max 15-20 mm/p/s , the trick with TPU is no retraction and all moves at the same speed ,top ,bottom , inner ,outer ,infill and travel all the same speed and use combing to reduce stringing .

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