Hi,
This is my first post in this forum and i hope I’m posting this in the correct way.
I built a one-wheel maybe a year back and thought that the build might be interesting and helpful for anyone doing the same.
Like many others (i imagine) i thought the price for a new onewheel was too damn high, and since I like to build stuff i set out to make my own.
I should add that i have a pretty well equipped workshop in my basement which made things easier.
Like all “build from scratch” projects, one of the hardest things i think, is to know where to start and to get the general dimensions right. So hopefully this post can be of help to someone building their own balancing board.
The rails i made from some U-profile aluminum 40x15x3mm. I milled down the sides to 40x10mm.
![IMG-20211208-WA0007|281x500, 75%] (upload://uKsW75X3cxnMFYfEPWYRiTgMooY.jpeg)
The shaft mounting block i milled from some 6063 aluminium square stock and soldered with low temp aluminum rods. The result was not visually pleasing… but it stuck on there. That “low temp” rods are not as low temp as you might hope. The melting temperature is dangerously close to the melting point of aluminium. It is also insanely hard to heat up the complete part to the right temperature, since you are basically heating up a heatsink-shaped part.
My solution (with only a propane torch in my toolbox) was to insulate the whole thing in fiberglass insulation and putting an extra propane kitchen stove under it. The old saying “it’s not stupid if it works” comes to mind.
The electronics box and the battery box i milled out from some teflon plastic i had laying around. I use the TE HDSC series connectors for foot pad sensor and motor power/signals.
I made the foot-pads from a bamboo cutting board i bought at IKEA. (Cutting boards are a great and kind off cheap way of getting plastic and wood material i convenient sizes I’ve come to learn).
The actual sensor i made from a sheet of velostat and some (double side conductive) copper tape. The first foot-pad i made was from wood and for that i 3d-printed a base to hold the tape and velostat and glued the whole thing to the board. I don’t have any pictures of this i tho, i think. I later made new foot-pads from some plastic (yup, another cutting board).
The battery was spot welded to a 14s2p configuration pack of INR18650-25R. The picture show the second battery pack i built, quite recently. The first one i made was 12S from some really crappy old cells i had laying around.
Current is limited via the motor controller so i don’t have any additional BMS. Motor controller is a VESC copy, 75100. I did also place an NTC resistor to have some idea of battery temp.
So, the motor was a bit tricky… The motor in the pictures was actually like revision 4 of the motor. Actually more like 4 different projects in them selves.
I first tried making a belt driven one-wheel, this turned out to be not so good due to the very large gear ratio required.
Second one i tried building from a ebike front hub motor with a planet gear system. This one was alright i guess and had some torque but lacked speed due to high gear ratio. The main reason why i abandoned this design was that there will always be some backlash in a gearbox. This is not very desirable in a balancing motor who’s sole purpose is to compensate my movement by very rapidly moving back and forth. So i abandoned this idea.
The third and forth motor design was made with stators from those self balancing “hoverboards” that was all the rage a few years back. These motors are extraordinary. They offer very high torque and can be acquired for next to nothing from the over saturated second hand hoverboard market.
The final motor is three of these bad boys paralleled and locked together on a shaft in perfect harmony.
I started with turning a aluminum shaft from 7075 T6 aluminium. I then press-fitted the stators on this, not bothering with alignment at this time.
I casted some scrap aluminium for the outer motor casing and turned this in to dimension.
The best thing about these motors is that the outer diameter perfectly fits a 5" go kart tire. It just slips on. With some force.
Picture of the rotor rings with magnets.
The three parts of the rotor can be rotated freely from each other. This way i could align them to where i had the least resistance rotating the motor by hand, - that way they aligned very good with the windings. It is importent to get them all very well aligned with their coresponding magnets to minimize power losses in the motor.
I then locked them together with some M5 cap screws and thread locking.
The finished product.
I weigh around 90kg and this thing manages to drive me up steep hills and carry me off-road. The top speed (loaded) is about 35km/h, I’ve managed to push it a bit above this but here it start to get real scary. With the current battery pack I can go about 15-18km on one charge As I mentioned before, the motor controller is a VESC copy from Flipsky 75100.
For balancing I use the BMI160 IMU and run the VESC Tool balancing app which is continuously updated and improved by some amazing people.
Please let me know if you are interested in more information or details from the build. I can also upload some CAD drawings to help with dimension.
Best regards
Can you share more detail? I might give a try. What are the size of the hoverboard motors, 6.5 inches? What is the kart tire specs you used?