DIY Electric Longboard: Part 2


Thanks for reading my blog, if you haven't read Part 1 already you can find it here...

Now that I have the motor I thought I'd move on to fabricating the motor mount and attempt to attach the sprocket to the wheel.

This is the electric motor, it's actually normally used for 1/10th R/C cars or medium sized aeroplanes. It has a low KV rating though (580kv) which means it produces quite a lot of torque, which is what I need when the board has to pull my fat arse along the road!
I got an Overlander Tornado Thumper, brushless outrunner. Outrunners work the best for this type of job.

Some stats for the motor:


When I bought the sprocket to put on to the motor I got one with a 6mm bore because that was the shaft size of the motor, which is probably the smallest you'd dare go for powering a longboard with a whole person's weight on it, any smaller and you might run in to stripping problems. Although when it arrived, I did have to drill and tap a 4mm hole in it's collar in order to insert a grub screw to connect it tightly to the motor shaft. I also needed to file down the shaft of the motor to have a flat spot for the grub screw to bed down on to.


Once I'd done that I moved on to the main sprocket. I decided I only wanted three bolts connecting the sprocket to my wheel, this way it will look better and there'll be less chance of it being offset and there being wobble.
I started by offering it up to the wheel, lining it up and measuring out where three holes would go for the bolts, each 120 degrees apart. The bolts are size M4 @ 80mm long, but that's way overkill, I'll be cutting them down to size. As you can see in the photos, I countersunk the holes because I want it to be flat and flush, I don't like protruding bolt heads. You may see bolt heads in some photos but they're just test bolts.


Once that was done I moved on to the motor mount. For this - for testing - I'm using a 50mm strip of carbon fibre-look ABS plastic @ 5mm thick. I do have some 4mm carbon fibre sheet that I'll use for the final mount, but for testing I'm using this cheap ABS.
I worked out where I wanted the motor to sit, how far from the sprocket etc. and how close to the deck from the underneath, taking lots of measurements as I went.
Bear in mind that when you lean on a board the truck twists slightly and the board gets closer to the ground and the truck the more you lean, so I had to take clearance in to consideration with motor position.
Once I was happy I drilled the holes for the bolts for the motor using it's handy aluminium mounting bracket it came with, for installing it into a plane as a template.

In the last photo above, you can see that the wires for the motor are up against the under-try where all the electrics will be. The next job was to drill a hole (not too big) in that tray in order to feed the wires through which will eventually be connected to the speed controller (ESC).

That looks OK to me, neat and tidy...

Next I wanted to offer up the sprocket in order to align the sprocket and pinion, and also to try the chain for fit after I'd split it and reduced it's size dramatically!

After offering it up etc. I decided that having the collar on the side of the shaft closest to the wheel wasn't the best way, so I flipped it over, putting it on the inside of the truck with the motor mount closest to the wheel instead.
This worked much better and was a much more straight fit between pinion and sprocket.

Next up I needed to make a spacer to fit inside the the inside edge of the wheel where the sprocket was as the chain needed 5-10mm clearance from the wheel to not rub.
I'd seen some videos on YouTube about melting plastic down to create blanks to work with, perhaps on a lathe so I decided to look for any suitable plastic in the house and do just that.
The most suitable thing I found was an empty milk bottle/carton, which was obviously plastic. I cut it up and placed it in the oven at 200 degrees for about 45 minutes. I used a recently used can of pop to cook/melt it in, just had to cut the top of with a sharp blade.
Once that was melted I put in the freezer to cool and harden. It came out round which was a good start, I cut it down to size with my band saw and then used a drill holder (my Dad's) on it's side as a make-shift lathe and began turning...
This came out really well and served great as my spacer!


Next up was to get the sprocket fixed to the wheel. For this I'd already pre-drilled the holes in the sprocket and the wheel, it was just a case of using my new spacer and new 70mm long M4 countersunk bolts. There was a little jiggery pokery needed to get the sprocket dead centre of the wheel, and then rid it of any side to side wobble, but I eventually got there in the end after lots of spinning and small tightening adjustments. I was pleased with the outcome, It span quite true indeed.


I bought two 5000mah 11.1v R/C batteries from HobyKing through Amazon, when they arrived one was completely dead, the other was fine so I'll be sending the dead one back. However, I could still use the board with one battery, just not for as long...
I made up a serial battery connector, to use two batteries in serial to give me twice the MAH, twice the voltage but with the same current as not to blow the motor or electrics and to enable this thing to go for a lot farther distance. However, for testing, and until I get a replacement battery I'm just going to be using one battery, without the serial connector cable.
In the photos below you can see the wire-up is very simple, just your typical R/C car set-up minus the steering servo.
I got a really cool Angel Eye on/off switch from ebay which you can see in the photos, it was a bit tricky to get the wiring right in my head, but I manged to sort it out with the help of Google as it didn't come with ANY instructions. Now it sits between the power source and the ESC and when it's switched on it has a cool lit-up glowing circle of red around the button itself so you can tell if it's on or not at a glance.
I changed all the connectors over to new XT60 connectors that I'd acquired - very cheaply - from ebay (The batteries came with Deans connectors), and now everything looks great!
The ESC I originally bought, a 45A cheapy from Banggood turned out to be wrong on two levels, (That's what you get for being out of the R/C world for so long!). Turns out the one I got doesn't have BEC, so it doesn't power the receiver as well, and also 45A with my weight is far too low, I needed at least an 80A which is what I got as a replacement, again a very cheap once, so it still might be an issue but at least I wont' have spent too much on it.
The reason the ESC was a problem is that after a short stint on the board it would overheat and cut out, only coming back to life once I'd cut the power and it'd cooled down enough.


Oh! And I fixed my issue I had with the size of the holes in the brackets to hold the under-tray on vs the size of the knurled thumb screw bolt I bought to use with them. I ended up getting one of the kids' dried up fat felt tip pens, cutting it in to small 15mm long tubes and then heating them up to make them pliable, then stretched them over the brackets that are screwed to the underside of the board. This basically cooled down hard again but wrapped around the metal. This enabled me to re-drill smaller holes in the plastic to enable the thumb screws to have something to bite in to. Problem solved! You can see what they looked like in the photo's below.


Finally I got to a point where everything was ready for testing. Took it to the park and had a short go until the power cut due to the ESC. However, IT WORKED! It was great and bloody fast! I think maybe too fast for me! lol.

I'll put up a list of all the components and parts I used, along with a video and total build cost soon. However, if you'd like your own powered board I'd be happy to build one for you for a cost. Send me a message through my contact form to discuss further.

Here's the build video:

Parts List:
Here's part 3 of this blog!

Author: Kevin Dark - 10/10/2016 11:16:43 PM