My FunWheel: A OneWheel work-alike
During COVID-19 quarantine in 2020 I decided to build myself a one-wheeled skateboard, aka self-balancing scooter, aka funwheel. The machine itself is not my ultimate goal, it is only one step towards my goal, which I will not reveal here. When I started, I had no CAD skill, and no desire to overcome what I felt was a large learning curve to get that CAD skill. Instead, I wanted to hone the ability to build a working electric powered personal transporation machine, and a funwheel seemed like a great way to do that. It was! Objective achieved! Would I do it twice like this? Overall yes, in detail probably not. If there's one thing I would do differently, it would be to have a motor mount that attaches to the frame, rather than mounting the motor right into the frame. The second is that as a follow-up to building the machine, I decided it would be a good idea to learn CAD after all, and so I retroactively modeled my build using Autodesk Fusion 360.
The result has been a very ridable, very fun machine. Here is a video of me riding it. It weighs 10.7kg/23lbs and I get about 20Wh/km, or 32Wh/mi. It isn't as capable as I want yet, but with some motor tuning and an additional voltage boost (up to 14s/50.4V) it should get there. Currently speed is not an issue, I am easily attaining 20mp/h (30km/h) on flat ground. Steep hills are a challenge when the battery is below 40% because of a low-voltage glitch that causes motor ticks; this is not a real issue for general ridability. Additional enhancements will round out the board's usability:
- An integrated BMS, so I can stop opening the lids every time I want to charge the batteries.
- A reliable on/off switch. Currently I'm using a power cut pull-key to disable the board reliably.
- Oh yeah, and footpads!
- Motor controller: Trampa VESC 6 MkIV
- Motor controller accessories from Trampa: Bluetooth module for real-time datastream and on-ride reconfig. Dust jacket. Both highly recommended.
- Motor: PHUB188
- Balance code: Thanks Mitch! Balance code is integrated into the VESC open source project.
- Batteries: 36 Samsung 25R 18650 batteries in a 2x6s3p arrangement.
- Frame: Aluminum sourced from home depot (1.5"x1.5"x1/8" L, 1"x1"x1/16" L) and some plywood scavanged from an old cabinet.
- Inspiration: Mohammad from the Fungineers
- Tools required: Chop saw, drill. Some relatively easy soldering for the motor hook ups. Useful: Step-up hole drilling bit, small crimping tool for JST-XT 2.0mm (VESC). Various types of rulers and markers. A grinder. Sandpaper. Drill press. Multimeter. Level.
- There is no foot pad (yet) which makes it a run-away hazard. The device mainly uses the roll sensor to detect a shut-off condition. It is dangerous and advised that users practice mounting and dismounting before doing so powered. See many videos about how to jump off a OneWheel; jump works, but I don't like it, instead I prefer the tilt & slide method of dismounting.
- Rear bay consists of the rear half of the battery pack, the motor controller, and motor, sense, power, wake-button wiring, and BLE wiring if there's a Bluetooth module.
- Front bay consists of the front half of the battery pack, and the main power fuse.
- Front top plate supports the fang wheels, the pair of little wheels at the front.
- Metal corners are softened by grinder. An out of control funwheel can cause a fair bit of damage to an infant, toddler, sports car, garden bed, or anything else you don't want scratched or squished. Consider adding a bumper of some type. My funwheel did in fact crash into me during early testing and tuning, and my ankle hurt like heck.
- Main rail length is 24.5"
- The rear bay lower bracket is not the right length. On the actual machine the length is 7.5", so that the rear bay lower bracket meets the rear of the main rail, just as the front bay lower bracket meets the front of the main rail.
- I haven't figured out how to express wiring in a good way with Autocad Fusion 360, so the rendering has only the basic large electronic components, none of the wiring.
- "Fang wheels" are essential. When the board nosedives, the fang wheels buy you a half-second or so in which to start running. That extra half-second makes all the difference in the world. The control logic is experimental even when well tuned. You will be happy not to get thrown when the PID control loop can't keep up with the oscillations due to some bumps.
- It is built out of at-hand supplies. I didn't want to get into 3D printing.
- Main member is a pair of aluminum L that are 1/8" thick and just over 2' long each. They are 1.5x1.5" on the long side of the L. This worked out perfectly, for the frame hight, but could have been less wide. 1x1.5" would have worked really well too.
- I weigh about 200lbs. The 1/8" thick aluminum main bar works really well, feels solid. I did try a 1/16" main bar prior and that was just not strong enough.
From PHUB188 vendor page, with annotations.
- what they don't tell you: Stopping the hub from turning is easier said than done. I screwed a "tight clearance" 10mm wrench that I happened to have lying around onto my frame.
- voltage is 24V 36v 48v 60v: I'm running 12s so 40.8/43.2/50.4 but more would be better. 14s would be perfect.
- optional power is bewteen 250w and 800w: aiming for the high end would be good. Riding over bumps can overwhelm the motor at low power. Recent ride attained 1000W up a hill.
- speed can be 20km/h to 35km/h: Yeah I am pretty sure it can go that fast, but honestly I chicken out at about 20km/h. So much could go wrong, including in the machine, that I just don't want to ride that fast. Hospitals are no fun. But on smooth asphalt with my protective gear on I have attained 30km/h.
- actully width of tire is 170 mm: Actually width of tire is not even close to 170mm, the tire is marked as 6 inches wide (152.4mm). What they really mean is that the unusable area close in to the motor is 170mm wide, that is the interior distance between the axle stops. Also notable is that the motor is slightly fatter on the left side, by about 5mm, due to the power/sense wires and the air valve both being on the right side. There is a right and left side, because the tire has a "direction of rotation" arrow on it, so I assume we ride forward in the direction of rotation (I certainly have a dominant foot and I think most people do, so safe to assume there is a "forward".)
- length of shaft is 200 mm: Seems to be. An extra 10mm (5mm per side) would be nice.
- diameter of hub wheel is 150 mm: The number you really want is diameter of the tire. I decided on 280mm of clearance between front and rear bays for the tire. That is pretty tight and leaves just barely enough room for flex and wobble. Juuust enough room to fit my gloved fingers in between the back topplate and the wheel, useful for when the board is disabled and needs to be carried.
- diameter of axle is 14 mm: I can't get my caliper to read less than 14.8 on this, so I would expect to drill a hole a bit wider. Aren't step up bits great?
- Power table: Notable is the top current at 60.39V is 30.54A
- 7.5Ah/324Wh battery pack
- Two packs split across the board, each 6s3p.
- No on-board BMS; cut-off is managed by VESC, remove packs to charge.
- High/Nominal/Low voltage: 50.4V/43.2V/38.4V
- Sustained discharge of 60 Amps!
Motor controller settings
There is a spreadsheet with various tuning options.
* VESC Tool & firmware: 2.06
The fang wheel is not as depicted. Instead, I found this wheel at the local home depot, named a "Richelieu Hardware 1-9/16 in. 20 kg General-Duty Rubber Rigid Casters":
Richelieu Hardware Link
Home Depot Link
I'm happy to talk about my project. Hit me up at firstname.lastname@example.org !
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