diff --git a/README.md b/README.md index ec4b034420bf44460d202e4e0fe85d13f9a77a3b..99fdfd5027d885603cf5d071fd0b25af04ad2af2 100644 --- a/README.md +++ b/README.md @@ -8,7 +8,7 @@ I want an encoder! Encoders<sup>1</sup> read position, generally by counting 'ti Then, you add the ticks together to get your position. In order to detect direction, a technique called 'quadrature' is used: - + Super simple, very neat. Here's picture of a *fancy* encoder: @@ -34,7 +34,7 @@ angular resolution = 360 / (((PI x D)/pole_length) x 160) Of course, I have to set the circumference equal to an integer value of magnets. I wrote a quick spreadsheet for this, and get that w/ a Diameter ~ 100mm (where the gearbox currently stands) I can get 0.017 deg/step with a 2.4mm pole pair, and ~ 0.03 deg/step with a 4mm pole spacing. Nice. - + Now, this is not so straightforward. The important thing to remember is that **Resolution != Accuracy** - while I have ~ 0.03 deg / step, those steps are not exactly mapped perfectly in a circle. I will actually be referencing magnets that are glued in place - so my glueing and magnet placement would have to be *perfect<sup>4</sup>* for Resolution to = Accuracy. In addition, not all magnetic fields will be identical, etc. @@ -154,6 +154,34 @@ Ok I got this mostly together - made one mistake, where the motor floats a bit b Before I get into the meat of programming interrupts etc for this, I'm going to first get some voltage on this board alone and scope the lines to see that I am getting (1) the voltage I want out of the magnetic-field sensing pin, and (2) the ticks I want on the ABI lines. +So, pretty upsetting. I am getting the bad magnetic field warning from the AS5304. The Index is High while A and B are low (the warning) and the output from the CAO (analog magnetic field indicator) is low, around 1.1 volts, meaning that I have a magnetic field that is way too strong. + + + +And my scope trace: + + + +And setup: + + + +In some sense, I should have anticipated this, and in hindsight I really should have read the datasheet in more detail, where I'm sure it outlines the required magnetic field strength... + +Yep, there it is + + + +So lesson learned - I really should have gotten into this beforehand, but it looks like I have *way* too much magnetic field - 13500 Gauss at the magnet pole and the AS5304 wants only to see 10 to 60 mT (milliTesla) - I have 1350 mT. Whoop! + +## NEXT TIME + +I think the best way forward, with all things considered, is to go bones deep <i class="em em-swimmer"></i> and get two Hall Effect Sensors, read those, and do the signal processing. It's a much more interesting project this way, etc. + +I may make a last-ditch attempt at the easy route, with skinnier magnets and a bigger spacing between the encoder and the ring. + +All I want is more time. + ## Programming, Measurements & Corrections I want to be like Sam. Sam measures *everything* and he does it really beautifully. This is some of the functionality I really want to be able to bring into mods - the ability to quickly pull test data out of systems, do computation with it, and learn. diff --git a/images/datasheet-cao.jpg b/images/datasheet-cao.jpg new file mode 100644 index 0000000000000000000000000000000000000000..09a5c5b5dc091b6a60fdcf5a478379fcabe74e78 Binary files /dev/null and b/images/datasheet-cao.jpg differ diff --git a/images/datasheet-magfield.jpg b/images/datasheet-magfield.jpg new file mode 100644 index 0000000000000000000000000000000000000000..eef4b5c0a7f3182937a8d00257a8cadcc28988b0 Binary files /dev/null and b/images/datasheet-magfield.jpg differ diff --git a/images/scope-sad-cao.jpg b/images/scope-sad-cao.jpg new file mode 100644 index 0000000000000000000000000000000000000000..95fc7ed33fd7eae799952b0497cea12d8e10374c Binary files /dev/null and b/images/scope-sad-cao.jpg differ diff --git a/images/scope-to-check-cao.jpg b/images/scope-to-check-cao.jpg new file mode 100644 index 0000000000000000000000000000000000000000..e4cebb60cc0ccc99d13cccdac35bf649f8a3143a Binary files /dev/null and b/images/scope-to-check-cao.jpg differ