Gas spring force, series vs parallel

[Stan]

While CNCing my X3, I'm considering putting a counterweight on the Z axis. In particular my thought was to use two gas springs in an offset, compound fashion. The combined stroke length will allow me to offset the weight of the head but not loose any Z travel.

My question is this: Are gas springs arranged in serial additive? If I use two 50 lb units, will I equal 100 lbs of total force?

TIA!

[Geof]

Serial connection you get same force but the travels add.

Parallel you get same travel at twice the force.

[JerryFlyGuy]

There was some discussion on this on the Mach3 yahoo list last week.

I've designed a extended travel system using pulley blocks [block/tackle] but in reverse. If you put the gas shock between the two pulleys in the system you need twice the force but only 1/2 the travel [or 3x the force but 1/3 the travel, depending on how many turns in the block system you use].

There are lots of high force gas shocks out there. I plan on using a 300lb one on my Z axis and it will only need to be 8" extended to work w/ a z axis which travels nearly 24".

Food for thought..

Jerry

[svenakela]

Originally Posted by Geof Serial connection you get same force but the travels add. Parallel you get same travel at twice the force.

Naah, hold on... Serial connection should give twice the travel but half the force. Even though we're talking gas springs, the should follow Hookes law.

[JerryFlyGuy]

Sven, are you sure.. I think that a series connection would double the travel at the same force while parrallel would double the force.. Hooks applies to deformation of a material, we're talking about the compression of a gas..

Jerry

[svenakela]

Originally Posted by svenakela Naah, hold on... Serial connection should give twice the travel but half the force. Even though we're talking gas springs, the should follow Hookes law.

Forget it, I was thinking wrong...
Serial connection is double travel at same force. Geof is soo right.

[svenakela]

Originally Posted by JerryFlyGuy Sven, are you sure.. I think that a series connection would double the travel at the same force while parrallel would double the force.. Hooks applies to deformation of a material, we're talking about the compression of a gas.. Jerry

I was not correct. But I was quick posting though!
Hookes law is not about persistant deformation, when a spring is stretched above its limit Hookes is not valid any longer. Hookes is always used when calculating springs. Gas springs will act the same way.

[Stan]

Thanks for the comments guys...

After hearing some feedback elsewhere from some fellow X3 CNCers, I've decided to hold off on the gas springs until necessary. I will design my system to accommodate the gas springs but will only apply them if necessary. I guess there is enough friction in the Z axis that back driving is not an issue. And with the mechanical advantage of the ball screw, at a 2:1 pulley reduction ratio, my 270 oz-in stepper will be OK.

Thanks again!

[Geof]

Originally Posted by svenakela I was not correct. But I was quick posting though! Hookes law is not about persistant deformation, when a spring is stretched above its limit Hookes is not valid any longer. Hookes is always used when calculating springs. Gas springs will act the same way.

If they are GAS springs surely it would be Boyles' Law.

[svenakela]

Originally Posted by Geof If they are GAS springs surely it would be Boyles' Law.

Yes, that's true. When it comes to estimating the size of gas springs and as long as the gas is constant in temperature, Hookes is working too. Both gas and metallic springs acts the same way. As long as they stay in temperature, that is.