WildBillKelsoe Posted February 5, 2015 Posted February 5, 2015 Here is what I know, please correct me if I am wrong. So pots come in different ohm, like 10K, 5K, 50K (CH products), and 100 K Ohm. So for building a trim box for P-51D, if I want to have more range inside a pot, use 100K pots. This means that for example a 1 degree right trim in sim would correspond to say 1.5 real turn on the pot. By the same principle, if I want to achieve that 1 degree in sim trim, on. 5 K pot would correspond to less than 1.5 real turn on the smaller ohm pot. I know I can control the sensitivity also from USB controller like teensy. Is that correct? I want the lowest sensitivity meaning it takes more turns in the real pot to achieve desired amount. AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.
FSFIan Posted February 5, 2015 Posted February 5, 2015 The total resistance of your potentiometer does not matter. A pot has three contacts, which I will call 1, 2 (the ones on the end) and S (slider). Electrically, it looks like two resistors in series: 1 --- R1 --- S --- R2 --- 2 By moving the slider, you change how the total resistance of the pot is distributed over R1 and R2 (i.e. R1+R2 is the constant total resistance of your pot). When you wire up "1" to Vcc, "S" to your ADC and "2" to ground, R1 and R2 form a voltage divider, so only the relative resistance matters. The amount of turns you need to go through the entire range is a mechanical property of your potentiometer. The total resistance will influence how much current flows. Too low (less than 125 ohm) and you overload your Arduino pin which can only handle 40 mA, too high (probably more than several hundred kOhm) and your signal will pick up more noise. Any pot between 1k and 100k should be fine. DCS-BIOS | How to export CMSP, RWR, etc. through MonitorSetup.lua
Viersbovsky Posted February 5, 2015 Posted February 5, 2015 (edited) Indeed, just look up voltage divider. HOWEVER, what you are looking for is resolution. The microcontroller must translate the analog voltage into a digital signal, using a built-in device called ADC (analog-digital converter). These have a set resolution, most have about 10Bit or in other words 1024 steps. An 8-Bit ADC will give you only 256 steps. Sooo, lets say we have a potentiometer that can be turned 260°, then with an 8 Bit ADC the angle for one step is rougly 1°. When using a 10 Bit ADC one step is about 0.25°. I must warn you though, even good pots tend to be quite jittery, due to ground loops and bad 5v supply from usb port. When using my notebook only on battery power, receiving signals from my microcontroller I get perfect 1024 steps from the potentiometer. As soon as I connect the power supply, I get only about 100 real steps, since there is significant jittering (about +-4 steps)! Trying to solve this problem is quite a hassle, most systems use filtering algorithms. A usb ground decoupler might be an easy the answer though. - I now try to go all digital. Also, pots usually can be only turned to a fixed degree, usually about 260°. There are multi-track pots that can be turned multiple times, but they still have a hard stop. Maybe you could use encoders? They output digital signals and can be turned freely. They might actually be better suited for trimming, but you need a bit more programming skills to use them. edit: The teensy might already have the necessary filtering though, just try a pot in the 1k-100k and see if it works for you! Edited February 5, 2015 by Viersbovsky Callsign "Lion"
WildBillKelsoe Posted February 5, 2015 Author Posted February 5, 2015 Wealth of information. Thanks guys AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.
FSFIan Posted February 5, 2015 Posted February 5, 2015 Another way to get really high precision trim wheels is to cannibalize an old analog PS/2 mouse. The image below is from a project I did last year over the easter holidays. Unfortunately I lost the code a day later when my SSD died. I used it with the A2A P-51 in FSX and was easily able to trim into straight and level flight within +/- 10 fpm climb rate (the scroll wheel was used for rudder trim). Link to image: https://www.dropbox.com/s/xtz0vfub5opngeq/20130331_005.jpg?dl=0 DCS-BIOS | How to export CMSP, RWR, etc. through MonitorSetup.lua
Random Posted February 5, 2015 Posted February 5, 2015 I've used 5 turn wire-wound pots for my trim box. Resolution of more than 4500 steps so more than the Leo Bodnar board they are wired to. PERFECTLY clean signal too unlike cheap carbon track pots. If you want to avoid the cost of a multi turn pot consider using a 270 degree one with a really big knob on it... you can make tiny adjustments that way. However you have to be careful not to break the stops with all the leverage. Finally make certain you use pots with a linear response. Most audio pots use a logarithmic response and are useless for controllers
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