25mm 4108 Motor Mounts and Optical Flow Sensor Mount

Hello again,

Presenting the 25mm tube motor mounts for the MH-01XL hexacopter.


Figure 1 - Render of motor mount design

This design is custom made for the RCTimer 4108 480kv motors, with cooling vents for maximum airflow through the motor itself. At the moment the main board is simply CNC routed out of a large PCB sheet, which worked out quite well and did lead me to the question of "would the large double sided copper surface of PCB perform any noise suppression generated by the motor or ESC's?"

Something I will endeavour to investigate in the coming weeks.

The intention is to mount the ESC's on the bottom plate of the motor mount to keep all the noisy RF generating AC signals as far away from the APM as possible. This would also allow for optimal cooling/air flow to keep the smoke in.

3689553161?profile=originalFigure 2 - Initial prototype/first cut

The PCB is fitted with CM03 Cinestar pressnuts, with the complete unit assembled with stainless steel 35mm hex head bolts for a compression fit. The images below only show the single sided version of the mount, (ran out of sharp tooling for the CNC after the last run) The rendered image shows both variants.


Figure 3 - Assembly of single sided variant

3689553176?profile=originalFigure 4 - Just a few extras - JIC

3689553273?profile=originalFigure 5 - Motor Fitted (just cleared the CF tube, might make some low profile bolts)


Figure 6 - Optic Flow sensor mount

3689553307?profile=originalFigure 7 - OF Sensor axial view

Thanks for reading my little blog, all comments welcome :)

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  • I need some for my Y6 tricopter.
  • Hi Luke,1

    1. As to 3D printing, it is based on my experience using a SteadiDrones Octo kit, fully paid for.

        All of the original motor mounts broke off way too quick, and eventually all the internal boom

        connectors broke and split, and I decided to machine my own replacements.

    2.  ~15k would put you close to the next class up as they are defined here in Israel, but it sounds like

        you are putting together a serious bird. I personally would go for an Octo, given the mad

         price of FLIR solutions.

    3.  Having a pre-planned break point is a great idea, provided you have ample and cheap replacements!

         I for one found I favor the small plastic 3mm screws - they are always the first to go and stocking

         up on them is dirt cheap.



  • @Euan

    Thanks for the compliments, however unfortunately the blue mounts are actually just a rendered image from the CAD model, yes they are 35mm s/steel bolts and the hole spacing is 30mm.


    Thanks for the feedback, it's good to hear some comments from experienced fabricators. =)

    I'm all too aware (from experience) that you should never trust 3D printed parts, delamination is a constant worry, however the parts in the photo are just for proof of concept and some initial test flights (as you mentioned, eventually I will use the CNC at work to mill out a set from 6061 or 7xxx series aluminium).

    The reason for the 25mm booms is that the hex will be used as a heavy lifter (approx. ~15kg payload) mostly for FLiR and complex sensor payloads etc... I'm not worried about the motor mounts shearing off as this design is to be tied in with the QuickFit centre mount from my previous blog to allow for easy replacement of the arms when it does fall out of the sky, the design is easily modified to remove the cooling feature of the motor mounting plate.

    A thought on the mechanical properties of using the printed braces is that, as you mentioned, they will break before the CF booms will, hopefully making this a 'feature' which makes the damaged parts cheaper to replace as they will break before the booms will... at least until the 7xxxAl ones are implemented =)

  • Hi Luke,Here are my 2c from experience, would save you some $$$ down the line:

    1. 25mm booms are used on Cinestar Grade craft = Big & Heavy ( & Pro Level )

    2. 3D Printed mounting braces WILL shear on impact, use Aircraft Grade aluminum or the standard issue types

    3. Whatever those big holes are for, the mounting plate is in danger of ripping up along

        the weakest path of resistance - leaving the motor hanging on 2 screws, if any, upon impact.

    4. Your UAV WILL fall out of the sky, one day, for whatever reason. Keep it as sturdy and fail-safe as you can,

        that is why the AeroSpace industry employs many engineers.

    That said, it is always fun to make stuff that works, at least between crashes :-)


  • What is the distance between the bolt holes, and I'm assuming these are M3 x 35mm bolts?

    I'd be interested in some of these (assuming the mount hole spacing is 30mm), particularly because you've got the blue colour I want :-)

  • I would love to see your wiring for the optical flow, I have been trying to get my optical flow working for a very long time and I have studied the documentation and forums for hours. Maybe your doing just something different that I am not spotting in the docs.

  • Thanks Gary,

    The large holes line up with the cooling vents in the RCTimer 4108 480kv motors, they allow greater airflow through the motor body to increase the cooling efficiency.

    The motor mount holes are also measured from the same motors.

    Not yet as I am reluctant to sell prototype designs before thorough testing, but I'm sure people could twist my arm ;)

  • Very nice looking mounts,

    What is the function of the large hole at either end of the PCB immediately adjacent to the motor mounting hole?

    What is the spacing on the motor mount holes?

    Are you thinking of selling these?

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