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I’m designing functional parts for competitieve RC Cars, like custom gearboxes and stuff like that. I know a guy that makes awesome parts and upgrades for cars, all his parts are printed by Shapeways in Nylon. Shapeways uses SLS as printing method. This method is expsensive and time consuming because you always have to order it from Shapeways. His parts seem functional and are used by pro drivers, so I asume they are strong enough. I have 2 FDM printers at home. I have recently also bought Carbon Fiber filament, I was wondering if it would be possible to print funtional parts with this filament for use in RC cars. It should withstand certain forces. But I don’t know how FDM Carbon fiber compares to SLS Nylon printed parts. Any help?

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Hi Andreas,

I would highly avoid the usage of Carbon Fibre filament for gearboxes !!

First of all let’s start by comparing the two printing methods and then go on to comparing possible materials:

SLS is much more precise, the surface of prints is generally speaking smoother and you can expect better tolerances and overall precision. However all that has it’s price so you should consider SLS for prints that need to be close to perfect.

FFF or FDM has some downsides with printing certain geometries (overhangs, bridges). The prints aren’t of such good quality, but due to the material variety you could find the perfect material for the job and since the filament is relatively cheap it would be possible to print multiple versions of one part and adjust the settings with each attempt (cooling, speed, scaling, …).

The material variety also allows you to find some exotic materials, that would allow post processing (drilling, sanding, …) while most industrial printers are limited to one or a few materials.

Now regarding your RC car:

As you said you design and print gearboxes. Gearboxes (talking about gears only) need to withstand a lot of friction when they are converting torque at really high rpm. The printing material’s main feature should therefore be a smooth, nearly slippery surface you should stay away from anything with fibres (<= very big hint!!).

Nylon has one of the best surface properties for this application, however Nylon is slightly flexible so you should adjust the settings accoringly: a thicker outer shell and higher infill percentage might be necessary, in the worst case yoü’d even have to adjust the gears geometry (making it taller).

There are a hand full of Nylons and Nylon-based alloys available at this point in time. I would definitely go with Taulman3d Nylons as i had the best experience with those, the so called “Nylon Bridge” or one of the earlier 618 and 645 Nylons will be appropriate.

When it comes to other parts of the car (which are not moving) you should look towards light weight and high stiffness.

As those parts aren’t moving or sliding on each other there’s no requirement for low friction surface or such. The priority are stiffness, strength, light weight and maybe machinability (possible to cut and drill the material).

PLA is known for it’s relatively high stiffness, compared to ABS and such, however PLA is brittle and will break under load easily. Carbon Fibres are also very stiff, additionally light weight and when they are blended with the right Polymer the composite filament won’t be brittle. There’s a material called XT CF-20 by Colorfabb, this material is based on Colorfabb’s Co-Polyester and includes 20% carbon fibres. The Colorfabb Co-Polyester (named “XT”) is similar to PET in it’s material properties, therefore you can expect it to not be brittle.

I’ve printed with XT CF-20 already and it’s amazingly easy to print and the material properties are overwhelming. As long as your printer can reach ~250C you are ready to go, however wear resistant nozzles are a must-have if you’re going to print more then just a test spool of 50g.

XT’s glass transition temperature is at around 70-80C. When the material reaches this point it will be permanently deformable (not good!). Stuff like PLA has a Tg of 50-60C so it will get soft a lot faster. To know this is important to estimate if the plastic can be drilled or machined with any other tool that might cause the print to heat up. XT’s Tg is high enough to drill the material as long as you don’t go too crazy with drill rpm and feedrate. Just drill carefully and you’ll be good to go!

So that’s my conclusion:

Gears and any other moving parts: Nylon* (by Taulman)

Frame and non moving parts: XT CF-20

*there are other low friction materials out there, ie Tribo from IGUS. IGUS produces bushings and gliding elements, their filament is the same material as what they use for the bushings, so it’s definitely worth a try for gears. However I’ve yet to hear a review about this material and I never tested it myself so I can’t tell if that material would work.

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Hi, thanks for your awesome comment! It’s allot clearer now!

About the gearbox, I will not be printing the gears, just the gearbox itself. I will be using the standard gears from the car, but I just want to change some things at how they are located and such. I added a picture of that. Could that be done with XT-CF20? Or also better nylon?

I like to avoid nylon because it’s time consuming, no? You have to bake it before you print with it…

About SLS vs FDM, would it be possible then, to print strong enough parts with and FDM printer. The guy I mentioned, that lets print everything from shapeways, says that FDM printing is a shitty method for RC parts, but I wan’t to actually know if it is, with all the materials there are on the market these days…

Thanks

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I use a lot of Taulman 910 nylon, with fantastic results. I use Simplify3D for slicing/printing and with some tweaking, I’ve gotten it to print very reliably with supports that work great and are still easy to remove. The parts aren’t as strong as injection molded parts, especially stuff that is glass filled (like a lot of RC parts are), but it works very well either way. The slight bit of flex actually helps the parts survive crashes that would otherwise crack or shatter parts that are printed in very rigid materials. For parts that you don’t expect any flex, I would print in the XT-CF20 or similar. For everything else, I would use nylon. Here’s a few helpful hints I’ve found with printing nylon

*If you are going to print with nylon, keep it in a sealed container with a cheap dehumidifier and you won’t need to bake the stuff before printing. My machine is warm inside because it’s enclosed, so I just keep the door closed with the material loaded inside. Works fine.

*Use a larger nozzle for MUCH stronger parts. I had the strongest parts when printing with a 0.8mm nozzle, but we sacrificed a small amount of fine detail. I would suggest nothing smaller than 0.6mm for better strength. I print with 0.35mm nozzle when doing very small parts that don’t need a ton of strength.

*My machine is pretty fast, around 250mm/sec for ABS and it CAN print nylon around 150mm/sec but the filament is slippery and the extruder will slip and the material will tend to extrude inconsistently and the parts will be weak. I slowed it down to around 80mm/sec and I got good results there. You’ll need to do some test part to find out what works for you.

*Nylon likes to warp as it cools. I would add some kind of enclosure to your machine if it doesn’t have one. I keep my bed around 80°C when printing and I use kapton tape with Elmer’s Glue sticks applied. I also found that adding a raft helps keep larger, thicker parts from warping as badly.

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Thanks allot for your comment.

I already ordered a spool of XT-CF20. I understand that parts that get big forces should have a little flex.

I think for the gearbox enclosure ands stuff like that, the CF20 filament is great. But I think I will buy Nylon too.

About printing with a bigger nozzle, I understand that bigger parts are stronger. But these RC parts are small and still also require some type of detail, so atm I’m printing with a 0.4 nozzle, 0.2 layerheight, wich seems a nice balance between quality and strength.

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I print RC parts almost exclusively…everything from small servo horns up to a full chassis…and the larger nozzles work best for strength. Unless your doing parts that have VERY fine details, like walls or features under 1mm thick, the larger nozzles will work fine. I honestly haven’t found a benefit of printing with the small nozzles (0.25-0.35mm) for anything RC since the detail increase isn’t worth the loss of strength. I think your 0.4mm nozzle will still produce strong parts though. If you ever find a problem with certain parts always breaking, it’s a cheap alternative to try printing with a larger nozzle rather than dealing with a re-design.

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Thanks! I will keep that in mind :wink: Do you have pictures from things you printed?

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I wish I could but work probably wouldn’t be really happy about that. Not sure if I’m giving too much away with that. :slight_smile:

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No problem mate :slight_smile: