Commutamatic II

development log, part two

in which the chassis is converted to tiltable.

last updated 6/27/1999

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The story resumes now, after a total cost of $240 and total time of 21 hours, with a work-in-progress three-wheeled rolling chassis. (The story started with Part One, of course.)

The arguments that got me to this design were these: Since December, thinking and planning adds these considerations: Which led me to these conclusions: And my answers to these problems are: But HO! Opportunity knocks: since I am cutting the rear wheel modules away, why not make them tiltable? Fine, but the lessons I learned from building the first Commutamatic must be considered: So here are the design rules for the Maxion now: The result is going to be something like a decades-old bike with sidecar design I read about, in which the sidecar was attached by a parallelogram linkage. More recently, Antonio Baptista Carlos Sanjuan built a proof-of- concept bike in 1998 that seems to be this way (see it on the TTW Motorized Prototypes page at the site).
And so it resumes. Happily, happily.

Through Feb 16, 1999. Incidental events, plus getting back to work cutting and preparing.

Total cost so far: $380. Total time so far: 28 hours.

Design note: what might have been...

Sketches of base-widening effects Sketches of effect of "rear wheel push" design. The trigonometry of a possible design. As The Fresh Prince once said, or maybe didn't, "Get Triggy With It!" (Big up to my students who groan over my jokes.)

One of the possibilities was an active tilting mechanism that would "push" the outside rear wheel down relative to the frame. The effect would be to lift the rear corner, while widening, a little, the track width, and shifting, a little, the cg toward the inside of the turn.

The result? A 12" lowering of a rear wheel (a 12" lift of a rear corner, therefore) would tilt the frame about 22 degrees, pitch it forward about 5 degrees, would widen the track by about 3", raise the cg by about 6", though it would also shift it toward the center of the turn by about 7". The combination of the shifting and lifting would have given the equivalent stabilty of a 48" track width; impressive compared to the 30.5" width untipped. It brings the theoretical topple acceleration from 0.6g up to about 1.0g.

There are reasons why I chose not to do this, not least of which is the difficulty in delivering torque to the rear wheel while pushing it around. Not to mention, "Automatic" tilt control (lateral acceleration is sensed, and actuators force the chassis into leaning) still hasn't won me over.

Design note: the stability effects of three-wheel tilting...

Sketch of tilt angle changes. Sketches of effect of three-wheel tilt design. The trigonometry of the current design. By tipping the wheels, the cg is shifted lower and toward the inside of the turn.

The ultimate choice is to have all three wheels tilt. The angle of tilt for all three wheels is identical; parallelogram linkages maintain this consistency.

The result? At the planned maximum tilt of 45 degrees, the cg is lowered fully 6", shifted to to the inside by over 12", and creates an effective track width of about 66". Together, these changes bring the theoretical topple acceleration from 0.8g (for the untilted 40" track width) up to about 1.9g. Now we're talkin'.

Total cost so far: $380. Total time so far: 30 hours.
Through Mar 19, 1999. Incidental stuff, and a little cutting and welding.

Total cost so far: $436. Total time so far: 34 hours.
Through Mar 21, 1999. Some real progress on the chassis. Today included a LOT of standing and staring and imagining. (It's frustrating, but you can't proceed until you know where you are going. And even when you think you know where you're going, you sometimes get lost.)

Total cost so far: $481. Total time so far: 41 hours.
Since there now follows months away from the project, it's time to roll to Maxion Log, Part Three.
Back to Back to Max Hall's homepage.

More information about the nifty kin of the Maxion can be found at the Tilting Three-Wheelers home page.

Send me email!