Sine cosine potentiometer - Page 1
Forum section: electronics / general

author: woodchips
author_rank: Frequent Contributor
timestamp: January 21, 2017, 12:13:16 pm
content: Another rather nice piece of eelctromechanical engineering from the 1950's.This is a sine cosine pot. A square mat of resistance wire with two sliding contacts at 90 degrees running over it.Came from a coupling unit used somewhere in an aircraft navigation computer, electromechanical, an air data computer. Had several servo motors, synchros and resolvers in it. Used to convert positions from or to cartesian co-ordinates judjing by the dials. Possibly from the VC10?

author: SeanB
author_rank: Super Contributor
timestamp: January 21, 2017, 02:43:37 pm
content: Used in a lot of older aircraft, not only in the autopilot. Did part of the conversion from angle and amplitude, from a beacon or other source, to a form that could be displayed on a moving map film unit.Had other uses as well, but those were rather proprietary in the aircraft, and often were used in the fuel system to provide correction factors.There often it was done with a biased resistance mat, with a resistance slope across it, used to give a non linear output using the standard pot style, the resistance measured across 2 points would vary depending on the position of the slider on the mat, and you could trim this to get the correct law in production.

author: Benta
author_rank: Super Contributor
timestamp: January 21, 2017, 07:36:55 pm
content: Beautiful!I love this kind of components, where mechanical and electrical precision come together.Like the multi-gang tuning caps in old radios.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: February 10, 2023, 10:08:58 pm
content: first sorry for rewake of this topic, but there are no other topics about this..and it really needs to go here for better search in the future.Anyways I finnally scored a handfull sine cosine potentiometersand wanted to demo they can be used to rotate a flat 2D image normally shown on a scope in XY mode,so here you go :https://youtu.be/sEgsdVFRDUU

author: berke
author_rank: Frequent Contributor
timestamp: February 10, 2023, 11:05:37 pm
content: Quote from: oz2cpu on February 10, 2023, 10:08:58 pmVery nice. I love this kind of stuff. Your rotating plot deserves to be displayed on a CRT though.Also, a logical extension of this would be a "2D" device that allows you to define a general 2D linear transformation by moving two cursors each with two degrees of freedom each, defining where the X and Y unit vectors go. I wonder if that kind of contraption was ever considered.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 11, 2023, 02:27:36 am
content: Nice! In case anyone is wondering what the rotation is based on, why you need four signals into the sin-cos potentiometer, and why you need to do that addition (with resistors) and difference (with opamp), is that$$\begin{aligned}x^\prime &= x \cos \theta - y \sin \theta \\y^\prime &= y \cos \theta + x \sin \theta \\\end{aligned}$$is how you rotate 2D coordinates around origin (0,0), with \$(x, y)\$ being the coordinate signals from the Arduino+DAC board, and \$(x^\prime, y^\prime)\$ the coordinate signals provided to the XY scope.(Sorry for pointing out the obvious! I just thought it might help clarify how that works, for those not familiar with rotations and 2D math. I like 2D and 3D math myself, from linear algebra to projections to raycasting and raytracing.)

author: oz2cpu
author_rank: Frequent Contributor
timestamp: February 11, 2023, 02:28:02 pm
content: thanks a lot for your comment, i belive that is the math lines i try to performhow ever i finally solved the scaling issues, ha ha how cool,spend / wasted another day just to get all that right :-)video updatehttps://youtu.be/xLDlZ7sRD1I

author: LaserSteve
author_rank: Super Contributor
timestamp: February 11, 2023, 04:39:55 pm
content: The other corrections for vector display:X Axis:shear: add coefficient * Ykeystone: add coefficient * (X * Y)linearity: add coefficient * (X^2)bow: add coefficient * (Y^2)pincushion: add coefficient * (X * Y^2)Y Axis:shear: add coefficient * Xkeystone: add coefficient * (X * Y)linearity: add coefficient * (Y^2)bow: add coefficient * (X^2)pincushion: add coefficient * (Y * X^2)Shear is add a summing op-amp and a potentiometer. You might want to try that next.Steve