Shooter Aiming with Tables

[btcshields6]

So Ether, I'd like to be able to determine these experimentally, but due to some build constraints, I'm left without a shooter to test. For now. I'd like to start by getting a table of theoretical values. Is the only way to go about it using the stuff you described in your most recent post?

Solving this has got my coach and I (a physics teacher) scratching our heads.

[James Juncker]

If I could link you over to my post of ether's trajectory calculator with my additions to the base framework of it all, I gave perspective to the field as to where you would be shooting from and the distance as well as ideal shooter values http://www.chiefdelphi.com/media/papers/3217

The base equations didn't change however I put in a few approximate values of upper and lower gates where the boulder this year would go into the goal. the range finder has lines placed on the field for where the boulder would need to shoot from to get into the goal. if you work out the direct output from your mechanism to the ball for speed you could also then adjust the rpm for launch velocity. at the peak time on the sheet the Velocity in the Y direction should be equal to 0 and would allow for you to get the ball into the goal.

I would recommend as high of an entrance point into the goal so that if there are variations in power or rpm the boulder will still pass the plane of the goal.

[Ether]

Originally Posted by btcshields6

For now. I'd like to start by getting a table of theoretical values.

Solving this has got my coach and I (a physics teacher) scratching our heads.

It's not clear to me what you're having trouble solving.

In my earlier post I gave the formula for finding launch angle and launch speed, given the coordinates of the apex of the parabola (the horizontal and vertical distances xp & yp from the launch point to the center of the goal).

This assumes there is no air drag, so it may be quite inaccurate.

If you want to include air drag, you'll have to measure (or calculate) the relevant drag coefficients... or measure the terminal velocity of the ball.

And when you include air drag, I don't think there's a closed-form solution. You'd have to use numerical methods and iteration. Not hard to do, just not as straightforward as an explicit solution.

Does that help? If you still have questions, please keep asking until it makes sense.

[btcshields6]

Thank you. I think I misunderstood your earlier post.

I'll try again tomorrow and ask again if I get stuck and can't figure my way through.

Benjamin

[btcshields6]

We actually had a bit of a breakthrough today. One of our teachers figured out that if the apex is at the same height (the height of the goal remains constant of course), the y-velocity and time to the apex must be the same. If the y-velocity is the same, then we can enter it along with our other variables, and calculate the combined velocity, angle, and distance. Now we have a corresponding velocity and angle for each distance. We haven't factored in drag, and I'm not sure we will, since these values were just some estimates to get us ready for the experimental value.

But we're happy it's done. Thank you all for your help!

[Turing'sEgo]

The next step is to implement it on the robot. Hope all goes well!

http://i.lvme.me/dljyhoh.jpg

[Ether]

@btcshields6: If I'm reading your last post correctly, you're going to write some code using a lookup table based on no-air-drag computed values, and after that gather empirical data to populate the lookup table. Yes?

[btcshields6]

@Turing'sEgo Thank you!

@Ether That is my plan. Sometime this week we'll be able to begin testing with our actual shooter.

I am not actually sure how to write code to reference a lookup table. I was going to start looking for related Labview documentation. If anyone has a link they can post here I'd appreciate it.

Thanks,

Benjamin

[Mark McLeod]

Here is an example of lookup tables from the NI developer community:
This one is good for use with a spreadsheet.
https://decibel.ni.com/content/docs/DOC-14653
It may need a bit of updating to LabVIEW 2015 (what we're using for FRC 2016).

A little less complex is something like Interpolate 1D Array found in the palettes under Programming->Array
or maybe Search Ordered Table.vi found under Mathematics->Interpolation & Extrapolation

[Greg McKaskle]

Mark beat me to it, but I generally use the Interpolate 1D function.

Your lookup table is an array of number. They can be typed into a constant or be read from a file as a 1D array. Be sure to run the subVI and enter some values by hand and ensure that the output values make sense.

Greg McKaskle

[btcshields6]

So I'm looking into using the Interpolate 1D Array. How can I convert my spreadsheet into the 'array of numbers or points' that the function requires? Also, should I store the file in the project folder?

Thanks.