Project Kalamazoo

[gfish]

I've been developing/obsessing over an idea for next year's Burning Man, based around the image of an old 19th century railroad handcar. I have decided to call it Project Kalamazoo, as Wikipedia tells me that is how such devices are known in Australia. Ideally it would carry the two drivers plus up to another four people sitting on the edges. I really like the idea of driving around, picking up random people, letting them swap out on the secondary drive position. That would be really fun, and I'm sure it would catch a lot of attention. I'd definitely need a kind of rough navvy outfit to go with it.

This weekend I got kind of bored and took the opportunity to play with Googles SketchUp and 3D Warehouse. This is the rough design I've been thinking of, with lots of smaller details (like support brackets) left out.



The front wheels are freely rotating caster-style (not shown). The hand pump turns the craftshaft which feeds into a small ATV differential. That turns two sprockets which drive the rear tires. Why add the complication/expense of a differential? Because the drive tires have independent brakes on them, which are also used for steering. This allows a very simple interface which can be operated while still pumping. Also, I like the quirkiness of it. Should be pretty nimble.

The connecting rod attachment point, crankshaft offset and gear ratios are just randomly chosen for this rendering. There are just too many question marks to try to decide upon those now. Once I have the platform built I can figure out just how much torque will be needed, and what pumping range of motion and force is comfortable. It doesn't have to go very fast, after all. Slow and steady is fine once it gets going, as long as pumping isn't too much work. I don't think it will need adjustable gears, but if so it isn't the end of the world. I'll probably be cutting up a pair of old bikes for parts anyway.

I can't start on this until I'm back in Seattle, obviously. And I'm going to want to get my forge back for some of it -- smithing the brackets by hand will be fun and a nice touch, visually. Most of the parts will be pretty cheap and easy. Standard wood floor design, iron pipe for the pump and connecting rod. One important design limitation is that it needs to be able to break down into pieces that can (comfortably!) fit in my car. Hopefully the longitudinal floor joists can be single pieces. They're 3 meters in this rendering, and the driver's mass is dangerously close to the rear axle. Wouldn't want to flip it while driving solo...

Comments

[bigbumble.livejournal.com]

I am very skeptical of turning by braking. My recumbent tricycle (see userpic) has one wheel drive on the left rear wheel. There is very little or no steering effect because of it. If you have rigidly aligned wheels I am confident you will have little or no turning ability by breaking. I suggest you test it first on an Lego or Erector Set type model before you start building.

[gfish.livejournal.com]

The rear wheels will be driven through a differential, so they aren't mechanically linked. If you brake one while letting the other one continue to rotate (or continue to power it, even better), the vehicle will rotate about it, no worries there. It's the same way that wheelie cars steer.

[zzyzx-xyzzy.livejournal.com]

It seems like it'd be hard to develop the torque for turning this way. Think of turning from a stop. If you lock one of the rear wheels, you effectively double the gear ratio to drive the other wheel, AND you're trying to rotate the vehicle around the single worst point as far as its angular momentum goes (if it's longer than it is wide like your sketch)

[gfish.livejournal.com]

Yeah, there is a reason you don't see many devices like this. If I wanted ruthlessly practical I'd buy a golf cart. What fun is that?

[bigbumble.livejournal.com]

Wheelie cars don't have their front wheels on the ground when they steer that way. You would have to pop a wheelie every time you wanted to turn. (Would be fun to watch though!)

[bigbumble.livejournal.com]

As I review the fine print I see you mention casters for the front wheels. So turning is no longer the issue, going straight will be!

[gfish.livejournal.com]

My intuition is that won't be a problem. Luckily the difference between front wheel drive and rear wheel drive is simply which side of the pump I put the brake levers, so I can switch it trivially if need be. I'd rather it be rear wheel if possible, so the driver has better visibility when turning.

[bigbumble.livejournal.com]

A pair of large caster wheels can be turned in tandem using a bar linkage, off center of the caster pivots, between the wheel mounts. Only a linear motion to move the bar left-right is needed for turning. The control could be nearly identical to what you had in mind for brake steering.

[ilmarinen.livejournal.com]

This sounds like promise. I don't thin Fish could get enough motion out of a cable-operated lever on the pump to actually steer something though. Maybe a foot-operated steering tiller?