This is part of my project of making a 3D printed 1/10 scale 4WD. This is more of a prototype of a 4 speed transmission I have made for it. I would highly recommend checking out Indeterminate Design on Youtube (e.g. https://www.youtube.com/watch?v=Gfx-vCVJx7Y) as most of the inspiration for this design came from his work as well. I also have not tested this with a high speed or load so know if it would hold up well.

Supplies

Filament and access to a 3d printer

I have used PLA+ to print all the parts so far and have had no issues. However, I have not tested it on a full model with much more weight. Nylon is a common alternative for the gears, but I think PLA would still be suitable for the casing. Keep in mind that to print nylon a printer with an enclosure is highly recommended.

3mm Rod

2xM3 nuts

2xM3*20 screws

6x 3x8x4 bearings

Step 1: The Design Proces

When I first started thinking about my design, I went through many different layouts. A significant challenge I faced was making it as small as possible, while also maintaining a large range of gear ratios. The design also was limited by the smallest gear I could make which can fit on the axle and have the indents to be able to be selected by the selector. Hence, another aim of the design was to allow as small a gear as possible.

I was originally inspired by the Lego technic selectors, and this is where my first design (in the images above) came from. However, despite spending a significant amount of time designing this form of the transmission, after printing it, I realised that this design wouldn't work. Firstly, it was too big, and the bulky selector meant that the smallest gear was not very small, so to achieve the desired ratios, other massive gears would be required. My original plan was to have a servo in the middle which would move the selector back and forth. However, after making a mockup with an SG90 servo, I realised that it would be quite difficult to have the servo reliably move the selector. Hence I tried to avoid the sunk cost fallacy and binned this idea.

However, the process of designing and getting rid of this design was quite educative, as it reinstated the importance of testing more often, basing the design on non-negotiable requirements (e.g. size), and making hand written drawings more accurate with measurements.

Random Transmission Drawings.pdf
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Step 2: Searching the Internet for Inspiration

After the failure of the first design, I jumped on the internet to find some inspiration. This is where I find Indeterminate Design and his absolutely amazing work desiging 3D printed transmissions. I am honestly in awe of what he has designed.

I gained a few pieces of key information which inspired the current design.

Firstly was the "dogs" on the gears. This is a rather simple, but it allows for a much more compact design.

The trouble I had in the initial design was getting linear motion to move the selectors. Indeterminate Design used a pin which is moved by a rotating piece (this is shown in the image above). A benefit of this solution was that the whole transmission can function on only one stepper motor. Each the pins and mover component aligned are designed so that there is a gear every 90 degrees.

Hence, I ended up with my current design which is shown above.

Step 3: Conclusion

So currently, the transmission does not actually work properly. There are some issues with the shifting mechanism which isn't very smooth and reliable. Also, I feel that I can make it a lot more compact. Hence, I honestly would not recommend that you actually create this project. Instead, I have posted this primarily for inspiration.

I am still working on this project, so if you would like to make a transmission for your own project, hopefully in the next few months I will update this Instructable with a perfectly functional version. When I update the Instructable, I will also add steps to help anyone make the transmission themselves. I have left the Fusion360 file below, but it also has a few weird things going on.