Post by Bobby Diggins on Oct 20, 2015 2:24:34 GMT
E-Flight Apprentice Reversed Servo
While fixing a problem servo in an Apprentice 15E RC Plane with AS3X, we came across something very interesting. One of our group (Kevin,) had changed both servos on his Apprentice for a higher quality metal geared digital Servo. The reason was he thought on of his stock servos might have a problem.
What we later found out was that the replacement Hyperion servos turned a different way than the Apprentice Servos or any servos we tried out at the field while trying to track down the issue.
It was not as easy to track down as you would think.
Putting either the new or replacement servos in most any other plane is not a problem. But the Apprentice with its built in AS3X stabilization system, made it a problem.
The AS3X is pre programed to make certain type correction based on the attitude of the plane.
Example: When the planes right wing falls the AS3X sends a signal to push the right aileron down to compensate and level the plane. It sends the signal to the servo to move clockwise or counterclockwise based on its programming. So putting in a “Reverse Servo” causes the plane to correct the opposite, making the problem worse, and most surely resulting in a crash. It makes me wonder how many people have replaced the servos in an Apprentice and crashed.
If you put the wrong servos in, the first thing you will see (Like any plane) is the ailerons move the opposite way. But like any other plane,,, Most people will go into their radio and Reverse the servos there. That would make most planes fly fine. Including the Apprentice, until the AS3X tries to correct for a gust of wind, IN REVERSE !
We learned a lot in the process.
First of all many of us did not know you can buy “Reverse Servos.”
Most of the time this is not an issue and few people ever know that servos can come in different travel directions for the same input, because there are several ways to correct a servo that turns the wrong way. Reversing the channel in the radio is one. It is what most people would do if they find a control surface moving the opposite direction.
Moving the control arm to the other side (180°,) if possible based on the placement is another way.
A third would be to flip the servo over. This only works one way. That is to flip the servo such that the top of the servo where the control horn hooks on, with the bottom of the servo. (Rotating it on the axes of the servo shaft will not change anything.)
Some, but not all Digital Servos are programmable.
You can reverse the direction, Slow down the Speed, and Center the arm to 90° with a Digital Servo Programer. Or you can take it to the local hobby store and most will be glad to do it for you. We went over to National Hobbies and they gladly preprogramed ours. The stock Apprentice servos are digital, but not programable.
Tom at National Hobbies on Baseline in Mesa Arizona is always a GREAT source of knowledge. Something else he taught us is that, on a servo has an Odd number of splines (gear teeth) on the top, when you put on the servo horn, if it is off just a little from 90°,,, you can rotate it 180° and it will not be in the exact same position. This can be good or bad, but once you have that piece of knowledge, it will probably come in handy sooner or later, and you can use it to your advantage when you have a control horn that doesn’t quite line up at 90º with the servo. With an EVEN number of splines, turning the control horn 180° will result in it being in the exact same position.
We also learned that although the ESC on the Apprentice will except a 4 Cell battery, it is not simple. It will accept the voltage, but you have to adjust the wattage by adjusting the prop size down. It seems simple but to be safe there is a lot of math involved, so its not something you should do without some research.
After much internet searching. I feel the below article OPJOSE on RCUNIVERSE explains the 3 to 4 Cell LiPo situation best….
4s battery on apprentice 15e (vs 3s)
The Eflite BL-15 950KV is rated at 34A continuous and 42A burst
The Motor used in the Apprentice has a lower KV rating so it is LIKELY to be at least 35A continuous capable if not 38A.
Assuming the LOWER rating for safety...
The ESC is rated for 35A continuous. Given that vendors LOVE to make their figure look as good as possible this is likely to be 30Amps AT 11.1v.
So that means the ESC can deal with 35 x 11.1 = 388 watts
If you increase the voltage you must keep the equivalent current draw about the same... sooooo...
388 watts / 14.8 = 26.25 A
You will therefore have to DECREASE the prop size to stay within this wattage range...
Pushing the numbers through ThrustHP...
14.8 x 840kv = 12432 RPM
388watts / 745 = .52 HP
You would need to drop down to a 9x6e prop to draw .54HP which should be within the safety range.
That will produce a static thrust of 2.95lbs but a prop airspeed of 70mph.
The 11x8 prop with the 11.1v pack produces about .67 HP which means that the original electronics were set up to run closer to the "edge", assuming you would use throttle management to keep things cool. The original setup provides 3.82lbs of static thrust and produces a prop speed of 70mph.
If you switched the 14.8v setup to a 10x5 prop you would get 4.49lbs of static thrust but only 58 mph prop speed...
So increasing the pack voltage CORRECTLY will onl net you more THRUST but less SPEED.
IMHO it's not worth doing, particularly on a trainer plane...
A 3D plane would be another matter….
Chime in if you have any comments. Again, I am posting this primarily so that someone Googling “Apprentice Servo Reversed” might stumble across this.
While fixing a problem servo in an Apprentice 15E RC Plane with AS3X, we came across something very interesting. One of our group (Kevin,) had changed both servos on his Apprentice for a higher quality metal geared digital Servo. The reason was he thought on of his stock servos might have a problem.
What we later found out was that the replacement Hyperion servos turned a different way than the Apprentice Servos or any servos we tried out at the field while trying to track down the issue.
It was not as easy to track down as you would think.
Putting either the new or replacement servos in most any other plane is not a problem. But the Apprentice with its built in AS3X stabilization system, made it a problem.
The AS3X is pre programed to make certain type correction based on the attitude of the plane.
Example: When the planes right wing falls the AS3X sends a signal to push the right aileron down to compensate and level the plane. It sends the signal to the servo to move clockwise or counterclockwise based on its programming. So putting in a “Reverse Servo” causes the plane to correct the opposite, making the problem worse, and most surely resulting in a crash. It makes me wonder how many people have replaced the servos in an Apprentice and crashed.
If you put the wrong servos in, the first thing you will see (Like any plane) is the ailerons move the opposite way. But like any other plane,,, Most people will go into their radio and Reverse the servos there. That would make most planes fly fine. Including the Apprentice, until the AS3X tries to correct for a gust of wind, IN REVERSE !
We learned a lot in the process.
First of all many of us did not know you can buy “Reverse Servos.”
Most of the time this is not an issue and few people ever know that servos can come in different travel directions for the same input, because there are several ways to correct a servo that turns the wrong way. Reversing the channel in the radio is one. It is what most people would do if they find a control surface moving the opposite direction.
Moving the control arm to the other side (180°,) if possible based on the placement is another way.
A third would be to flip the servo over. This only works one way. That is to flip the servo such that the top of the servo where the control horn hooks on, with the bottom of the servo. (Rotating it on the axes of the servo shaft will not change anything.)
Some, but not all Digital Servos are programmable.
You can reverse the direction, Slow down the Speed, and Center the arm to 90° with a Digital Servo Programer. Or you can take it to the local hobby store and most will be glad to do it for you. We went over to National Hobbies and they gladly preprogramed ours. The stock Apprentice servos are digital, but not programable.
Tom at National Hobbies on Baseline in Mesa Arizona is always a GREAT source of knowledge. Something else he taught us is that, on a servo has an Odd number of splines (gear teeth) on the top, when you put on the servo horn, if it is off just a little from 90°,,, you can rotate it 180° and it will not be in the exact same position. This can be good or bad, but once you have that piece of knowledge, it will probably come in handy sooner or later, and you can use it to your advantage when you have a control horn that doesn’t quite line up at 90º with the servo. With an EVEN number of splines, turning the control horn 180° will result in it being in the exact same position.
We also learned that although the ESC on the Apprentice will except a 4 Cell battery, it is not simple. It will accept the voltage, but you have to adjust the wattage by adjusting the prop size down. It seems simple but to be safe there is a lot of math involved, so its not something you should do without some research.
After much internet searching. I feel the below article OPJOSE on RCUNIVERSE explains the 3 to 4 Cell LiPo situation best….
4s battery on apprentice 15e (vs 3s)
The Eflite BL-15 950KV is rated at 34A continuous and 42A burst
The Motor used in the Apprentice has a lower KV rating so it is LIKELY to be at least 35A continuous capable if not 38A.
Assuming the LOWER rating for safety...
The ESC is rated for 35A continuous. Given that vendors LOVE to make their figure look as good as possible this is likely to be 30Amps AT 11.1v.
So that means the ESC can deal with 35 x 11.1 = 388 watts
If you increase the voltage you must keep the equivalent current draw about the same... sooooo...
388 watts / 14.8 = 26.25 A
You will therefore have to DECREASE the prop size to stay within this wattage range...
Pushing the numbers through ThrustHP...
14.8 x 840kv = 12432 RPM
388watts / 745 = .52 HP
You would need to drop down to a 9x6e prop to draw .54HP which should be within the safety range.
That will produce a static thrust of 2.95lbs but a prop airspeed of 70mph.
The 11x8 prop with the 11.1v pack produces about .67 HP which means that the original electronics were set up to run closer to the "edge", assuming you would use throttle management to keep things cool. The original setup provides 3.82lbs of static thrust and produces a prop speed of 70mph.
If you switched the 14.8v setup to a 10x5 prop you would get 4.49lbs of static thrust but only 58 mph prop speed...
So increasing the pack voltage CORRECTLY will onl net you more THRUST but less SPEED.
IMHO it's not worth doing, particularly on a trainer plane...
A 3D plane would be another matter….
Chime in if you have any comments. Again, I am posting this primarily so that someone Googling “Apprentice Servo Reversed” might stumble across this.