Idle thoughts on - constant force spring mechanism - 1kn*1m

[G]

I'd like something (which weighs considerably less than 100kg!) to be able to provide a constant force of 1000N on a cable or similar for 1m.
Ideally not too expensive.

I could get a few constant force (spiral) springs and do that, but for the specs required they would be expensive and not have that long a life.

An electric motor may well be the best way for my purposes if I can get an appropriate motor and controller - I've seen this done elsewhere - any ideas on this? Ideally the controller controlled from some computing device - ie android or pc.
It would need to handle being held still under tension, and being moved at a rate of maybe 50mm/s-500mm/s.

The other way I'm thinking is a cam design and something like either an air spring, or maybe car/bike suspension spring as both can be got cheaply.
Then a cam to counteract the spring rate - I'm thinking pushing directly on to some bearings on a plate on top of the spring may work better than a the cable going around the cam.

Have seen something that more resembled the triangle often used in a mountain bike shock pivot doing a similar job, but think this wouldn't be as easy to get the right rate - as you're a bit stuck with trigonometry while at best a spring is a linear rising rate.

[Tristan.]

Could you sketch what you mean, I can't understand why you couldn't just apply 1000N of tension to the cable by fixing it at both ends. Or does the tension have to be variable?

[ZebraDriver]

How exact does it have to be? How about an air cylinder, in parallel with a second oil filled cylinder, the second one can be run through a throttle valve to damp the motion of the first and provide speed control, the main cylinder can be pressure regulated to control the pull (or push) force

[1198]

100kg weight, suspended on wire, pulley arrangement to transfer force to desired location.

[G]

Tristan, basically I want to achieve this...

[Sload]

Hydraulics?
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Honda Varadero >> Triumph Speed Four >> Honda CBR1100xx

[Tristan.]

I still don't understand why it has to be complex, How about a pulley attached to a threaded bar that slides in a rigid channel parallel to the cable, slide to where needed then torque it to give 1000N of tension

https://i41.tinypic.com/1z5ngw5.jpg


edit, I'm, a tard, missed this sentence

[Sload]

Well I wasnt thinking complex, more along the lines of bastardising old trolley jack / motorbike brakes.

Possibly help if you could give a clue what its for?
____________________
Honda Varadero >> Triumph Speed Four >> Honda CBR1100xx

[G]

I'm not that up on Hydraulics - but it would require a hydraulic pump I presume? And then I would guess we're back to the electric motor and controller, but probably more complex relatively as you'd also need damping controls I would guess?

Incidentally, another way to get a pretty linear force with an air spring I expect is to have a significantly large reservoir at the appropriate pressure.
However, on that - I think when I looked in to the sizes required to get 1kn over 1m (or say 5kn over 20cm then using a lever to reduce it), it got pretty silly big/high pressure.

[edit] - as per 1198, I basically want something to replicate a weight hanging off a pulley the best possible. But it needs to light weight and fairly compact.

Now when set up it may not need to be THAT compact, so one option would be just to go down that route and use some water containers filled up with 100lt. However, I'd definitely need inflatable containers and 100lt is more space than I want to be taking up when deployed, too.

[Tristan.]

The other element, whatever you will be forcing the cable away from, does that have limitations on where it can be? also how far will the point thats tensioned have to be from the axis of it's two ends ie

[Sload]

Not really, think of a trolley jack that you pump with a lever, as simple as it gets. That's why we are both curious about details.

To be fair, let Tristan run with his as he does this for a living, I'm just the guy that usually has to frig the designers abortion to get it to work
____________________
Honda Varadero >> Triumph Speed Four >> Honda CBR1100xx

[G]

Sorry, should have also clarified that I want it to do it 'hands off'.
Otherwise, if I was actively working it, I could just hang off the end of a pulley with a 5kg weight hanging around around me (really need to lose some weight!)

Just drawing up something.

[Tristan.]

[Sload]

[G]

Paint skillz:

https://dl.dropboxusercontent.com/u/18968307/pics/somestuff/cams.png

Hopefully all should act fairly similarly - though the weight will have some momentum of course, which the others won't.

I have seen people claim that their gas-filled pistons provide an consistent force, but not been able to find out where to get them or how they work etc.
Mountain bike air shocks often do often already use a 'negative' spring chamber, but not sure how tunable this is as far getting it consistent. Also, similarly could have two coil springs that work against each other.

[lihp]

The thing is, there are hundreds of solutions to the problem you pose, however, how practical, and reasonable they are depends entirely on the circumstance on which it is being used.

It would be very helpful to constructing a reasonable suggestion for you, if you can explain what the application of it is, and in what location?
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covent.gardens: lihp is my most favourite member ever

[Tristan.]

Of all those solutions, surely the only one capable of being 'moved' is the one with the motor, depending on what you mean by moved

[trevor saxe-coburg-gotha]

[Sload]

[G]

Easily moved, so that it can fit in to a vehicle and not take up too much space.

It's for making a barbell based 'multifunction trainer'.
I've got a decent set of Olympic weights and DIY 'power cage' at home, but would like something to stick in the motorhome when working away.
After having the amazing ideas, it seems people have stolen them and made them a few years ago .

The pistons in the 'bio force multigym' claim to do what I want.
https://resources.sport-tiedje.com/bilder/finnlo/bioforce/finnlo_bioforce_001_d.jpg
I'm not convinced they do. Apparently you could get replacement pistons before, but it's not clear where - it seems to be a generic item re-branded by various companies.

The 'bowflex revolution' uses elastic bands inside a disc. A nice idea, but not consistent again, unless you an extra cam - the one that they use inside isn't that great apparantly.
https://www.bowflex.co.nz/data/media/images/Spiraflex%20Plate%202.jpg

The 'arxfit' has made it work with an electric motor. Or so they claim. A lot of the 'reviews' etc seem to be people being paid by them. And not much been done since it was first shown.
I'm not sure how they handle stalling. It may be it uses quite a lot of power, which isn't ideal for me - but also not the end of the world.
https://www.thedreamlounge.net/wp-content/uploads/2012/05/2012-05-25_13-15-12_131-1024x577.jpg

So, basically - I want to make something along the lines of the above, but more portable. I'd be doing it a little differently too, but that's not an issue for the basic mechanism behind it.

[Tristan.]

ah ok

A spring and linkage seems most sensible. Linkage design will be dependant on the spring rate, easily measurable with a ruler and some weights. I have an excel tool that I made for my dissertation which can give you an 'effective spring rate' at the end of a linkage from an actual spring rate, I'll see if I can dig it up and still understand it

Or just do pull ups with a 5kg weight

[Sload]

Not what I was expecting at all. There is already something on the market that might fit your bill. We use them at work in varying sizes and call then balancers. They comprise a coiled spring to provide a certain amount of resistive force to suspend tooling from.

https://www.molex.com/woodhead/products/family?key=aeromotive_ab_balancers&channel=products&pageTitle=Introduction

The problem though will likely be the cost and durability. you could possibly fabricate something for the task.

For what you are trying to achieve, you could also fabricate a collapsible frame and utilise pulleys and weights but would take a bit of hauling.

Another off the cuff idea, how about bungee type bands. You will not get a linear resistance but ill bet you could work it pretty close, and should be easily engineered to be adjustable.
____________________
Honda Varadero >> Triumph Speed Four >> Honda CBR1100xx

[G]

Pull ups are fine as I don't use a massive amount of weight anyway . (Before I got fat again, I think I was up to 15kg added for pull ups - I've now pretty much added that to my body, which is convenient!.)
This would be for squats, deadlifts, bench press and the like. Cable just shown that way for illustrative purposes - obviously if done like that (as a traditional dual cable machine would be), another cable would be used to pull it down

Cheers Sload. They do seem pretty much ideal. But I SUSPECT the durability will be the issue.
I SUSPECT they use a constant force spring, like one of these:
https://sdp-si.com/eStore/CoverPg/Hardware/Constant_Force_Spring_Negator.jpg
The ones rated for a high weight tend to also have a fairly low number of uses. Something like 4000 is probably not an issue if it's been pulled up and down a few times a day.

But even for the relative conservative workout which 3x5 *3 - 45 a day. Make that 3 times a week for 135 and you're talking a little over half a year's use.

Can't find anything that details expected life so far.

[Sload]

Without investigating further I couldn't say, the ones on the line manage several thousand cycles to failure but as with anything mechanical it can be a bit pot luck. It would all depend on cost as if you make a unit yourself then you could build it for quick changing.

Edit: you could also build it to use more then one spring (parallel) and thus use smaller rated springs as well as giving it safety against failure. The unit size would be potentially bulkier and more complex though.
____________________
Honda Varadero >> Triumph Speed Four >> Honda CBR1100xx

[G]

My thought had been to do it kinda like the bowflex revolution does and use multiple discs which you slot on to a spindle to get the desired weight. So, just like 'real' weights, I could get a couple of 20kg and a 2.5kg disc each side to make a 85kg bench press, say.
That could also mean each disc may be used a bit less and I wouldn't need a lever system to reduce it.

You can get longer life for the same force by using a bigger spring - some are up to about 20000, which starts to make it more reasonable. But those ones weren't for that much force - so I'd have to use a lot and it'd really push the price etc up.
I looked into this all a while ago after getting some resistance bands and wondering how I could make them better.

However, when I was last looking in to it, I decided the reality would be prohibitive on cost/size for using these.

I might drop a message to a manufacturer of a tool balancer and sse what they say anyway. I'm guessing it will be something like that several thousand to failure - which is going to be a little low for me needs.