While searching on-line for a unicycle, I saw something similar to this. It looked like a fun project and a good addition to our collection of dangerous toys. The kid next door came up with the name. Others called it a unicycle with training wheels.

Step 1: Parts List

3/4" Plywood. A little more than 3 sq.ft.
2x6. About 24" long
1/2 NPT Steel Pipe. 2 pieces @ 8" long.
1/2 NPT Steel Pipe Flange qty 4
1/4-20 x 1" Flat head screws qty 16
1/4-20 Nuts (I used T-Nuts) qty 16

Cost To Build. I had everything except the plumbing parts which were about $18.
Duration: About 2 hours not including the decorating time.

Step 2: Pedal Assembly

Put one flange on each end of an 8" x 1/2 NPT steel pipe. Tighten as tight as you can.
Measure the width of the exposed pipe to determine the proper pedal width. Mine measured about 7.00"

I made each pedal out of two pieces because my drill was not long enough to go all the through and I was worried about keeping the hole straight through such a long length.

Rip the 2 x 6 to half the pedal width on a table saw. Subtract about 1/16" more for clearance.

Cut into (4) 4" long pieces.

Mark the center of each piece on the 4" x 1-1/2" face and drill through 7/8" Dia.

Glue the pedals together with the holes lined up.

Clamp and set aside to dry.

Update: OK...The squeekyness got a little old. A quick squirt of silcone lube inside of each pedal took away the squeek. It has not come back even after many days of play.

Step 3: Wheels

Cut (3) 12" diameter circles out of 3/4" plywood.

I used my homebuilt CNC router, so I added some extra details. A jigsaw or bandsaw would work just as well.

Place a flange on the wheels to to mark for drilling the attachment holes. The center of the flange is located 3.5" below the wheel center. The (2) outside wheels require (1) flange pattern and the center wheel needs it on both sides of the wheel.

Optional: Use a round over router bit around both outside edges of each wheel. This will make it look a little better and limit the chipping of the edge as it is used.

Step 4: Final Assembly

Assemble the pedals onto the pipe and attach the flanges. Tighten the flanges as tight as you can, but make sure the mounting holes are oriented correctly for the wheels.

I was worried about this coming loose so I added a few tack welds from the backs of the flanges. Epoxy would probably work as well.

Attach the pedal assemblies to the wheels using the screws and T-Nuts. You could probably use standard hex nuts or woods screws.

Step 5: Decorate

I finished mine with some cabernet stain and clear spar varnish.

I routed a diamond plate pattern into the pedals, rounded the edges and painted them black.

Step 6: Ride.

Be careful. Wear a helmet and wrist guards.

While it is quite intimidating to get on the first time, it is easier than it looks to ride. I am upper 40s and have never successfully ridden a unicycle (yet) and I was able to figure this out in about 10 minutes without a single crash to the ground.

Start along a handrail or ledge where you can steady yourself. Set the pedals with one high and one low (6 and 12 o'clock). Step on the low pedal first. Then step onto the high pedal, while keeping more weight on the low pedal to keep it from moving. Now slowly roll forward until the pedals are even (3 & 9 o'clock). Now try to pedal forward. Avoid stopping at the 6 & 12 position at first because you have the least control there. Try to keep a little pressure on the rising pedal. This will limit the speed and jerkiness.

If you feel like you are going to fall, step off with the high foot first. The lower foot will rotate the cycle a little, but it gets pretty stable. It does not turn sideways well, but you can usually get it to rotate on smooth ground.

The video is my daughter's first successful run across the garage. She is quite good at it now.