Servo setup: EPA, current, and linkages

GYRO said:

Jacob, the 100 EPA you're using has been killing your servo's torque. Please check your other aircraft as well. This might have been why you felt like you were experiencing blowback on all your planes, when nobody else is.

-G

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All my other planes have had the EPA maxed out.

I will make sure I put the EPA to full on the laser.



As for the servos on my 104 extra, I just received a report on them from horizon. The bushing mounts for the gears were worn out causing my gears to shift under load; the pots were worn out, and the motors were in need of replacement on a few of the servos.

GYRO said:

Jacob, the 100 EPA you're using has been killing your servo's torque. Please check your other aircraft as well. This might have been why you felt like you were experiencing blowback on all your planes, when nobody else is.

-G

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Don't you want to set the system up so that you get maximum travel that is physically available with the EPA as close to max as possible? In order to do this you have to play with the length of the servo arm in order to make it all work out.

If you simply max out the EPA, then your servo MAY be trying to deflect the control surface farther than is physically possible. This causes the servo motor to continue to push without movement which causes heat build up and failure.

Am I right about this or am I missing something?

YellowJacketsRC said:

Don't you want to set the system up so that you get maximum travel that is physically available with the EPA as close to max as possible? In order to do this you have to play with the length of the servo arm in order to make it all work out.

If you simply max out the EPA, then your servo MAY be trying to deflect the control surface farther than is physically possible. This causes the servo motor to continue to push without movement which causes heat build up and failure.

Am I right about this or am I missing something?

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You're exactly right, I didn't think I was suggesting otherwise.

YellowJacketsRC said:

Are you talking about checking current to the servos? I never thought that would be necessary while using the Castle Creations 10 Amp BEC???

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This would be like saying I don't need to check how many amps my foamy size eletric motor is pulling because I am driving it with a 50amp ESC. Of course the ESC would be fine in this situation, regardless of prop size. The same can be said about the 10amp CC BEC. The BEC will be fine regardless of the current draw to the servos (unless a servo shorts though when it burns up, then it would more than likely take out the BEC too.) My point is that in both cases you will burn up something if you don't check current.

If you check the amperage being pulled by the electric motor and find out it is too much for the motor to handle, then you reduce the prop size to keep it from burning up. Same goes for a servo, if you check the amperage being drawn by a servo and it is too much, then you need to set it up better mechanically (check for binding, increase resolution, ect..)

Hopefully that makes some sense. It is very important that you check current draw everytime you setup a servo. Even a dead quiet servo can be fully stalled pulling 2+ amps.

Joe

Yea, like I said, I'm pretty sure as my flying has progressed that this has saved at least a servo or 2 so far. I just made some adapters for my wattmeter and hook it in line with the servo to check amps. Im sure one of the meters just for testing servo current is more accurate but hopefully my WattsUP meter will get me close.

Say on my 7245's I just set up. I maxed out the EPA's , I set them to 150, set my dual rate to 100. I deflected the servo full up on my elevator and it was reading about .44 but between center and close to full up I had a max of .12 amps . So I backed the epa down to about 147 and amps where at .18 at full deflection. On my angle finder I only lost 1.5 degree of throw but also lost almost .3 amps of current drawn on the servo.

I think im doing this right but im not 100% sure. I don't have anybody close to show me in person. If this is the correct way, I can see why you would ALWAYS want to set your servos up this way. Like Joe said you just don't know until you hook them up to a meter.

I was also wondering if you guys rotate out your servos.

It seems like im the harder on my elevator and rudder servos. I though it may be advantageous to rotate those 2 out with the ailerons after awhile?

wedoitall said:

Yea, like I said, I'm pretty sure as my flying has progressed that this has saved at least a servo or 2 so far. I just made some adapters for my wattmeter and hook it in line with the servo to check amps. Im sure one of the meters just for testing servo current is more accurate but hopefully my WattsUP meter will get me close.

Say on my 7245's I just set up. I maxed out the EPA's , I set them to 150, set my dual rate to 100. I deflected the servo full up on my elevator and it was reading about .44 but between center and close to full up I had a max of .12 amps . So I backed the epa down to about 147 and amps where at .18 at full deflection. On my angle finder I only lost 1.5 degree of throw but also lost almost .3 amps of current drawn on the servo.

I think im doing this right but im not 100% sure. I don't have anybody close to show me in person. If this is the correct way, I can see why you would ALWAYS want to set your servos up this way. Like Joe said you just don't know until you hook them up to a meter.

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Your process sounds great! The current they are pulling close to center should be very close to the current they are pulling at full deflection. Your's looks to agree with that, plus .18 is a very good number. I'd be happy with that.

Cool thanks Joe. Where I get all of my info on the internet and don't have anybody to show me in person. Im always second guessing, especially on setups.

Gyro,
I was asking for clarification, not suggesting you were wrong

Joe I do understand. What I was thinking was on the CC I could set voltage where I wanted it and did not need to check. Obviously I was missing the point. I understand clearly now that the amps are going to go up as the servo begins to bind.

So now I have three questions. The first is how do I check current on the servos?

Second, I often find that as I break a new plane in, the control surfaces will loosen up after a bit of use. If, as in Wedoitall's case, I am getting high amps in the last little bit of throw, Should I back down, and then try again after 10 or fifteen flights?

I understand that I get better resolution with EPA at max. I also understand that I should use as short a servo arm as I can and still get proper max throw so that I can max out the EPA AND get maximum mechanical advantage. My question is, what happens if I have EPA at max and I use the dual rate to cut back the throw? Do I still get maximum resolution?

YellowJacketsRC said:

Gyro,
I was asking for clarification, not suggesting you were wrong

Joe I do understand. What I was thinking was on the CC I could set voltage where I wanted it and did not need to check. Obviously I was missing the point. I understand clearly now that the amps are going to go up as the servo begins to bind.

So now I have three questions. The first is how do I check current on the servos?

Second, I often find that as I break a new plane in, the control surfaces will loosen up after a bit of use. If, as in Wedoitall's case, I am getting high amps in the last little bit of throw, Should I back down, and then try again after 10 or fifteen flights?

I understand that I get better resolution with EPA at max. I also understand that I should use as short a servo arm as I can and still get proper max throw so that I can max out the EPA AND get maximum mechanical advantage. My question is, what happens if I have EPA at max and I use the dual rate to cut back the throw? Do I still get maximum resolution?

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Rob, to check current, here is an easy way. Hook up a watt meter between ESC and battery. Unplug all servos except the one you want to test. Then move as desired, and note the draw. Repeat the method for each servo.

I would do exactly as you suggested for high amps at last bit of throw on a new plane. Back down until the draw is acceptable, then fly and check again. It may improve as the plane breaks in, and it may not, but the high draw should be avoided regardless.