So I am working on a new vehicle. It isn't a DMV vehicle per-se, since the plan is to make it bicycle powered, but I thought I would record some of the process in case others want to get some clues to follow (or avoid!)
The concept is to make a bicycle powered tracked vehicle (go here for other thread
http://eplaya.burningman.org/viewtopic.php?t=11769) The goal is to have a crew of 2 and 1 passenger. Another goal is to allow the attachment of lightweight panels to the superstructure to make it into a "tankette" (small tank popular in peacetime between WWI and WWII) to fit into the Apokiliptica theme. Without these panels the vehicle will function as a unique bicycle conveyance - with the panels/turret it will become a device of terror and domination!
The first concern is weight. With 2 persons pedalling and another riding, that is 450-600 lbs of weight alone! Add 2 bicycles and some extra for a frame, and you are somewhere between 500-700 lbs. Then there are the treads.
The treads are crucial to this concept. They must be as light as possible, since the pedallers will be moving this weight in addition to the weight of the vehicle. Also, the only way to steer a tracked vehicle is to "pivot steer", where one track moves faster than the other (in the extreme one track will lock and the other pulls the vehicle around). As you might imagine (or as any old war movie with tanks will show) this generates considerable friction with the ground as the vehicle is dragged for a short distance. The literature talks about turning requiring as much power as moving at full speed does...
Real tracked vehicles need excellent traction and have cleats - this tracked vehicle is for the smooth dry playa only, and so the tracks will be smooth also to minimize drag during turns. I began by researching how to make tracks, and quickly found some pretty impressive scale RC tank hobbyists (who use paint markers for cannons!) During the search I came across the idea to use industrial conveyors made of plastic, and currently that is my plan assuming the cost is not too high. This will minimize the weight and maximize strength, while providing a cool industrial look that would be hard to achieve with handmade treads. These weigh only 20-25 lbs per side, a huge reduction from the 100lb+ estimate I had for handmade treads.
So the design weight is between 550-750 pounds, and that is without the "tankette" parts added! Those should add between 100-150 lbs (lightweight panels plus acetylene cannon) and when a battery (50 lbs) and misc other stuff is added (50 lbs) the total design weight becomes 750-1000 lbs (I am using 1000lbs for my calculations). That is quite a bit of weight for two persons in the summer to be pulling, so a multi-gear low range shifting setup will be essential (and the speed will no doubt by snail-like, with a very limited radius of operation) I want a ground pressure that is less than a person walking, so I am shooting for a max. of 2-3 psi. The treads are 6" wide, so that means that between both treads I need 50"-75" of coverage. As I have 7 feet available, and the treads appear to give ~75% coverage, this should be very easy to meet. It may even slide too easily on the playa (say in a windstorm)....The design has a side cross section of 9' x 3' (27 sq.ft.) plus a turret that is 2' x 2' (4 sq.ft.) - that adds up to around 31 sq.ft.
I am using the 50-75 lbs / sq.ft. "rule" that is used in some of the BM-ish literature, so that equates to 1550-2325 lbs of windforce in a storm. As this exceeds the design weight alone by 2x, it may be that wind will push this around without "cleats" in the treads. An anchor may be a good idea also to tie it down when not in use (there the vehicle weight is only ~300 lbs). Theft may also be an issue, so a lock will be included.
People climbing on the "tankette" is also a concern, as the lightweight panels could be damaged by this. The plan is to have various decorative projections to make such look uninviting, as well as some signs, and the "commander" in the turret with a super-soaker to disuade boarders.
I already have several old mountain bikes and a pile of scrap steel, so my cost will hopefully be minimal. The largest cost will be the tracks, the cannon ($200), and the gearing and chain parts. I am initially guestimating $1000 for the total cost (trailer excluded). Logistically the plan is to trailer it on a flatbed, either driving it on or pushing it on, then getting 4 persons to hand rotate it, and drive or pushing it off (there is no reverse). Much of the time it will no doubt be parked, so it will need a locking mechanism for both the drive and firing mechanics. The cannon will require a pyrotechnics art permit (with a deadline of around june/july to apply) Minimum trailer size is 6' x 8', with 6' x 10' preferred.
Next I need to look at gearing and how the pedalers will sit... (to be continued)
Talent hits a target no one else can hit; Genius hits a target no one else can see.
Arthur Schopenhauer
