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REMB - Razor Electric Mountain Board

An electric mountain board, built from Razor scooter parts.

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I had accumulated enough 18650's Li-Ion cells to build something cool with them.
A mountain board popped up on Craigslist for dirt cheap, and so this project was born.

Pricing out a dual BLDC motor drivetrain to go with my $30 board put me quite a bit north of $400, from China. Well, that's not going to work. Back to the drawing board.

Razor scooters in the 100-150W range seem to be prone to eating the batteries or blowing out the control electronics regularly. This means you can get a motor, chain, two sprockets, bearings, hub, wheels, wire, etc... for cheap. I picked up two of these on Craigslist for $24 total.

Here we go.

This is coming together.  Time to start documenting it.

First, I needed a cell discharger to test the capacity of my scavenged cells.

Then, I needed a way to weld them together to build the pack.

After charging all the cells in my BMS initially, I realized I would need to do so a second time to get good capacity numbers.  That prompted building a 10 cell charger.

I've already worked out the drivetrain by cannibalizing two Razor scooters I got off Craigslist for $24.  The scooter rear wheels were 'turned' to free the sprocket mounting hub from the wheel, a groove cut in my mountain board wheels, and the two were joined x2.  The entire process was captured on video, but needs a lot of editing..

Instead of hanging the pack below or mounting it on top of the existing board, I want to inlay the 10s5p battery pack.  I would like the cells to live within the thickness of the board more/less, but 50 cells requires a good deal of the board to be removed to do so.  So far I'm leaning towards routing out linear channels the diameter of the cells from end to end.  I would need to make the board about 4mm thicker to accommodate the cells, which I plan to do via gluing on two strips of luan plywood.  The board is curved though, in two directions, and both ends kick up at a 20 degree angle so all of this is going to be a little complicated.

For the hand control I've decided to adapt an aftermarket Wii Nunchuck.  They have an I2C interface, which I already have talking to a 3.3v Arduino Pro Mini.  Using the 3.3v version allows me to directly power the NRF24L01 module I intend to use to talk to the board.  The plan for the control protocol is to just send everything the Wii Nunchuck produces, with a prefix (to key the board to the controller).  I may scale down the accelerometer data if it proves to be too much.  There was originally going to be a small OLED display in the remote (it is clear/blue), but I think I destroyed it trying to desolder the pin headers it came with.  Two of the traces lifted and I haven't gotten it working again yet.

The board electronics also have a couple pending points of contention.  I have 6 appropriately rated logic level power mosfets slated for this project, but I had another thought.  The BMS I purchased for the battery pack I'm building has 5 hefty power mosfets onboard for over-current/under voltage cutout.  They are not logic level, but do have two 'competing' onboard BJT transistors driving them.  As in... the outputs are tied together... directly to the gates.  I don't get that bit, but I do have two good spots now to inject some signals and see what happens.  I would ultimately lose the ability to independently control the drive motors if I did this (power steering of sorts), and I would still need to implement braking mosfets outside this package.  Since I do have the spare mosfets to do everything externally anyway, without messing with the BMS, I'm torn right now.

That is about it.  Lots of video, waiting to be processed...  Stay tuned.

  • Motor happy accident.

    Daren Schwenke02/10/2019 at 08:45 0 comments

    I theorized that the brushed DC motors from the scooters might be biased to run better in a particular direction.  This appears to be true.

    I hooked them both up to a supply and compared the audible tone they produced in both directions.  They both ran a little faster in the forward direction.

    Craigslist had provided me with one E150, and one E100 scooter.  They look identical in size/shape/specifications, but the E150 motor does run a bit faster in the forward direction.

    However, I discovered that both motors run at the same speed when I run the E150 in reverse, and the E100 forward.

    Given I will need to mount one of them running backwards, that is a happy accident I can live with.

    Now I don't need to go messing with taking them apart to tweak the brush advance.

  • Production value...

    Daren Schwenke02/01/2019 at 03:13 0 comments

    I have now accumulated about 10 gigabytes of media on this, and have gone much further in the project.

    The board was broken down, drive system figured out, parts made... etc.

    However.. I'm trying to bring the production value of my videos beyond the one shot, one take, straight to Youtube pattern of the past.  That is going to take some time, and some help, and we don't have it streamlined yet.  

    We are working on it.  :)

    Stay tuned.

  • Revised expectations and/or progressive enhancement

    Daren Schwenke01/17/2019 at 05:27 0 comments

    Pricing all the parts for 2 bldc motors, two vesc controllers, charger, etc for what I wanted to build here put me at about $400.  That was a bit high...

    I have revised the plan.  Do what I can using what I got on hand, and spend less than $100 total for the missing stuff.

    I grabbed two dead razor scooters off craigslist for a total of $24, and bought a bms board, charger, and nickel strips off Amazon fo another $32.

    Parts arrived today.  

    I have settled on a 10 cell li-ion setup.  That gives me 42-36v for my motors.  I am trying to work 5 cells in parallel into the thickness of the board, mostly.  I plan on building up the sides and carving out the middle.  That capacity will allow me to move to bldc later.

    The motors from the scooters are rated 100w@24v, but tolerated 36v just fine.  I will need to watch the temperature of them and I could always just limit my PWM to 75% anyway.

     Time to make some final design decisions and get to work.

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