Jump to content

P51 Aileron Trim Test Piece


No1sonuk

Recommended Posts

One of my "challenge pieces" has been the P51 trim system.
I decided to have a go at it after seeing a video on Youtube where someone used a potentiometer, rather than a rotary encoder.
The DCS-BIOS implementation of the P51 trim system is  buggy to the extent I gave up on it, so this video was an eye-opener.  I could bypass DCS-BIOS entirely by using an analogue channel.

These are the 4 main considerations:

1) The Handwheel does 2 complete turns - 1 full turn each way
2) The display needle rotates only about 60 degrees.
3) The potentiometer can turn a maximum of 270 degrees.
4) It's better to use as much of the potentiometer travel as possible.

 

Looking at the gear ratios, reducing the handwheel to needle rotation would require a ratio of 1:12.  That's OK if you don't want to keep it compact, or if you can use small module gears.  I want to 3D print mine, so I have to use larger gears than would be practical.
Besides, that would then mean the potentiometer only running about 60 degrees, so not a lot of resolution.
 

The solution is to do the reduction in 2 stages:
1:3 for the potentiometer, then 1:4 from the potentiometer to the needle.
This gives far more manageable gear sizes.  It also has the benefit that if the gears are chosen right, there's enough tolerance that both can be done on the same 2 axes, reproducing the original's layout of the display needle under the handwheel.
 

This is the layout of my prototype:
EOGQgDJ.png

Here's how it works:

The handwheel (not shown) is connected to the shaft A.
Shaft A only turns gear B (hidden under, but not connected to, gear F or needle G).
Gear B (11 teeth) turns gear C (33 teeth), reducing the 720 degree handwheel rotation to 240 degrees.
Gear C is connected to the potentiometer D and gear E (9 teeth).
Gear E turns gear F (36 teeth) reducing the rotation further to 60 degrees.
Needle G is connected to gear F.
 

Not shown is the top panel, which has a step for the handwheel, cut out to accommodate the needle and restrict its travel.

FwZi2bG.png
OUiNXdy.png
yaAeA3O.png


Electronically, it's connected to an analogue channel of a Leo Bodnar BU0836A.  This is then set for (in the prototype) the aileron trim as an axis - this gives absolute position control, rather than step up/down.
The full extents are calibrated in windows, so it gives maximum throw readings for the full extent it can move.
 

And video:
https://youtu.be/k-wwvCGNP0k


Improvements:
I used 1.5 module gears.  I might be able to use a smaller module number and reduce the size a bit.

Gear F doesn't need a full set of teeth as it only rotates about 60 degrees.  I may cut it to a sector to save on space and print time.
The top and bottom plates have extra holes I put in for more spacers in case they were needed for rigidity - they weren't.


Edited by No1sonuk
  • Like 1
Link to comment
Share on other sites

Nice work. Matches DCS nicely. DCS doesn't match the real P51s trim knob movements exactly, but we only use a tiny bit of that range in DCS anyhow.

The knobs outside diameters are 3 7/16in at the base and 1 1/8in tall. That should give you a bit more pleasant feel to the grip if you're going for a bit of realism.


Edited by doright
Link to comment
Share on other sites

 

13 hours ago, doright said:

Nice work. Matches DCS nicely. DCS doesn't match the real P51s trim knob movements exactly, but we only use a tiny bit of that range in DCS anyhow.

The knobs outside diameters are 3 7/16in at the base and 1 1/8in tall. That should give you a bit more pleasant feel to the grip if you're going for a bit of realism.

 

I'm not going for a realistic cockpit myself - just a bit more than a "button box", so the smaller size is fine.  My wheels are about 50mm across, so the same mechanism would fit a realistic size cockpit - IF the potentiometer position was moved to the opposite side of the wheel.

 

 

59 minutes ago, flyco said:

Pots with two and a half rotations from one end to the other are available.  I have use one with a Spitfire.  
 

I just have standard ones.  Besides, the 2-stage geared reduction is convenient for the size reduction, so might as well save some cash on what would undoubtedly be a more expensive pot.

Link to comment
Share on other sites

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...