Saturday, January 7, 2012
Art, Physics, and the "Adult" Tricycle for the Three Year Old in all of us.
This project started out as lawn art and bike parts salvaged from road dumped garbage. The resulting ride is even more fun than I expected, but also a bit squirrelly too.
Bike Artists of Cuba, except they would have done a much better and more inventive job of creating a fully functional and practical.
As I looked at the trike, I realized that the back axel was made as a sort of bolt-on adapter to convert a bicycle in to a tricycle. I was traveling by Amtrak but the last leg of my trip was going to be on a bicycle, so I did not want more baggage. I realized I could put the wheels and axel in a box and mail them home for the seed of a very interesting project. My friend graciously sacrificed his lawn art for my peculiar amusement.
Once home with my treasure, I quickly realized it was going to take a lot of reenforcement to get this mysterious gizmo to support my weight and even a light cargo. Lawn duty is hard on spokes, and bearings. I bought a box of spokes and gathered a wheel barrow load of metal tubes and 1/4 inch bolts. Fortunately, the bearings were salvageable with generous use of mineral spirits, wire brush, and grease.
On most heavy duty trikes they use a very substantial axel so that the wheels are only supported from the inside. This contraption is less substantial and uses regular 24 inch bike wheels supported with a light tubing arrangement that braces both sides of each wheel. The axel is cantilevered behind the bike frame, bolting directly to the bike frame rear wheel slots. The frame must have slotted grooves for the rear wheel so that the chain can be tightened. There is one speed, using a wheel with a bendix coaster brake. Only one wheel is driven and that wheel has the only brake. (I will be adding a front brake.)
My first attempt at mounting the trike axel to the bike revealed that the mounting bolts could not hold the torque of the cantilevered axel. I had anticipated this problem, and had a plan in mind. I devised a sort of extremely long turnbuckle to add a brace from the axel to the rear seatpost to create an adjustable triangle of support. Some of the original structure was missing, so I added other braces. I needed an extra long seat post because of the short BMX frame. This post is also integral to the bracing of the axel, so I found a 1 inch aluminum tube with 1/4 inch thick walls. It is very sturdy.
The BMX frame came from a road ditch mixed with other trash. I had one 20 inch wheel for the front. I figured I could adjust the angle of the cantilevered trike axel to compensate for the size difference between the front and back wheels. Past experience with other cobbled up blended bikes has shown me that steering is quite sensitive to the angle of the headset. My first attempt at riding around the block on the freshly assembled trike sent me gyrating into the ditch when the side slope of the street increased. A slight re-adjustment of the cantilever angle changed the headset angle a few degrees at most, but that made enough difference to give more manageable ride. The next change I made was to move the seat back and down relative to the crank bottom bracket. This lowers the center of gravity, and this change also made a big difference in the feel of balance and control.
Weight: 67 pounds.
Headset angle: 74 degrees
Effective Seat tube angle: 71 degrees
Wheelbase: 44 inches
Width: 25.5 inches
Capacity: me and two or three bags of groceries.
What's It Like to Ride?
My only other recent experience on a tricycle was riding a very heavy-duty three speed trike. It was disappointingly cumbersome and sluggish.
My blended trike feels much lighter and very nimble, but it also feels as if the riders's weight is too high and it could get tippy. One quickly learns to do a lot of leaning. A bicycle inherently stays vertical, and leans appropriately on turns. The trike leans with whatever tilt the roadway has and that feels weird. Perhaps if it had a lower center of gravity like a recumbent this would feel less dramatic. So, one learns to go slow while turning, but it feels very nimble to turn and maneuver. I have read that trikes can induce surprising turns because of the three wheel dynamics, the fact that you cannot really lean with the turn. The net result is a lot of shuffling of the upper body to compensate. You have to pay attention.
Three wheels actually feels tippier than two, in motion. Also, the tilting of the wheels as side slope changes can cause much more side stress on the wheels. The nature of a bicycle keeps the stress centered between the spokes, the tricycle put worrisome lateral stress and therefore needs a much stronger wheel.
But, the biggest surprise is that the trike just feels fun to ride. Maybe it is the novelty. Maybe it is the one speed simplicity. Maybe it is the fact that I can turn around and look backward in a way I would never do on a bike. Maybe it is some long forgotten pleasure that precedes my earliest vague memories of childhood. I do not remember ever riding a trike. My first bicycle type memories are of a wild attempt down the driveway at about the age of 5 when my mom took the training wheels off the bike. I don't actually remember the training wheels, but I do remember my dad insisting that the training wheels needed to come off if I was ever going to learn to ride properly.
Try telling a 5 year old that a bicycle is actually more stable than a tricycle. But now, that is exactly what I am trying to say.