Hey guys, So. The autopilot I'm using is only rated at 1.5amps. The DC trim motor is rated at 10 amps. What is the most effective way of reading the autopilot's output voltage (-12 to +12 volts) and instead of only 1.5amps making it able to supply 10amps?
I need something that measures -15 to +15 volts(to be safe), outputs that same voltage at up to 10 amps instead of just 1.5 amps.
Also how reliable would it be using an Arduino to do this? Do I even need to use an Arduino?
Arduinos are toys, for learning and experimentation, usually with unreliable breadboards and loose wiring.
You should never use an Arduino in situations where lives might be threatened.
You don't need an Arduino for this. Just a DC current amplifier.
I don't think the G3X servos are that simple. The include a lot of features such as current feedback, which allows the G3X to trim properly while on autopilot.
If you must have a G3X then you must have the correct servos for that system. Trying to modify an existing servo is unlikely to be productive.
jremington - Yes true. The plane flies fine with a stuck full up/down elevator trim. There is also a manually switch that bypasses all autopilot controls too.
MorganS- This is just a bonus feature that will allow the autopilot to control the DC trim motor making it easier on the elevator servo. I would never mess with the real servos.
Aarg - DC current amplifier, Yes sounds like a winner.
What is the transfer function from +/- 15V to WHAT voltage range ? (@10 A)
raschemmel - The output voltage needs to be the same as the input voltage. (just with more current)
Wire the op amp as a Voltage Follower. ( Google it).
Input : + V pin
-V pin to output pin
Output from output pin
+Vcc = +15V/ 10A power supply
-Vee = -15V / 10A power supply.
This is typically done usjng two identjcal 15 V power supplies. ( in case you are not an expert at electronics there is NO SUCH THING as a "+15V" supply or a "-15V " power supply. There
are only "15V" supplies. The POLARITY is simply a matter of WHICH wire you connect to GND..
( if there is a GND). ( The input signal MUST be referenced to a GND . The +15V/10A P.S. has it's negative output connected to the referenc GND.
The -15V /10A P.S. has it's POSITIVE output connected to the reference GND. The 10A op amp has NO conection to the reference GND. It has +15 V on it's Vcc pin and -15V on it's Vee pin.
If this is not clear to you then maybe you do not have enough electronics experience to attempt this project.
In addition, a 10A op amp wiuld need a heat sink or it would burn up.
Do the MATH
P= I×E = 10A × (+15V - -15V) = 10A×30V = 300W !
Hold your finger on a 300W heat sink ! ( OUCH !.
What is the power source ?
That would require TWO 4S LIPO batteries because 3S could not supply 15V.
A 4S Lipo is 16.8 V fully charged.
What is the target flight time ?
Do you , or do you not understand my last post ?
Yep, Thanks. I just PMed you to confirm you were talking about the op amp I had linked.
300W of heat is kinda a deal-breaker tho! Gotta be a more reasonable way?
Aarg - Was the DC current amplifier you were talking about work the same as the op amp? If not could it be used with a forward and reversing motor.
I don’t think so.
Ask aarg to read my Reply#8 and ask him if that’s a DC current amplifier because by my math, if Output current/Input current >1, it’s a current amplifier.
Saying “get a DC Current Amplifier” is like saying “get a car”.
Saying "get a 10A/op amp Voltage Follower " is like saying “get a Porche”.
Both are cars, but you know what you are looking for in the latter case.
the 10A op amp Voltage Follower is , by definition, a dc current amplifier.
The DC current amplifier aarg referred to is general, not specific.
Ask aarg, since you don`t seem to believe me.
“If it walks like a duck, quacks like a duck, and swims like a duck…”
Is it a duck ?
FYI, there, no such thing as an “AC op amp”.
“AC” means Alternating Current" , ( could imply positive and negative ).
With op amps, whether the output is positive or negative ,even if was an “AC” sinewave output, it’s still DC, it’s just running off a “split rail” power supply instead of a single ended supply.
What makes it “DC” is that the power supplies are DC power supplies. If I generate a perfect 60 hz , 120V sine wave using an op amp powered by a +/- 180V split rail DC power supply , is that a "DC op amp " or an “AC op amp” ?
( for the sake of discussion, we are ignoring the question of whether such a. Op amp is currently available, since thst’s irrelevant to the discussion)
“300W is kind of a deal breaker”
If I told you I miscalculated and it’s only 150W, would you feel better ?
It is what it is.
YOU said +/- 15V @ 10A, which is 150W by definition ( Ohm’s Law). Are you saying you didn’t know Ohm’s Law ? (at any.given moment , the output , whether positive or negative , does not exceed 15V @ 10A)
Yes, "current amplifier" is a generic term. It might be integrated like the IC that you linked to, or it might be an op amp with an external transistor current boost circuit.
Indeed, there is a problem of inefficiency with both of those. A lot of energy will be wasted as heat. That is why most motor controllers use some kind of PWM.