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Approximate Color Legend:lt blue/grey = iron
black/gray = motorcycle
green = power reduction
blue = v-belt tensioners
beige = wood
This wheelbarrow was made in 1984, I sold it a few years later when I moved. Based on a medieval Chinese design, it was built to transport unlimited firewood by deer trail (where a 4x4 won't go) from nearby logging slash piles to my house for heat, without leaving obvious tracks for the lumber company to follow (in case they needed their refuse back). The drawing (above) is from memory and shows how I'd make the next one. I used an electric motor instead of gas because it's quiet, though a gas motor would be lighter, cheaper, and go farther between refills (hours instead of 20 minutes).
It has only one speed. The power is from a ford starter w/ a 1.25 inch v belt Spindle Pulley (they seem to be hard to find, I had to make one to get the right dimensions). The "Go" switch is a momentary button connected to a starter solenoid. The 10 inch driven pulley turns a jack shaft with the starters' bendix attached to the drive sprocket, so the wheelbarrow can be pushed forward without disengaging the belt, but that makes it tricky going downhill with a load because nothing's holding it back, so the left hand controls a hand brake to the motorcycle wheel. If the grounds muddy, the tire will skid, so use a knobby instead of one like mine. Two Jack shafts drive a chain & sprocket that turns the wheel. The fender hump in the middle isn't a problem and the big wheel will push 250 pounds over soft ground, and 400+ over hard ground. More can be carried but balance becomes awkward, and a lot of weight overwhelms the brake on hills. It's easier going uphill than downhill because the feet don't drag as easily on the uphill, but dropping a load going uphill could be dangerous.
~ 1/2 inch
and floor ~ 1/2 inch
shown, has no
and on 3/4 inch
which are also
the handles ~ Brake Cable ~ Angel-iron
from bed frame ~ Volt meter Removable wooden wheel cover is not shown ~ 6 inch sprocket ~ 8 inch pulley
(extra was unnecessary) ~ Ford Bendix * ~ 1.25 inch spindle pulley ~ Grounded Starter Solenoid ~ 10 inch pulley ~ wire to 'go' switch ~ belt tensioner
The crooked Hinge Pin* (right) was a quick solution to pulleys that moved out of alignment when under load. A real engineer would redesign the whole thing, but a mechanic settles for whatever works.
Space, weight, and balance could be improved with a worm drive gearbox, but they cost $130 - $300 as of 2012.
A used 50 Amp Hour battery (which fit in back because of it's low profile) gives 15 - 20 minutes of pulling. Without a load, the handle weight is noticeable, so a larger battery could be mounted far forward below the bed (see above drawing), to help balance and give more operating time. Some kind of flat pack battery would be even better. The original didn't have one because I thought the front might be lowered flat to the ground and used as a ramp for rolling awkward stuff on & off, but that didn't work too well. The liability of the battery in front is from hitting things that can't be seen when walking behind. But anything that big would tip everything over if it struck amidship, so think of it as a bumper.
I totally recommend used angle-iron from an old bed frame, they're made with laminated strips of high and low tensile steel which is lightweight and resists fatigue. You'll see when you try to cut it w/ a hacksaw. The motorcycle fork is welded to the angle iron.
All the plywood (except the wheel boot and motor cover) is fastened to the frame with 1/4 inch carriage bolts spaced about 14 inches to 20 inches apart.
The single speed was a compromise between rough & smooth terrain. It's sort of tedious to move (without weight) because it's heavy if you push, and relatively slow if you don't. But a higher fixed speed in the woods with a load invites disaster. Another design might use a current-chopper to slow the motor, with a thumb levered control to regulate the speed. It depends on your preference & wallet. A chopper will also extend the battery's charge.
I've heard that a current-chopper can be made from 2 additional motors (see below), which are: another (un-wired) starter (B), driven by a smaller dc motor (C ) with a variable speed control (like these: google, or maybe a heater fan rheostat control from a car). Remove the copper windings from a junk starter (B), shorten it down with a hacksaw to save space, and twist the cut wires together for every other opposing copper contact plate so the current goes in through one brush, and directly across to the opposite plate (contact brush), and on to starter-A. When the shaft turns, the contact becomes intermittent (chopped) because very other plate is un connected. Install the chopper so the (+) power to starter-A passes through the contact plates of starter-B. When the chopper turns, it delivers juice to (A) in short pulses, the closer the pulses are together, the more continuous the current and the faster the wheelbarrow goes. The small motor (C ) should have a 1 or 2 amp speed control (and not suck 60Amps). Jack-shafts & pulleys will still be necessary, but it'll have a wider speed range. The front large green pulley could be reduced from 8" to 5 or 6" dia. Possibly smaller so slow chopping won't make the wheel lurch.
This kind of tech is 40 yrs out of date, but on the bright side: it's proven and won't fry a circuit board (doesn't have any) (emp survivable). A solid state chopper would use less electricity but one big enough to handle 60 amps could be expensive. So maybe replace the rheostat with a small solid state chopper. Or you can find the right size 12v rheostat in '50's - '60's cars & trucks used to control the heater fan, interior lights, etc.
If you insist on circuit boards, check out this Radioshack video about making a variable speed DC motor control (YouTube).
If you make one of these, send me a picture & I'll post it here.
Meanwhile in Japan: (YouTube @ 3:59)