Equation for joystick input to Talons

[jtrv]

hello all, we currently have decided to look into tweaking the operator controls of driving the robot. we currently have the joystick to Talon equation as a linear equation: y=x. What the joysticks get is sent to the talons. Each get values between -1 and 1. I'm sure you know this. y is what the Talons receive and x is the joystick input. What we're looking for is an equation that starts out slow, but once you get x to be around .4 to .6, y should be roughly equal to the x value. Past that, the y value should rapidly increase until you reach where x is around .75 or .8, where it should become very close to 1.

Example point table:

x,y

0,0
.1,.005
.5,.5
.6,.8
1,1

I know it may not be much, but I am also wondering what you may have used. this isn't really an issue with sensitivity, we are just looking to drive a little more slowly when the joysticks are lightly touched, but once they get past .6 or .7, drive very closely to full power if not full.

I understand we can do this with simple if statements, but an equation would make it... "flow"... much better.

Thank you for your help

[Ether]

Something like this?

Here's how to do it.

[apalrd]

You could use an interpolation table.

Basically, you make a table like you already made, and the software linearly interpolates between the points. Super easy to write, calibrate, etc.

I wrote a LV VI to do this (it's in the BuzzLib download here). I can try to dig up my C version if anyone wants it.

[jtrv]

Here is an sketch I drew up, I'm not entirely convinced that if I found it's equation we would use it, but it was my first idea.

http://i.imgur.com/57TuSZw.jpg (ignore the scribble )

@ the posted image:

yes, i have come across those equations in my searches. i would like something that changes concavity once it reaches roughly .5. nothing extremely fancy like my sketch, but something of the likes. my sketch doesn't reflect this paragraph, btw. i'm probably confusing you all. sorry about that.

[Ether]

Originally Posted by jtrv

i would like something that changes concavity once it reaches roughly .5. nothing extremely fancy like my sketch, but something of the likes.

Post or PM me a set of (x,y) points defining your desired curve, and I will generate a function for you.

Or I can show you how to do it yourself.

[jtrv]

Originally Posted by Ether

Post or PM me a set of (x,y) points defining your desired curve, and I will generate a function for you.

Or I can show you how to do it yourself.

I've know the basics of how to do it with f'(x) and f''(x), but the only problem I run across is changing the way the curve "bends" per se... If you could PM me how you do it that would be fantastic.

[apalrd]

If you must have an equation, you could type your in->out pairs into Excel, graph them (x vs y), then add a trendline and use the equation.

[jtrv]

Originally Posted by apalrd

If you must have an equation, you could type your in->out pairs into Excel, graph them (x vs y), then add a trendline and use the equation.

Will try that now, completely forgot about this. thank you.

[Ether]

Originally Posted by jtrv

I've know the basics of how to do it with f'(x) and f''(x), but the only problem I run across is changing the way the curve "bends" per se... If you could PM me how you do it that would be fantastic.

apalrd beat me to it. see his post.

[connor.worley]

http://www.wolframalpha.com/input/?i...nd+%281%2C1%29

Wolfram Alpha can do some magic... try tweaking this around a bit

[jtrv]

Thank you for that wolframalpha link! I didn't know you could do that. We will definitely be tweaking that. I've found an equation to use for now by means of Excel - y = 0.9703x^5 - 2.673x^4 + 0.3901x^3 + 2.0981x^2 + 0.2075x. It seems to look good and we will be testing it on the drive train soon. Thank you to all your posts! Definitely helped.

[apalrd]

If you have even powers in your equation, you will have to take the abs of the input variable and multiply the output by the sign of the input, because you will lose the sign on the even terms but not the odd terms.

An equation with all odd powers would not do that.

[jtrv]

Yep, I've got that accounted for.

[ekapalka]

For a basic interpolation given a few points, this should give you an idea. Your particular data points wouldn't produce a perfect equation fitting into ±1 range, but that can be fixed with some scaling. I would really like to know if there's an alternative to doing it this way, though :)

[Ether]

Originally Posted by ekapalka

I would really like to know if there's an alternative to doing it this way, though

Cubic splines