Wear on 3d printed gears (Mechanical engineering question)

MakerWorld
1

I have 3d printed gears driving an RC vehicle. When the drive train is obstructed, the gears grind and wear down.

I could buy metal gears and modify my project to use them, or send my CAD files to a machine shop and have them produce a metal gear. But should I?

  1. Are the PC/GF etc filaments sufficiently tougher to alleviate this?

  2. If not, if I make one of the gears out of a more resistant filament, and the other from regular PLA, is the difference enough to keep the damage to a single gear? This would make repairs much easier.

  3. PS: Why isn’t there a category for mechanical engineering questions relating to 3d print? (Or why can’t I find it if there is).

edit: To provide information on why we want to continue to drive against an obstruction to motion, the vehicle is fully tracked and using twin motors. It is intended to power over obstacles. In this case we have sufficient motor torque to drive the track and continue to move, but the gears cannot deliver it.

2

Couldn’t you use a slip diff in the model?

3

I have had good experiences with gears that have a PETG gear and a (hard) TPU gear meshing together.

4

My mistake, you have a good idea but I should have mentioned the vehicle is fully tracked and twin motor, and therefore would not be wanting a differential. I’ve updated the post to indicate this.

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5

Thank you, I had not considered hard TPU gears. Do you mean hardness above 95A? I have seen 97A and 98A filaments easily available. They will certainly last longer against grinding. However, do you have any advice on how much power they can deliver? (I will print a TPU gear and test within week, as my print schedule allows it)

6

Conventional engineering wisdom would suggest Nylon is the best candidate for gears amongst the common FDM filament options. I’ve had good luck with it. Go for something without CF/GF, as those only serve to increase friction. You can also try decreasing the number of teeth so each is larger, but perhaps you’ve already optimized that variable.

7

UnfortunateIy I don’t have numbers for the power.
I used the PETG/TPU gear combination in order to to reduce the speed of A2212 1000KV brushless coptor motors für a tank like driven rc car (1 motor each side, 3s lipo). The car is pretty heavy, fast and unsprung. The teeth of pure PETG gears broke in no time, while the TPU-PETG combination didn’t fail up to now.

I used Extruder TPU D58 but I will test the Bambulab TPU for AMS soon. The TPU gears have been printed with 100% Infill.

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8

I’ve have done some research into nylon now. The main benefit is lower friction which means they run smoother and require less lubricant. Nylon’s resistance to damage is actually quite low and would be a downgrade in this case.

9

Thanks to everyone for help. I’ve traced down the problem to vibration in the motor mounts causing the parts to be mis-aligned. A CAD error on my part with the number and position of fasteners. Having now fixed the mount to retain the alignment of the gears, they mesh properly and no longer grind. Now when a track is obstructed, the power causes it to loosen against the track tensioner, and the track slips on the sprocket (“safely”) or just pops off, which is a quick repair.

I really do like the idea of TPU gears and I’m still waiting for print time to try them out.

For anyone who was wondering, the motors are brushed 895s geared down for torque.

edit Having fixed the grinding, I could I suppose now upgrade the gears to nylon, assuming I can find it in the right color or it is dyeable without the heat of the dyeing process damaging it.

10

There are companies that exist for no other purpose than to sell small gears and other related mechanical parts. Unless there’s something really wacky about your setup, you ought to be able to find some metal gears that’d do the trick. A google for “companies that sell small gears” will return a wealth of hits. :slight_smile:

No matter what you print the gears from, if you overload them they’re going to deform/wear/break. Happens with metal gears, too. Except metal gears will be significantly stronger than plastic gears of the same size.

It’s a better idea to limit current, though. Motor torque is proportional to current. If you stall a DC motor and don’t limit current, it can burn out the motor controller or motor windings or both.

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11

I haven’t done much testing on the long-term durability and wear of 3D printed gears but in my experience herringbone gears (aka double-helix) work the best for 3D printing since they allow for smooth power transmission without the axial load of helical gears. The other parameters you can modify to increase strength would be the thickness/height of the gear as well as increasing the gear module to add more “mass” to each tooth.

As far as print settings go I’d recommend using Arachne wall generator with a larger outer wall thickness such as 0.5-0.6mm. You can also add more outer walls and increase infill density for more strength but you might find the design works well with those settings and just 2x walls and 15% infill.