How I built the electric longboard

 

Since I made the board as a prototype for my Bachelor's thesis I didn't fully document the actual board construction. 

 

I wanted to compensate for the large wheel diameter so I decided to build a dropdown deck. I started by designing a form which I could then build the board on. The board is made out of carbon fiber which allows complex surfaces and skips the need for a two-part press. 

The CAD model should be shown below, you should also be able to see the toolpath for the CNC by selecting CAM.

Here is a photo of the form on the CNC. Since the CNC isn't big enough to fit the whole thing I machined one half at a time. In the photo, the left side is only cut with the rough pass while the right side has been finished. I used a carbide 8mm ballnose endmill for the whole form. I used good MDF so the material had similar density the whole way through. If you use bad quality MDF the different density can lead to rough surfaces.

After machining I sanded the surface flat. The photo underneath shows the surface finish.

 

Before starting the composite layup the form was covered in epoxy and then sanded up 1200p. 

The board has a big cutout through the center of the deck which puts high requirements on the materials used. Since most of the strength is needed only in one dimension, the main component was unidirectional carbon fiber (UD CF). I used 200g/m² UD CF.

I cut out a square for the RGB matrix in the carbon fiber layers. I was scared of messing up the fabric so I tried to wet the whole layup at once. In hindsight I should have done it layer by layer since it was hard getting the epoxy through all the layers.

I made a graphic showing the composite layup. On the top is the outside of the board. This is mirrored on the other side of the 3D printed and foam core.

Here's a photo of the when the top layup was done. 

To make it easier to remove excess epoxy I used a thing called "peel ply". It is a type of fabric that the epoxy dosen't adhere to, so when the epoxy has hardened you can rip it off. 

I had to mill the foamcore. Once again I had to do two passes since the whole core wouldn't fit in the machine. I started with the concave side and then put it back on the form to machine the convex side.

The 3D printed parts and the foam core fit together with simple dovetails.

Since the 3D printed parts only need full strength around the truck I tried using Slic3r PEs modifier options to get a higher percentage infill.

To adhere the core to the bottom of layup I used some epoxy filled with glass micro balloons.

After laying up the last layer of carbon fiber I cut off the excess and lacquered the board in a layer of epoxy.

Lastly I sanded the epoxy down to 600p and covered it with some matt spraycan varnish. 

For the boards wiring I started by constructing the power distribution board. You can see a schematic underneath.

The circuit board was milled on a two sided copper CFR4 board. For the highest current traces I added extra copper by just soldering it on top.

I was really low on time when I did the wiring so I don't have any photos. I do however have a schematic on how everything is connected. Orange is data and low current connections, black is for power connections.

 

How I made the controller

The controller is made using a Maytech MTSKR1712 remote. Since the board needs a horn I thought it was best to put it in the controller. The existing controller housing was however too small to fit the horn I was going to use. The photo underneath is the PCB from the Maytech remote.

The new shell for the controller was 3D printed in 0.1mm layers.

After some wet sanding the shell looks like this:

I covered the shells in spray body filler.

I sanded the shells to 600p.

Lastly I coated the shells with the only spray paint I had around

The paint sticks really well. Even after it accidentally flew some meters over asphalt, the paint never flaked.

Design © Leo Södergren 2020

LeoaSodergren@gmail.com

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