Cessna 172 Replica Production

[AK Mongo]

Are you going to have the vernier functions and locks on the prop and mixture? Very cool animation!

[cjellwood]

Are you going to have the vernier functions and locks on the prop and mixture? Very cool animation!

no fancy functions unfortunately, just an O ring stretched around each rod to make friction for a realistic feel.

Chris

[jsfboat]

The airplane that I instruct in has a vernier throttle, which is the first airplane that I've seen that has one.

[cjellwood]

In this video, watch from 1:27 where the guy has both a lock and vernier function on the controls



At times like this I debate on whether such functions are required in a simulator. A mixture knob control system that has vernier function costs around $120 from Spruce which is good value but at what point does one draw the line between building a simulator as opposed to a real aircraft? The engineering cost for a basic knob with no special function is £30 so a complete set of knobs including electronics and rack will be around £150 (simulator - no special function). Use real knobs and the cost goes to £250+ before you have even thought about connecting it to the PCB and mounting it.

Looking at the features from an engineering perspective it would probably be easier to implement both lock and turn rather than just having turn. I will play with some ideas today to see what is possible.

Chris

[No Longer Active]

I personally, will not invest in the turn and lock feature, I am saving alot of cost and headache by not having this feature. If I was building a cockpit that was specifically for flight instruction, flight school or practicing for my ppl then I would definitely have the function. As my sim is a fun VFR Flyer with the odd bit of IFR equipment, the actual function of my sim does not require the precision of precise tuning where as flight sim simulates the lock and turn function by just providing a push and pull lever which is more than adaquate for my sim's needs. Its my cockpit, and I am totally happy with not having fine tuning on the mix knob, its something that I rarely touch and not worth the added expense where as the money could be spent on other parts!

Alex

[Leo Bodnar]

Can you place a coaxial encoder on each shaft for precise trimming?

I don't understand why Cessna decided to use Vernier friction nuts in the first place.
Other planes somehow manage to fly without them.

[cjellwood]

I personally, will not invest in the turn and lock feature, I am saving alot of cost and headache by not having this feature. If I was building a cockpit that was specifically for flight instruction, flight school or practicing for my ppl then I would definitely have the function. As my sim is a fun VFR Flyer with the odd bit of IFR equipment, the actual function of my sim does not require the precision of precise tuning where as flight sim simulates the lock and turn function by just providing a push and pull lever which is more than adaquate for my sim's needs. Its my cockpit, and I am totally happy with not having fine tuning on the mix knob, its something that I rarely touch and not worth the added expense where as the money could be spent on other parts!

Alex

There is definately no middle ground on this issue, the controls either need to be as complex as the original or completely basic. There is also the issue of FSX even responding correctly to minor screw adjustments as it would in a real plane? For teaching purposes a control system with screw function could be dangerously misleading if a student makes adjustements in a real plane according to how it reacted in FSX when turned. Given the sensitivity of the average potentiometer it would probably be a case of [7 turns in FSX = 2 turns in real cockpit] or like effect (if you know what I mean .

But no harm with the lock function if that can be implemented easily.

Chris

[cjellwood]

Can you place a coaxial encoder on each shaft for precise trimming?

I don't understand why Cessna decided to use Vernier friction nuts in the first place.
Other planes somehow manage to fly without them.

Sensing the turn electrically did cross my mind but there is still the problem of mechanically following the adjustment that has been made.

The vernier turn mechanism seems to be popular in marine engine control too so maybe there is the possibility of buying the screw/lock mechanics off the shelf and modifying them to fit the machined Cessna knobs. All depends on price really but there is hope because the Chinese are on it.


Chris

[cjellwood]

Things have taken a rather bizarre turn since the vernier issue was raised. Obtaining vernier controls like the one pictured below is not a problem, they cost as little as £5 each from China and can have the knobs replaced with the Cessna type quite easily. The manufacturers of these verniers are also happy to modify them to have 100mm of protruding rod at the end rather than just having a hook for the cable which helps with linking to a sensor. But while going through all that trouble to adapt the vernier i wondered if it would be possible to get away from the slide potentiometer setup which I believe is a wee bit crude considering the effor that is going into other areas. Maybe there is another option?

Well it seems there is another option but it is not an easy one. If this pulls off then there will be a sensor available that will help everyone in every area of sim building, not just throttle controls. No doubt this will be controversial, allow me to explain....

There seems to be a big whole in the market where linear position displacement sensing is concerned. On one end of the market is the slide pots that are pence each and on the other end is the industrial linear sensors that are £150 each at least (below).



How perfect are those for everyday sensing of lever positions in cockpits, especially throttle quadrants! But the price makes me heave

The solution seems to be Optical Sensors, like the type your mouse probably uses to detect movement. It sounded like a bad idea at first but then I discovered that a steel rod was detectable over the scanning surface and was picked up perfectly. The surface of the rod is ideal due to its reflectivness and all the abrasions that are common with this material. The resolution is amazing too!



The components require to form an optical sensing circuit are simple and cheap. £1 a pop! The output from the PIC can be a voltage of between 0-5v (PWM) depending on the sensor output so acting like a potentiometer and the PIC can be programmed to output that voltage for any distance required! because it senses both x and y axis motion of a rod then it would be great for sterring yokes too. Perfect?



So the idea is to create an Optical Position Displacement Potentiometer Module, a bit like this....

(Picture will be here when I make the drawing later)

Of course there is issues such as the position being relative, not absolute. But that is just a matter of having all controls in their default position when the electronics are booted.

Watch this space

Chris

[wannabeaflyer]

Hi Guys correct me if i got this wrong but have you guys just decribe a way to use cheap optical mouses for linear displacement measurement ?? i ask becuase whilst building my motion platform one of the issue i can across was finding good Cheap position sensors which did not really on Rotary potentiomers -- having read this thread i like the concept and can see it having applications for diy project all over the place -- so in a nutshell i need a pic Micro - the internals of a optical mouse and some reflectable medium ( steel rod ) and a little mechanical savvy and a means of starting my platform at a known defualt position