Making and Riding the Crab Cycle

David Bagley Shows His Stuff

Video of David riding crab cycle

Video of David riding crab cycle in reverse

Video of David pausing crab cycle


Idea of Crab Cycle
Design of Crab Cycle (Tom Miller of The Unicycle Factory)
Build Steps from Tom Miller
Start of Build
Boring Box
Creating Axles
Adding a Gear to Axle
Wow! It Fits
Creating Gear with Sprocket
Completing Gears
Making of Threaded Clamps
Gear Housing Complete
Bending and Drilling of Frame
Crab Cycle Complete
Packing Crab Cycle
My Crab Cycle
Experiences Riding

Idea of Crab Cycle

original idea

The next logical step after a double wheel unicycle. Also wanted the it to be easily switchable (within a half hour) from pedal forwards go left to pedal forwards go right. David Bagley sent this idea to Tom Miller of the Unicycle Factory. Tom Miller did the hard part turning the idea into reality.

off the shelf gear box

Off the shelf gear box (not used).


Ordering parts.


Design of Crab Cycle (Tom Miller of The Unicycle Factory)

Main Gear Design

color draft

Early design, sprocket later moved to be inside gear box. Also bearings for sprocket axle were moved up as there was just enough room.

rough design

inside design

gear design

box design

bearings design

spindle design

chain design

Frame Drawings

frame_design 0

frame_design 1

frame_design 2

frame_design 3

Build Steps from Tom Miller

Start of Build

starting AL block

weighing blocks

Boring Box

rough cut

housing rough cut

boring holes for bearings

housing bearing

boring box

Creating Axles


Starting with 3/4" 17 - 4 Stainless Steel



Cutting cotterless crank axle




3/4" - 16 threads per inch for threading for shaft collar



Cutting key-way slot for miter gears


Axle for Sprocket


Adding a Gear to Axle

Locating new set screw holes



Remove excess material 0.300"


Before and after Miter Gear


Fitting of gears


Wow! It Fits




Creating Gear with Sprocket


Boring Sprocket



Marrying Sprocket and Gear



Completing Gears

Drill for roll pins


Installing roll pits to set gears in place


Thin Miter gear to reduce weight



Making of Threaded Clamps

These clamps allow one to shift from "go west" to "go east" easily.

New Aluminum shaft collar

clamp start

adding the threads 3/4" hole with 16 threads per inch

clamp threads

clamp predrill

drill slot for allen screw

clamp drill

clamp square

was square now round

clamp round

knerl the clamp

clamp knerl

slitting shaft collar

clamp cut

Gear Housing Complete

housing and chain

housing chain

in case

top slot (faint) for chain clearance


weighing closed

amazing it weighs the same, closed or open

weighing open

fits together

Bending and Drilling of Frame




25 Year Old Tooling



Narrowing 2" Frame to the 1.5" for the Crushing Cupping Die ("Schwinn")



Drill Jig Stop Gauge



Frame Crush Die


Frame Drilling

frame drill0

frame drill1

frame drill2

frame drill3

Post Drilling

post drill

Crab Cycle Complete

complete tom

complete side

16" wheel

complete front

learning crab cycle vehicle

2 wheel crab cycle for learning

Packing Crab Cycle


Cost Breakdown

My Crab Cycle


Now has a 20" wheel ... just enough room.

Side view of Crab

Its Yellow! (Tom Miller had it powder coated for me).

Its Yellow!

Experiences Riding

I needed about 3 months to learn to ride. For reference, it took me about 1 month to learn to ride the double wheel unicycle.

I practiced along a high fence and have it set to go west (pedal forwards, go left). I kept going from right to left until I needed to hold on less with both hands, eventually brushing lightly with the right hand. One has to lean left, then pedal forwards.

Next I learned how to fall off gracefully (it really helped me gain confidence). I held the right pedal down and let myself drop to the left.

Next I tried to see how far many revolutions I could get without touching the fence. I had to get up to about 40 revolutions, until I felt confident to leave the fence behind.

By 6 months I could ride a figure-eight with it. By 9 I could do a few and also riding by pedaling backwards, this took me many months to learn and found it took me longer to learn than forwards. Then at 10 months I just got idling with right foot down (it feels like a "Manual" or Skateboard Wheely) with the "required": ride in, 25 idles, and ride out. I am quite ambidextrous, but idling with the left foot down is too strange yet (it feels like your balancing on the front wheels of a skateboard, which is hard).

At 11 months, I could reverse direction on the fly. Also got a figure eight while pedaling backwards. And I was was finally able to mount it a few times, with the right pedal down, not too bad once I put my mind to it (knowing idling sure helps). At 12 months I was able to just barely juggle clubs on it (learned first to idle with hands behind my back).

Finally, at 15 months I got some left foot down idles... (ie ride into, idle 25 times, ride out). Just as hard for me, but maybe more impressive is the left foot on box idles. If I start holding on to something, I can do this one foot idle and then get my foot back on pedal and riding away. Still working on consistency and trying to figure out how to get my foot on the box from an idle.

I hope to get more consistent mounting and get better at juggling clubs on it. Also trying full turn of the wheel idles (did about 4-5 ie one full revolution and then reverse).

For 2 months now, I had the mechanism reversed to a "Go East" mode, ie. pedaling forwards one goes right. I was a total beginner once again! It took me a month to learn pedaling backwards and another month to learn pedal forwards. For some reason, I am more "left leaning" it seems. I rode in a circle the various ways and I was learning idling.

Switched back to "Go West" mode. I felt I was not progressing quick enough. After 5 min of disorientation, I was riding again with ease. Today, after numerous attempts, too many to count, I did my first mount into an idle.

Special thanks to Tom Miller for making it possible.

Back to Unicycle Factory
Back to David Bagley's Home Page

Send comments/suggestions to:
David Bagley's mail

Last Revised: 28 May 2020