Introduction: Electric Monowheel
This is what is called a monowheel. A vehicle made of a large hoop or wheel that encircles and rotates around the driver.
The one we (my brother and I) made is capable of reaching a speed of about 30 mph. It is hard to ride at first, but after some practice it's easier. You can think of it like riding a continues wheelie on a motorcycle.
If you are interested in building something like what is shown above, I would strongly suggest that you double check your financial and time budget first. This project takes some special tools and knowledge, so make sure you have access to those (listed below). At about 8 months in duration, the monowheel was one of the longer builds we’ve done. If you are considering undertaking this project, make sure you've thoughtfully considered the full cost of your resources.
I will attempt to describe the build as concise as is prudent. Partly because:
-I have never fully trusted my money to the parts or tools lists of the other Instructables.
-I know that you are a busy person and don’t have the time to read through a long Instructables.
-Lastly, I am not a professional and you can find great sources online for how-tos on specific skills.
Before we get started, I just want to point out that this Instructables will be more of a 'how I do' rather than a 'how to'.
Time - about eight months of mid to light work
Price - roughly $1500
Special tools - access to a 2” pipe bender, lathe, mill, welder, and experience in metal working.
Supplies
Supplies:
Note: supplies without a price that just have the ''-'' are products that may have a price that will vary depending on your situation.
Motor - $110
Chain - $12
Sprocket - $40
Honda CRF50 wheel + brake + axle -
Batteries (2) - $300
Nylon guide wheels - $40
Bearings - $10
20’ of 2” OD ⅛” steel tube for outer wheel -
20’ of 1” OD X ⅛” steel tube for inner frame -
20’ of ¾” square tube for inner frame -
Assorted 1/8'' steel plate for inner frame - $25 (roughly)
Electrical switches - $10
Hardware - $25 (roughly)
2 handle bars -
Optional materials:
Carbon Fiber - $60
Epoxy - $30
Thin plywood -
Tools:
Access to a metal pipe roller
A lathe and mill are nice to have, but can be done without if you have proper knowledge and some pneumatic drills.
Normal welding and metal working tools
Normal electrical tools
(Optional) 3D printer
Step 1: Bend Metal Tubing for Main Wheel and Upper Frame
First you want to bend the main wheel and inner frame piece. This will probably be the biggest limiting factor for most people. Not many fabrication shops have a bender that big. If you can through this step, you’re well on your way. We made ours about 4 1/2' OD. Rule of thumb in determining diameter: the smallest the main wheel can be, while maintaining proper driver comfort.
As a note, just realize when you're sizing the wheel to yourself, it's not necessarily the main wheel you want to size. You want to measure your fit in the monowheel to the ID of the inner curved piece that runs around the inside of the wheel and houses the upper roller. If you size your fit to the main wheel, when you build it, you will find that the head space inside will have shrunk.
Step 2: Rollers
Next, you need to make or get the rollers. We made ours from a bar of nylon plastic off Ebay. If you’re a bright sort of person, you could figure out a way to buy some, maybe the rollers that they use for boat trailers would work. Maybe even 3D printing some. Another way to make these, would be to use a drill and a file. After cutting a section off the bar, drill a hole in the stock and hook it up in the chuck of a drill. Spin the piece and use the file to cut in a radius.
We used a lathe and clamped the nylon bar to the chuck and then just cut a radius into it. Once a radius was cut, that segment was then removed from the rest of the bar. We also cut little holes on either side of the roller in order to press fit the ball bearings. Included are the specs for our rollers.
Note: We made a special tool to cut the radius. It's made from a piece of an old file welded to a piece of steel. Included is a picture.
Step 3: Drive Wheel, Sprocket, and Tire
Finding a drive wheel and sprocket is next. This is probably the last majorly hard part, from here everything starts to become downhill. We used a Honda XR50 front wheel and bolted on a sprocket that would work with the motor chain type. We used four grade 8 bolts to mount the sprocket to the hub. We used a mill for this, but you can just do it with a drill. One of the pictures shows a 3D printed jig we made to line up the holes, you can do something like that if you want. Keep in mind that it's very important to square up the sprocket with the wheel so that the chain won't fall off during a ride. Also, during this step, you can go ahead and cut the center tread off the tire, this helps maximize the contact between the main wheel. We just used an old knife.
Step 4: Lower Frame
The past few steps were probably the hardest and if you’ve made it to this point, congratulations. Now begins the actual fabricating of the frame. This part of the build requires moderate welding and metal working knowledge, I will be discussing the steps assuming you have that knowledge or that can find it on your own. There are plenty of YouTube videos that can help you with welding tips.
You will want to start with the lower half of the frame (not the part with the bent 1'' tubing). We drew out our design to a 1:1 scale on a piece of cardboard. All we had to do was cut the metal pieces to the shape and size of the drawing. We suggest starting by welding the 2d parts of the frame first and then connecting them all together at the end. Also, make sure that you try your best to get everything square and symmetrical.
In this step you will also need to fabricate two pars of steel plates. These will be welded to the lower frame and will house the two lower rollers. We made ours using a mill, but you can do it with normal metal tools if needed. Included is a drawing of the back roller housing. These parts do not need to be a specific size or dimension, they just need to allow the rollers to ride comfortably in the main wheel.
Sorry that I don't have better pictures. The device I had them on was locked out and they couldn't be saved. There are many different ways of making the frame. Just whatever works for you (your height, weight, available materials, ect...).
Step 5: Upper Roller Housing
Next you will weld up the part that houses the upper roller. You’ll need to cut out two matching pieces of plate with a slot for adjusting the roller up and down. We used a mill for this part, but it can be done with a normal drill and file, just might take a while. You will weld two pieces of square tubing (we used 1"x1") to one side of a plate. Then you’ll weld the other plate to the open ends of the tubing. This will make a sort of box in which the upper roller can be bolted into. Having the slot in the housing is important because you'll need to adjust the tension of the roller on the main wheel. Although you might like to think that you're a perfect builder, like everyone else you're not, and the slot will help take up any slop in the build.
Step 6: Finishing the Upper Frame
Next you’ll weld the bent piece of tubing to the lower frame. Then you’ll need to weld the upper roller housing in between the pieces of bent tubing. To do this, first put the lower frame into the main wheel with the bottom two rollers into their places. Next weld on the front bent tubing. Make sure it’s parallel with the main wheel. Next weld the upper roller housing to the piece you just welded on. You can then finish it by welding on the last piece of 1'' tubing to the back of the frame. Make sure that the upper roller fits into the housing and rides on the main wheel, not too tight or too loose.
Step 7: Plates for Motor and Drive Wheel
The next thing to do is to fabricate the plates to mount the drive wheel and the motor. We made ours with a mill, but you could probably do it with just regular metal tools.
The exact detentions and shapes of the plates don't really matter it's just important that everything lines up.
Once they're done, you can go ahead and weld them to the frame. This step will require considerable precision. You will need to line up the drive wheel with both the main wheel and the motor. Take your time to get it right.
Step 8: Last Bits of Stuff - Tensioner
After the last step you're pretty much just finishing up the project now. With the rollers, motor, drive wheel, and inner frame all installed, you can next find out where to put the batteries. We put both of ours under the seat because the weight distribution worked out better that way. It may or may not be the same for you. We built a box out of thin plywood and skinned it in carbon fiber. You can make yours out of whatever you want.
Now there’s just a bunch of little odds and ends that need to be made for the monowheel. I will briefly discuss each:
Chain Tensioner: The chain tensioner is an essential part. We made ours from a piece of aluminum sheet metal. We drilled a hole in each end, one end bolted the frame, the other has a small wheel that fits the chain. We then drilled another hole at the bottom of the tensioner and hooked up a spring into the hole. The spring was then tied to the frame of the monowheel.
Step 9: Seat
We 3D printed a block to cover over the batteries and then bolted the seat on top. Our seat was made by D’cor Visuals, but you can use a motorcycle seat or whatever. It’s up to you, it's a free country, or at least it was. Just make sure your geometry is good.
Step 10: Handlebars
We got handlebars from an old Chinese quad, but you can get handlebars off almost anything. Whatever works for you. Just make sure the geometry is good, keep in mind the elevation of the inner frame will change based on your speed.
Step 11: Foot Pegs
We just made our foot pegs from some inverted bike handlebars and conduit. We 3D printed the grips for the pegs, but you can make yours out of whatever you want. Just make sure that they’re placed low enough to keep you center of gravity as low as possible. Even though you want them low, make sure that they don’t go past the outer wheel or they’ll hit the ground.
Step 12: Tire
We made our tire by cutting the bead off of about 3.25 26” bike tires. You can use any size you want, it just needs to cover the full circumference of the wheel. After you cut them, you can screw them onto the main wheel about every 8 inches. We also glued the end points of the tires to the main wheel to make it last longer. I can’t say whether or not the glue actually helped. When mounting the tire just be sure to make it to where it doesn’t interfere with the rollers.
Step 13: Controller
We mounted the controller in between the frame. There’s no wrong place for this, it’s totally up to you.
Step 14: Electronics
You won’t need too much electrical experience to put the motor kit together. Most of the kit we used was pretty straightforward, just realize that much of the information is in Chinese and you might need to check the Q&A on Amazon for help.
Step 15: Dial in the Geometry
Throughout the build, make sure that what you’re making is actually rideable. Make the geometry of the handle bars, seat, and pegs work for you. Just remember that the inner frame will change angles based on your speed.
Step 16: Paint and Then You're Done (hopfully)
You will want to paint it last. Doing it last helps prevent you from accidentally scratching the paint during the building process.
We had our monowheel powder coated by Powder1 in San Diego CA. They were kind enough to do it for free. You will definitely need to paint yours one way or another, even a good brand of spay paint should be okay.
If you've gotten this far and your monowheel works and is ridable, then I congratulate you. If you got this far and your monowheel doesn't or can't work right, I still congratulate you. Failure is one of the best ways of learning... unfortunately.
If you had trouble with understanding some or all of what was said in this Instructables, I included a few link to YouTube videos that are helpful, or just cool.
Cool monowheel for a little kid
This was a fun and educational project for my brother and I. I hope it was the same for you.
Have fun riding!
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