Designing a Disc Golf Launcher: Feasible & Accurate?

[Kaura]

For my Engineering class I have to work with three other people to design a device that launchers a disc golf. So far we have a basic design plan but we are unsure if it is actually viable.

Essentially there will be a platform that holds the disc in place and will be propelled by 2 to 4 springs of length 1 to 2 feet. The platform will travel on wheels along a set of rails on either side and will push the disc until hitting a stopper causing the disc to continue forward. We also need to give the disc significant spin and are planning to apply some sort of friction to one edge of the disc during its acceleration to give it a moment.

We have a project budget of $40 which is a significant constraint. We don't have specific numbers at the moment aside from the above measurements so my basic question is whether or not this design seems feasible and realistic. We need the device to shoot the disc around 40 feet or more ideally and it has to be reasonably accurate as it is to be used in a competition at the end of the semester where scoring into the disc golf goal gives a decent bonus score.

I apologize if this is vague at the moment but I can post an AutoCAD draft we have later on when I get the chance. Any feedback on this idea is appreciated. I am primarily curious if the springs will be able to hold enough potential energy to shoot the disc proficiently without exerting too much internal force on the device. Thanks for any feedback.

 

[berkeman]

I believe another word for the object is Frisbee, right?

Have you looked at existing Fisbee launchers and throw assist clubs? Here is one that is commonly used when playing with dogs (to make it easier to throw consistently at distances far enough to be interesting for the dogs). You could just adapt one of these with a single spring to fling it about a pivot attached to the bottom, for example:

https://www.disabled-world.com/pics/1/folf-club.jpg

Or you could make something like this home-brew launcher in this YouTube video (this is sweet!):

 

[Kaura]

That was one of our possible designs however I forgot to mention that a project constraint is that the device must fit within a boundary of a cube with side length 2.5 feet.

That means that a design similar to the one in the video would have to use a path of rotation with a radius at most about 1.25 feet which could be doable but could also potentially not provide the necessary initial velocity and spin.

The main reason we chose springs instead was due to the fact that we can just find the best type of spring to provide the required energy to the disc.

 

[jrmichler]

Something like a clay target thrower? $29.99 from Midwayusa.com and numerous other sources.

 

[berkeman]

That was one of our possible designs however I forgot to mention that a project constraint is that the device must fit within a boundary of a cube with side length 2.5 feet.

That means that a design similar to the one in the video would have to use a path of rotation with a radius at most about 1.25 feet which could be doable but could also potentially not provide the necessary initial velocity and spin.

The main reason we chose springs instead was due to the fact that we can just find the best type of spring to provide the required energy to the disc.

So it looks like one of the things they are looking for in the better team entries in this project is some research into what makes a Frisbee fly well and far. What research have you done into this so far? Can you post some links into the Frisbee physics and aerodynamics that you have found so far? What is the minimum spin rate with respect to linear velocity that gives stable flight? And how should you factor that into your linear spring based design?

BTW, after seeing your size constraint and watching the YouTube video that I posted, I think I have a pretty clever variation on his design that is much more compact and just as effective. Can you say what you think that improvement might be?

BTW2 -- I was also thinking about an unusual slingshot based design that also imparts sufficient spin to the Frisbee. I may have to try building one of these this weekend to try it out... Need to find a dog somewhere...

 

[Kaura]

So it looks like one of the things they are looking for in the better team entries in this project is some research into what makes a Frisbee fly well and far. What research have you done into this so far? Can you post some links into the Frisbee physics and aerodynamics that you have found so far? What is the minimum spin rate with respect to linear velocity that gives stable flight? And how should you factor that into your linear spring based design?

BTW, after seeing your size constraint and watching the YouTube video that I posted, I think I have a pretty clever variation on his design that is much more compact and just as effective. Can you say what you think that improvement might be?

BTW2 -- I was also thinking about an unusual slingshot based design that also imparts sufficient spin to the Frisbee. I may have to try building one of these this weekend to try it out... Need to find a dog somewhere...

I plan to run a few calculations later. I am going to use initial linear velocity of 20.0 m/s and rotation of 30.0 rad/s which I think are both reasonable goals. The first issue is I cannot seem to find the moment of inertia for a standard disc golf. I don't think it is close enough to a standard disc to use the associated equation and I cannot seem to even find its mass distribution so I am not sure how to proceed from here. Anyone got any ideas or resources? I need the moment of inertia to calculate the total energy transferred to the disc by the device.

 

[Kaura]

After looking for a while I found a mass distribution of half uniform and half on the edge which may or may not be correctly. Anyway, using this along with a mass of 0.175g and radius of 0.137m gave a moment of inertia of 0.0025kgm^2 which I also saw posted somewhere probably using the same distrubution as me. If this is incorrect please correct me someone, thanks.

 

[berkeman]

I cannot seem to find the moment of inertia for a standard disc golf. I don't think it is close enough to a standard disc to use the associated equation and I cannot seem to even find its mass distribution so I am not sure how to proceed from here. Anyone got any ideas or resources?

Roll one down a ramp...

 

[Kaura]

Roll one down a ramp...

Good idea actually. I am going to do that when I get my hands on a disc which will be soon hopefully.

Also here is some preliminary work I have done. I am sure it is riddled with errors and probably far off from any real values but I managed to determine that the spring constant should be might be around 224 N/m which seems pretty high.

 

[berkeman]

224 N/m which seems pretty high.

I think it's coming out high because your launcher arm looks like it weighs 4 times the Frisbee's weight. Can you work on lightning the launcher arm? Do you have any sketches of your current launcher design?