Closed loop control system.

**wonwinglo** · 26-09-2004

Ever considered a closed loop control system for your model ? there are certainly advantages but a few pitfalls for the unwary,the biggest problem is keeping the wires taught whatever the weather or stretch on the cables,to be effective you must have some means of adjusting the system easily on the flying field and the following method using standard easily available parts takes this into consideration-
Whether we are starting at the servo arm end or the dual output to the rudder or elevator horns the same applies as to the method used,first get hold of some threaded collets and attach these to the servo arm carefully adjusting them to avoid undue slop but making them easy to rotate in the arms,do the same at the horn ends on the model,now take some small split pins and place these into the horizontal holes in the collets and just nip up the grub screws,with some fishing trace line with two crimps slipped onto the line,thread this through the eyes of the split pins and with a pair of pliers crimp up the servo end,neutralise the servo and stretch this through the fuselage and to the tail repeating this process until two equal lines are in place,now with your transmitter trims set at centre gently pull the split pins through the collets tightening them up in turn.
Thats it,job done a system that enables you to keep a check on the tensions which will slacken off due to inflight loads and differences in temperature,should you need to adjust for any bias in trim on your model this can be done from the cables rather than slewing the servo arms.
Just make sure that you check your cables as part of your pre-flight check,better safe than sorry.

bartley · 27-03-2005

Quote:

Originally Posted by wonwinglo

Ever considered a closed loop control system for your model ? there are certainly advantages but a few pitfalls for the unwary,the biggest problem is keeping the wires taught whatever the weather or stretch on the cables,to be effective you must have some means of adjusting the system easily on the flying field and the following method using standard easily available parts takes this into consideration-
Whether we are starting at the servo arm end or the dual output to the rudder or elevator horns the same applies as to the method used,first get hold of some threaded collets and attach these to the servo arm carefully adjusting them to avoid undue slop but making them easy to rotate in the arms,do the same at the horn ends on the model,now take some small split pins and place these into the horizontal holes in the collets and just nip up the grub screws,with some fishing trace line with two crimps slipped onto the line,thread this through the eyes of the split pins and with a pair of pliers crimp up the servo end,neutralise the servo and stretch this through the fuselage and to the tail repeating this process until two equal lines are in place,now with your transmitter trims set at centre gently pull the split pins through the collets tightening them up in turn.
Thats it,job done a system that enables you to keep a check on the tensions which will slacken off due to inflight loads and differences in temperature,should you need to adjust for any bias in trim on your model this can be done from the cables rather than slewing the servo arms.
Just make sure that you check your cables as part of your pre-flight check,better safe than sorry.

Evening Barry, I've just been scrolling through the tutorials, many of which will be of great help to me in completing my aeroplane, not the least of which is the closed loop system which I've decided to use.

Steve.

Greyhead · 28-03-2005

One useful tip for closed loop or pull / pull systems is to incorporate the Ackerman Principle ( a Google search will explain it fully). Basically make the connections to the control horn slightly behind the hinge line (towards the TE). If the cables are set with no slop at neutral then as the controls are moved the pull side moves slightly more than the other, the "non-pull" cable goes slightly slack, therefore ensuring that there is no undue force on the servo bearing. I’ve used this principle on all my models with no problems; it may not be acceptable to the out and out aerobatic pilots as it is in effect introducing very slight slop into the system, but for all others it certainly is the way to do it.

**wonwinglo** · 28-03-2005

Quote:

Originally Posted by Greyhead

One useful tip for closed loop or pull / pull systems is to incorporate the Ackerman Principle ( a Google search will explain it fully). Basically make the connections to the control horn slightly behind the hinge line (towards the TE). If the cables are set with no slop at neutral then as the controls are moved the pull side moves slightly more than the other, the "non-pull" cable goes slightly slack, therefore ensuring that there is no undue force on the servo bearing. I’ve used this principle on all my models with no problems; it may not be acceptable to the out and out aerobatic pilots as it is in effect introducing very slight slop into the system, but for all others it certainly is the way to do it.

*** That is exactly how it is done on full sized cable operated aircraft as well Grahame,a very useful tip.
No doubt this has connections with Mr Ackermans steering principles as well I would imagine ?

Greyhead · 28-03-2005

Barry

It was originally devised for the steering of motorcars but I’ve found this site that explains the science behind the principle as applied to aircraft controls.

http://members.cox.net/bdfelice/Ackerman/ackerman.htm

Grahame

*** Grahame fascinating stuff,like the writer says I too have been introducing this into my control systems without even realising it in the past,also note how the Futaba rotary arms also allow for Ackerman in being pre marked as such ready for drilling,one important thing to remember is the introduction of standard differential to ailerons via cranking the horn forward is nothing to do with the Ackerman principle it only applies if a closed loop system is introduced,but what a useful system it really is.
Differential is a way whereby the upgoing aileron has more throw than the downgoing to avoid aileron reversal as the worst scenerio ( usually happens with aileron wings having some dihedral )
I only mention this to avoid confusion between the two.
The explanation & drawings on that page are first class and well worthy of study.

fli48rc · 28-03-2005

A member of an Electric Group in belong to posted this on our Group's website

PULL PULL SYSTEM FOR LIGHT WEIGHT MODELS

After having trouble trying to keep the lines tight on lightweight models I have come up with this system.

Spider wire is high priced fishing line, which I got at K-mart.

1. String spider wire though servo horn and back to rudder in one piece.

2. Drill a hole though the round toothpick just big enough to accept spider wire.

3. Thread Spider wire though hole and slide small fuel tubing over toothpick adjusting for wanted rudder throw.

4. Adjust wire at servo horn to center rudder.

5. Push fuel tubing over front of horn to take up any slack in lines.

6. If lines get bumped and become slack all you have to do is pull the tubing back and take out the slack.

**wonwinglo** · 28-03-2005

Mark,thanks for this useful system,I am just thinking how it could be beefed up to apply to larger models ?,these simple ideas are always the best,above all it allows for that important adjustment on closed loop systems,I have never heard of spider wire but will call into my local fishing tackle shop shortly to buy some and experiment.

**wonwinglo** · 28-03-2005

Those with Meccano sets can easily fabricate a jig that reproduces exactly the Ackerman principles,I have also in the past made up differential steering systems and gearboxes in Meccano,they are very educational to young and old alike.

Antony · 04-10-2006

Hi folk, Ive not built any models for many many years. I can see that several things have changed. Now that I am starting to get back into it again I was wondering if someone can explain the difference between closed loop and what I was used to back in the 70's please?
Oh and can anyone suggest a few sources of where I can get kits from in the UK - I am not into these modern ARTF kits and prefere to build them.
Thanks Antony