Homemade hydraulics??

[Fv2]

So. I had this idea to use an office chair lift to make something like hydraulics for this bike.
In my head, I wanted the seat at ride height to be where it sits lowered. But stepping back to look at it, the raised height isn't so bad.

Now I just have to figure out how to connect that piston to the swing arm so it will raise and lower as one.

Then I'll have to figure out something similar for the forks.

Anyone have any ideas?

 

[Captain Awesome]

Your design so nothing says it has to run vertically correct?

What about cantilevered like some do with airbags?

 

[Fv2]

Your design so nothing says it has to run vertically correct?

What about cantilevered like some do with airbags?

View attachment 248665

That's what my initial thought was. But I'm having trouble "seeing" it, even with this picture. Still drawing a blank.
If I still drank, I'd have a beer and ponder...

 

[Captain Awesome]

I’d try and make some plywood test units to get the range and leverage correct

Maybe some of our engineering staff can give some ideas

@Ulu @BartRidesEternal

 

[Ulu]

My experience with those chair cylinders is that they are weak. Everything will likely depend on having enough leverage so it will even lift an unladen bike.

If the cylinder moves 6” and it only has to lift the bike 3” you can use 2:1 leverage, and the cylinder will lift twice the load.

To design this we need to know the travel of the cylinder and it’s lifting capacity.

So…..Test time!

 

[Fv2]

My experience with those chair cylinders is that they are weak. Everything will likely depend on having enough leverage so it will even lift an unladen bike.

If the cylinder moves 6” and it only has to lift the bike 3” you can use 2:1 leverage, and the cylinder will lift twice the load.

To design this we need to know the travel of the cylinder and it’s lifting capacity.

So…..Test time!

That helps. I'll see if the paperwork for the chair mentions anything about capacity.

 

[Ulu]

Just test it. Set it up straight and hang weights on it until you know. Do not trust any printed numbers. Too many translation errors.

 

[Ulu]

Your design so nothing says it has to run vertically correct?

What about cantilevered like some do with airbags?

View attachment 248665

This guy uses a bent crank approach: A very strong airbag with limited travel uses the crank leverage to provide more travel (but less force.)

I think the chair cylinder will have too little force for it’s approx 6” travel. It will need leverage to reduce the travel and increase force, or multiple units will be required to lift the bike.

One very important factor we don’t know is, how much will the bike have to rise from the ground in order to ride it?

 

[Fv2]

This guy uses a bent crank approach: A very strong airbag with limited travel uses the crank leverage to provide more travel (but less force.)

I think the chair cylinder will have too little force for it’s approx 6” travel. It will need leverage to reduce the travel and increase force, or multiple units will be required to lift the bike.

One very important factor we don’t know is, how much will the bike have to rise from the ground in order to ride it?

Bike only has to rise 4 inches. The piston is about 6.
I'll dig into after work.

 

[Ulu]

I’ve had quite a number of office chairs over the years, and all of them eventually had the pistons leak and fail while the rest of the chair was still perfectly serviceable.

I have a couple expensive leather and aluminum ones at home in this condition, and how I fixed it was just to take the chair apart and put a spacer tube on the cylinder, so the chair would sit how I like it.

Anyhow, these cylinders are designed not to lift the weight of an average person, but to descend in a controlled manner under the weight. Whatever that weight is.

I would be surprised if a chair cylinder (with one to one mechanical advantage) can lift 50 pounds, but I don’t have one in good condition to test.

 

[Fv2]

So the piston will lift 60# and has a 4.5 inch travel.
After 60# it needed a nudge, so I think 58 is a good number to consider.

I know the weight of the rear swing arm with everything attached is going to be around that. I weighed the motor/wheel, and old set of 3 12v ebike batteries, a red clay brick, the seat I'm using, the tubing I plan to use, and my old tool bag.

So I know it should work, just have to build the rest of it.

 

[Ulu]

Good luck, and remember that friction in the mechanism can force you to “give the thing a nudge” every time.