I really want to build a ropetow in my front yard this winter for riding a snowboarding jump I plan on building [4' high, 6' wide kicker, 3-4' high, 10' wide landing] out of pallets, old wood and lots of nails. I was thinking I could possibly power this with a salvaged powerwheels motor [though I'd need help with the power, it's not too hard to change 120VAC into 12VDC, right?]. Beyond that I couldn't think of any other sources of motors though, so I'm wondering if anyone else has any good ideas. Also- I'm looking to propel 150lbs across the snow at 5 ft/s, and if it's not prohibitively expensive, 300lbs at the same speed so two people can ride at the same time. I can't imagine it takes much effort to move a snowboarder, I've pushed friends to get speed for a jump and it's obviously not like pushing 150lbs against gravity [duh] I'm going to use one of the force measuring things in physics to test this on my skateboard [I think this takes almost the same amount of force, probably a bit more on snow]. So yeah, hit me up with ideas.

Note- for the main counstruction I'm thinking two terminals with big wooden wheels [~3' diameter on metal axes. The motor would be running a home made gear on the outside rim of the pulley at the uphill terminal. The pulleys would be horizontal, on top of terminals made of pallets bolted to wooden stakes in the ground to keep the rope from pulling the terminals together, and the lower pulley would have a two garage doors spring rated at something like 150lbs to constantly pull the lower pulley on a track and keep tension on the rope. I have no clue what to use for rope, I'd imagine anything decently strong should hold up fine, it's about a 100' distance to pull the rider, and it's only slightly uphill [there's a drop in for speed].

So yeah, hit me with some ideas.

Draw a picture of your anticipated design. The best idea would be to find a quick motor that could spin a small wheel directly from it's shaft to pull in the rope. LEss gears means less places to have something break. Plus a small diameter wheel spinning fast will pull the same rope the same distance but with less torque on the motor's part than a large wheel pulling slower.

RDP

Excellent point. I have to find a 1.5"D pulley though, I haven't seen any of those yet. I'm thinking maybe the motor could drive another regular pulley on a shaft with a kid's bike wheel [10"] which would directly drive the rope. Oh and by the way, the wheel will be horizontal because it's better to have the rope to your side than right above you and possibly on you. I think some kind of large flange over the bottom of the bike rim will be necessary to keep a long, heavy rope nice and taut.

What do you think of my plan to keep tension using the lower terminal?

I don't think a powerwheels motor is going to work to well, unless you have some that are way bigger than the ones I have. It would be very slow. You should look into using a fan motor or some other low-speed ac motor.

I have ac [i think] motors powering a few of my tools. Would any of these be up to the task?

Specs-

-Lathe motor-
-1/4 hp
-110V
-60 cycles
-5 amps
-1750 rpm

-Scroll Saw Motor-
-115V
-60 cycles
-5 amps
-1750 rpm

-Bandsaw Motor-
-1/3 hp
-115 volts
-60 cycle
-7 amps
-1725 rpm

The scroll saw/lathe motors are short and stocky, and the bandsaw one is about the size of a coffee can. I'm thinking the lathe/scroll saw motors would work good together so I get more torque and it works better. I'm thinking two motors each turning a pulley with a belt on either side of an axle with the bike rim in the middle. The spinning bar would be securely held in place and run with bearings to keep everything going smooth.

We did the skateboard test today in physics. 40 newtons, or 9lb of net force forward constantly up to 10m was plenty fast. I'd imagine pulling a snowboarder would be maybe 4 times as hard because of friction, so does this mean if I can make something that pulls 40lbs @ 5 ft/s I'm good to go?

This whole set up would be slightly jacked up on the uphill side to angle the wheel so the rope's sagging doesn't derail it from the rim if my flange isn't 100% effective. The same will happen on the other end [downhill end jacked up].

And can anyone suggest a cheap alternative for a rope? Lowest price I've found so far is $85 for a 180'X3/4" rope. I'd like to have 1.5", but I think it would be prohibitively expensive. I'll deal with 3/4", maybe make a gripping system to hold so we don't shred our gloves.

For that, imagine a cylinder, cut in half into two extruded hemipheres, then hinged on the seam on one side. It's hollow on the inside but there are teeth cut into the top and bottom that grip onto the rope, so you just grab the rope with this in your hand and you clamp on.

An electric wheelchair motor is what you want.

For pulleys, use the wheelchair axle without the tires! :)

Also consider wrapping the cord around the power pulley at least twice for extra grip on the rope, else it may just slip.

As for grip, wear leather gloves. Hey, rope burn will keep your hands warm.

[1] So where do you suggest I look for broken-down electric wheel chairs? And would it be easy to do the electronics to make it plug into a regular 110V socket?
[2] Sounds good.
[3] Good call on the double wrap, I wouldn't have thought of that until after I built it.
[4] I shant. Riding gloves will get shredded, and it's too cold to wear any other gloves. I'll just make a gripping device. Tips on that would be appreciated, I've only thought of two ideas so far.

A power supply for a 12 or 24 volt wheelchair motor shouldnt be hard to find or build, i'm sure someone here could help you with that.

As for finding them, try old folks homes. People there die all the time and you can be sure there's at least a few of those had wheelchairs, and maybe a handful that are outdated and cant be refurbished/resold.

Yet another alternative is to rig up something with an old bench grinder motor and some kind of gear/belt-pulley reduction. This requires no power supply and will plug into a 110v outlet.

For a grip i'm not sure, possibly a piece with a sort of cam on on it, where you pull two grips together and it grabs the rope would work. Just make sure it's heavy enough (or has rollers) that allow it to slide back down the rope to the bottom. Make sure to put some sort of stop before the pulleys to make sure they dont get wrapped up in the works.

I vote for the band saw motor connected directly to the wheel.

and for rope, get wire rope. 1/4 inch will be small and hard to grip, 1/2 inch would be better but may be expensive. maybe 3/8

I think I can shorten the tow length to 50', and I found a 100' roll of 1/2" manila rope for $21, so that'll do. I'll figure out how to grip it when the time comes, but I don't think it'll be too hard.

The bench grinder motor is exactly what I have right now. I have 1 1/3 hp and 2 1/4 hp AC motors, but I don't even know if it's reasonable to think 1/3 hp could pull someone up a slope.

I calculated it out, I'm guessing about 30 lbs of force will be required to pull one person with ease. It took about 10 lbs of force to move someone on a skateboard in physics at a reasonable speed. I'll try and nail down better numbers soon. The problem is that we did the experiment in the hallway with glass-smooth floors, so it'll likely take more effort than we used there.

I like the idea of the wheelchair, I'll search more later. I got lots of homework so I have to go for now.


Got some more time now...

I did some calculations, and it seems as though the 1/3 hp motor will pull 5lbs at around 5.5'/second, basically a perfect match for what I need [work checked by my physics teacher]. A 3/4" drive pulley will be driving a 24" bike rim using some sort of heavy duty rope [I'm thinking of using the same 1/2" manila rope just because I'll have some]. Both wheels will be double wound to ensure grip on the rope.

The bike rim will be attached to another 24" rim on the same axle, and this second pulley wheel will be the bullwheel, driving the main pulling rope, which will be double wound for super grip.

The motor will be suspended on a hinged flap, with a spring pulling it away from the drive wheel to keep good tension on the drive rope.

For the bottom terminal, the return wheel will be mounted on a cart that can slide back and forth on tracks, with garage door springs pulling the cart in the opposite direction of the other terminal to keep good tension. I think I'll double wind the rope around the return wheel as well, just for kicks.


-Questions-
I'd like to think the rope won't fray at all from rubbing up on itself where it is double wound on wheels, but I don't really have any experience with anything like this, so could anyone make a more educated guess as to whether this will be a problem or not?
Anybody know if the motor will be damaged by the cold? If so I'm planning on making it detachable from the set up so I can take it inside, but if it's fine with low temps there's no need to over engineer. It might get -30°F at the minimum this winter, and it probably wouldn't be running in temps under 0°F
Also, any ideas on how to connect the two ends of the rope?