Voyager
Joined: 30 Jun 2020
Posts: 77
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 Posted: Mon Nov 20, 2023 8:38 am Post subject: Power, signal, and Coax - How should they be bundled? |
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Well, not exactly. Your point seemed to be that there is never a problem running power and signal lines together so just do it. My point is that this is true most of the time, but not all of the time. Given that, unless if requires jumping through some pretty big hoops, and it seldom does, I always separate power and signal as there is seldom a reason to not separate them and it removes one more possible source of issues. So why not just do it as normal practice. Generally, it costs nothing or next to nothing in either dollars or time so why not just run power and signal separately as a matter of course? This is as close to a free lunch as engineering ever gives you.
Matt
| Quote: | On Nov 18, 2023, at 4:44 PM, Charlie England <ceengland7(at)gmail.com> wrote:
Thanks for generalizing on my specific point about running power & signals down separate sides of the fuselage for a trim servo. 
On 11/18/2023 1:19 PM, Matthew S. Whiting wrote:
| Quote: | The answer is: it depends. For most power (>12 V, low current <10A) and most signal (>1 V, slow transition ms to μs) lines, it won’t matter much. However, add in higher currents >>10A, lower voltage <1 mV, fast transition (ns) and things get dicier. Now, there aren’t many such signals in a light airplane, but some items to pay attention to are magnetometers, GPS antennas, cables and connections, CANbus, and higher speed switching devices like strobes and such. Even audio related devices and cables can be bothered as these often operate at mV signal levels.
My philosophy is to do the things at the outset that are fairly easy to do. I generally use twisted pair wires for power and return to each device unless using the airframe as the return. You can easily twist your own with a drill or buy premade twisted pair wire at a very small cost premium. And the twisted wires tend to be easy to tie into a bundle.
I separate higher current and fast switching wires from signal wires such as communication (CANbus, Ethernet, RS232, ARINC 429, etc.), coax antenna, etc.
These two simple practices, combined with proper single point grounding, will eliminate 99% of possible issues with almost zero additional effort and cost.
Sent from my iPad
| Quote: | On Nov 18, 2023, at 12:47 PM, Charlie England <ceengland7(at)gmail.com> (ceengland7(at)gmail.com) wrote:
Looks good. I suspect that the same point that I was trying to make would still apply; There's no worry about running power & signal in the same bundle.
On Sat, Nov 18, 2023 at 10:04 AM wsimpso1 <wsimpso1(at)comcast.net (wsimpso1(at)comcast.net)> wrote:
| Quote: | --> AeroElectric-List message posted by: "wsimpso1" <wsimpso1(at)comcast.net (wsimpso1(at)comcast.net)>
Charlie,
Not Menzimer, using Actuonix P-16P for elevators, P-16L for rudder and aileron. As light as MAC, fits in my stabilizers, less expensive, rated for dust and condensation, right speed, and enough back drive resistance to hold settings. I get the off-axis pushrod loads off the servo with a little bellcrank, and put adjustable limit switches on the bellcrank after I know where the limits should be. Using the P version for elevators for position data - calcs say I may need to fly two trim tab. Flight test will let me know if I can omit the motor and lock that side, then fly the other or if I have to run them both.
Thanks for the feedback on cable. After searching I just bought separate wires in same color scheme and will twist them into sets. Stein had not popped in my search, but I just looked at their site and there it is.
Billski
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=512404#51240
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