Bell Crank vs. Direct cable mounting
03-21-2003, 03:23 AM
#52
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Bell Crank vs. Direct cable mounting
There a few other things one can do with pull/pull cable rudder control.
The rudder wheel with a wheel at the servo which gives a perfectly linear system.
Also, if one wants to increase the force at the rudder itself, with the same servo , use a boost tab
Also, don't foget the Ackerman system, where the lines are tight only at the center with a few degrees deflection.
The rudder wheel with a wheel at the servo which gives a perfectly linear system.
Also, if one wants to increase the force at the rudder itself, with the same servo , use a boost tab
Also, don't foget the Ackerman system, where the lines are tight only at the center with a few degrees deflection.
03-22-2003, 08:34 PM
#53
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Bell Crank vs. Direct cable mounting
FWIW:
I mocked up a SWB 5" arm with 2.5: spacing at the bell-crank and binding was not an issue. At 3" spacing slight binding occurred about 5 degrees prior to maximum deflection, didn't seem to be a big deal but it exists and if fully deflected for extended periods of time might cause excessive current draw.
I mocked up a SWB 5" arm with 2.5: spacing at the bell-crank and binding was not an issue. At 3" spacing slight binding occurred about 5 degrees prior to maximum deflection, didn't seem to be a big deal but it exists and if fully deflected for extended periods of time might cause excessive current draw.
03-23-2003, 12:02 AM
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Bell Crank vs. Direct cable mounting
Wow, you guys have made this into an overcomplicated mess!
Let's do this easy.
How to calculate torque at the rudder? After you hook up your system.....
Measure angular rotation of servo, full lock to lock - call this A.
Measure angular rotation of rudder, full lock to lock - call this B.
Rudder torque = rated servo torque x A/B
If you gang together N servos, then
Rudder torque = N x (single servo torque) x A/B
This works if you use cables, bellcranks, direct pushrods, gears, hydraulic fluid.....whatever.
Let's do this easy.
How to calculate torque at the rudder? After you hook up your system.....
Measure angular rotation of servo, full lock to lock - call this A.
Measure angular rotation of rudder, full lock to lock - call this B.
Rudder torque = rated servo torque x A/B
If you gang together N servos, then
Rudder torque = N x (single servo torque) x A/B
This works if you use cables, bellcranks, direct pushrods, gears, hydraulic fluid.....whatever.
03-23-2003, 12:05 AM
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Diablo,you've got alot of guts jumping in this late,with such a simple equasion!Hang on buddy,it could be a rough ride!
Mike
Mike
03-23-2003, 12:25 AM
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Diablo,Have you read this from the start? We weren't trying to figure out rudder torque, it started out on the discussion of whether or not a bellcrank for pull-pull increases the servos force at the rudder. I've said no from the beginning if the geometry is all correct. By the way, do you have a formula to figure the ratio of servo rotation to surface deflection for any given servo arm length/control horn length combo without actually having them installed? Now that would be great!
03-23-2003, 12:36 AM
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We weren't trying to figure out rudder torque, it started out on the discussion of whether or not a bellcrank for pull-pull increases the servos force at the rudder.
03-23-2003, 12:46 AM
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Yeah, your right. I guess what I was trying to say is that if you've just jumped in on this you won't know how it started out.
03-23-2003, 12:54 AM
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Actually stick,I believe we started out discussing if using a bellcrank was better for the servo?Somehow we strayed to force,who remembers what we started with anyway,Hmmmm,seems like I've said that to my wife several times!!
I'll bet they guy who started this thread still soesn't know what to do
Mike
I'll bet they guy who started this thread still soesn't know what to do
Mike
See, even I don't remember how it started out!
03-23-2003, 02:31 AM
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And the correct answer is that IT DOESN'T MATTER if you use bellcranks or direct cables to the servo. The only thing that matters is the angular rotation of the rudder and the angular rotation of the servo in degrees. Use the equations provided.
03-23-2003, 05:39 PM
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Diablo,
No disrespect, but I said the exact same thing WAAAY at the beginning of this thread. There were a few that needed more of an explanation than just a simple equation to convince them as to why the bellcrank doesn't provide a mechanical advantage. That's how this thread got to where it is.
No disrespect, but I said the exact same thing WAAAY at the beginning of this thread. There were a few that needed more of an explanation than just a simple equation to convince them as to why the bellcrank doesn't provide a mechanical advantage. That's how this thread got to where it is.
