# Linear Path Shooter vs. Circular Path Shooter?

Has anyone considered a linear path shooter for their design?

Everything I’ve seen on YouTube is built with a circular path. I’m curious if this was for design convenience or there is some magic to the disc following a circular path. My team has proposed creating a linear path shooter with two parallel motors to “spin” the disc down the launch path. Has anyone tried this? If it works, it would make a nice compact shooter.

Beaten to the punch, but:

in particular

A circular path shooter allows more distance while the disc is in contact with your shooter wheel. This will allow the disc to speed up to more closely match your shooter wheel speed. That isn’t necessarily good or bad. Last year it was important because you needed very consistent speed and spin.

This year, I’m guessing not so much.

A linear shooter seems, from all that I’ve seen, much easier to deal with. Easier to load, easier to fit, and potentially easier to manufacture (you’ve got to get that curve just right, and keep it that way).

This comes at the expense of being slightly less accurate and slightly less powerful. Our team hasn’t made it that far into the prototyping stage yet, so I can only speak from what I’ve seen others do.

As has been said, its a matter of contact speed.

The circular pathway allows more contact time between your spinning wheel and the frisbee. This gives the wheel more time to accelerate the frisbee to more closely match its own tangential velocity.

In a linear pathway, the wheel touches the frisbee for a fraction of a second; thus, a fraction of the speed of the wheel is delivered to the frisbee.

Of course, there’s dark magic with various other variables such as the compression of the frisbee, space between wheel and a guide rail, type of wheel, surface area of wheel, as well as the torque and speed of the accompanying motor.

It’s a matter of testing

What says the linear shooter only touches the frisbee at the tangential point of the wheel? I can think of a way to have the frisbee in contact with the mechanism for a longer period of time.

A linear pathway with a belt along the length to give the spin and forward speed might just do it.

So you’re going to run a linear belt, essentially a conveyor on it’s side, at thousands of rpm and expect that to work the same as a wheel going thousands of rpm?

We built a prototype and it had two parallel wheels as you were saying you might try. I must add that it was in a linear fashion. But what i really want to tell you is that the frisbees go much further if one side is stationary compared to both sides spinning. Additionally our team has not tried to make a half circle shooter design only a linear so i can not take about that aspect of your question. What i can ask you is why would you use a half circle shooter that takes up much more space especially this year with smaller robots rather then building a linear shooter that works just as well?

In our tests in the shop we have found that linear shooters are not as accurate as circular shooters and don’t shoot as far. I hypothesise that it is because the wheel doesn’t get to work on the disk as much (W=FxD) and will therefore put less energy into the disk before it is released.

Here are videos of our attempts:

they should all be on there.

Theoretically there is no difference. For a given contact length, CoF, compression, and surface speed, and a given energy supply (including any storage of rotational energy via flywheel effect) the shape of the pathway is irrelevant.

Theoretically.

*You are not limited to one wheel with a linear shooter design. Watch the videos posted here.

I am not saying that a belt is the best way, rather just pointing out that it is a method that would work or maybe I should say, should work.

A multi ribbed flat belt will run at 3600 rpm with no problem at all on a 4 inch diameter wheel which translate to a very fast linear speed.

It translates into approx 21 mph, assuming no slipping.

3600 rpm / 60 min/sec = 60 rev/sec

60 rev/sec * pi*4/12 ft/rev = 62.8 ft/sec

62.8 ft/sec / 2 = 31.4 ft/sec

31.4 ft/sec * 3600 sec/hour / 5280 ft/mile = 21.4 mph

In Lunacy we ran timing belts instead of wheels in our shooter, in an attempt to compensate for the holes in the orbit balls. The belts were driven with only a small gear reduction from a CIM motor, and we never, at any point in the season, had an issue with them. They never came off, never wandered, no issues at all. A lot of design and work went into building a stable, adjustable system that would allow us to ensure everything was perfectly parallel, and using belts with teeth in them also helped.

I’m not saying I recommend going this path, but it certainly is possible to get your belts up to speed and keep them there without any issues.

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Ether. That 31.4 ft/sec sounds like it might do the job. I wonder what a CIM motor at full speed with a direct drive 6 inch wheel would be? Just don’t have the CIM specs handy.

A circular shooter gives the Frisbee spin and more accuracy

It can be argued that 1 circular shooter may use less space than 2 parallel shooters, if you are trying to minimize the length of the shooter, and width doesn’t matter.