I need Engineer to calculate the ouput of a mechanical system 3

[kingofjong]

Hello

I am looking for mechanical engineer that can estimate the output of my mechanical system. My system is compound bow design I did. Compound bow is cantilever spring system with a wheel axle pulley bending the limbs. I need some one to estimate the power. They can use any tools like matlab, simulations, pure math, or etc. Can some point me to some one credible that does this.

Thanks

 

[3DDave]

Use a high-speed camera to measure the rate of acceleration of the arrow. The power output will change depending on the mass and flexibility of the arrow. Or buy one of these: VELOCITIP BALLISTIC SYSTEM - $1995.00

 

[rb1957]

how do you define the power of the bow ? the strength of the draw ? (that's easy to measure)

another day in paradise, or is paradise one day closer ?

 

[hydtools]

Force of the draw times the length of the draw.

Ted

 

[LittleInch]

Have you tried Google?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[kingofjong]

Hello

I have tried google and all the engineers focus on building stuff. I don't have the full bow built. My bow is different from normal compound bow it has more cams and longer limbs. I was wondering if some one could measure the power without building the bow. If they do need to build the bow then do it for cheap and test the power. It cost a lot of money to manufacture a bow.

Thanks

 

[rb1957]

it'll cost a lot of money to model the bow too !

first you'll need to model an existing bow, as similar to yours as possible, to calibrate and validate the modelling.
Then model your bow.

Or talk to bow manufacturers. Get an NDA first.

another day in paradise, or is paradise one day closer ?

 

[hydtools]

https://www.outsideonline.com/outdoor-gear/tools/how-compound-bows-work/

Ted

 

[TheTick]

Force of the draw times the length of the draw.

Hydtools is on to the simplest solution. However, because the system is likely not linear, you may need to break the draw up into small increments, and calculate the work energy form each increment of draw. (Or maybe you can find a machine to measure continuously.)

For each increment, work W = distance * [(F[sub]start[/sub]+F[sub]end[/sub])/2]

The total work of the draw becomes the maximum possible kinetic energy that can be imparted to the arrow (neglecting friction, etc.)

KE = 0.5mv[sup]2[/sup]
where KE = energy (from bow draw)
m = mass of arrow
v = velocity of arrow

v=sqrt(2*KE/m)

Do all the work in metric. It will make more sense. Do any conversions to the Old Dead Kings' units after the calculations are done. (That's how NASA got us to the moon.)

 

[rb1957]

but like the OP says, he doesn't have a bow to test.

modelling the bow seems to me to be very specialised (and easy to get wrong).

but "power of a bow" is it draw force, which would be the force launching the arrow, or draw work (draw force*distance) which would be the KE applied to the arrow ?
I'm now going with "draw work".


another day in paradise, or is paradise one day closer ?

 

[3DDave]

The reason to sell instrumented arrows is that some of the work put into the bow is captured as kinetic energy in moving parts of the bow and do not go into propelling the arrow.

If building the bow is too expensive then that's the end of that. Current bow makers will have been tinkering with alternatives, getting access to increasingly sophisticated materials, fabrication techniques, data collection, and experiences. Someone off the street with no such background is not going to out-tweak the thousands of others with hands-on experience.

 

[kjoiner]

Compound bows are quite complex especially with the advent of cams. I'm sure the manufacturers have ways of simulating the draw weights and energy. Just the cams alone affect the energy output of the bow. Here is a screen shot of profiles of a recurve bow vs a couple of different cam profiles on a compound bow.

 

[rb1957]

FDC ?

another day in paradise, or is paradise one day closer ?

 

[hydtools]

FDC = force draw curve

Ted

 

[zeusfaber]

Guess "force-distance curve".

A.

 

[GregLocock]

The problem as alluded to above is that it is a dynamic problem, you are accelerating a variable proportion of the mass of the bow and the string as well as the dynamics of the arrow itself - which is not a point mass, it bends as it accerlerates.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[SnTMan]

I need Engineer to calculate the ouput of a mechanical system

You paying?

The problem with sloppy work is that the supply FAR EXCEEDS the demand