Help with Launcher

[jeremy5561]

I'm using wheels for the ball launcher I'm building. This is my first year and I'm not sure how to do it. My teammates suggested that I use am-0914 but 75 RPM is too slow, and if hooked directly to the 15cm diameter wheels, would launch at only about 2 km/h.

We've already reached the maximum 4 CIM motors so I'm wondering if am-0912 motor will do the job. I would attach it to the CIM-sim gearbox and then attach it to this sprocket. A chain and another sprocket will connect to the 6" wheel that came in our kit. Will there be enough torque? since I can only use two of those andymark motors, can I mix an andymark motor and a fisherprice motor and put them onto the cimsim? Is there a better solution?.

I don't know how to do torque but I read it from the Internet. The gearbox will increase the torque of each motor to 2.14 Nm. With a wheel of 0.075 radius, that means the force out of the wheel is 28.5 N. Assuming that the load cuts the motor speed into 1/4 of it's free speed, that leaves 4000 RPM reduced to 800 RPM by the gearbox. 800 RPM is 13.33 RPS. The 15 cm diameter wheel has circumference 0.47 m. 0.47m*13.3 gives me a speed of about 6 m/s or 22.5 km/h. Will this work?

[Cem8301]

Your thought process seems pretty sound. What is your team's strategy? With that speed I don't think you will make the top basket.. and you will have to position yourself within a few feet of the other baskets.

If you still want to use that motor set-up, you could use larger wheels? Or you could look into a gear box with a lower gear reduction. My team is using this gear box with that motor. The reduction is 3.67: 1. We are also using 8 inch wheels. Our estimated exit velocity is: 9.5 m/sec (includes a 1/4 speed reduction). That would allow for us to shoot from 15 ft away- for the top basket. If these motors come back in stock we are going to use them instead and get an exit velocity more about 14.3m/s (also includes 1/4 reduction). We could then potentially sit 30 ft away.

If you haven't already you might want to find a trajectory calculator or run your own equations in Excel.

[JamesCH95]

You want seemingly insane roller speeds to get good shots.

Squirrel has posted some really good videos and specs on his team's shooter. They're rocking about 4,000rpm axle speed with a single 8" wheel. That's about 42 m/s surface speed on their shooter.

Our shooter is substantially slower, around 6.4m/s and we're getting around 2.3m range with a high-arc shot (65deg from horizontal) with no roller slippage. This is about 70% of 'ideal'. Our range is very limited even though we have over twice the motor power of Squirrel's shooter. We are rebuilding our prototype for a much faster roller speed and using smaller, lighter, less powerful motors.

TL;DR notes:

-go for very fast roller speed
-ball-park 70% free speed for ideal trajectory calcs
-power/torque matters, but rollers/wheels will store lots of energy

[Cem8301]

Originally Posted by JamesCH95

You want seemingly insane roller speeds to get good shots.

Squirrel has posted some really good videos and specs on his team's shooter. They're rocking about 4,000rpm axle speed with a single 8" wheel. That's about 42 m/s surface speed on their shooter.

Should that be in ft/sec?

[jeremy5561]

OK I'll talk to my team about using the planetary gearbox. We have more torque than we need.

[jeremy5561]

Ok well I made an excel spreadsheet to calculate this stuff and I figured that if we use the sprocket we're going to lost more speed, where if we use just the gearbox we could shoot at 10 m/s. Is there any way to directly connect the 8mm shaft to a wheel?

How would I attach two wheels to one axle and directly turn that axle from the output of the gearbox?

[JamesCH95]

Originally Posted by Cem8301

Should that be in ft/sec?

Nope. meters/second

Check out this thread: http://www.chiefdelphi.com/forums/sh...hreadid=100540

If they're indeed running a CIM geared up 22:15 with a 6" kit wheel they're rocking about 190ft/s or about 58m/s tangential speed.

I would theorize that nearly all of the imparted energy from most roller/wheel shooter systems comes from the kinetic energy stored in the rotating mechanisms.