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torque requirements for launching a ball

torque requirements for launching a ball

(OP)
I am designing a soccer ball launcher (like the one in the attached picture) for school and am having trouble figuring out how much torque I need the motors to have. I am trying to follow an energy analysis approach to get these calculations done. Attached is a file of my calculations so far. The idea behind them is that the wheels are already spinning with a tangential velocity equal to that of the ball launch speed so that there is then a transfer of energy from rotational energy in the wheels to kinetic energy in the ball. Then, the torque the motors must be able to provide is dependent on the time desired for the wheels to get balk up to speed after launching the ball. Just looking for advice from anyone who can tell me if this is the correct approach and if not what the calculations should look like for this part of my design. Thanks.
Replies continue below

RE: torque requirements for launching a ball

I've never designed a soccer ball shooter.. but your approach sounds generally correct from first principles.

When spinning at 'launch' speed, your wheels have some amount of kinetic energy. After the ball is launched, the ball has some amount of kinetic energy. The amount of energy you need to get back into the wheels will be very nearly equal the kinetic energy of the ball immediately after launch; I would expect the launch itself to be highly efficient. You'll have a tiny amount of energy lost as heat in the ball cover/wheel surface, but this will be very small.

So - calculate your ball KE, which in rough terms gives you double the rotational KE you need to restore to each wheel. Then back calculate how much torque you need to supply in order to get the wheels back up to speed in whatever amount of time you've alotted for that to happen. Not too complicated.

RE: torque requirements for launching a ball

Swinny - he attached those calcs.

RE: torque requirements for launching a ball

The wheels and motors act as flywheels for energy storage. You need to worry about motor power only if you launch balls in very rapid succession. 1/4 hp motor should be perfectly adequate, and will keep you in the capabilities of a standard electrical outlet. The ball will only be in contact with the wheels for a fraction of a second. The torque applied to the ball will be far greater than the motors are rated for, and would be of only theoretical interest.

RE: torque requirements for launching a ball

The attached pdf was looking at how long to return the wheels to the original speed.

Anyone with electric motor experience care to chime in on the torque curves for motors operating near their unloaded speeds? I'm guessing it's not linear all the way from stall, but is close to linear over the small region near the unloaded speed, at least for DC motors.

OTOH - yeah, combined, nearly 1/2 horsepower should be enough to do this job, no calcs required.

RE: torque requirements for launching a ball

Thanks for the example calcs; this is an area of engineering that I've never been in. Surely you can make it go faster...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: torque requirements for launching a ball

Going by this: https://www.ball-launcher.com/shop-c8/ball-launche... it would seem like your notional specification is a bit light; the maximum ball speed should be more like 35.8 m/s vs. 27.7 m/s. Note that the product advertised has variable commanded launch speeds.

TTFN (ta ta for now)
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