2 wheels vs 1 wheel in a linear shooter

[ksafin]

Our understanding is the additional contact time results in higher speed.

With one wheel, the frisbee just touches the wheel for a fraction of a second. Two wheels allow for a preliminary speed-up followed by a final acceleration and fly-out of the shooter.

A circular pathway shooter allows vast amounts of contact but has its own flaws. It seems like the linear shooter compensates for this lack of contact by having two wheels.

[wireties]

Originally Posted by ksafin

Our understanding is the additional contact time results in higher speed.

Additional contact helps as does avoiding slippage but I think it is more about the relative rotation. The max velocity you can impart with one wheel is half the tangential velocity (because the frisbee is also rotating in proportion to the wheel's rotation and in the opposite direction). With two wheels you can approach the tangential velocity.

You want the firsbee to spin for stability so if using 2 wheels I think one might try running the two wheels at slightly different speeds.


HTH

[Ether]

Originally Posted by wireties

With two wheels you can approach the tangential velocity.

I believe the 2 wheels we are talking about here are on the same side of the frisbee (i.e. both wheels are opposite the guide rail).

With 2 wheels, the maximum frisbee speed is still half the wheel tangential velocity.

[ctccromer]

Just out of curiosity, has anyone tried using two wheels with one on each side of the shooter? My team prototyped the common build with 2 wheels on the same side, but I'm curious how the other 2 wheel build would work

[pleaseignore]

What's wrong with a circular path?

[CalTran]

Originally Posted by pleaseignore

What's wrong with a circular path?

Search is your friend. Discussed at length in that thread.

[Ninja_Bait]

Originally Posted by ctccromer

Just out of curiosity, has anyone tried using two wheels with one on each side of the shooter? My team prototyped the common build with 2 wheels on the same side, but I'm curious how the other 2 wheel build would work

Frisbees, in general, work by spinning, so having wheels on only one side is just a more elegant and efficient way of imparting spin.

Here's another reason why two wheels is theoretically better than one: Let's say you spin your one wheeled shooter up to a set speed. When the Frisbee contacts it, momentum will be lost, so the Frisbee will leave at less than half the original set speed. The motor can compensate by accelerating the wheel back to its original speed, but more likely than not, the Frisbee will already be gone by then. Two wheels allows you to "sacrifice" the first wheel's momentum so that you don't have as much of a momentum loss at the final wheel.

This is also why a curved track or a belt on a linear track is nice for hurling discs because there is a long period of contact during which the flywheel/Frisbee system recovers any lost momentum.

Of course, I may be unintentionally exaggerating - I have no idea whether the loss of momentum is actually consequential, since I haven't done any of the math.

[Andrew Zeller]

Originally Posted by Ether

With 2 wheels, the maximum frisbee speed is still half the wheel tangential velocity.

I also followed your math here:

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

I understand that the rotation of the frisbee as it contacts the wheel causes less than its full velocity to be transferred in an ideal situation, however why is it that the maximum exit velocity of the frisbee will theoretically be one half that of the tangential velocity of the wheel?

[Ether]

Originally Posted by boarder3512

why is it that the maximum exit velocity of the frisbee will theoretically be one half that of the tangential velocity of the wheel?

Think of a car traveling down the highway at 60 mph.

The geometrical center of each tire is traveling at 60 mph.

At any instant in time, the bottom of each tire is traveling at 0 mph, and the top of each tire is traveling at 120 mph.

It's the same with the frisbee.

[Andrew Zeller]

Originally Posted by Ether

Think of a car traveling down the highway at 60 mph.

The geometrical center of each tire is traveling at 60 mph.

At any instant in time, the bottom of each tire is traveling at 0 mph, and the top of each tire is traveling at 120 mph.

It's the same with the frisbee.

Makes sense - thanks for the explanation.

[Ether]

Originally Posted by wireties

Oh - sorry! Why would anyone want to do that?

To allow for more contact time with the frisbee so the acceleration can be distributed over 2 wheels instead of just 1, to minimize slipping and improve final exit speed and consistency.

Lots of discussion going on about this in this thread, and other threads.

[Squeakypig]

https://www.youtube.com/watch?v=ARUhI8Qob5w

This is our prototype 1 wheel shooter. We made a 2-wheel shooter but the video we have of it is poor in quality. We will post a new video of the 2-wheel in the very near future.

Here is the video anyways: http://www.youtube.com/watch?v=EYpbyVbMbD8