6 Position Knob for APM mode control - DIY for around $16 total



After reading a recent blog I have decided I REALLY need to get out there and fly this year. I spend far too much time in front of my computer... So thanks to Max Levine's wonderful blog, http://diydrones.com/profiles/blogs/ardupilotcopter-mega-6 I've decided to go ahead and modify my Turnigy 9X to add a 6-position switch. This is going to be more or less a mini-build log as all I've done so far is order the parts....and they're all available from a single supplier, so save money on shipping!!!



Again, props to Max Levine for his original blog on this topic.


Parts ordered (the resistor values came from an experiment with a Turnigy 9X and potentiometer):


(1) X ALPS 6-position switch = $7.06/ea or (1) X ALPS 6-position switch = $9.40/ea

(1) X 6mm knob = $0.59/ea


7 resistor solution:

(1) X 1.3K ohm resistor - $0.11/ea

(5) X 1.5K ohm resistors = $0.11/ea = $0.55

(1) X 1.0K ohm resistor = $0.15/ea


5 resistor solution: 

(1) X 2.8K ohm resistor = $0.15/ea

(3) X 1.5K ohm resistors = $0.11/ea = $0.33

(1) X 2.5K ohm resistor = $0.15/ea




EDIT Sorry to keep changing the resistor values on you, but I'm trying to get as close as possible to the middle of the band for everyone. AR Projects read a min and max of 1085 and 1921, where I read a min and max of 1047 and 1878.


Current Cost (not including shipping all ordered from Mouser.com) = $8.46

Shipping is "estimated" at $6.40 so I'm in for $14.86 so far.


For those that don't want the hassle, you can buy a 6 position switch pre-made from one of our fellow DIYdroners - AR Projects - http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120731012907...


UPDATE 6/11/2011

I didn't wait for Mouser to get the switch in stock, so I ended up spending $9.40 including shipping to get the switch from eBay. If you can wait, the original price of $8.46 plus shipping still stands. If not, you're looking at $3.40 for the knob plus $6.00 shipping and $1.40 for the resistors and knob plus Mouser charged me $5.20 in shipping. Total cost with shipping was $16. If I could have waited I would have saved about $2.00 on the total cost.



These are the target and actual PWM values achieved using 7 resistors. (6) 1.5K and (1) 768 ohms


Pos 0: <= 1230 = 1165 Target - 1175 Actual
Pos 1: 1230 - 1360 = 1295 Target - 1300 Actual
Pos 2: 1361 - 1490 = 1426 Target - 1431 Actual
Pos 3: 1491 - 1620 = 1556 Target - 1555 Actual
Pos 4: 1621 - 1750 = 1686 Target - 1684 Actual
Pos 5: >= 1750 = 1815 Target - 1811 Actual


That's about as perfect as it can get.



A few things worth mentioning during the "build."


1) Before you try to solder the wires going to the switch, take a pair of large cutters and trim off the bump on the switch. If you look at the top of the switch, you'll see a keyed piece of metal that would be used to keep the knob from rotating, if the plastic housing was designed for it. If you try to clip it after the fact, you may run the risk of breaking off a resistor like I did.


2) Take an x-acto knife and ream out the hole a little bit. The threads on the switch won't go through otherwise.


3) The radio case will be a bit tight to get back together in the corner where you installed your switch. I forced mine ever so slightly....but I could have done a better job cutting the metal tab off my swtich.


Views: 4273

Comment by ARHEXA on June 1, 2011 at 2:10pm

Hope these values work for you,

Tomorrow morning, i'll go get 845 ohm and 1.5K resistors to make some testing....
Comment by Paul Feely on June 1, 2011 at 3:32pm

Comment by Max Levine on June 1, 2011 at 5:18pm
Thanks Happy ;)
Here is my PWM output using those resistors
Pos 0: 1077
Pos 1: 1304
Pos 2: 1440
Pos 3: 1570
Pos 4: 1702
Pos 5: 1930

So yes, it need some tuning :)
Comment by Paul Mather on June 1, 2011 at 5:46pm
I did some thinking while cutting the grass.... To get the numbers "perfect" from 1000 to 2000...it will take 7 resistors. 1K on both ends (between + and the first and ground and the last) and 5 200 ohm's between each of the 6 settings.

Comment by Max Levine on June 1, 2011 at 6:04pm

@ Happy. Good idea, i'll try it. 

btw here is Grayhill switches 56 and 50,52 that should fit in the radio, also some nice knobs here.


Comment by Jason Short on June 1, 2011 at 6:35pm

With this work with any swicth on the radio? I'd hate to loose my Aux2. I'd rather replace my Aux1 three position. 

I have a Futaba.

Comment by Max Levine on June 1, 2011 at 6:54pm

It will work on any knob, normal switches need some extra wires.

I don't know how it set in Futaba, but i guess its the same potentiometer.

If it is different ... Just check the resistance of the potentiometer in each position.

Comment by Greg Fletcher on June 1, 2011 at 7:35pm
@ Jason, the three position switch is most likely digital not analog. I made a 4 pos setup a while back that replaced the aux pot on an old airtronics. It used ch 5 for gear and that's all it could do, up or down. You need to open that futaba up and carefully poke around with a DVM to see whats going on with the 3 pos switch. I'll bet it's  3 digital lines, but you never know.
Comment by Paul Mather on June 1, 2011 at 9:10pm

Max, have you tried replacing the resistors between position 1 and 2. Those seem to be throwing all your numbers off.


According to Max's numbers for 0 and 5 of 1077 and 1930, those are the min and max of +5 and ground. So the "ideal" setup would be to try to hit the middle of the range for each mode. In my searching, I found a post that claimed he found the range values in the APM code.


Pos 0: <= 1230 = 1165

Pos 1: 1230 - 1360 = 1295
Pos 2: 1361 - 1490 = 1426
Pos 3: 1491 - 1620 = 1556
Pos 4: 1621 - 1750 = 1686

Pos 5: >= 1750 = 1815


Which after doing some funky math, I came up with these values.

Between +5V and 0 = 667 ohms

Between 0 and 1, 1 and 2, etc = 1K

Between 5 and ground = 884 ohms.


Comment by Russell B. Sutton on June 1, 2011 at 9:42pm

Could u  add in  small or micro variable pot's at each switch position to help dial them in maybe?



You need to be a member of DIY Drones to add comments!

Join DIY Drones

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service