Revisiting an unfinished prototype – sociable tadpole trike

In 2001, I decided to tinker in the garage with my angle grinder.

Once in awhile, I like to dig through my photo archive labeled “the Graveyard” where I keep photos of unfinished or failed bike and trike concepts made over the years. Sometimes these ideas just fail completely, or they become too complex to make into plans since I try to ensure that anyone with nothing more than a basic welder and a grinder can do the same work I do.

So, I was waiting for some microcontroller code to compile the other day and I want for a photo trip down memory lane and found an old project called “the Sociable Tadpole Trike” and it sparked some new ideas.

I remember building this thing sometime around 2001 or so. I scoured the ‘Net for any examples of a side-by-side (sociable) tadpole trike (two wheels up front) and there was nothing out there at all, so I thought it would be cool to make the first one. Without any forethought, I spent a free Saturday cutting up tubing to make the trike. I don’t think I even measure a single tube, but sometimes that’s how it goes when you are driven by an idea – cut first, measure things later!

I had some leftover machined 20mm tubes that were part of another project and they fit nicely into a 20mm hollow axle hub wheel set that I built the year before (these were eventually used on the Warrior and Viking Trikes). To make the front steering, fashioned a bracket from two pieces of angle iron and then welded the 20mm tubes to another tube that held some brass bushings. A bolt acted as the kingpin. The odd angles shown between the kingpin and axle tube are there to allow for center point steering (this makes the wheels pivot in their center on the road).

My first attempt at center point steering.

This steering system worked out quit well, but I never used it on any of our plans because it requires four machined tubes to be made and unless you have your own lathe, these small jobs cost a lot to get done at a machine shop. But, for this prototype I decided to just use whatever bits I had on hand in order to make the trike functional in the one free day I had to work in the garage. Yeah, back in 2001 I had a garage to work in, so I didn’t have to dodge the weather all of the time!

The prototype trike required machined tubes for the steering system.

The Sociable Tadpole Trike went together in a hurry and actually looked pretty good when it was done. The steering was almost perfect and the frame seemed stable and strong. I even had an independent transmission system rigged up that ran the two cranks to a transaxle that had independent derailleurs for each rider and a main drive system to the rear wheel, but sadly, I did not take any photos of this unit. I thought for sure that this trike would make it to the plans page, but after rigging up some temporary seats the next day, I found an unfixable flaw in this design – elbow room!

My prototype Sociable Tadpole Trike
 

It seems I misjudged how much room two people sitting side-by-side would need, especially with the captain having under seat steering, so the trike would need to be almost 5 feet wide in order to steer properly and not have the rides sitting shoulder to shoulder. I made the trike exactly 4 feet wide, and decided that a 5 foot wide trike would be too wide for any practical use. Eventually, this design was flipped around and made into the Kyoto Cruise Sociable Delta Trike, which was no wider than 4 feet.

But, the point of this musing is that I intend to revisit this concept once again, and have a wild and crazy idea on how to make the trike less than 4 feet wide, have an independent transmission, suspension, and need only simple components. Are you ready for this one? Front wheel drive and rear wheel steering!

Yeah, that’s right! It will have fixed front wheels driven independently like on the Kyoto Cruiser and run a linkage to a rear steered wheel.

Now, normally I would recommend against a rear steered vehicle as they have quirks, but in this case, the width of the trike along with the riders being placed over the front axles would make the trike stable. I wouldn’t use it as a racing trike, that’s for sure, but for a fun sociable trike, I think the rear steering would work just fine, and allow for a nice stable ride with a great turning circle.

Richard Buckminster Fuller, inventor of the Dymaxion

There was an interesting rear steered three wheel car called the Dymaxion invented in the 1930s by Richard Buckminster Fuller and it seemed to be quite maneuverable and stable from the text I was reading. The length and width of the trike seem to make the difference, which would make sense if you think about how a rear steered vehicle would handle.

A short wheelbase rear steered trike would want to oscillate due to momentum of swinging the rear during a turn, which would then cause the pilot to counter steer and create a hard oscillation that could lead to a rollover. Add speed to this equation, and you have a ride that would not be easy to tame. Add a wide track and a longer wheelbase to the vehicle and it should steer more sensibly, allowing the vehicle to make nice tight turns and handle in a controllable manner.

Now, this is just my “guess” on how the thing will actually work, but I have been thinking about making this my next trike project for 2013, since I really miss the aspect of cruising side by side. If this new FWD Sociable Tadpole Trike actually works, it may be the base for a full body, since it would be easy to make one due to the fixed front wheels and the teardrop aerodynamic shape. In fact, the body might look like a mini Dymaxion!

Well, there you have it, a new idea is born and it will involve some things that have not yet been tried, so I am all charged about either making a new plan or adding to my folder called “the Bike Graveyard”.

~ Brad

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