

Joined Apr 2012
5 Posts

Help!
who know the algorithm for exponential curve in RC.
Hi, guys:
I'm building a radio control transmitter, software is going to be finished. But i encounter a hurdle. I don't know the algorithm for exponential cruve. In RC system, when we input a number that range from 100% to + 100%,we can see a exp curve in the LCD screen, can anybody impart the exponential algorithm to me? Thank you very much. 







Joined Apr 2012
5 Posts

Thud_Driver:
Thank you very much! I am about to have a try! 



Quote:
FYI, I was looking for the simplest function that would look like the generic graphs we've all seen showing what "expo" does. Keeping in mind that this might be implemented on lowpowered hardware and math functions would likely have to be implemented from scratch, I decided to simplify exponential functions to only the lowest order terms, i.e. linear and cubic. As hardware (microcontrollers) continue to get more and more powerful, it is probably now practical to implement more sophisticated functions. In particular, I think the tanh() and sinh() functions are worth investigating. It looks to me as though the sinh function is what we want for "soft around the centre" exponential, and tanh looks like the way to get the opposite behaviour. It would be interesting to represent sinh and tanh as polynomials, keep only the first two or three terms, and see what comes out of that. Quote:
Most likely including the x^5 term in addition to the x and x^3 terms I used would do the trick. As a corollary, I think the reason why all the formulae you looked at agreed with each other is this: all of them are essentially cubic representations (i.e to order x^3) of exponential functions with the same boundary conditions. Flieslikeabeagle 




Actually, I tried higher order fits when curve fitting the data I took from the transmitter and the 3rd order fit nicely enough. In fact, I just went back to the original spreadsheet and did a 5th order fit and it was some improvement on some of the data. Considering that taking data from the Tx doesn't get data as precise as you'd like, I thought the "simplified" 3rd order polynomial was good enough.




Quote:
Actually my personal preference is for no "expo" at all. I simply adjust the fulldeflection control throws to give the model the roll, yaw, and pitch rates I want. With no expo, the controls feel much more precise and linear to me, and this approach works well for the kind of flying I do, though I have no doubt it wouldn't work for extreme 3D flying. Flieslikeabeagle 





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