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Feb 18, 2020, 11:34 AM
Knuckle dragging pilot
Thread OP
Discussion

Motor Mounts - Strongest Material?


I'm relatively new to 3d printing and would appreciate your comments/guidance in regards to material selection.

I've been printing custom motor mounts for the Parkzone Strykers that our club is currently flying. We do full contact combat with them, so the planes and the motor mounts can be put through a lot of stress! So far I have used both PLA and PETG for the mounts, and broken all of them, lol.

I am now considering the following filaments: Polycarbonate, Nylon and ABS

We also run into quite a variance in temperature, varying from -15C all the way up to +30C. When the two PETG mounts broke on the weekend, temperature was about -5C

Your thoughts are greatly appreciated!
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Feb 18, 2020, 11:51 AM
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Lynxman's Avatar
Taulman 910 is extremely durable if you get it printing right. The main landing gear fork struts on my Macchi MC-205 are printed from that:
Piccole Ali / Hobbyking 75" Macchi C.205 Veltro maiden flight. (5 min 44 sec)
Feb 18, 2020, 12:18 PM
Knuckle dragging pilot
Thread OP
Thanks! Funny enough, that is one I was looking at, as it is available locally. Any recommendations on how to get it printing right?
Feb 19, 2020, 12:10 PM
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Lynxman's Avatar
Over 250C. You will need to test. If you get poor layer adhesion youneed to increase the temp even higher. It's also difficult to avoid warping during printing. I usually have to use a raft with 910 to keep warping manageable. A printer enclosure would help.
Feb 19, 2020, 01:01 PM
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rpstar's Avatar
Does Taulman 910 offgas things like Nylon does that require you to print in an enclosure and ventilate? A random google returned this "Taulman 910s MSDS sheet has "none" listed for fumes which I found awesome but slightly skeptical. "

I agree, I'm skeptical. What printer did you print the 910 on Lynxman and with what hot end?
Feb 19, 2020, 02:01 PM
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Lynxman's Avatar
Wanhao Duplicator i3 with Unicorn PTFE tube. I don't remember if it smells. I don't have any way to measure particle counts. I have only sprinted relatively small things. It's wraping hell to print big things from any nylons in my open printers.
Feb 19, 2020, 03:09 PM
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rpstar's Avatar
Quote:
Originally Posted by Lynxman
Wanhao Duplicator i3 with Unicorn PTFE tube. I don't remember if it smells. I don't have any way to measure particle counts. I have only sprinted relatively small things. It's wraping hell to print big things from any nylons in my open printers.
Ok cool. Yeah, not surprised it would probably need an enclosure anyways for temp reasons and if I did that I might as well just vent it outside. I saw a dude just use a cardboard box with a plastic sheet taped onto a cutout in the front. Could be made reasonably airtight and then just add a venting system to draw air out and outside. I liked it as it was cheap and easy to throw into the closet when not needed.
Feb 21, 2020, 05:23 AM
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Thoemse's Avatar
Nylon + Carbon, Greentec Pro Carbon, ABS, ASA.

Nylon + Carbon is a bitch to print but that stuff wont melt or break for sure. It is however expensive and not really needed ofr a motor mount.

Simple cheap ABS will do the trick really. If ABS melts your motor is dying from heat allready. I have used PETG for motor mounts with success allready but I wouldn'd do it anymore since its temp resistance is on the lower end for a motor mount.
Feb 21, 2020, 06:01 AM
Me and a guy with a mustache
babblefish's Avatar
Quote:
Originally Posted by Lynxman
Wanhao Duplicator i3 with Unicorn PTFE tube. I don't remember if it smells. I don't have any way to measure particle counts. I have only sprinted relatively small things. It's wraping hell to print big things from any nylons in my open printers.
Unless you're using an all metal hotend I hope you're not cranking the hotend temperature above 240C. A standard hotend where the PTFE tube extends all the way to the nozzle is not safe at temperatures of 245C and above. PTFE emits toxic and noxious fumes when overheated above around 250C. AT 235C it will start breaking down and will char within a few hours. Capricorn offers a version of PTFE tubing called "XS Premium" that they say can resist heat up to 360C. I don't know if that's true or not. I use their standard blue tube with an all metal hotend and have not had any problems other than self inflicted ones (not correctly tightening the nozzle against the heat break, or not cleaning the heat break and/or nozzle well enough).

With an all metal hotend the PTFE tube stops at the top of the heat break so there is no chance of it getting overheated. Just make sure you get a quality all metal hotend and assemble it correctly. Some of the cheaper versions leave the internal bore of the heat break a little rough or may have burrs due to the machining process. Or the mating surface of the heat break on the nozzle side is not perfectly flat causing filament ozing and leaking resulting in a clog. This can lead to snagging of the filament and eventual clogging and/or under extrusion issues.

Interesting reading: https://3dinsider.com/all-metal-hot-end/
Feb 21, 2020, 09:44 AM
Registered User
If you have broken the motor mount printed with PLA and PETG the problem is the design not the material. Can you share some pictures of that motor mount?
Feb 21, 2020, 09:54 AM
Knuckle dragging pilot
Thread OP
This is my current design, but previous versions that broke were very similar to this.

In both cases the mount broke above the two horizontal screw locations and partially along the back support. I think what may be stressing the mount is when there is contact, the prop is damaged and becomes unbalanced. Its not always apparent right away that the prop has been damaged until we throttle back up and can hear that it is.

Thanks
Feb 21, 2020, 10:48 AM
Registered User
Lynxman's Avatar
Quote:
Originally Posted by babblefish
Unless you're using an all metal hotend I hope you're not cranking the hotend temperature above 240C. A standard hotend where the PTFE tube extends all the way to the nozzle is not safe at temperatures of 245C and above. PTFE emits toxic and noxious fumes when overheated above around 250C. AT 235C it will start breaking down and will char within a few hours. Capricorn offers a version of PTFE tubing called "XS Premium" that they say can resist heat up to 360C. I don't know if that's true or not. I use their standard blue tube with an all metal hotend and have not had any problems other than self inflicted ones (not correctly tightening the nozzle against the heat break, or not cleaning the heat break and/or nozzle well enough).

With an all metal hotend the PTFE tube stops at the top of the heat break so there is no chance of it getting overheated. Just make sure you get a quality all metal hotend and assemble it correctly. Some of the cheaper versions leave the internal bore of the heat break a little rough or may have burrs due to the machining process. Or the mating surface of the heat break on the nozzle side is not perfectly flat causing filament ozing and leaking resulting in a clog. This can lead to snagging of the filament and eventual clogging and/or under extrusion issues.

Interesting reading: https://3dinsider.com/all-metal-hot-end/
I meant capricorn when I said unicorn. Don't exaggerate.
Feb 22, 2020, 06:20 AM
Registered User
I see. The problem is that you have a concentration of stress in only four holes ( the ones closer to the reinforcement) The other 4 are not really working. I recommend you to put more holes closer to the reinforcement. Also reduce the thickness of the upper part.! One part is very stiff and the other very weak
Feb 25, 2020, 05:41 AM
Registered User
I have a couple of suggestions. Try using a "tough" PLA. I have had great success with eSUN PLA Plus, available quickly from Amazon at a good price and in many colors. It's easy to print and likes higher printing temperatures. It's stronger than ordinary PLA and much less brittle. I use it for all my 3d printed RC planes.

Try adding an additional web to your mount design and/or increase the part thickness slightly, especially if the mounts are breaking in ordinary use. rather than during a mid-air collision.

But what I would strongly suggest is having a bolt-in mount design which is easy to change. Just print some spare parts and consider the mounts as a replaceable component.

Breaking the mount in a mid-air isn't really such a bad thing, especially if you don't damage the foam where the mount attaches. If you can quickly install a spare mount, bolt on the motor, and get going again, a broken motor mount might be much better than an indestructible mount which tears off the back half of your airplane when you have a mid air.
Feb 25, 2020, 07:56 AM
Knuckle dragging pilot
Thread OP
Funny enough, that was my thought as well, in regards to the two piece construction (see the attached photo). As you said, this would allow for a quick change over should it break after a mid air. And it would be easy enough to print multiple copies of the upper portion and have them ready to install.

I will also look into the tough PLA as I am planning to place an order on Amazon for an enclosure for my printer. Did a test print using ABS last night, but my basement is too cool to allow a slow hardening of the ABS and I got some cracks and warping.


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