"lumpy" inputs from joysticks - adapting real controls?

[Guest]

I recently completed adapting a real Baron throttle quadrant to flight sim using long linear taper slide potentiometers. I expected the longer travel distance of the throttles to provide greater sensitivity for adjusting power but that is not necessarily the case.It becomes clear as the control distance increases that the inputs for FS2K2 are not gradual. I expected there to be an infinite number of settings depending on the resistence in the pot. Instead I find that the inputs move in steps. For example,moving the throttle 1/4" might make not affect the power setting at all. Move it another 1/4" and power jumps up a step. These steps are really annoying in a twin, since the steps need to be callibrated exactly to coordinate the synchronous movement of the handles with the changes in power. Using reverse thrust is disasterous if the handles aren't completely synchronized!FSUIPC helps callibrate the pots but looking at the actual numbers confirms the "lumpiness" of the conversion between resistance and actual change in input. If your lever is currently at -13021, for example, no amount of dexterity will allow you to reach -13022. If you are lucky it might only jump 50 or 100 units, but typically it is more than that.Am I doing something wrong? Sensitivity for the controllers is maxed, the null range is at the default (not sure what that does for me anyway!). I've callibrated through Windows XP and use FSUIPC to set the limits. Any ideas?David

[rcbarend 37]

Hi David,Since you don't mention anything about "jitter" (small, spontaneous fluctuations) I assume you have connected the pots to a USB port, either by a Gameport-to-USB convertor or via the electronics of an old USB joystick.Right ?If no: if you use a direct gameport connector, you will never see such small changes (50-100 units in FSUIPC over a range from -16383 to +16383 if you calibrated well), because the random "jitter" will far exceed these small changes.If you use a USB convertor or old USB electronics: the reason why you get this "lumpy" behavious is the caused by the conversion of the analogue resistance input to a discrete value ("A/D conversion").Especially the standard USB-to-Gameport convertors (Radioshack, Sitecom, and alike) have a very low resolution: if well calibrated, only 30-40 discrete steps over the full range. Standard USB controllers (which usually use pots as well) will have this same problem, although may have more discrete steps.Only some controllers (like I believe MS new Sidewinder) uses optical control instead of potmeters. They might be more accurate (don't know that).An obvious advantage of the USB convertor, is that the "jitter" is eliminated (if the "jitter" fluctuation lies between two discrete steps).Conclusion: using ordinary pots (being sliders or rotational), you'll never be able to get the small resolution you want, if only because of the "jitter" problem. Only with high-advanced electronics in a USB convertor you would be able to get "infinite" resolution (>10000 values on a FSUIPC scale of -16383 to +16383)The above are my experiances on WIndows98; it could be possible that the gameport driver in XP is different (hence no "jitter"), but then it does the same A/D conversion as a USB convertor. But I doubt that.Rob

[Guest]

Rob,You may have hit the nail on the head! I am using two Radioshack converters to handle the 6 axis needed for the full quadrant. I had ordered a more expensive converter from US Cable (think that's the company) because I thought the Radioshack ones weren't working (turns out it was just really important to have a momentary switch installed in the circuit for callibration!). Guess I'll give the converter a try rather than send it back. Thanks!David

[rcbarend 37]

Hi David,I thought so :-).And indeed, you do need a temporary 'button' for calibration; although there's are Windows program around that simulates a pushbutton (can't remember the name).I understand you use the convertors o.a for 2 throttle axis which need to be 'synchronous'. By itself, I feel that 30 discrete positions are more than enough for throttles.Rob

[Mike A 337]

Hi RobI'm also trying to put together a multi-engine throttle quadrant. I created a 4-axis 4-button gameport control using ordinary hook up wire, & the only problem encountered is the "jitters". Would using shielded wiring help?I've also taken out the electronics from a USB joystick, and I find that some of the axis don't output a full range of movement (-16,000 to 16,000), even after changing the pot & adjusting the sensitivity in FS2K2. Could this be due to the USB electronics limiting the output from this particular axis?Thanks for any comments or suggestions that could shed some light on this.Mike A.

[rcbarend 37]

Hi Mike,If you connect the pots to the gameport: Yes, shielded wiring helps a lot !! You won't be able to get rid of it totally though.Keep unshielded wires (near the pots) are short as possible.Solder the cable shield:- To the connector (NOT A PIN) of the 15-pins plug.- To the housing of the potmeters.Depending on the cable length (keep it as short as possible, certainly not longer that 2-3 meters) and quality, you'll reduce the "jitter" with at least 50 % (and probably more)ABout the old USB electronics:Make sure the axis are properly calibrated in WIndows first (you do need a 'button' for that). So max. swing of the pot must result in max. swing of the indicators in Windows Controller menu. If not, you didnot calibrate correctly. (this is independant of the USB electronics or potmeter value; no matter how small the min-max difference is, you can always stretch that with Windows Calibration.Only after you have that correct, use FS2K2 and FSUIPC for further refinement of the calibration.NOTE: if you use FSUIPC: there's only **one** proper position for the Sensitivity and Null zone sliders in FS2K2: Sensitivity MAX and Nullzone MIN.RobRob

[Mike A 337]

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[Guest]

Thanks to the great advice here I was able to solve my problem. The USB converters I was using were from RadioShack (about $12 each or so). I ordered a different converter made by Rockfire even though it was almost twice the price. At the time I ordered it I thought the Radioshack units had a different problem that I've since solved. Confusing, huh?Well, bottomline, the Radioshack units have a resolution of about 1000 units as measured by FSUPIC. That means that no matter how little you move the control, you will never see a change in the actual output of less than 1000. Over the full range of 32,000 units you will really only get 32 discrete values. That's really noticeable if you are using dual controls for a twin because it's virtually impossible to callibrate the sliders well enough that the 1000 unit jumps happen synchronously. The Cheyenne was pretty much unflyable because of its overabundance of power. While the controls might have looked like they were moved together, one might well have an output of 1000 units more than the other. The Cheyenne would careen off the runway almost as if you lost an engine.What's the answer to this? The Rockfire units have a resolution of 500 units. Now there are 64 steps between idle and full power, feather and full pitch. It's incredibly smooth and it makes a huge difference in the control sensitivity. No more runaway King Air or Cheyenne. I can finally get to idle. If you were concerned about spiking, I haven't seen any yet. Sure the Rockfire is twice the price but it is well worth it!Thanks to everyone for their help!David

[rcbarend 37]

Hi David,Thank YOU for the added comment.I guess you are referring to the Rockfire RM203 ?For those interested:There's a description at: http://www.usbcable.com/47-1932.htmDavid, Have you found a URL where there's a better specification ?I haven't been able to find one.Even worse, I live in the Netherlands and have yet to find a place where I can buy it :-(Rob

[Guest]

Rob,That is the company I bought mine from. I'm sure they will ship overseas but if you do a search, you might find someone on that side of the pond who sells it. I seem to remember there was some company in the UK that sold it. Good luckDavid