SV-AP-PANEL Trim With 7-amp Brushed DC Motor

[chriscalandro]

Ok I’ll bite one more time.

I can type random numbers into an online calculator too to make a single ohm be a tiny change. I can also type a random number into the same calculation to make a single ohm a huge change.

At 12v, a 160ohm resistor measured on the other end is 12v. A 10000000kohm resistor measured on the other end is 12v.

Connecting an output to an input as per the drawing the above poster provided does NOT create a voltage divider.

If I’m going to create my own amp to control a flight control I’m going to make sure it’s correct. So far, nothing you have said here is correct. Again, I’ll go ahead and get the info from someone who has the REAL data I need.

 

[Rhino]

12 volts and 2 amps are the specs for the autopilot panel, and the resistor values are what both steve_izzet and you posted. In what universe would those be considered random numbers?

I don't see any drawings connecting an input to an output. What I saw was a list of "board connections" that had a 62 ohm resistor in parallel with the INx inputs, and a 160 ohm resistor in series. That is in no way random, it does make a voltage divider, and for all intents and purposes would produce the voltages I posted. Even if the voltages did differ somehow, the output spread between a 158 and 160 ohm series resistor would still be miniscule at best, which is the point I was making. Please point out any diagram that shows an output connected to an input, because I simply don't see it. If you do though, that would definitely explain why you don't seem to understand what I'm telling you.

 

[Rhino]

This is the configuration I got from what Steve posted.

I'm no engineer, and God knows I'm not infallible. But I did work avionics systems for many years, and even taught them in the Air Force for a few years, so I'm no novice either. So if you see something about this you think I'm missing, please point it out. And if you know how using a 158 ohm series resistor in place of the 160 ohm resistor would create a significant voltage difference, definitely point that out too. I'm always open to learning new concepts. This old dog does actually learn new tricks occasionally.

 

[chriscalandro]

For anyone that wants it. I chose a bigger motor driver, the VHN5019. It's capable of higher current than ever needed without getting hot.

 

[Rhino]

Looks like it has more fault protection built in than the TB67H420FTG too.

 

[Rhino]

Are you using the ST carrier or the Pololu? Your voltage divider suggests you could use either one.

 

[chriscalandro]

I’m probably going to make my own breakout board and set it up for a 9pin.

 

[Rhino]

Great. Please come back and let us know how things turn out so future visitors can benefit from your experience.

 

[vlittle]

For 10 years, I have been flying behind a custom autotrim controller that I designed to work with my SkyView system (and predates Dynon's offering). It can drive up to 7 amps per motor, and it has built in take/off and landing presets for both trim axes and flaps. That's the good news.

The bad news is that I never commercialized it because it interacts with the primary flight controls and I don't want to assume any liability. So, think about that for a minute... p.s. The only way to get one is to buy my Harmon Rocket!

Vern

 

[Rhino]

... because it interacts with the primary flight controls and I don't want to assume any liability. So, think about that for a minute... p.s. The only way to get one is to buy my Harmon Rocket!

But if you tell us what parts you used and we build our own, you shouldn't be liable because you didn't market it to us.

By the way, trim is not a primary flight control

 

[Marc_J._Zeitlin]

By the way, trim is not a primary flight control

Depends how it's implemented...

 

[Rhino]

Now you've piqued my interest. If it doesn't go to the ailerons, elevator or rudder, how do you implement it so it would be a primary flight control? You know way more about that stuff than I do.

That detail aside though, the discussion here is about trim, so at least in a traditional sense, it wouldn't be used as a primary flight control. And if someone did do that somehow, the liability would be on them anyway. Using a product in a manner other than what it was designed or intended for doesn't make the designer liable. And since Vern wouldn't be marketing either the design or a finished product, he wouldn't be liable for how someone else implements it. However, he is from Australia, and I freely concede it's quite possible liability law is different there. But we're all implementing stuff designed by someone else, and often manufactured by someone else. If that made the original designers or marketers liable, there would be no homebuilt aviation. So I have to say, I find it difficult to see how this situation would be different.

 

[RV8JD]

Now you've piqued my interest. If it doesn't go to the ailerons, elevator or rudder, how do you implement it so it would be a primary flight control?

I'll take a stab at that. In the last Century before hydraulically boosted controls were widely used, the control surfaces on certain large airplanes had such large forces that the pilot would have been unable to move them. So the pilot's controls (stick/wheel and rudder) were directly connected to the servo tabs on the main control surfaces, and in-turn those tabs then moved the main control surfaces. So the pilot flew the airplane by moving the servo tabs. I guess in that sense you could call the servo tabs primary flight controls, but they by themselves would not change the attitude of the airplane, like the main control surfaces do. Also, technically, servo tabs are not trim tabs per se, but they could also be used for the trim function.

Note that geared servo tabs nowadays are used to reduce the forces on the main control surfaces (that are not hydraulically boosted), therefore reducing the forces required by the pilot to move the main control surfaces.

 

[Rhino]

Thanks. We could go back and forth over whether or not that's a primary flight control, but I see what you mean. I kinda think that doesn't really apply here though.

 

[chriscalandro]

I built this as drawn above and it works perfectly with no temp or current issues.

I just wired it straight into the pololu board, used heat shrink on everything, the wrapped it in electrical tape and zip tied it to the wiring. (It was small enough).

No problem.

 

[Rhino]

Congrats, Chris. Ands thanks for letting us know.