Servo setup: EPA, current, and linkages

[flylow3d]

8.4v

Ahh. I have been working with the guys at MKS and they recommended to me that when using a BEC the voltage should be set to 7.4 volts. Their explanation for this was that a 2s lipo doesn't remain at 8.4 volts. A 2s lipo drops down under 8 volts very quickly and will drop to 7.2-7.5 volts under load.

Heat seems to what is killing servos, hence the reason they work for quite a few flights but start to fade out. Basically, higher voltage=higher temp. A heli doesn't "load" the servo like rifle rollers do, so heat dissipation could be the problem. I have a set coming and I plan on running them at 7.4 and watching the temps.

 

[3dbandit]

Ahh. I have been working with the guys at MKS and they recommended to me that when using a BEC the voltage should be set to 7.4 volts. Their explanation for this was that a 2s lipo doesn't remain at 8.4 volts. A 2s lipo drops down under 8 volts very quickly and will drop to 7.2-7.5 volts under load.

Heat seems to what is killing servos, hence the reason they work for quite a few flights but start to fade out. Basically, higher voltage=higher temp. A heli doesn't "load" the servo like rifle rollers do, so heat dissipation could be the problem. I have a set coming and I plan on running them at 7.4 and watching the temps.

Thanks Joe,

I am not using a BEC, I'm using a 2s lipo.

So I guess my voltage is around 7.4v...

Once i get a replacement set I am going to try and put a telemetry temp probe on and see if i can collect any data.
What do you think a safe max temp is?

 

[flylow3d]

Thanks Joe,

I am not using a BEC, I'm using a 2s lipo.

So I guess my voltage is around 7.4v...

Once i get a replacement set I am going to try and put a telemetry temp probe on and see if i can collect any data.
What do you think a safe max temp is?

Ah, ok.

I'm not sure what a safe temp. would be and definitely don't want to make a guess. I recently read a review about these servos and the reviewer said that he "...checked the temperature after each flight, and as expected the servos were hot to the touch, and the heat quickly dissipated through the aluminum case. "

This review was for a Goblin 500. In my experience, a heli puts quick loads on a servo but never sustains it for very long. Just the opposite can be said for today's "freestlye" aerobatics.

So with all of that said, cooling seems to be the main concern. I'm guessing a lower voltage (maybe 6.5-7 volts) would help reduce the amount of heat a little. Another idea I have had for awhile is ducting air to the aileron servos. There is a ton of airflow going over the wing, why not harness a little bit of this to help keep our servos happy? I hope to implement this on a few airplanes over the winter.

Any idea what your current draw is? surface deflection? epa? Those numbers would really help determine if it is perfectly setup mechanically.

 

[3dbandit]

Ah, ok.

I'm not sure what a safe temp. would be and definitely don't want to make a guess. I recently read a review about these servos and the reviewer said that he "...checked the temperature after each flight, and as expected the servos were hot to the touch, and the heat quickly dissipated through the aluminum case. "

This review was for a Goblin 500. In my experience, a heli puts quick loads on a servo but never sustains it for very long. Just the opposite can be said for today's "freestlye" aerobatics.

So with all of that said, cooling seems to be the main concern. I'm guessing a lower voltage (maybe 6.5-7 volts) would help reduce the amount of heat a little. Another idea I have had for awhile is ducting air to the aileron servos. There is a ton of airflow going over the wing, why not harness a little bit of this to help keep our servos happy? I hope to implement this on a few airplanes over the winter.

Any idea what your current draw is? surface deflection? epa? Those numbers would really help determine if it is perfectly setup mechanically.

Not sure of current draw.
My Deflections are 45 degrees at the ailerons.
EPA is 100.

I wonder if I could use something similar to a NACA duct for cooling.

 

[flylow3d]

Not sure of current draw.
My Deflections are 45 degrees at the ailerons.
EPA is 100.

I wonder if I could use something similar to a NACA duct for cooling.

Definitely want to check current. It sometimes really is the "silent" killer.

About the epa, they should be set to as close to max as possible. So the linkage will get moved in on the servo arm until an EPA of 140 or so gives you 45 degrees. This will help the servo out a TON, and make the plane feel even more precise due to the increased resolution.

 

[3dbandit]

Definitely want to check current. It sometimes really is the "silent" killer.

About the epa, they should be set to as close to max as possible. So the linkage will get moved in on the servo arm until an EPA of 140 or so gives you 45 degrees. This will help the servo out a TON, and make the plane feel even more precise due to the increased resolution.

Ok,

I will check current on the new servos and try increasing the EPA.

 

[gyro]

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

 

[wedoitall]

Definitely want to check current. It sometimes really is the "silent" killer.

About the epa, they should be set to as close to max as possible. So the linkage will get moved in on the servo arm until an EPA of 140 or so gives you 45 degrees. This will help the servo out a TON, and make the plane feel even more precise due to the increased resolution.

How exactly do you go about checking current and what numbers do you look for to setup perfect mechanically? Say like a 7245?

Ive been using a amp meter on the last few planes ive set up and IMO probably has saved a servo failure or 2 already but im not 100 percent completely confident that im doing it correctly.

 

[dth7]

Good subject for an article if no one has done it.

We are also kicking around a "winterizing" (for those who have an end of season!) or annual inspection power point to discuss how to go through your plane nose to tail after the flying season ends.

 

[YellowJacketsRC]

How exactly do you go about checking current and what numbers do you look for to setup perfect mechanically? Say like a 7245?

Ive been using a amp meter on the last few planes ive set up and IMO probably has saved a servo failure or 2 already but im not 100 percent completely confident that im doing it correctly.

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