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Step 4Testing and additional info
Now that you've made some air muscles it's time to put them to use.
Stretch out the muscles so they reach their maximum extension by adding weight. A good test rig would be to use a hanging scale- unfortunately I didn't have access to one so I had to use some weights. Now slowly start adding air in increments of 20psi until you reach 60psi.
The first thing you notice is that the muscle contracts a progessively smaller amount with each incremental increase in air pressure until it fully contracts. Next you'll find that as the load is increased the ability of the muscle to contract decreases at an increasing rate until it can no longer lift the increased load. This is very similar to how a human muscle performs.
It is immediately noticeable that a change in the size of the muscle has a huge effect on the performance of the muscle. At 22lbs. @60psi, the smaller muscle can still lift, but it is nowhere near obtaining full contraction while the larger muscle can very easily obtain full contraction.
The dynamics of air muscles are fairly difficult to mathematically model, especially given the number of variables in their construction. For further reading I recommend having a look here:
http://biorobots.cwru.edu/projects/bats/bats.htm
Several applications of air muscles include robotics (especially biorobotics), animatronics, orthotics/rehabilitation and prosthetics. They can be controlled by microcontrollers or switches using three way solenoid air valves or by radio control using valves operated by servos. A three way valve works by first filling the bladder, holding the air pressure in the bladder and then venting the bladder to deflate it.
The thing to remember is that air muscles must be under tension to work properly. As an example two muscles are often used in conjunction to balance each other to move a robotic arm. One muscle would act as the bicep and the other as the tricep muscle.
Overall, air muscles can be constructed in all sorts of lengths and diameters to suit a wide variety of applications where high strength and light weight are critical. Their performance and longevity varies according to several parameters regarding their construction:
1) Length of muscle
2) Diameter of muscle
3) Type of tubing used for bladder- testing I've read states that latex bladders tend to have a longer service life than silicone bladders, however some silicones have greater expansion rates (up to 1000%) and can hold higher pressures than latex (much of this will depend on the exact tubing specification.)
4) Type of braided mesh used- some braided meshes are less abrasive than others, improving bladder life span. Some companies have used a spandex sleeve between the bladder and mesh to reduce abrasion. A tighter woven mesh allows for more even pressure distribution on the bladder, reducing stress on the bladder.
5) Pre stressing of the bladder (the bladder is shorter than the braided mesh)- this causes a reduction of contact area (and hence abrasion) between the bladder and braided mesh sleeve when the muscle is at rest and allows the braided mesh to fully reform between contraction cycles, improving its fatigue life. Pre stressing the bladder also improves the initial contraction of the muscle due to initial lower bladder volume.
6) Construction of muscle end housings- radiused edges reduce stress concentrations on the bladder.
All in all, given their power to weight ratio, ease/low cost of construction and ability to mimic the dynamics of human muscles, air muscles offer an attractive alternative to traditional means of motion for mechanical devices.
Have fun building them! :D
Stretch out the muscles so they reach their maximum extension by adding weight. A good test rig would be to use a hanging scale- unfortunately I didn't have access to one so I had to use some weights. Now slowly start adding air in increments of 20psi until you reach 60psi.
The first thing you notice is that the muscle contracts a progessively smaller amount with each incremental increase in air pressure until it fully contracts. Next you'll find that as the load is increased the ability of the muscle to contract decreases at an increasing rate until it can no longer lift the increased load. This is very similar to how a human muscle performs.
It is immediately noticeable that a change in the size of the muscle has a huge effect on the performance of the muscle. At 22lbs. @60psi, the smaller muscle can still lift, but it is nowhere near obtaining full contraction while the larger muscle can very easily obtain full contraction.
The dynamics of air muscles are fairly difficult to mathematically model, especially given the number of variables in their construction. For further reading I recommend having a look here:
http://biorobots.cwru.edu/projects/bats/bats.htm
Several applications of air muscles include robotics (especially biorobotics), animatronics, orthotics/rehabilitation and prosthetics. They can be controlled by microcontrollers or switches using three way solenoid air valves or by radio control using valves operated by servos. A three way valve works by first filling the bladder, holding the air pressure in the bladder and then venting the bladder to deflate it.
The thing to remember is that air muscles must be under tension to work properly. As an example two muscles are often used in conjunction to balance each other to move a robotic arm. One muscle would act as the bicep and the other as the tricep muscle.
Overall, air muscles can be constructed in all sorts of lengths and diameters to suit a wide variety of applications where high strength and light weight are critical. Their performance and longevity varies according to several parameters regarding their construction:
1) Length of muscle
2) Diameter of muscle
3) Type of tubing used for bladder- testing I've read states that latex bladders tend to have a longer service life than silicone bladders, however some silicones have greater expansion rates (up to 1000%) and can hold higher pressures than latex (much of this will depend on the exact tubing specification.)
4) Type of braided mesh used- some braided meshes are less abrasive than others, improving bladder life span. Some companies have used a spandex sleeve between the bladder and mesh to reduce abrasion. A tighter woven mesh allows for more even pressure distribution on the bladder, reducing stress on the bladder.
5) Pre stressing of the bladder (the bladder is shorter than the braided mesh)- this causes a reduction of contact area (and hence abrasion) between the bladder and braided mesh sleeve when the muscle is at rest and allows the braided mesh to fully reform between contraction cycles, improving its fatigue life. Pre stressing the bladder also improves the initial contraction of the muscle due to initial lower bladder volume.
6) Construction of muscle end housings- radiused edges reduce stress concentrations on the bladder.
All in all, given their power to weight ratio, ease/low cost of construction and ability to mimic the dynamics of human muscles, air muscles offer an attractive alternative to traditional means of motion for mechanical devices.
Have fun building them! :D
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I made a couple of the muscles that chewee threw up here that worked well but it just seems like an awful lot of wasted air that could be recycled and make any reserve tank last longer.
Just throwing that out there.
I come back along from year to year to see if anyone else has pooped another gem of amazing. First time I've ever posted. Good luck!