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A question for the physics brains out there.

  • Thread starter Thread starter arveejay
  • Start date Start date
A

arveejay

Guest
Yeah maybe I've got too much time on my hands but here goes. I just aquired a wheelchair lift from an old handicap van. It is rated at 1500 pounds. It is about 50 inches long and the average street bike needs about 85 inches of base to sit on. I have it raised off the ground 2 feet, bolted it to the floor and cabled it to a main support beam, this will give me 2 feet of lift, but I need to add about 3 feet of base so I can roll a bike on and lift it up which will make for easier working. My question is by adding 3 feet of deck and moving the center of gravity back won't a 500 pound bike feel like it is much heavier being farther from the lifting point. It lifts the whole setup from the end so all the weight is concentrated on the end of the lifting mechanism. From what I remember from school the farther the weight is from the lifting point, the heavier the work load. Will doubling the lifting base and stretching out the weight, won't the 500 pounds feel more like 1000 pounds? Am I waisting my time only to find out it won't work. Any thoughts?
 
Dink, the whole thing bolts to the wall and raises in on itself so it cant be centered. I thought about making it enter sideways with the base sitting sideways. That would keep the weight close but wouldn't allow working on the side up agains the frame.
 
Fully agree with Dink. Simple solution, too.

You might try making the extensions fold when not in use...weld full width steel plates from the original base so that the extension, when lowered, rests on the the plates and will not permit flex. Alternatively, weld at least two pieces of black gas pipe on each end of the original plate and then on the extensions. Mount them close to the edge to minimize flex and make them at least six inches in length.

Use 1/2 inch bolts or larger, or steel bar stock to hold them in place. If using 1/2 inch supports, you should use three supports on each end of the plate. The support bars should fit the pipe fairly closely, not snug, but just loose enough to allow sliding movement. Drill the rods and use roll pins on each end to secure them, once in place.
 
I would think that it all depends on what is the mechanical constraint producing the 1500 lb. lift limit. The efective weight limit (vertical component) wouldn't change. What will change is the effective torque applied to the lifting base, where the lifting base attaches to the lifting mechanism, or to any attachment points to which that torque is transmitted.
 
Simon, I agree. Adding additional length will increase the torque applied to the lifting mechanism. Without knowing how lift is created it is difficult to provide any suggestions. Do you have any pictures you can post?
 
Is it possible to get the bike on the center stand on the deck space you have now? If so just forget the extra real estate and let the wheel hang off. your bike will be solidly supported by the center stand and which ever wheel is on the lift. For extra safety you could tie down the wheel thats on the lift with ratchet straps. This would also allow you to strap down the rear to raise front wheel off the ground.

BTW this sounds like an excellent DIY project, I've been racking my brain to figure out how to build a bike lift at home without spending mega bucks......

Please post some pics....
 
HiSPL said:
Is it possible to get the bike on the center stand on the deck space you have now? If so just forget the extra real estate and let the wheel hang off. your bike will be solidly supported by the center stand and which ever wheel is on the lift. For extra safety you could tie down the wheel thats on the lift with ratchet straps. This would also allow you to strap down the rear to raise front wheel off the ground.

BTW this sounds like an excellent DIY project, I've been racking my brain to figure out how to build a bike lift at home without spending mega bucks......

Please post some pics....
Click to expand...

Costco and Sams Club has them for $89.00. They are good ones (Ihave the one from Sams Club). You will have to make and adapter to get from the lift to the bikes frame. I made two, one for the GS and one for the Valk. Works great. I'm in the process of having a friend weld up a small drain pan that I can slip between the adapter so I can drain the oil while its on the lift.
 
Lots of good thoughts out there. I can take a picture but I don't know how to get it here. I'll try some of the suggestions and see what happens. Thanks again.
 
Id try it...... i dont think extending it 3 feet will mattter that much. IF you have all the weight on that last 3 feet , MAYBE it would be an issue. but since you have a 500 pound bike spread out over that whole distance,,,, wich originally could handle a 1500 pound bike, i dont thikn its going to matter and i thiink it will serve its purpose well.

but you got to watch out for them thinkers!
 
Well, from what you describe you need to make it a reverse fulcrum.

Extend the lifting arm a bit, but leave the current lift point where it is. That way you gain the leverage of a longer lift arm for the same lift distance.


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Does that make any sense whatsoever? It's hard to describe without a decent picture.
 
By extending the lift three feet you increase the moment acting on the rigid mounting point. What I would do is increase your base by your three feet and make more then one rigid mounting point. Support the base towards the the top of the "wall" with some bracing. The lift can handle it, its a matter of if your connecting point can handle the downward force without shearing off. I built a lift out of hydraulic cylinders and some channel to support the bike. i had it all mounted on the side of a barn wall. the base was 5ft long, with a tool tray near the wall. I should have taken pics of it. The guy moved.....don't know who lives there now. I don't even know if that lift is still in the barn!
 
I will describe it as best as I can. The thing sat at the back of a van. When it was in the van it was at it's raised point so it was actually mounted at the height of a big van. When the lift was letting someone out it was letting gravity pull it down at a controled slow speed. When it lifted up the pump has to withdraw the cylinder and pull it up. The frame bed is big enough for a wheelchair and thats about it. The lift has a frame work over it and still allows a wheelchair to pass thru it. The frame I made is 2 feet high and made out of square tubing, it is the same size as the base of the unit. It is bolted to the frame and the frame is anchored to the floor and the wall, that is why I can't go closer to the center, heck because of the lifting frame work I cant even use the first foot of the base as it would be too high for the bike to go in, although I could move it forward once I goy it lifted but that makes me a little nervous.once I also have a cable attached to the unit and thru the wall to a frame post in the shed behind the garage. The frame work is what worries me. There is an iron rectangularly shaped 4 sided channel that slides into a bigger channel of the same shape. There is a nylon button on the outer channel where the weight slides, There is one of these per side. Since I have it 2 feet off of the ground I only have 2 feet of lift so that part doesnt really scare me. Picture it sideways, its shaped about like a 4 feet high 4 feet long 110 degree shape. All the force is on the corner of the brace, and it doesn't really look that impressive. Add to that extending it and doubling the pressure or more had me wondering if I was looking for trouble. I'm probably going to make supports for the corners and reinforce there.That's my quandry. I have not tried rolling it on and putting it on the center stand and let it hang. I like that but had not even thought of it yet myself. I will try that as soon as I add to the support frame work as I'm still not confident.
 
Allright, the base is not long enough to put the bike on the center stand. Here's what I'm going to do. I'm going to buy 7 ft channel iron, bend the front for the bike to sit against, bolt it to the table and then roll the bike on, tie it down, and raise it up. I'll work on it this weekend and try to post a pic. I got to reinforce a little first then try it. I'll let you know. Thanks for all the ideas. You guys never fail to come up with ideas.
 
Scotty, I'm having too much fun to just stop now. It's just a toy which I may only actually use it once a year. A friend of mine has one of those lifts which just rolls under it and lifts it up. I couldn't see a simple way to make it lift on the frame and not the exhaust pipes.Not wanting to put undo stress on any place not designed to handle that weight I just figured I'd wait for something better to come along. I traded the lift for labor and have less than $50.00 into it. Another $10.00 to finish it and I'll roll it on, push the button and stand there and watch it go up.

The ultimate toy for a lazy bas**** like myself.
 
arveejay said:
Scotty, I'm having too much fun to just stop now. It's just a toy which I may only actually use it once a year. A friend of mine has one of those lifts which just rolls under it and lifts it up. I couldn't see a simple way to make it lift on the frame and not the exhaust pipes.Not wanting to put undo stress on any place not designed to handle that weight I just figured I'd wait for something better to come along. I traded the lift for labor and have less than $50.00 into it. Another $10.00 to finish it and I'll roll it on, push the button and stand there and watch it go up.

The ultimate toy for a lazy bas**** like myself.
Click to expand...
I was just being a wise ass as usual. I really admire you for the project
 
This is just off the top of my head but based on the set-up you describe, would it be possible to build a short cinder block, concrete, and rebar "knee wall" in a more centered location in your work space and then bolt the lift to that? Then you could run the bike up length wise on the lift and still get to the side that would have been blocked by the wall. You'll have to sink some rebar into the floor to make the short wall strong enough to do the lifting. Which actually makes me want to ask this question: Are you sure your existing wall is strong enough to take the strain the mechanism will generate if you bolt it to the wall as planned?
 
I know what you're talking about - part of my job involves inspecting wheelchair vans, so I'm familiar with the lifts like you've got.

You're correct about extending the ramp to support the bike putting more leverage on the lift itself. Still, with a 500lb bike, I don't think you're going to get the equivalent of 1500lbs of force on the shorter ramp by extending it. So that idea should work fine, whether you use the centerstand or not.

My concern is how well you've got the lift itself bolted down. Don't want to get the bike in the air, then have the whole thing come crashing down on you. 8O But it sounds like you've thought this through. I can't quite picture how you've got the lift secured there, mostly because I'm used to seeing them installed properly in wheelchair vans. :) But it sounds like a reasonable idea.

Last I checked, there was a crashed wheelchair van at the local junkyard. Now you've got me thinking...
 
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