MD500 Tow Defender Build Page 10
Electrical Systems: Main ESC Power / Main & Aux Power for Radio and Accessories, Part 2 of 2.
This is a continuation from page 9. I have done lots of work since my last update. I had to add two diodes to the FLIR power input because it was being fed 6+ volts and blew out the MCU
thar controls the FLIR movement, oopps.. I also added one more diode in series with the MLC controller for the same reason. Neither of these devices are flight critical, but I still want them working as designed of course.
I have built wiring harnesses to go from the front cockpit fuse section to the main fuselage section. These harnesses control the aft nav lights, provide main and aux power to the receiver, and bring signals from the receiver back the the cockpit electronics to control the two lighting systems, and to provide a trigger pulse for the FLIR controller. There is also a main and aux battery harness. This is used as the main on/off switch, and as a plug for charging the two flight batteries. This way the batteries never have to be removed for charging, nor do I have to try to dig out the connectors for charging. Very simple and easy to use and maintain.
At this point in the build I am taking a break until after my clubs first fun fly this May 14, 2011. Then I will put one to two dozen flights on the mechanics before tearing it down for painting..........Fast forward a little. Did I say painting. I meant all the other electrical things I didn't think of. This section will finish that up as I am far enough along that I believe there will be no more additions to the electrical system. Ha, yeah right. Wait until you get near the bottom of this section. Major rework time.
Here you can see some of the wiring for the navigation lighting.
These two harnesses carry nav light power, signals from the receiver to control the cockpit lighting, and to
power the FLIR. they also carry the main and aux battery power. Main in one and aux in the other. That way if
one harness fails the other will hopefully still work. These two harnesses connect to the front fuselage section.
The connector on the bottom right is used as an on/off switch for the flight and accessory electronics.
It is an extremely tight fit with a snap lock tab to keep it connected. It is very hard to pull apart so I don't
think it will ever come apart in flight.
Here I am trying to get all the wires put in place while I stick the mechanics back into the fuselage.
Here is the X-era4025 670Kv motor and Castle Creations ICE HV80 ESC. I plan to use 10S A123 as the main power.
Starting to build the battery packs. The 6S pack will sit under the mechanics just in front of the main shaft.
The 4S pack will be farther forward just under the rear of the cockpit. These will be wired in series to form the 10S pack.
Here you can get a rough idea where the batteries will go. You can also see I have the balance leads soldered on now.
Although some do, I will never charge this pack without using the balance mode on my charger. I think it's the best way.
-- Plan B --
I am stopping here even though I had more photos of the completed A123 battery pack installs. The reason for this is because the A123's are not working out
like I thought. I did not realize they had such a high voltage drop under higher current loads. My 10S pack would go from 33 volts before take off, to 26 - 27 volts
at lift off. I lost 6 volts of power before ever getting airborn. This of course dropped my rotor speed to lower than I wanted, and I lost tail rotor authority. So I have
abandon the A123's in favor of Lipo's. Now I have two 5S1P 4000mA packs in series to give me a 10S1P 4000mA battery pack. Initial testing looks much better with
this setup. It does however mean my idea of hiding the batterys out of sight just flew out the window. Don't want to risk charging Lipo's on board. I will always remove
them when charging. So now I needed a totally new mounting method for these Lipo's. So below is what I came up with.
I made two battery mounts, one a mirror image of the other (port and starboard sides). I am pretty happy with the way they turned out. I was initially going to mount
them to the fuselage floor, but after thinking about it decided that mounting them to the mechanics framing would put less stress on the fuselage when flying around,
and that is always good. So I mounted them to the frame and used standoffs in between the frame halves. This makes for a very rigid and sturdy setup. I also used the
swiss cheese method to lighten the mounts up a bit. I also attached velcro to the mount, and to the batteries. I will also use a velcr strap to help secure the batteries.
Here is you can see the two mounts and how they are a mirror image.
I removed some matterial to lighten them up. I should have weighed the before and
after to see how much this helped. Didn't think of that soon enough. Oh well..
Here you can see one mounted with the velcro strap, and the velcro to
hold the battery to the mount.
Another view. You can see how I had to mill out for the existing frame bolts.
Here my little helper has installed one of the Lipos to check the fit.
Here are the ESC / Battery power connector mounts I made. Top one is for Santini Air, the six plates below
are for the Defender. The three on the left go on the port side, the other three on the starboard side. The port side
will just be motor power, the starboard side will be motor power, flight electronics power plug (the ON/OFF switch),
and the interface to the ESC for programming and data downloading. I am using the Castle made interface adaptor
so I don't have to unplug the ESC signal wires anymore. Well worth the money.
