Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[kallend]

Sure. But you can infer a lot from his measured voltage drop. If the voltage goes down from 4.9V at the receiver to 3.5V at his servo at a current of 2.5A, then we have a wire resistance of 1.4V/2.5A = 0.56 Ohms. If we assume the wire resistance is about constant at these currents and temperatures, then we can calculate the voltage drop for a normal servo. If it stalls at about 1A, the voltage drop will be 0.56 Ohms * 1A = 0.56V. That means a 1A-stalling servo will see about 4.34V.

Does the servo run well at 4.34V? Do we have the stall current for the replacement servos?

Cheers,
Henrik

The reported stall current for the "replacement" servos was 0.7A. That would give a drop of 0.39V. The integrated Freewing BEC gives 5.4V according to several reports (including my own) so the servo would see 5V

[Evan D]

The external BEC in the MiG puts out 5.01v in mine.

[kallend]

The external BEC in the MiG puts out 5.01v in mine.

Yes, I wonder why they are calibrated differently.

Regardless, that's a worst case scenario (servo actually stalled so the airflow is pushing hard against the stab. . . - Newton's 3rd Law suggests the stab surface is exerting a lot of force on the airflow so there should be a response from the model). I don't see the wires as the root cause of the problem although it can't hurt to use a heavier gauge.

[Borat]

Folks,

I received the Mig29 little less than 3 weeks ago. I’ve flown it at least 15 times. I love this plane and I think it flies great. But word of caution. I tested a hypothesis today out of concern that you could inadvertently crash this plane. I know there has been issues with this plane regarding elevator control and there maybe different issues involved. My hypothesis is that this plane may lose control with flaps deployed and going to full throttle. This is not something that’s routinely done but could happen if you’re not aware that your flaps are deployed. Every time I tried that today, the result was the same. Of course I tried this at high altitude. Flap deployed, nose of the plane pointed down at around 20-30 degrees, full throttle and the plane pitched down further with no elevator control. Only way to bail out is to raise the flap, lower throttle-to give your self time before you hit the ground- and you will regain elevator control.

All of you who still have this plane can try this maneuver to prove it but please do it from high altitude. If I can capture on video I would be happy to post. But for now, be very careful with going to full throttle with flaps deployed. No issue with landing this plane with throttle management during landing using flaps. I suspect there maybe turbulent airflow over the elevators at higher speeds with flaps deployed. But I don’t know that for sure

[leithalweapon]

Imagine going 120mph in a car and sticking one of these elevators out the window. It has to be flexing. Especially when you consider how much more surface area is behind the elevator axle as compared to ahead of the axle. The force on the conrol horn has to be substantial.

[Captain MoMo]

Folks,

I received the Mig29 little less than 3 weeks ago. I’ve flown it at least 15 times. I love this plane and I think it flies great. But word of caution. I tested a hypothesis today out of concern that you could inadvertently crash this plane. I know there has been issues with this plane regarding elevator control and there maybe different issues involved. My hypothesis is that this plane may lose control with flaps deployed and going to full throttle. This is not something that’s routinely done but could happen if you’re not aware that your flaps are deployed. Every time I tried that today, the result was the same. Of course I tried this at high altitude. Flap deployed, nose of the plane pointed down at around 20-30 degrees, full throttle and the plane pitched down further with no elevator control. Only way to bail out is to raise the flap, lower throttle-to give your self time before you hit the ground- and you will regain elevator control.

All of you who still have this plane can try this maneuver to prove it but please do it from high altitude. If I can capture on video I would be happy to post. But for now, be very careful with going to full throttle with flaps deployed. No issue with landing this plane with throttle management during landing using flaps. I suspect there maybe turbulent airflow over the elevators at higher speeds with flaps deployed. But I don’t know that for sure

Perhaps others can test this as well and report back? A video would be great!

[Wefinance01]

An old anecdote that ive heard from a bunch of rc pilots over the last 14 years is to not use y connectors as much as possible. Its something ive followed over the years and the only reasoning that the older "experienced" pilots had was that adding more connectors to a wire is just adding another point of failure. Be it the amount of contact that the connector can make to the quality of metal used to pass the signal and current through. I have choosen to follow this with my builds over time and hope that it saves me from whatever issues have been hapoening with others migs. i have put my elevators on seperate channels on the rx and the throttle connectors have been soldered together into one connector instead of using a y. Im even tempted to take out the elevator connector and solder the servo leads directly to the extension just like my gassers. If you believe in rf chokes or not, or y connectora or not, or using battery power supply for rx, a stand alone bec, or esc bec; im sure they all have there bit of evidence in working. Whatever gives you piece of mind.

Smart man, a lot of folks here have written off what sonic vibration from these edf units can do to connector pins. Not all connectors are equally put together..thats why we have a lot folks still flying this plane at with stock setup at correct CG. Folks also forget that this has a full flying scale stab..which doesn't take much angle to change the planes angle at high speed.

[Wefinance01]

Imagine going 120mph in a car and sticking one of these elevators out the window. It has to be flexing. Especially when you consider how much more surface area is behind the elevator axle as compared to ahead of the axle. The force on the conrol horn has to be substantial.

Depends on the angle. They work as a starting lever to rotate the plane at angle...then wide fuse assists the plane to rotate vector. 3D guys understand this..for example in doing a wall maneuver.

[Firebird]

Sure. But you can infer a lot from his measured voltage drop. If the voltage goes down from 4.9V at the receiver to 3.5V at his servo at a current of 2.5A, then we have a wire resistance of 1.4V/2.5A = 0.56 Ohms. If we assume the wire resistance is about constant at these currents and temperatures, then we can calculate the voltage drop for a normal servo. If it stalls at about 1A, the voltage drop will be 0.56 Ohms * 1A = 0.56V. That means a 1A-stalling servo will see about 4.34V.

Does the servo run well at 4.34V? Do we have the stall current for the replacement servos?

Cheers,
Henrik

Thanks Henrik, you got it - that’s what the test is showing. Not more and not less.

If you run upgraded servos in combination with the stock elevator cables (especially in combination with the y-cable) - don’t be surprised that they can’t provide the full torque as the voltage at the servos under load drops due to resistance in the cables.

Keep in mind that the bluebox was not connected (additional resistance and even longer cable)

Interesting would be how much torque the (upgraded) stock servo can give you at lower voltages.

[leithalweapon]

Depends on the angle. They work as a starting lever to rotate the plane at angle...then wide fuse assists the plane to rotate vector. 3D guys understand this..for example in doing a wall maneuver.

If that's the case then the servos must not see much load at all.

[Wefinance01]

If that's the case then the servos must not see much load at all.

Correct..these are not 3D planes and has enough force to handle this plane with the MRC provided/updated servos. I've used the Hs225 on an Extremeflight 60in MXS which is a subpar servo for 3D and did plenty of 100 mph walls without failing. I believe the Hs225MG is about the same torque as the provided servo for this bird. Besides, at least 10% of that force is wasted by that stupid servo placement angle..that angle should be 90 degrees for optimal force.. I would be more concerned about checking those servo wire connectors for slop or weakness as those are the first to go under sonic vibration generated by the edf units. I would bypass the Distribution board with the elevator servos and individually assign those to its own channel directly into the rx without the y harness....happy flying.

[Firebird]

Firebird - Your results are strongly suggesting that using upgraded servos beyond MRC-supplied product needs a wiring upgrade as well.

Data summary suggests:
(a) MRC stock or MRC upgraded servos - Stock wiring has minimal voltage drop even under stalled condition at the rear servos (info from the YouTube video and your 0.7 amp readings)
(b) Upgraded servos that draw more current than MRC servos may need a wiring upgrade to minimize voltage drop at the rear servos

Have you had a chance to look at signal strength telemetry data?

Thanks again for this effort.

-GG

Hello Gliderguy,

correct - in order to get the high torque out of your upgraded servos - you should consider that they need cables capable of delivering the required voltage / amps at the servo.


I‘m flying real size jets for living and unfortunately i won’t have too much time in the upcoming two weeks as i will be on rotation. I will look deeper into the signal analysis when i‘m back home.

Safety first

Happy landings

[Firebird]

Sure. But you can infer a lot from his measured voltage drop. If the voltage goes down from 4.9V at the receiver to 3.5V at his servo at a current of 2.5A, then we have a wire resistance of 1.4V/2.5A = 0.56 Ohms. If we assume the wire resistance is about constant at these currents and temperatures, then we can calculate the voltage drop for a normal servo. If it stalls at about 1A, the voltage drop will be 0.56 Ohms * 1A = 0.56V. That means a 1A-stalling servo will see about 4.34V.

Does the servo run well at 4.34V? Do we have the stall current for the replacement servos?

Cheers,
Henrik

Telemetry test 3

First of all: Henrik, your calculation regarding the voltage at the (upgraded) stock servos is correct!

As many of you are concerned about the voltage situation at the (upgraded) stock servos, I did run another quick test to show what is happening with the voltage at the upgraded stock elevator servo in stall condition.

Setup:

Jeti Mui150 telemetry sensor soldered into the servo power line directly in front of one upgraded stock servo.
Both upgraded stock servos connected via the stock elevator cables and the MRC y-cable into one channel of my jeti rex12 receiver. Stock BEC directly powering the receiver. No Bluebox.

1: Both servos idle - no movement - voltage at the servo 4.9Volt.

2: Both servos running in servo test program on half speed. Both servos stalled by hand to zero movement.
Voltage at the servos in stalled condition: 4.3Volt.

[PieterO]

Folks,

I received the Mig29 little less than 3 weeks ago. I’ve flown it at least 15 times. I love this plane and I think it flies great. But word of caution. I tested a hypothesis today out of concern that you could inadvertently crash this plane. I know there has been issues with this plane regarding elevator control and there maybe different issues involved. My hypothesis is that this plane may lose control with flaps deployed and going to full throttle. This is not something that’s routinely done but could happen if you’re not aware that your flaps are deployed. Every time I tried that today, the result was the same. Of course I tried this at high altitude. Flap deployed, nose of the plane pointed down at around 20-30 degrees, full throttle and the plane pitched down further with no elevator control. Only way to bail out is to raise the flap, lower throttle-to give your self time before you hit the ground- and you will regain elevator control.

All of you who still have this plane can try this maneuver to prove it but please do it from high altitude. If I can capture on video I would be happy to post. But for now, be very careful with going to full throttle with flaps deployed. No issue with landing this plane with throttle management during landing using flaps. I suspect there maybe turbulent airflow over the elevators at higher speeds with flaps deployed. But I don’t know that for sure

That's a brave thing to do! Unfortunately the weather in the Netherlands is really bad, so no flying for me. But it would indeed be interesting if people could repaet/verify this test.

[GliderGuy]

Telemetry test 3

1: Both servos idle - no movement - voltage at the servo 4.9Volt.

2: Both servos running in servo test program on half speed. Both servos stalled by hand to zero movement.
Voltage at the servos in stalled condition: 4.3Volt.

Thanks again Firebird. As I see it....Here is where we are.

1) The published min voltage spec for the MRC servos is 4.8V for the recommended operating condition.
2) Operation outside the ROC is not typically guaranteed by a manufacturer.
3) MiG drivers, yet, have no hard proof (video) that servos are stalled.
4) “IF” MiG drivers suspect servo stall is happening or could happen, it is up to us (not MRC) to mitigate and ensure servo stall doesn’t occur which will keep the servos within the published ROC.
5) MiG pilots most probably are aware of the flying style that might induce servo stall.
6) Stock wiring and servos are sufficient to operate the MiG w/o crashing as long as the ROC is not exceeded.

We must select the mitigation method of our choice.
- Flying style to ensure servos won’t stall
- Upgraded wiring and stronger servos if we intend to fly with a style which might induce servo stall

Pretty much up to us. If I were MRC, I might say something like...“Operating as to cause the ROC to be exceeded is not recommended. Operation outside the ROC may induce stresses which may impact successful operation.” In other words....not guaranteed.

Consider a car which you take to the drag strip occasionally to race. If you want the car to last, you will take actions to mitigate the extreme stress of drag racing. Common sense, if you want the car to last.

And....it now appears we need to avoid flying flaps down with high throttle/speed conditions.

We are getting a handle on the mystery! Bottom line, flight styles which might possibly cause operation conditions outside the servo ROC is at your own risk. It ain’t pretty, but that’s where we currently are IMO.

-GG

[Firebird]

Telemetry - test 4

Test 4 is showing the voltage at the upgraded stock elevator servo in stall condition connected to my upgraded, rerouted servo cables:


Setup:

Jeti Mui150 telemetry sensor soldered into the servo power line directly in front of one upgraded stock servo.
Both upgraded stock servos connected via upgraded servo cables, each connected to it‘s own channel at my jeti rex12 receiver. Stock BEC directly powering the receiver. No Bluebox.

1: Both servos idle - no movement - voltage at the servo 4.9Volt.

2: Both servos running in servo test program on half speed. Both servos stalled by hand to zero movement.
Voltage at the servos in stalled condition: 4.8V

Thanks Gliderguy,
in order to keep the voltage at the servo within the recommended operating voltage area, i recommend to exchange both elevator servo cables with 0,5qmm x 50cm drilled upgrade cables with goldcontacts. This is a done for 15dollars and you get better torque and bigger voltage safety margin at your elevator servos.

[GliderGuy]

Firebird - One missing data point.

What is the current/voltage when the servo is not being commanded to move and you apply a load in an attempt to move it? In other words, what are air loads doing to the stationary not stalled servo?

Can you post a link to the better cables?

-GG

[Jacckall]

This is my favourite brand: Hacker Motors

Servo extensions:
https://www.hacker-motor-shop.com/Se...0025050&p=8312

[Firebird]

Firebird - One missing data point.

What is the current/voltage when the servo is not being commanded to move and you apply a load in an attempt to move it? In other words, what are air loads doing to the stationary not stalled servo?

Can you post a link to the better cables?

-GG

copied, working on it. I used exactly the servo cables which Jacckall posted just now.

[Jacckall]

Telemetry - test 4

Test 4 is showing the voltage at the upgraded stock elevator servo in stall condition connected to my upgraded, rerouted servo cables:


Setup:

Jeti Mui150 telemetry sensor soldered into the servo power line directly in front of one upgraded stock servo.
Both upgraded stock servos connected via upgraded servo cables, each connected to it‘s own channel at my jeti rex12 receiver. Stock BEC directly powering the receiver. No Bluebox.

1: Both servos idle - no movement - voltage at the servo 4.9Volt.

2: Both servos running in servo test program on half speed. Both servos stalled by hand to zero movement.
Voltage at the servos in stalled condition: 4.8V

Thanks Gliderguy,
in order to keep the voltage at the servo within the recommended operating voltage area, i recommend to exchange both elevator servo cables with 0,5qmm x 50cm drilled upgrade cables with goldcontacts. This is a done for 15dollars and you get better torque and bigger voltage safety margin at your elevator servos.

Hello!

I like your test! One question for you :) - its possible to do a test with elevators connected to bluebox? I am interested in result with this stock connection(with bluebox). Thank you very much!
Even better 2 tests - stock servo extension with upgraded servos and upgraded servo extension with upgrades servos - both with bluebox connection. Thanks very much!