Idea
02-22-2002, 05:55 AM
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Idea
I have an idea, and I have tried and happy results.
Normally a servo draws 250 to 300mA current from Rx battery pack, and if there are 4 servos (out of which 2 are constantly used, ailerons and elevator and 1 partially used, throttle, and rudder is used under certain conditions), so an average current of 800mA.
Also the servo motor draws maximum curent during rotation or initial start and average current during loading.
Now the point over here is that almost all of us have computer radios, and we can control the travel throw of servos. Now if we reduce the throw and put the push rod down to 1 or 2 holes in the control horn (this will not effect the sensitivity) then the servos will have to move less and correspondingly will draw less current on the average and this inceases the flight time (Rx battery will serve 2 to 3 more flights) .
Normally a servo draws 250 to 300mA current from Rx battery pack, and if there are 4 servos (out of which 2 are constantly used, ailerons and elevator and 1 partially used, throttle, and rudder is used under certain conditions), so an average current of 800mA.
Also the servo motor draws maximum curent during rotation or initial start and average current during loading.
Now the point over here is that almost all of us have computer radios, and we can control the travel throw of servos. Now if we reduce the throw and put the push rod down to 1 or 2 holes in the control horn (this will not effect the sensitivity) then the servos will have to move less and correspondingly will draw less current on the average and this inceases the flight time (Rx battery will serve 2 to 3 more flights) .
02-22-2002, 05:19 PM
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battery idea
When I had to replace the rx pack in my plane, I went to radical rc's website, and got a ni mh 1600 battery pack for 16 bucks, including soldered on connector, and shipping. Thats less than a 600 nicad from futaba. He uses all sanyo cells, so there shouldnt be a concern about quality. Nimh packs are also alot lighter and offer more power for the same physical sized nicads. I leave mine on the futaba wall wart charger when the plane is not in my truck, because the charge rate of the wall wart works out to right around trickle range. I have flown all day on a single charge, and still had plenty of power in reserve. I think I could go about 3-4 days on a charge, but I dont want to risk that. This is flying a fun-fly plane, standard servos, banging all 5 servos from endpoint to endpoint.
They are well worth the money.
Steve
They are well worth the money.
Steve
02-22-2002, 08:50 PM
#3
Idea
What you are doing by decreasing throw, is increasing load/leverage. Be careful! This is where the power of your servos are tested, and things happen. The correct leverage is ever-so important here. If your having issues with flight-time already, see how your leverage/loads are placed. If correct, see if your batt. capacity is decently matched with the needs of your system.
GiantScale takes advantage of the power of the servo/linkage system, you don't have the advantage by decreasing the throw of the servo though.
I'm glad it works for you FCC, and it is an interesting idea, just don't know if I think it's viable, at least for me. Thanks,
GiantScale takes advantage of the power of the servo/linkage system, you don't have the advantage by decreasing the throw of the servo though.
I'm glad it works for you FCC, and it is an interesting idea, just don't know if I think it's viable, at least for me. Thanks,
03-03-2002, 03:49 AM
#5
Idea
The way I took the idea was to reduce the overall travel of the servo, and increase the movement of the surface again by increasing the leverage points.
This will place severe stress on servo horns and clevis's. To increase throw with minimal servo movement, you will have to place pushrod to the outermost longest point on servo, and the tightest, closest point on control horn. This will place all stress in areas that weren't necessarily designed for it, instead of distributing it evenly. This is just my thought here, and I'm totally open for other concepts. Anyone else?
This will place severe stress on servo horns and clevis's. To increase throw with minimal servo movement, you will have to place pushrod to the outermost longest point on servo, and the tightest, closest point on control horn. This will place all stress in areas that weren't necessarily designed for it, instead of distributing it evenly. This is just my thought here, and I'm totally open for other concepts. Anyone else?
03-04-2002, 04:44 PM
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Nahhhh!
I'm an electronic engineer and I've monitored the current draw of servos on the bench.
They take a brief pulse of current while moving, but when they're still the current drain is very low. When a load is imposed the current increases to hold the servo in place.
The best way to minimize current drain is to arrange the linkage for maximum servo travel. Then the in-oz torque required at the servo will be minimized.
They take a brief pulse of current while moving, but when they're still the current drain is very low. When a load is imposed the current increases to hold the servo in place.
The best way to minimize current drain is to arrange the linkage for maximum servo travel. Then the in-oz torque required at the servo will be minimized.
03-06-2002, 06:48 AM
#7
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Might want to take another look :-)
Hate to crash your party, but changing control linkage setups will not affect the total electrical energy consumed by the servo, thus will not extend flight time (with a caveat below). If you’re experiencing longer flight times following your linkage mod’s, it’s for some other reason or variables not accounted for.
First the basics - Current drain (amps) depends on torque, not servo travel. Electrical energy consumed is the product of current and time (amp-hours), but since time depends on the distance the servo travels, the energy (work performed) can be equated to the product of torque and the angle that the servo sweeps as it applies that torque.
The kicker is that you can't get energy from nowhere - Output torque and servo travel are inversely related – If you decrease load torque by changing the lever ratio, the servo has to travel proportionally farther (just like with gear ratios). No matter the configuration of the linkages, no matter if they’re linearly or non-linearly associated, no matter how they’re related, the mechanical work required for a given control surface throw will be the same, thus the electrical energy (amp-hours) consumed will be the same.
Now the caveat. From a physics standpoint, the above applies, however from a real-world engineering standpoint, reducing the load on the servo may be justified if, for example, the servo is running hot due to high torque, causing inefficient operation and associated high current drain vs. output torque.
Effective ways to decrease battery drain (for a given aircraft and control setup) include the old standbys:
1) Reducing friction and binding as much as possible: pushrod friction, clevis binding, misaligned control horns, hinge friction caused by warped control surfaces, misaligned hinges, glue in hinges, etc. Friction is (generally) the enemy.
2) Ensure that servos don't go beyond the limit of travel of the control surface. Stalling a servo is the worst (sky high battery drain plus heat). If your radio has it, adjust EPA’s accordingly.
3) Avoid unnecessary servo motion - Re-assess how many control functions you need, and whether they really need to be mixed or coupled. Also smooth flying, not bang-bang hardover stick action, but that comes naturally with experience.
First the basics - Current drain (amps) depends on torque, not servo travel. Electrical energy consumed is the product of current and time (amp-hours), but since time depends on the distance the servo travels, the energy (work performed) can be equated to the product of torque and the angle that the servo sweeps as it applies that torque.
The kicker is that you can't get energy from nowhere - Output torque and servo travel are inversely related – If you decrease load torque by changing the lever ratio, the servo has to travel proportionally farther (just like with gear ratios). No matter the configuration of the linkages, no matter if they’re linearly or non-linearly associated, no matter how they’re related, the mechanical work required for a given control surface throw will be the same, thus the electrical energy (amp-hours) consumed will be the same.
Now the caveat. From a physics standpoint, the above applies, however from a real-world engineering standpoint, reducing the load on the servo may be justified if, for example, the servo is running hot due to high torque, causing inefficient operation and associated high current drain vs. output torque.
Effective ways to decrease battery drain (for a given aircraft and control setup) include the old standbys:
1) Reducing friction and binding as much as possible: pushrod friction, clevis binding, misaligned control horns, hinge friction caused by warped control surfaces, misaligned hinges, glue in hinges, etc. Friction is (generally) the enemy.
2) Ensure that servos don't go beyond the limit of travel of the control surface. Stalling a servo is the worst (sky high battery drain plus heat). If your radio has it, adjust EPA’s accordingly.
3) Avoid unnecessary servo motion - Re-assess how many control functions you need, and whether they really need to be mixed or coupled. Also smooth flying, not bang-bang hardover stick action, but that comes naturally with experience.
03-06-2002, 12:44 PM
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Idea
One other thought. On a funfly with large control surfaces ,moving the rods to the inside holes creates more slop on the surface as they wear . More chance of flutter.For that reason I always use the longest servo arm and the furthest out hole on the control surface hornI can and still maintain throws. when the wear the slop is not near as bad. I have never had a flutter issue when doing this.
John
John
03-06-2002, 02:01 PM
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Re: Might want to take another look :-)
Originally posted by wildblueyawner
Hate to crash your party, but changing control linkage setups will not affect the total electrical energy consumed by the servo, thus will not extend flight time (with a caveat below). If you’re experiencing longer flight times following your linkage mod’s, it’s for some other reason or variables not accounted for.
First the basics - Current drain (amps) depends on torque, not servo travel. Electrical energy consumed is the product of current and time (amp-hours), but since time depends on the distance the servo travels, the energy (work performed) can be equated to the product of torque and the angle that the servo sweeps as it applies that torque.
The kicker is that you can't get energy from nowhere - Output torque and servo travel are inversely related – If you decrease load torque by changing the lever ratio, the servo has to travel proportionally farther (just like with gear ratios). No matter the configuration of the linkages, no matter if they’re linearly or non-linearly associated, no matter how they’re related, the mechanical work required for a given control surface throw will be the same, thus the electrical energy (amp-hours) consumed will be the same.
Now the caveat. From a physics standpoint, the above applies, however from a real-world engineering standpoint, reducing the load on the servo may be justified if, for example, the servo is running hot due to high torque, causing inefficient operation and associated high current drain vs. output torque.
Effective ways to decrease battery drain (for a given aircraft and control setup) include the old standbys:
1) Reducing friction and binding as much as possible: pushrod friction, clevis binding, misaligned control horns, hinge friction caused by warped control surfaces, misaligned hinges, glue in hinges, etc. Friction is (generally) the enemy.
2) Ensure that servos don't go beyond the limit of travel of the control surface. Stalling a servo is the worst (sky high battery drain plus heat). If your radio has it, adjust EPA’s accordingly.
3) Avoid unnecessary servo motion - Re-assess how many control functions you need, and whether they really need to be mixed or coupled. Also smooth flying, not bang-bang hardover stick action, but that comes naturally with experience.
Hate to crash your party, but changing control linkage setups will not affect the total electrical energy consumed by the servo, thus will not extend flight time (with a caveat below). If you’re experiencing longer flight times following your linkage mod’s, it’s for some other reason or variables not accounted for.
First the basics - Current drain (amps) depends on torque, not servo travel. Electrical energy consumed is the product of current and time (amp-hours), but since time depends on the distance the servo travels, the energy (work performed) can be equated to the product of torque and the angle that the servo sweeps as it applies that torque.
The kicker is that you can't get energy from nowhere - Output torque and servo travel are inversely related – If you decrease load torque by changing the lever ratio, the servo has to travel proportionally farther (just like with gear ratios). No matter the configuration of the linkages, no matter if they’re linearly or non-linearly associated, no matter how they’re related, the mechanical work required for a given control surface throw will be the same, thus the electrical energy (amp-hours) consumed will be the same.
Now the caveat. From a physics standpoint, the above applies, however from a real-world engineering standpoint, reducing the load on the servo may be justified if, for example, the servo is running hot due to high torque, causing inefficient operation and associated high current drain vs. output torque.
Effective ways to decrease battery drain (for a given aircraft and control setup) include the old standbys:
1) Reducing friction and binding as much as possible: pushrod friction, clevis binding, misaligned control horns, hinge friction caused by warped control surfaces, misaligned hinges, glue in hinges, etc. Friction is (generally) the enemy.
2) Ensure that servos don't go beyond the limit of travel of the control surface. Stalling a servo is the worst (sky high battery drain plus heat). If your radio has it, adjust EPA’s accordingly.
3) Avoid unnecessary servo motion - Re-assess how many control functions you need, and whether they really need to be mixed or coupled. Also smooth flying, not bang-bang hardover stick action, but that comes naturally with experience.
03-06-2002, 06:37 PM
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Yes, but.
Sure work and energy are related, but in this case most of the time the servo is stationary, either at rest or deflected some amount so the majority of the time we are concerned with the static load on the servo which is not work (no movement), but translates into electrical current.
Take the rudder for example. If we're flying straight and the rudder is at neutral, the load on the servo is little. If we are slipping in for a landing the rudder is deflected into the airstream during the slip. The air rushing by imposes a load on the rudder which is taken up by the servo (torque). This load becomes current. If you move the control rod at the rudder further out on the control horn it will take less servo torque to hold that same displacement, thus less current. It will also take more servo travel to reach the same rudder displacement, but that additional movement is a secondary effect.
You should always try to maximize servo travel during setup, that does not mean that you should maximize control surface deflection. By maximizing travel you will also maximize resolution, another good thing.
Take the rudder for example. If we're flying straight and the rudder is at neutral, the load on the servo is little. If we are slipping in for a landing the rudder is deflected into the airstream during the slip. The air rushing by imposes a load on the rudder which is taken up by the servo (torque). This load becomes current. If you move the control rod at the rudder further out on the control horn it will take less servo torque to hold that same displacement, thus less current. It will also take more servo travel to reach the same rudder displacement, but that additional movement is a secondary effect.
You should always try to maximize servo travel during setup, that does not mean that you should maximize control surface deflection. By maximizing travel you will also maximize resolution, another good thing.
03-07-2002, 03:35 AM
#13
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I love this thread!
But work (torque and travel) is what dictates (or limits) how our control linkage is set up; neither of those variables can be left out of the picture.
Let's consider the rudder example: We change the pushrod attachment point on the control horn to double its original distance from the hinge axis. Yes, IF we change nothing else, we've doubled resolution and cut holding torque in half, BUT we've also lost half of our control surface deflection. To restore the original range of motion, the attachment point on the servo arm needs to be changed to double its original lever arm length, which cuts resolution in half and doubles holding torque.
>>> If we consider the need for additional servo travel as a "secondary effect", there's no end to the amount of "improvement" we could rationalize, e.g. use a foot-long control horn, but don't worry about rudder deflection 
So we halve a doubled resolution, or double a halved torque, either way the product is 1 (no change
). The only way to increase res and reduce holding torque for a given surface deflection would be to use a servo having greater total range of motion acting through a reduced linkage ratio.... which calls for a different servo! Sorry, another case of “Can't get there from here” 
Diverging from FCC’s original topic, the post made by John B cites a good point that didn’t hit me until after building umpteen kits - By using the outer holes on servo arms and control horns (provided surface deflection reqmt's are met), linkage slop is minimized, both initially and due to wear. Reason is simple - a given distance (slop clearance) gets taken up by a smaller angle of surface deflection the farther out you go from the axis of rotation. Another advantage to using outer holes is that it reduces the load throughout the entire linkage, from servo to control horn, WITHOUT increasing the torque load anywhere, nor reducing resolution, again provided that the range of surface deflection isn't changed.
Let's consider the rudder example: We change the pushrod attachment point on the control horn to double its original distance from the hinge axis. Yes, IF we change nothing else, we've doubled resolution and cut holding torque in half, BUT we've also lost half of our control surface deflection. To restore the original range of motion, the attachment point on the servo arm needs to be changed to double its original lever arm length, which cuts resolution in half and doubles holding torque.
It will also take more servo travel to reach the same rudder displacement, but that additional movement is a secondary effect.
So we halve a doubled resolution, or double a halved torque, either way the product is 1 (no change
). The only way to increase res and reduce holding torque for a given surface deflection would be to use a servo having greater total range of motion acting through a reduced linkage ratio.... which calls for a different servo! Sorry, another case of “Can't get there from here” Diverging from FCC’s original topic, the post made by John B cites a good point that didn’t hit me until after building umpteen kits - By using the outer holes on servo arms and control horns (provided surface deflection reqmt's are met), linkage slop is minimized, both initially and due to wear. Reason is simple - a given distance (slop clearance) gets taken up by a smaller angle of surface deflection the farther out you go from the axis of rotation. Another advantage to using outer holes is that it reduces the load throughout the entire linkage, from servo to control horn, WITHOUT increasing the torque load anywhere, nor reducing resolution, again provided that the range of surface deflection isn't changed.
03-07-2002, 10:44 AM
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Idea
Hello!
It is really very simple.....There are Two things to remember!
Aways strive for as short servo arm as possible on the servos(to reduce play in the gearbox)and to use as much area on the potentiometer.The servo is also stronger as closer you get to the center
AND always strive for as long arm on the rudder/Aileron /elevator horn as possible to minimize play.
THIS IS THE RULE!
Never minimize the throw on any servo if it is possible as this gives you the whole gearbox-play and a shorter traveling distans for the servo arm (that induces play).
Regards!
Jan K
Sweden
Pylonflyer!
It is really very simple.....There are Two things to remember!
Aways strive for as short servo arm as possible on the servos(to reduce play in the gearbox)and to use as much area on the potentiometer.The servo is also stronger as closer you get to the center
AND always strive for as long arm on the rudder/Aileron /elevator horn as possible to minimize play.
THIS IS THE RULE!
Never minimize the throw on any servo if it is possible as this gives you the whole gearbox-play and a shorter traveling distans for the servo arm (that induces play).
Regards!
Jan K
Sweden
Pylonflyer!
03-07-2002, 03:43 PM
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I think we're coming to an agreement!
Let's talk about a scenario we can (hopefully) agree on. This is a common scenario too.
Say you setup the plane without thinking too much about linkages details but you want +/- 1 inch rudder travel when its all done.
1) You try it out, and find you have a +/- 2 inch swing... so you program the radio to cut down rudder servo travel to 50%, and you're done.
2) You try it out, and find you have a +/- 2 inch swing... so you rearrange the linkage connections to cut this down to +/- 1 inch without changing the (100%) servo travel.
Now, one of these responses will give both greater resolution and lower battery drain at a given rudder deflection. Do we all agree?
Say you setup the plane without thinking too much about linkages details but you want +/- 1 inch rudder travel when its all done.
1) You try it out, and find you have a +/- 2 inch swing... so you program the radio to cut down rudder servo travel to 50%, and you're done.
2) You try it out, and find you have a +/- 2 inch swing... so you rearrange the linkage connections to cut this down to +/- 1 inch without changing the (100%) servo travel.
Now, one of these responses will give both greater resolution and lower battery drain at a given rudder deflection. Do we all agree?
03-09-2002, 03:41 AM
#16
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Idea
so you program the radio to cut down rudder servo travel to 50%, and you're done.
so you rearrange the linkage connections to cut this down to +/- 1 inch without changing the (100%) servo travel.
2nd option is the way to go!
But the linkage should be changed by moving the pushrod attachment point on the control horn outward, NOT by moving the attachment point on the servo inward.
always strive for as long arm on the rudder/Aileron /elevator horn as possible
I choose pushrod attachment points like this:
1) Decide amount of surface deflection needed, then
2) Attach pushrod to the outer hole in servo arm, then
3) Attach other end of pushrod to whatever hole in the control horn provides the desired deflection (for me, usually the outer hole or next hole inward).
A long control horn (which forces using a long servo arm) reduces the effect of linkage slop AND reduces pushrod force, while not changing torque anywhere in the linkage setup AND not compromising resolution.
I agree that using the outer hole in servo arm worsens the effect of servo backlash, but (at least for me) linkage slop is always greater than servo backlash. And pot resolution will not be compromised by using the outer hole because, as long as the linkage ratio is maintained, the travel of the servo stays the same.
That's why I emphasize John B's post - because it's not immediately obvious. In fact, I think many people avoid using the outer hole in servo arms, believing that it will cause higher torque load on the servo or reduced resolution.
What limits the length of servo arms and control horns? Offhand, I see 4 things:
- Width of fuselage
- Pushrod routing problems
- Drag from large control horn
- Ugly appearance
03-09-2002, 05:42 AM
#18
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Idea
For us dummies, we just need to buy a bigger batt
LOL! - - Considering the number of words I put into this mini-dissertation, "buy a bigger batt" would have been the intelligent thing to do :stupid: I could have been flying / building / doing something constructive :cry:
05-10-2003, 02:22 AM
#20
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too much info not to acknowledge
wildblueyawner
Nah, you were teaching, and sharing! Good thought material.
Considering the number of words I put into this mini-dissertation, "buy a bigger batt" would have been the intelligent thing to do
Good thought material.
05-12-2003, 05:04 PM
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another view point
This is my rule of thumb,,
I use computer radio's and I set up like this...
atv/epa on my radio will allow servo travel to 140%,for the most torque and least stress and load to the servo you would start at 140% and install push rod as close to servo center and as far out on control horn as possible(I set at 135% to leave 5% to play with),at this point if your high rate control surface travel is short of what you want then adjust the linkage at one end or the other just enough to obtain the high rate travel you want.
this is the best for torque out of a servo and least load on a servo,,,however this also creates the slowest servo transit time so if you need more speed you would head towards the opposite end of this set up or better yet find a servo with the same torque rating but a faster transit time.
For what it's worth!
I use computer radio's and I set up like this...
atv/epa on my radio will allow servo travel to 140%,for the most torque and least stress and load to the servo you would start at 140% and install push rod as close to servo center and as far out on control horn as possible(I set at 135% to leave 5% to play with),at this point if your high rate control surface travel is short of what you want then adjust the linkage at one end or the other just enough to obtain the high rate travel you want.
this is the best for torque out of a servo and least load on a servo,,,however this also creates the slowest servo transit time so if you need more speed you would head towards the opposite end of this set up or better yet find a servo with the same torque rating but a faster transit time.
For what it's worth!
05-13-2003, 02:30 AM
#22
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Thank You ALL!!!!!
Now I've challenged. I'm going to try all of this on my experimental model just to see which configuration I like best. I have really enjoyed all of this thread and I believe There is a lot of useful information here. Thanks Guys!!!!!!!
Now I've challenged. I'm going to try all of this on my experimental model just to see which configuration I like best. I have really enjoyed all of this thread and I believe There is a lot of useful information here. Thanks Guys!!!!!!!
