What are the advantages to having two wheels in a linear shooter? Disadvantages?
your frisbee has better momentum with two wheels. Unless your motor is good enough that it can take care of that. Also to make sure that after you shoot it reaches top speed faster with two since when using only one youre asking your motor to do more work. Hope this helps!
the down side is that youre using an extra motor and adding some more weight.
Does it have better momentum because of the increased contact? And wouldn’t the frisbee have the same speed of the last motor?
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.
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
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.
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
What’s wrong with a circular path?
Search is your friend. Discussed at length in that thread.
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.
Others answered, but here is the physics 1 equation:
The impulse momentum theorem
F Δt = m Δv
How much force AND how long you apply it determine your change in momentum. More contact = more time
Has anyone out there tried three wheels in a linear shooter?
Our team is also interested in people’s thoughts and/or experiences with a 3 wheel linear shooter. If we go with a linear shooter we’re thinking of allowing to add a third wheel if it should be necessary.
There are other ways of adding speed to a two wheel shooter, such as a pneumatic or spring trigger mechanism. Until we finish testing, we’re keeping all options open for now.
Graham.
*I’m skeptical that a third wheel is necessary.
My engineering intuition tells me that the first wheel should be governed at a speed approx 75% of the second wheel. You should then be able to get plenty of exit velocity without slipping.
Has anyone out there tried a speed difference of this magnitude?
We’re hoping two are sufficient. Our tests indicate that it can probably be done with two.
I also question why a speed differential is needed. Why not just impart as much energy as you can with each wheel? We’re not looking to maximize efficiency here, just fire discs as fast as possible. What is wrong if the first wheel got the disc to near full speed, then the second wheel doesn’t have to do much more.
Graham.
By that logic why would you need a second wheel if you’re attempting to impart as much energy as possible with the first wheel? As stated, the idea behind the two wheel shooter is because of the contact time between discs and wheels. If you use the first wheel to accelerate the disc and the second to propel the disc, you get comparable results to a circular shooter.
I didn’t say it was “needed”. I was speculating that you can squeeze more performance from a given shooter by doing so.
Why not just impart as much energy as you can with each wheel?
If that’s your goal, then the first wheel should be driven slower than the second.
There’s a wheel speed above which the exit velocity of the frisbee from that wheel actually starts decreasing, presumably due to excessive slipping. The first wheel reaches this point before the second one does because the frisbee speed coming into the first wheel is so much slower than for the second wheel.
I think if you can control the speed of the 1st wheel from like 40% to 75% of the second wheel, you can also effectively control the distance. Am I correct?
The second wheel probably has more effect on the exit speed.
May I suggest the following equality:
sum(“wheels”) from 1 to infinity = “belt”
I know it’s not really the same, but still.