Mechanical Accelerator Doubts

[boyntonstu]

I did some rpm calculations to see how many rpm are needed to pull a string at 100 fps.

I was thinking of using a tachometer to measure string speed.

100 fps = 1,200 in/sec

Assume a 2" diameter pulley with a 6.28" circumference.

1,200/6.28 = 191 rev/second or 11,465 rpm needed for just 100 fps.

Am I missing something?

It seems that we are chasing a technical impossibility.

Another concept is to use a 1:2 lever catapult.

Hitting the lever like a bat to a baseball would create an impulse force.

Comments most welcome.

BoyntonStu

P.S. The Airowgun demonstates that speed can be increased with compressed air.



Comments?

[spudtyrrant]

Are you speaking of compound bows and such?
if so then they work on the principle of tension that is stored in the fiberglass arms.

But if you talking about mechanical accelerators the only ones that i could find use hydraulics or a compressed gas for their power.

If you aren't talking about any of those than you will have to clue me in because i don't know what application you are talking about.

[Technician1002]

boyntonstu,

The figures look correct. Traveling at nearly 80mph and making a u turn on a 1 inch radius (2 inch diameter) does involve very high forces. This is why pitching machines use larger diameter wheels to propel the ball.

For feet per minute measurements, it is common to use a wheel with a circumference of 1 foot. RPM = FPM. A tach will directly read feet/minute. Lathe tachs use these to directly measure cutting speed on the diameter of the work.

[boyntonstu]

Are you speaking of compound bows and such?
if so then they work on the principle of tension that is stored in the fiberglass arms.

But if you talking about mechanical accelerators the only ones that i could find use hydraulics or a compressed gas for their power.

If you aren't talking about any of those than you will have to clue me in because i don't know what application you are talking about.

http://www.spudfiles.com/forums/viewtop ... html#18593

This is what we are discussing.

[jimmy101]

Traveling at nearly 80mph and making a u turn on a 1 inch radius (2 inch diameter) does involve very high forces. This is why pitching machines use larger diameter wheels to propel the ball.

Also, they use large diameter wheels because the actual launch energy comes from the momentum in the wheels at the time of launch and not the power output from the motor at the time of launch. The massive wheels (compared to the mass of the baseball) are energy storage devices.

[boyntonstu]

boyntonstu,

The figures look correct. Traveling at nearly 80mph and making a u turn on a 1 inch radius (2 inch diameter) does involve very high forces. This is why pitching machines use larger diameter wheels to propel the ball.

For feet per minute measurements, it is common to use a wheel with a circumference of 1 foot. RPM = FPM. A tach will directly read feet/minute. Lathe tachs use these to directly measure cutting speed on the diameter of the work.

A 1 ft radius would have to turn 360* in 1/600 second to propel a projectile at 600 fps.

A possible 6"x12" rubber propelled see saw catapult might do it.

Mechanical speed increase is a challenge.

Perhaps an Atalat?

http://www.primitiveways.com/pt-spearthrower.html

BoyntonStu

[spudtyrrant]

boyntonstu,

The figures look correct. Traveling at nearly 80mph and making a u turn on a 1 inch radius (2 inch diameter) does involve very high forces. This is why pitching machines use larger diameter wheels to propel the ball.

For feet per minute measurements, it is common to use a wheel with a circumference of 1 foot. RPM = FPM. A tach will directly read feet/minute. Lathe tachs use these to directly measure cutting speed on the diameter of the work.

A 1 ft radius would have to turn 360* in 1/600 second to propel a projectile at 600 fps.

A possible 6"x12" rubber propelled see saw catapult might do it.

Mechanical speed increase is a challenge.

Perhaps an Atalat?

http://www.primitiveways.com/pt-spearthrower.html

BoyntonStu

your talking about directly accelerating something why not use centrifugal force like say one of these that way higher speeds are easier to obtain

[boyntonstu]

boyntonstu,

The figures look correct. Traveling at nearly 80mph and making a u turn on a 1 inch radius (2 inch diameter) does involve very high forces. This is why pitching machines use larger diameter wheels to propel the ball.

For feet per minute measurements, it is common to use a wheel with a circumference of 1 foot. RPM = FPM. A tach will directly read feet/minute. Lathe tachs use these to directly measure cutting speed on the diameter of the work.

A 1 ft radius would have to turn 360* in 1/600 second to propel a projectile at 600 fps.

A possible 6"x12" rubber propelled see saw catapult might do it.

Mechanical speed increase is a challenge.

Perhaps an Atalat?

http://www.primitiveways.com/pt-spearthrower.html

BoyntonStu

your talking about directly accelerating something why not use centrifugal force like say one of these that way higher speeds are easier to obtain

Baseballs and clay pigeons are very slow compared to spud guns.

Imagine a 12" horizontal ruler with a pivot hole in it at the 4" mark.

If you release a downward relaxing rubber going 300 fps attached to zero and pivoting on 4, the 12" position will be going at 600 fps.

If there was a sudden stop at vertical, anything in a basket at the 12" position would fly out at 600 fps.

BoyntonStu