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 (http://www.andymark.com/product-p/am-0914.htm) 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 (http://www.andymark.com/product-p/am-0912.htm) motor will do the job. I would attach it to the CIM-sim gearbox (http://www.andymark.com/product-p/am-0932.htm) and then attach it to this sprocket (http://www.andymark.com/product-p/am-0505.htm). A chain and another sprocket (http://www.andymark.com/product-p/am-0737.htm) 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 (http://www.andymark.com/amplanetary-p/am-0002.htm) with that motor (http://www.andymark.com/product-p/am-0912.htm). 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 (http://www.andymark.com/product-p/am-0821.htm) 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]

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]

Should that be in ft/sec?

Nope. meters/second

Check out this thread: http://www.chiefdelphi.com/forums/showthread.php?threadid=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.