Shooters

• From zachary jj’s flywheel shooter basics for designers and prototypers
  Flywheel Shooter Basics for Designers and Prototypers

Slow-down

You'll notice that when you put a ball through your shooter, it will audibly slow down a fraction because it is transferring energy from the flywheel to the ball. The speed that the ball exits (if it has actually accelerated to the flywheel's speed) will be closer to the speed of the flywheel when it slowed down.

To decrease this slowdown you can either increase your flywheels momentum (adding mass) or increase the motor power (add another motor, etc.)

A side-effect of adding more mass is your motor will take longer to come back up to its free speed. You may find that you don't need more momentum or power to shoot from small distances.

Contact time

The ball needs a bit of time to actually catch up to the speed of the flywheel. Having the ball spend a longer amount of time in contact with the wheel (by making the arc longer, using two shooter wheels in-line) can help this. Again you might want to check if you need to worry about this by taking a slow motion video of your ball traveling through your shooter.

Compression

The amount of compression on the ball is usually measured in the number of inches that the ball is "squished" by the shooter as it passes through the wheel / hood. I have no idea how or why compression has such a large effect on the performance of a shooter, but if I could guess it would be increasing grip so that the ball accelerates to the speed of the flywheel.

In 2020, Many teams have found an area between 2" and 3" of compression to be good for long distance shots, but if you're shooting from up close 1" works also. I would definitely recommend testing different amounts of compression as it is easy (given the right setup) and makes a huge impact on your performance.

The wheel

A smooth and even wheel is really important in our experience. The AndyMark compliant wheels are good but we've found with hard balls (ping pong balls), depending on if they exit with the spoke or the open part, the shot will go at a different range. they also might explode if they go too fast

Teams have had good luck with Fairlane wheels (available from McMaster-Carr), AndyMark stealth wheels, AndyMark High Grip wheels, colson wheels, etc.

The Crowned Pulley

https://woodgears.ca/bandsaw/crowned_pulleys.html

This page gives some insight on how crowned pulleys work and what they do. What it means in a shooter context is that a "crown" on a roller will pull a ball towards the peak of the crown, which is pretty counter-intuitive.

This video illustrates this effect.

Monkey Box - Shooter Ball Centering

Motor & Reduction Selection

TLDR:

• Use powerful motors

• 6krpm is usually a pretty good range to start at

This is a performance curve for a 775pro motor running at 12 volts, and I

 have annotated in MS Paint highlighter the “comfy zone” for a motor to 

operate in. As efficiency rises above 50%, more of the electrical power 

being put into the motor is being turned into mechanical power than heat

 energy. However, what you may notice is that even when inside the 

“comfy zone”, at the leftmost side (low RPM, high current) a motor may 

still be producing 450W of heat. (Power = Voltage x Current.) In fact 

there is yet another graph that shows how long this particular motor 

will last when running at this peak power.

The motor totally dies after about 90 seconds, and no doubt its 

performance would have been permanently reduced at a point well before 

that. This particular motor actually needs to be running at closer to 

70W of heat power so it can dissipate its heat fast enough not to burn 

out. Looking back at the data we see that at about 20 amps and roughly 

16krpm, the motor is running at about 70% efficiency, much better than 

the <50% from before. The catch is that its mechanical power gets 

reduced to just 180W, almost half of the peak power.

But how do we get our motor to run at that higher speed?

All of these numbers - current, rpm, power, and torque are all related. 

When you want to increase efficiency your speed must get higher and your torque must decrease. What this tells us is that the motor needs to be pushing less hard in order to avoid burning out. When they don’t have to push as hard, they can run faster. Sounds a lot like a person!

One way to reduce the amount of torque the motor needs to produce is to increase the gear ratio so that the torque on the end is higher than the motor, but the speed is lower. It makes it easier for the motor, so it can run faster, and thus cooler.

In 2016, 254 ran a 30:19 reduction with two 775pro motors for a flywheel speed of ~6krpm. It could shoot a whole exercise ball!

Sometimes a motor simply doesn’t have enough power to achieve what it needs to - it can’t provide enough 

speed and torque at the same time. (Speed x Torque = Power). In this case, you need a more powerful motor. (Or use another one of the motor you're already using)

Wow, look at this motor! When generating only 70W of heat, it produces almost as much power as the 775pro at full power! Not only that, it’s running at 80% efficiency.

There are also motors that, when run at their peak power, don’t burn out for a while. They still produce a lot of heat, though!