Balsa USA Bristol M-1 Part 1: Motor mounting

A while back, my flying buddy Gary gave me a Balsa USA M-1 Bristol as a thank you for some work I had done on an airplane of his… or maybe it was a few airplanes… or a bunch!  Anyway, we had both seen it at a swap meet and I had admired it but he bought it.  I think it may have been traded off and then reacquired at some point before it found its way to me but in any case it has been sitting in a corner of the shop for a while now and I finally picked up what I think will be an appropriate power system for it, the E Flite Power 46 and a Castle Creations Talon 90 Speed Controller.  The Talon is a bit of overkill but for some reason seems to always be available at a relatively lower price point in the Castle line (my favorites).  It has an outstanding BEC capability and can handle up to 6S and 90A.  Castle and E Flite are among my favorite brands.  

The first task was to build up a good engine mount for an airplane that was kit built to mount a glow engine.  To mount the motor out far enough to get the back plate beyond the cowl face means spacing out somewhere around 3″ to the back of the motor in this case.  Nose weight is also not a consideration since the Bristol is so short nosed and more likely would need more weight up front if anything.  Finding some 3″ spacers is difficult at best, and I like the idea of something more rigid anyway (long spacers tend to flex or twist a bit under load).

To accomplish this I decided on using some shorter spacers mounting to what I refer to as a sub-firewall and then more short spacers to the X mount on the back of the motor.  This assembly is very strong and uses a few easier to find smaller spacers and some rigid plywood to put the motor out where it is needed.  Here are some pics showing the assembly.


Motor attached to sub firewall

Sub firewall bolted to firewall

Mounting plate tie wrapped to spacers used to mount speed controller.

With the cowl in place

There are a few other necessary installation tasks… servos to be mounted, an arming switch to mount, and making sure the battery can be located in a spot where the plane will balance… but progress is being made.  Looking forward to flying.

Dumas Windy… now “This sucker’s electrical!”

After swapping in the power system from an E-Flite Timber, the Windy seemed to be ready to go but then I started to notice what sounded like a stutter on startup and sometimes even at higher power settings.  I did some research and found a lot of speculation around causes. 

Some report that connection issues cause the problem.  It seems a poor connection on one of the 3 wires coming from the speed controller can be to blame.  Others claimed it was a setting in the speed controller (timing) that creates the issue.  As best I could determine the connections on the motor end seemed fine so I tried re-soldering the bullets on the speed controller, then replaced the wires entirely but neither made a difference.  Since the motor is fairly inexpensive, I decided to try that next and placed an order.

While awaiting the new motor, I did some research and tried to program the timing on the 40A ESC that comes in the Timber.  I didn’t consider this to be a very likely scenario as most Timber’s don’t seem to make this sound but I thought I’d give it a try.  Based on my experience… don’t bother!  I have programmed several brands and types in the past and I tried to follow the published directions to no avail.  After researching on-line, I have found that this is the experience of all but a lucky few with this ESC.  Remind me to bypass the E-Flite line of speed controllers in the future.

Unfortunately, in my experience, E-Flite tends to have an appalling lack of information on the products installed in many of their ARFs.  This makes it very difficult to pick an upgrade part or replace a failed component, especially in the case of a part that is difficult or impossible to acquire from the manufacturer.  I am quite fond of the “Power” line of motors however, but I usually stick to that product set and avoid the motors that come only as part of an ARF.  I only tried this one as it was so inexpensive.

In any case, after the new motor arrived I tested and found it made ZERO difference!  Back to the drawing board.  The next step was to get a new speed controller.  My “go to” on speed controllers has always been Castle Creations.  In my experience, not only has the quality of the Castle products been high, but they offer many features that your average ESC doesn’t come with.  With the Castle ESC, I can get real time or recorded telemetry, programming either through my radio or via a cable to my laptop plus features like a throttle cut switch.  Yes, they are one of the more expensive manufacturers but I think they are generally worth the extra dollars.  Of course I am always looking for a discount!

A few days later I found a good deal on a 50A Phoenix Edge.  With a little extra overhead in the current handling capability plus the ability to handle up to 8S, programmable setting concerning timing, braking, etc… along with telemetry capabilities, etc… (I like to be able to move my gear on to other projects down the road) I cashed in a gift card to help soften the blow and made the purchase.  

After soldering on the appropriate bullets and power connectors, I tested with the Castle and the motor purred like a kitten… or screamed like a vacuum cleaner gone berserk once the  prop was affixed!  Since this controller is not water proof I decided to take some precautions.  First I hid it away in the pod to shield it from most water and second I did a quick water resistant treatment with my handy bottle of Corrosion X.  I have had good luck with components treated with Corrosion X being dunked (complete submergence)  and continuing to run so it has become my go to for insurance against water damage.

Here’s the dunk process to apply the Corrosion X. 


Then I let it drain for 10 minutes or so.

After a quick wipe with a paper towel to remove some excess from the wires I nestled it in the top of the pod with some foam around it to keep things snug

Then I buttoned it all up and tucked the wires well away from the propeller!

In testing with a 4 cell battery, the Windy was able to taxi around on my short carpet in the shop and readily pick up speed and turn.   I am looking forward to getting some test runs on the snow and later at the pond.  Best guess is that I may have a bit more power than before… I’ll try to at least add a comment here after some testing.  Wish me luck!


Re-Programming the AR636a in the E-Flite Timber

Please read Part II (located here) when finished with this post… it has vital information if you are reprogramming as I did!

After a dozen or so flights on the Timber I started thinking it was time to either replace the receiver with a non-SAFE/AS3X model or find a way to disable the SAFE mode (which I will never use) and be able to at least switch off the AS3X mode.  There is a fair amount of contradictory information out there and apparently there is no reliable way to tell which AR636A can be adjusted and to what extent.  Some, you can adjust the rate gain and priority but not the heading (this seemed to be the case on the Timber) while others apparently are locked down.  It wasn’t clear to me if I could setup the receiver from the Timber to keep the safe switch selectable as well as have multiple AS3X settings or not…  

I did find one place saying you could “upgrade” the code on some of these receivers and basically bring the receiver back to standard AR636 functionality.  Of course there are all sorts of warning that you are on your own if something goes wrong.  Since I’ve got a new receiver sitting on the bench ready for install… I decided to take the shot.

So I went into the Spektrum web site and registered my AR636 so I could download the code.  When the site took the serial number successfully I was heartened that just maybe this would work.  After viewing a few videos about how to program the receiver I decided to just go forward with sending the code and see what happened.  The software recognized the 636 SAFE receiver and allowed me to download the code.  To do this using a PC you will need the USB cable.

Here’s a link in case you decide you need one of these.

I immediately went in and changed a few settings and quickly thereafter the SAFE mode was lost for good!  No big loss for me… would be nice to be able to reactivate that somehow just in case I wanted to sell this plane but it seems unlikely I would do that… it will likely crash or be cannibalized at some future point.  Hopefully thousands of flights from now.

I now have all the settings set to zero gain for all three (switch selectable) modes… as well as taking away a couple servo reversing settings.   So I have effectively converted the the 636a to a dumb standard receiver!  Well actually it seems to be equivalent to a 636 now with expo, channel assignment and reversing and all the “gyro” settings available.  I can see where this would be really nice for someone with an inexpensive radio that didn’t have all the expo, assignment etc… already available.  For now I’ll just use it as a standard receiver and be happy with that.  Looking forward to flying the Timber without the stabilization to see how it goes.  Will be nice to see what the air frame and my skills can do without any help from the receiver.

Eventually I may re-institute some of the stabilization settings on a switch in case I want to do some “poor condition” flying and need a safety net or perhaps if some other folks want to get a flight or two in on a stabilized aircraft.  I kept an export of the original settings so hopefully, I can go back and re-import the original settings if I want to.

Looking forward to getting a flight or two on it soon to test it out.

Extreme Flight 74″ Laser – Build nearly complete

The Extrem Flight Laser has been in the shop now for about a month and I’m finally getting close to flying status!  My final items to complete are to get the speed controller and receiver installed, do the radio setup and then go back through and do final checks on bolt tightening, gluing any joints that need it and seal all the hinge gaps.

Overall, the instructions and included hardware seem to be good quality and short of flying it, I am pretty happy with it so far.  I’m going to get a bit nit picky over the next couple of paragraphs in hopes that this will help anyone else who is working on putting together.  There are a few shortcomings in the instructions worth noting and a couple tips I can pass on as far as what to do (or not) that may prove useful.   So here is my summary of the good, the bad and the ugly of building this ARF.

First off, when installing the control horns you need to remove some covering in order to get a good glue bond.  The instructions for this are pretty good but I would recommend a couple of ways to make this easier.  First, when drawing around the control horn base in order to know where to cut, I suggest a white board marker.  They are easier to wipe off with just some alcohol or window cleaner.  Also when removing the covering I remove only to just inside the line so that the base plate actually slightly covers the edge of the material.  This helps ensure that the material will never peal up around the horn and the result looks very professional.  Secondly, not only here but pretty much anywhere you need to remove covering… I highly recommend use of a soldering iron.  With minimal practice you can move at a rate that doesn’t char the wood underneath but just melts the covering.  It also seals down the edge as you go.  I find this method far superior to use of a razor blade or Xacto knife.  Extreme Flight’s manual mentions this option in one place but then often says to use a blade in many others.  I’d stick with the Soldering iron in pretty much all cases.

While on the subject of control horns, for some reason I got two sets of of rudder horns with no explanation as to why or what I might want them for… still don’t know.  In any case, I would install these dry and mark them once you measure for proper centering.  The “barb” on one side that I thought would end up against one side of the rudder to aid in alignment… does not seem to be any such thing and I don’t know why it is even there…  Just be cautious that you get the centering correct here.

One preference/ nitpick of mine is the tail gear mounting method.  I’m used to having blind nuts embedded but this gear mounts only with wood screws.  I would love to have the blind nuts as I think they result in a stronger mount.  Hopefully this mounting method will be strong enough.

The next note I made while building was regarding the rudder pull-pull mechanism.  First, if you have never put one of these together before you should go find a step by step instruction set that will walk you through everything you need to know ’cause what is in the manual for the Laser is not that!  If you’ve done a couple you probably will have no issue with this one.  One odd note is that they specify to crimp the aluminum tube with side cutters???  If your side cutters are worth a darn and you squeeze firmly you will end up cutting that tube and probably the cables themselves clean through.  A standard pair of pliers works quite well, thank you.  Don’t use side cutters!

Next, I noted that the instructions for installing the wheel pants had a couple of shortcomings.  First, when they have you drill a hole, they do not tell you what size hole… you can figure it out of course but it would be nice if they just told you… sorry I didn’t write it down or I would have provided that here (silly me).  Also when they have you install the blind nuts it required an excessive amount of force to get the little sharp prongs to push into the wood because the back of the wood inside the wheel pant has a fairly heavy coating of fiberglass/resin which necessitated a pair of channel locks to get the prongs to penetrate!  I felt like I was risking a good amount of damage when I did this but that is what it took to get them to embed flat…  and you need it to lay flat to keep it from rubbing against the rim/tire.

One error I ran into as I mounted the motor is the stated distance from the front face of the motor box to drive washer should be 6-3/8″… My ruler says it is actually 5-3/8″!  If you extend it to 6-3/8″ the cowl will not go back far enough to mount.  Luckily, I checked before I got things mounted.

OK, that’s about it.  Everything else seemed straight forward to me and I appreciated the packaging of the parts (individual bags with labels for each set of pieces).

I’m looking forward to getting started flying soon and the real test will be flying characteristics and how well she holds up over time.  Looking forward to messing with setups, props, batteries and telemetry to see what works best.

Using my Hero 4 GoPro Session and the Carbon Cub to search for a downed RC Glider

Recently one of my flying buddies (George) lost one wing panel on his glider while sailing along over the cornfield adjacent to our field.  A couple of us who own multi-rotors with decent cameras were called upon to go on a little airplane hunting expedition.  Unfortunately, my only available batteries for the quad (a 350 QX) are a bit weak and I was concerned that with the expected distance to cover, I would have a hard time getting enough time over the search area to be effective.  Also, at that distance, the QX was going to look very small and I just don’t  have enough time flying it to be comfortable at that distance.  On the appointed day of the big search I arrived at the field and started planning some way to get out there and do a decent search.  Starting out at the very edge of the field or perhaps even staging in a bare spot somewhere further out were considered but in the end I decided to hold out a bit until my friend Martin arrived with his much more capable Yuneec Typhoon H.

In the meantime, I decided it might be fun to do a survey of the field with the Carbon Cub and GoPro Session.  I had a vague idea that if the aircraft was sitting high atop the corn stalks I might have a chance of getting a glimpse!  Even if we did see it in the video it seemed unlikely to do more than confirm a rudimentary vector to look on and perhaps a little more refined idea of how far off the field, but since it involved flying my cub… So shortly after I had the Session mounted and a fresh battery installed in the cub and away we go!

I angled the camera down 60 degrees or so and then started the video and took off over the corn.  I made three passes out and back along the line that the pilot reported his lost plane.  5 minutes later we fired up my laptop and started playing the video and carefully advancing a second or two at a time and looking on the video for anything that didn’t look like corn and especially anything white (which is the predominate color of the down airplane).

So here is a short clip of that flight… I highly recommend full screen for this one.

Did you spot it?  Here’s a single frame with a bit of help on what to look for.


If you want to go back to the video around the 39 second mark you can probably pick it up for yourself now that you know what to look for.  Also notice that later in the video as I pass over the edge of the field you can get a line on where you would have to exit the field to find the downed craft!

In fact, after viewing the video a few times and following the row where we saw the plane out to the edge of the field and marking that spot as best we could… I walked out into the corn with one other person and we found it as soon as we got out far enough into the field.  In fact I walked to within 2 rows of corn on my first attempt and had no trouble finding it!

At this point I have no idea if we were just lucky or what.  It helps that the plane is mostly white… a military camo pattern would have been tough!!  I do know the video created by this camera is pretty amazingly detailed.  What your seeing here is very compressed version but even in this clip it is possible to spot that nice white spot in the corn!

For those who are interested, we were able to recover all but the one wing panel which we didn’t spend much time looking for after we realized the aircraft was pretty much destroyed in the wreck.  With what we had it what fairly obvious what happened that caused the wing to collapse.  After a stern talk with the ground crew (George mumbled to himself for a while) we were assured this particular error would not happen again!  ūüôā

The GoPro Hero 4 is an awesome little camera with all of the quality you expect from the folks at GoPro packed in a small little cube that can mount on a variety of RC planes in many ways.  It’s significantly lighter and smaller than the full size bodies with very similar quality video output.  It is NOT an FPV camera…  it is a great way to record the action and then view/edit and enjoy the awesome airborn views.  Here’s a link:

And if you need a great platform to carry it the carbon cub is hard to beat.  It can fly slow (almost walking speed with the flaps dropped) or move along briskly and carrying the camera has little to no affect on it’s flying characteristics.  Here’s a link for that as well.

The Carbon Z Cub isn’t perfect… it has some paint peeling issues, the main gear mount could be sturdier and the motor has been known to occasionally give up the ghost… I’ve documented all that in other posts here…  but I still recommend it because it just flys so darn well and it’s just a blast to fly.  Add in top notch support from Horizon and you have  pretty good airplane.

Anyway, it was fun and felt good to help a fellow flier get his airplane back.  Even staring at video of the corn passing underneath the plane was interesting.  Who doesn’t like a good video from an “elevated” perspective.  Hope your search patterns yield equally good results.  I’ll try to post some more soon on other interesting projects and happenings at the field.  Until then, happy 4th of July!  Or as we always called it at my house… “Happy dad’s birthday!”

Carbon Z T-28 Recommended modification

As I may have previously mentioned, my flying buddy Kelly has one of the big E-Flite Carbon-Z T-28s. ¬†He has trouble wiping the smile off his face when he’s doing one of his usual low speed, flaps down, no bounce, land like a butterfly with sore feet touchdowns. ¬†With the AS3X keeping things even more stable on breezy days, this thing is just smoooooooooooooooth.

We initially had some nose gear issues (replaced) plus we added some Multiconnex and there was an issue with the flap hinge cracking (the flap/wing surface is the hinge) which was rectified with some Blenderm style wound tape/hinge tape. ¬†As I recall, when we applied the tape we also replaced the wing control linkages. ¬†Everything about them is undersized for this big aircraft and some folks have had small issues… others not so small.

So after an early spring flight recently, I guess we shouldn’t have been surprised when the rudder linkage lost it’s center pin. ¬†Funny thing is we bought the additional parts way back then but never installed them. ¬†It’s funny because it wasn’t the elevator that quit working!! ¬†Kelly was able to get the airplane safely back on the ground and I have just finished manufacturing the replacements for both the rudder and elevator.

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As you can see the original is just plain scrawny looking and our replacement is only 2-56 rod.  I consider even that small for this size plane but since they are so short (kudos for that E-Flite) 2-56 is sturdy enough I suppose.

The moral of the story however is if you are going to buy the big T-28, I would highly recommend you just go ahead and buy the hardware and replace all the flight linkages (6 short rods and your favorite clevises) before it even leaves the ground.  One less thing to worry about!

While you’re at it, order the Multiconnex (see that post here) and really make it easy on yourself!

P-51 Redtail… More progress. Wing repairs progress.

Further work is occurring on my quest to reassemble the Redtail without spending significant dollars and simultaneously lightening it up a bit in the hopes of improved flying traits.

The latest is around the port side (that’s left if you were to sit in the cockpit of the P-51 facing forward) main landing gear mounting area and wheel well. ¬†That area took significant damage during the abrupt meeting between the retracts and beans at about 35mph! ¬†Yep, that is about stall speed… or at least is was that day.

Here is a sequence of pictures showing the progress. ¬†Most of this was simply measuring, cutting, fitting and a fair injection of TLAR engineering methods to try to get something put back together that will stand the strain. ¬†TLAR… you know… “That Looks About Right”!

After cutting out the sheeting and getting rid of the various splinters and unidentifiable fragments here is what I was left with.


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I cut away even a bit more before adding back a bit of structure… ¬†Rebuilding the rails so that the screws have something solid to bite into required some temporary bracing…

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Then I started building the actual rail structure and piecing them together with an eye toward making sure there was some interlock to help add some strength.  This rail notches into the rib and creates a lip for the rear rail to rest on.

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Here, all the rails are in place and all of the mounting screws have been drilled and put in place… lots of advanced TLAR to get the placement right (I hope).


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Then came the puzzle of re-sheeting around the fiberglass wheel wells.  I cut the existing sheeting back to expose a bit of the top of the spar and then pressed the sheeting down over the fiberglass to give me a cut line.  This created shapes like this ones.

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Then I added some small “railing” to catch the sheeting and give me some glue surface for the larger span of this piece of sheeting. ¬†There was also some reinforcing and rebuilding of the ribs that contact the wheel well that had to be done.

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Here are the pieces going into place.

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And the final bits of woodwork are glued in.

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From here is will just be some recovering work, though I have considered adding a bit of light fiberglass reinforcing underneath the landing gear mount area… ¬†We’ll see.

Next up is finishing up the covering and the last of the repair work on the fuselage.

Glow Carburetor Adjustment

Just a note to let folks know I just unearthed a little gem of an article on how to adjust your glow engine carburetor. ¬†I believe this was originally posted to RCU back in 2004 but couldn’t find it when I needed it. ¬†Now that I found a copy I did manage to locate it on RCU as well but I decided I would just post it here to my articles page just to insure I could always find it when I want it. ¬†You can click on Articles above or you can just click this link to pull up the article directly.

Tim Mills Carburetor tuning 101

This was originally written by my late friend Tim Mills who passed on February 20, 2011. ¬†Tim had an amazing touch with engines from Motorcycles to Airplanes… Gas or Glow, 2 or 4 Stroke. ¬†Tim always said that you just had to listen to what the engine was telling you but he was one of the most fluent in that language that I have ever known. ¬†I’m happy to share just a bit of his wisdom on the subject.



Throttle lock/Kill Switch programming on the DX8

A couple years ago I was taxiing back toward the pits with one of my smaller gas powered¬†planes and had stopped to observer another flyer doing a nice touch and go… My plane was sitting by my feet at a sedate idle during this distraction. ¬†When I turned back, I returned my left hand to my radio and inadvertently slid the throttle stick to full!! ¬†Luckily I was pointed at the pit chain link fence 6 feet away with no other obstructions… like people… so as I grabbed the stick and returned the throttle to idle the plane made a dash for the fence and quit as a result of the impact and¬†the prop breaking into several pieces. ¬†It did no real harm to anything except the prop and my pride… but it woke me up and from then on I have been much more attentive to my models while they are running. ¬†When I am idleing, my thumb is hooked across the top of the throttle stick so that it cannot easily be moved upward. ¬†As well, I now have a kill switch on every fuel powered airplane and it is always in the same position on the radio so I don’t have to hunt for it! ¬†With gas planes I have¬†a mechanism hooked into the ignition circuit that kills power to the ignition. ¬†Depending on the type of engine and ignition system it may work a bit differently but each disables the ignition which kills a gas motor immediately.

With the advent of more electrics in my fleet this became even more problematic. ¬†Electrics, once the battery is connected, should be considered to be “running” in all cases and therefore treated with the respect that would be due any idling engine. ¬†Since you can forget the battery is plugged in at times, I try to be especially careful to restrain my electric powered aircraft whenever I’m not holding on to them and a battery is installed. ¬†I have also setup a throttle cut switch that limits the throttle channel output to zero or as close as possible. ¬†In some radios this is simpler than others. ¬†In my Spektrum DX-8 there are two ways to accomplish this… maybe more… but I’ll show one of them here that I use most. ¬†(I believe the 7s, 9 and 18 all do it similarly)

Note: You can do all of the following without the plane even being present and certainly don’t want to play with this with the plane powered up!  I highly recommend you test after you finish however with the plane well restrained or the prop removed.

First, the DX-8 has a throttle cut option in the setup menu. ¬†If you go into that menu and change the inhibit to a switch label (I tend to use Gear0 as I’ll show below) you get a screen that looks like this.

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You’ll notice that the switch is set to Gear0 (that’s a zero). ¬†I use this setting as I tend to setup my radio so that starting point for all airplanes when I fuel up or attach a battery is with all switches pushed away from me. ¬†It really doesn’t matter which way you do it. ¬†I’ve worked with computers and electronics so long and the way I was taught logic you generally consider 0 to be off and 1 to be on…. I guess position 2 is “really on” in the case of a 3 position switch!

With my radio set this way the throttle is locked so it cannot inadvertently start up without moving both the throttle stick and moving the gear switch out of its starting “safe” position. ¬†The other thing you may notice is that the position reads 30%. ¬†I played with this and came upon this setting by trial and error. ¬†I believe this has to be done because of two factors. ¬†First, the designers created this for (I believe) primarily fuel powered aircraft where the stop/kill position is significantly different from the idle/standard starting position. ¬†In an electric aircraft you generally don’t want an “idle” with the prop moving when you pull back to the lowest position on your stick. ¬†You want a full stop. ¬†Second, most speed controllers in my experience will look at the throttle setting on power up (as long as it’s at least somewhere near one end of travel or the other) to be the zero/stop point. ¬†That’s fine until you combine with point 1.

So imagine you plug in the battery with the throttle 30% lower than “idle”… which is what the throttle position would be if you left that setting at zero and had the switch pushed forward/off when you plugged it in. ¬†All seems fine… Your speed controller makes its little tunes and if you move the throttle stick nothing happens but your servos are energized (this may vary by manufacturer of the speed control). ¬†Great, you are ready to taxi and you flip the switch to the armed/on position and immediately the prop spins to a “high idle” setting!!! ¬†That’s not convenient, nor especially safe. ¬†This is because with the kill switch in the forward/off position the throttle was at a point 30% or so below the idle point and when you plugged in the controller reset that to be “zero”. ¬†By testing I have found 30% to be about the right point to avoid this issue. ¬†Now the kill switch doesn’t really change the position of the throttle at all and acts more like a throttle hold then a cut. ¬†Ideal for what we want when dealing with electrics.

There are other ways and other radios do it differently. ¬†On my DX-18 which I fly more than anything else I use the F switch instead of gear because I use the gear for other things… like retractable gears! ¬†But whichever switch you use, I suggest you keep it consistent. ¬†This way your routine on each plane is the same at least as regards to a safe “startup” and also because occasionally you may want to hit it in a hurry and not having to think about which switch it is can make a big difference in response time.

I’ll try to post on a different method in the near future. ¬†Hope this is helpful. ¬†Fly safe!


Packs, Chargers, Power Supplies and more – Power Supplies

With the FMA PL6 ¬†chosen as the charger I ran right into the realization that I could never use the full capability without some increased power supply capacity… ¬†My standard rig at the field was a low end, unlabeled supply that I got surplus at a hamfest. ¬†It had never failed to deliver but I also don’t think it was designed for more than about 20A at ~12-13VDC. ¬†In the shop I have a bit better solution where I have a 52A 12-15 VDC supply available.

However… ¬†there is a limit on the charger in that the input side of the charger can only accept 40A maximum. ¬†That translates to a max of ~500W of charging power on 12VDC. ¬†In order to get near the full 1000W you would need something closer to 25VDC at 40A. ¬†Of course no charger is fully 100% efficient so the real numbers are 15% or so less but the basic idea holds. ¬†So what am I to do? ¬†My first thought was to start hauling my 52A bench supply to the field but that has two drawbacks. ¬†One, is I would be limited to the 12V max of something less than 500W. ¬†Not terrible, but having the max power available at the field could be even more important that back in the shop where I have (figuratively speaking) all day to charge batteries. ¬†So, off in search of a way to get 25V or so at 40A.

First, I started looking for commercially available, purpose built supplies to do the job and quickly realized that such supplies are both unusual and very expensive! ¬†I really didn’t want to spend 2-3 times as much on the power supply as I did on the charger. ¬†Keep looking… and then I happened to come across high amperage 12V supplies for what I thought were very reasonable prices. ¬†$60 each. ¬†They were converted from computer (Dell server) power supplies and could supply 57A at about 12-13V. ¬†Ok, that’s much more reasonable… maybe I could just use one of those and get along with slightly less than 500W of charge power… at least for now. ¬†But then I recalled I had seen information mentioning using two identical supplies in series to get twice the voltage… Now we’re talking!!

Based on that vague remembrance I bought two of these supplies. ¬†Both together were cheaper than I had paid for the bench supply a few years ago and each was more capable. ¬†After a modicum of research I started experimenting and found that I could get a good working 25V supply at 57A by wiring the two supplies in series. ¬†My first attempt resulted in one of the supplies shutting down… but with a little more research I found that by isolating the ground I could avoid the second supply from seeing a short when both were plugged into the same AC source.

I believe the power supplies likely include bonding the DC output ground terminal to the AC ground. ¬†This means that when the two¬†supplies are plugged into a common outlet and are sharing the same AC ground they are also sharing a common DC ground. ¬†The result is that when the positive lead of supply A is plugged into the negative side of supply B… it is essentially creating a dead short. ¬†Luckily, these supplies are very sophisticated and include the ability to clamp down the output in a case such as this so no damage was done.

Once the grounds were isolated from one another the supplies powered up and supplied a nice steady 25VDC. ¬†I created a carrying case from a Styrofoam cooler and built a power panel in order to have a single 24V output as well as the availability of either 12VDC output if desired. ¬†It is well protected in the cooler (which opens up when in use for better cooling) both from the elements as well as vibration and “bumping” around in the trailer. ¬†I’ll update this post with a picture or two in the next couple days.

This whole rig worked great on my bench, so I took it to the field and after 3 flights on the CZ Cub decided to do a nice 1 hour parallel charge. ¬†I fired up my low cost 900W generator, plugged in my new power supplies and… nothing!! ¬†Further testing back at the shop confirmed that the whole rig worked but just not with my generator. ¬†I’ll go into that in the next post on the subject detailing my search for a new generator.