Boeing 737 rudder pedals construction

[mauriceb]

I have finally completed my linked rudder pedals (minus interface). I used real Boeing pedals but the linkages started with an idea from Alain Tremblay (thanks Alain) which I modified as I wanted to use gas springs instead of elastic bands for the tension on the pedals.

Well, this turned out to be an ordeal as I am very lousy at visually how things work mechanically and I had to basically try & fail a hundred times before I got them working the way I like them to work.

The gas springs for the brakes were easy enough to figure out, but the gas springs for the pedals were another thing. I finally found a way that works perfectly and the key part was to have one end of the gas spring not attached to anything but still be able to remain in a certain track at all times. I did that by enclosing them inside a tube. The tube itself is attached at one end and is able to pivot.

http://i32.photobucket.com/albums/d38/mau_ben/P1020807.jpg

http://i32.photobucket.com/albums/d38/mau_ben/P1020783.jpg

http://i32.photobucket.com/albums/d38/mau_ben/P1020801.jpg

http://i32.photobucket.com/albums/d38/mau_ben/P1020788.jpg

http://i32.photobucket.com/albums/d38/mau_ben/P1020786.jpg

This is how it works. When I push on one pedal, the associated gas spring compresses normally and the gas spring on the other pedal is simply pulled out of the tube by the other pedal since it is only attached to the pedal arm and is free at the other end.

When I release the pedal, the centering is done automatically since both gas springs exert just a tiny bit of pressure on the pedals without compressing the gas springs at all, so the pedals always come back to exact center. If the gas springs were attached at both ends, then the gas
springs would both have to be compressed half way at the center neutral position and the center position would be hard to maintain properly unless both gas springs exerted exactly the same tension at the center of their travel. I'm not an expert with gas springs, but I would think this would be very hard to achieve due to different tolerances.

I must say I love the feel of the gas springs. It is always smooth and never jerky at all for both for the pedals and the brakes and I'm very happy with the results.

http://i32.photobucket.com/albums/d38/mau_ben/P1020802.jpg

http://i32.photobucket.com/albums/d38/mau_ben/P1020804.jpg

http://i32.photobucket.com/albums/d38/mau_ben/P1020805.jpg

And now, all I have to do is figure out how to add the pots & interface. Piece of cake! :roll:

More pics here:
http://good-times.webshots.com/album/560928860GxpIoQ

Maurice

[dodiano]

Beautiful!!! Simply Beautiful!! Hope you can make a tutorial of some sort or some links to get the materials!! This is amazing Work!!

Regards,

Roberto

[Michael Carter]

Outstanding engineering. They are beautiful Maurice.

What is the weight of compression for the springs?

[Westozy]

Great work Maurice, a big thumbs up from this engineer! I would suggest a linear (straight) pot on one of your pedal push rods.

Gwyn

[NicD]

Superb work Maurice - thanks for the pics and information too .. very helpful. All I gotta do is find the inspiration to start on them now! :(

[Tomlin]

Awesome to see them put to good use Maurice, and Im still elated you bought them from me! They obviously went to very capable hands. I wish you the best in getting them interfaced.

[PaulEMB]

Excellent Maurice,

An inspiration for us - shows what you can do when you keep at it. The engineering work is very good, and I like Nic have put it back on my list of things to do!

[mauriceb]

Beautiful!!! Simply Beautiful!! Hope you can make a tutorial of some sort or some links to get the materials!! This is amazing Work!!

Regards,

Roberto

Thanks, but the best tutorial I could produce would be pretty bad compared to the one I copied the idea from. As I said, I 'borrowed' the idea from Alain Tremblay and he has a very good PDF document available in his website. I'm sure Alain won't mind if I include the links here:
http://www.sim-737ng.com/rudder/rudder.htm
http://sim-737ng.com/rudder/Assemblage_pedaliers.pdf

The main changes I made were to add gas springs instead of rubber bands for the tensioning and the pictures are self explanatory I think (I can answer other questions you might have though)

Maurice

[mauriceb]

What is the weight of compression for the springs?

I have no idea, but I guess about 25 lbs. I got the springs from Eric when I bought the pedals and Eric likely has a more accurate idea. It's not that critical though as you can vary the tension by the location of the springs. That's why I have so many extra holes in the linkage T bar ;). Lots of trial & error.

Maurice

[Michael Carter]

I like yours better.

What weight of compression are the gas struts?

[mauriceb]

Awesome to see them put to good use Maurice, and Im still elated you bought them from me! They obviously went to very capable hands. I wish you the best in getting them interfaced.

Thanks Eric, but I must say, I did hate you now & then :D. Just kidding of course, but maybe you can answer the question about the gas springs. Do you know/remember what was the force needed to compress them? I guessed about 20 to 25 lbs. Is that close enough you think?

Thanks,
Maurice

[Tomlin]

I really dont recall how much weight it took- I bought them from an auto parts place called Pep Boys, and the guys there just let me go in the back and take 'em outta the sleeves and push on them. Did I mail them to you in the sleeves? If so look up the numbers on there.

[mauriceb]

I really dont recall how much weight it took- I bought them from an auto parts place called Pep Boys, and the guys there just let me go in the back and take 'em outta the sleeves and push on them. Did I mail them to you in the sleeves? If so look up the numbers on there.

Good idea. Will check now

[mauriceb]

What weight of compression are the gas struts?

As I said, I don't know for sure, but here is the Manufacturer & part number:

Its a SACHS LIFT-O-MAT Part #: SG459005

Maurice

[Bob Reed]

As I said, I don't know for sure, but here is the Manufacturer & part number:

Its a SACHS LIFT-O-MAT Part #: SG459005

Maurice

If these are the "shocks" that hold open a rear hatch on like a mini van they require about 18lbs to compress, but that is with the wight of the door hanging from it. These doors are made from various materials some are steel, some are fiberglass and some aluminum. So it depends on the ones you have.

[Michael Carter]

I've pushed quite a few automotive lift-struts. All lengths and diameters. I'm here to tell you most won't even compress with all of my body weight on them at 180 Lbs.

I'm looking at some struts from McMaster-Carr that are lightweight compression and also some that are adjustable, once. Meaning after you let the air out of them they're set and cannot be re-inflated.

I'm thinking of replacing the heavy springs for my yoke with struts. If my math is correct, I need about a 17-20 Lb strut to get a force of about five pounds at the yoke.

[mauriceb]

I've pushed quite a few automotive lift-struts. All lengths and diameters. I'm here to tell you most won't even compress with all of my body weight on them at 180 Lbs.

I'm looking at some struts from McMaster-Carr that are lightweight compression and also some that are adjustable, once. Meaning after you let the air out of them they're set and cannot be re-inflated.

I'm thinking of replacing the heavy springs for my yoke with struts. If my math is correct, I need about a 17-20 Lb strut to get a force of about five pounds at the yoke.


I can push mine fairly easily, so no way they need 100+ pounds.

I just did a little experiment with dumbbell weights I had lying around (I knew these would come in handy some day :D) and the spring was able to lift at least 45 lbs (that all I had). So, my new guesstimate is that they are at least 50 to 60 pounds. 45 lbs was not enough to compress and I had to push on the weights a bit more to get the spring to compress.

They feel just right though for the pedals (for me at least) and the pedal pressure can be changed by moving the springs closer or further from the pivot point to increase or reduce the leverage. The net force for me doesn't feel more than about 20 pounds, but I could be way off since legs have much more power than arms.

Maurice

[W9XE/Project777]

If you would like to get a close measurement of the pull of the springs you can use a simple fish scale to give you an idea how much friction is on the pedals. By attaching the scale to one of the pedals, hold the other end of the scale and pull evenly. The gauge will give you your breakaway lbs of pull and the weight through even travel. This is a good was to test yoke friction as well.

We used this method on our Bell Helicopters for adjusting collective friction with both hydraulics on and off. Simple but works :cool:

[spitfire9]

Those hydralic/spring struts used to close screen doors have a screw on one end to adjust tension.
I wonder how those would work?

[mauriceb]

[QUOTE=W9XE/Project777;42998]If you would like to get a close measurement of the pull of the springs you can use a simple fish scale to give you an idea how much friction is on the pedals. QUOTE]

Have you read my post about 'Insane builders'. Likely not ;). Insane builders would worry about duplicating the exact force required to push the pedals on a real plane. Me, I'm happy because they just feel good to me whether they need 20 lbs or 200 lbs :D

Seriously though, if I had a fish scale I would do the test out of curiosity (or to satisfy the curiosity of insane buuilders :wink:, but I won't have time for fishing until "the year 2525... if man is still alive" thanks to the million things I still have to do in this damn flight deck. So, I won't buy a fish scale until that time. :D . Excellent suggestion though.

Thanks,

Maurice

[mauriceb]

Those hydralic/spring struts used to close screen doors have a screw on one end to adjust tension.
I wonder how those would work?


I believe Gwyn used those with a very clever design in his yoke mechanism. You can find pictures in the Photo Gallery section I believe. One thing to keep in mind is that those things are normally fully retracted instead of fully extended.

Maurice

[PaulEMB]

Unfortunately, most of the fish scales I had recently , I washed down the sink whilst cleaning the fish for the BBQ. Still, an ingenious idea.

(Sorry I'm on a business trip, and forgot my tablets, was that tablet PC, or tablet that drops down on FSUIPC buttons menu)

ps its still sun below the yardarm time here, in case you are wondering...

pps sometimes lateral thinking can be viewed as being insane. (or was that lateral viewing..):-x

[blueskydriver]

Hey Maurice,

Nice job on the rudder setup. Have you thought about motors to automate it for AP; it looks like if you attached a reversible motor to that rod that goes between the Capt and FO rudder sets, it would cause them to move automatically. You just need to add an electric clutch to engage the motor when you want it on for AP and off when you move the pedals by your feet. Thus, that relieves the pressure of the motor.

John

John

[vitabutch]

Hey Maurice,

Nice job on the rudder setup. Have you thought about motors to automate it for AP; it looks like if you attached a reversible motor to that rod that goes between the Capt and FO rudder sets, it would cause them to move automatically. You just need to add an electric clutch to engage the motor when you want it on for AP and off when you move the pedals by your feet. Thus, that relieves the pressure of the motor.

John

John

Hi John, as far as I know AP doesnt move the pedals in any way :) However the motor can be used for rudder trimming.

2 Maurice - the pedals are very good. You can call me insane builder, so I will not grouse about the load forces. I think one thing you have missed - pedal adjustment system. Its very easy to build - you need to have your cam mounted on the thread. The same design is used on the real plane.
I think adjustment system is even more important then motorized trim. :)

Cheers, Vitaly

[Westozy]

I believe Gwyn used those with a very clever design in his yoke mechanism. You can find pictures in the Photo Gallery section I believe. One thing to keep in mind is that those things are normally fully retracted instead of fully extended.

Maurice

True! I used two screen door closers to center the pitch motion and it works and feels great. I used two that were different types and I've just bought two new ones which will be fitted when I install the new yokes from Roberto. They are finished and are being painted gloss black in two-pack by a pro painter mate at the moment, I hope to fit them this coming weekend.

http://www.mycockpit.org/photopost/showphoto.php?photo=821 This pic shows how the centering device works, both yoke columns are attached to the chrome 'torque' tube which synchronizes them.

Gwyn

[Jacobbartz115]

What is your dimensions? btw I am an engineering student and I found your design to be the best after about 3 days of looking though designs. Good Job!