Electric Pattern

Thanks to Rex Lesher for the following detailed report on his winter Electric Pattern project. Rex’s write-up gives you a lot of detail about his project; he has done an excellent job of recording the costs and the vendors giving you a reference point. I will be adding more detail as the season progresses.

*includes Carbon fiber, balsa, glue, and anything else I can't remember!!! Most of which I probably had laying around. The flight batteries cost is for four full flight packs.

First and foremost, I would like to say that I have no affiliation with any of the products or suppliers mentioned. I have no motives in the listing of these products. It's just what I used and thought I would share this info for those who may be interested.

The electric acc. kit consists of firewalls, motor mounts, and battery tray mounting materials. The kit has firewalls and mounts for both the Plettenberg and Hacker Motors.

The motor is pretty self explanatory. It is of the outrunner design, direct drive and therefore very quiet and maintenance free. I chose the Plettenberg because of the quiet operation, the lack of a gear box, hence the absence of maintenance. I have witnessed both the Hacker and Plettenberg in action, and don't see any viable difference in performance. Both motors have way more than adequate power. I just based my decision on the lack of noise from the Plettenberg. I guess if I hear some bad noise, I will know something is wrong...

The Speed controller is a very nice piece that is capable of handling 85 amps continuous, and is configured with firmware. Downloads are available through the Castle Creations website. The Castle Link USB, is a USB cord that connects between the controller and your PC and is used to download programming and updates in the programming. The really nice thing about the programmer is that it has quite a few more variables that you can program in controller, than if you manually program with moving the stick and listen for beeps. I had originally decided to create a manual arming device outside the plane, where I would make the final battery connection just prior to flight. The idea being, not to have the plane sitting there with a basically live motor while waiting to fly. However, upon researching the Castle Creations Phoenix HV85, I changed my decision on the arming device and just soldered the Deans Ultra Plugs directly to the speed control wires in a series fashion. This controller is Dual-Opto Coupled. The chance of interference or "noise" getting through the coupling is nill. This also means that it has no BEC and requires that you use a separate battery for your receiver and servos.

The batteries for motor power are wired in series. The Flight pack consists of two, five cell 5300Mah Li-Poly battery packs. They can be charged and balanced in series by using the Thunder Power 1010C charger/ 210V balancer. I purchased eight packs so I could makeup four flight packs. This makes going for some practice flights a cinch as I don't have to recharge at the field to get in four flights. After four flights, my mind starts to gel anyway... Part of the problem with charging at the field is the process. Fly, wait for the pack to cool down, charge, wait for the pack to cool down, fly, and repeat the process. The actual time of "charging is small compared to the rest of the process.

The Thunder Power charger/ balancer combo is a real bargain when you look at the ease in operation. The TP210V Balancer has the ability to balance all ten cells at once. It has two 6 pin connectors on one end. These two connectors are labeled "Group A" and "Group B". This is to identify which pack is which. There is a certain order in which these are plugged in. A wiring diagram comes with the balancer that explains which pack to plug where. The other end of the balancer has both a 4 pin and a 6 pin connector. These connectors are for use of balancing single packs. The balancer and charger also have a data port and data link cable which connect the balancer to the charger. This allows the two to share information, cell count, etc., and make for a fairly automatic operation. If the balancer detects any abnormally, it will send the data to the charger and the charger will adjust, or stop the charge and issue an error. The charger comes without the output charge cord, which you have to make up. That is because of all the different connectors that are available. I used Deans Ultra Plugs for all the Motor battery/speed controller/ charger connections.

The Voltmeter is a very nice piece. It is very accurate and has a temperature probe. The probe can be placed anywhere you can't aim a non-contact infrared thermometer.

The infrared thermometer is a Craftsman product from Sears, and seems to be fairly accurate. I have tested it on surfaces that I used the Fluke Temp Probe on and the results where very close, usually the same.

The spinner is a regular FAI model from True Turn. The big electric props fit the factory cut 120 slots without modification. The spinner adapter, also from TrueTurn consists of a 5mm stud which is threaded into the hollow shaft that protrudes out the nose of the Pletternberg motor. An 8mm bushing is placed in the spinner backplate, and the backplate is slid down on the motor shaft. Place another 8mm bushing into the back recess in the prop and slide the prop down over the remaining motor shaft. The only piece remaining is the prop nut and washer. This prop nut is just like most any spinner adapter nut we generally use. The side facing the motor has 5mm threads and the other side is the typical 10-32 thread for the spinner bolt.

The most interesting part of building in terms of Electric instead of Fuel, is providing for cooling air passage through the motor, speed controller, and around the batteries. Then the air has to find its way back out of the fuse. I suppose there's a lot of ways to do it, but has to be planned into the building process so you don't run into problems with trying to get access into some area that's already covered up... Sounds pretty simple, right up until you realize that you don't know where the batteries are going to be placed for CG balance. And to do that, you basically have to have the plane almost completed. It sure helps to have people that have already built what you are building. The Composite-ARF instruction manual does a great job of giving you an idea where things go. Good enough that you can just go ahead and build without running into real problems. With the method of cooling air routing that I chose, it allowed me to complete the build before I placed the battery tray in its final position. As most of you know, pressurizing your fuselage can be a pretty dicey experience. You are always walking out to find your canopy after it explodes off the fuselage... I ended up blocking off the cooling air at the wing tube, using a removable door that seals the flowing air from entering the area behind the wing tube. In front of the tube, I cut out the pipe tunnel, forcing the air to flow back down into the tunnel area. Then I made some exit holes in the fuselage bottom. The front of the pipe tunnel is blocked off to prevent air from the bottom cowl area from entering. The removable engine cowl has a ramp built into it to force the cooling air up over the pipe tunnel and around all the Electrics. I have provided some pictures to shed some light on my arrangement.

I decided to depart from the instructions on Antirotation pins and used a set of Gator wing adjusters for the wing, on the rear. When I get all the trimming done, I will make a set of pins for the front of the wing. I mounted the stab as per instructions in the manual, at 0 degrees incidence. I realize that adding the wing adjusters adds a little weight, but makes trimming life much easier.

After getting all the hard work done, figuring out how it all works, sorting out the wiring, getting the charger/balancer all studied, I decided to start charging batteries and getting ready for first flights. I went out and purchased a large deep cycle battery to charge off of. Yea Right!!! One charge, fine. Start the next charge, and beep! The charger gives an error code for "Low Input Failure". I read the book on power requirements. Minimum of 25 amps required. So, I fixed that problem, buying a 45 amp power supply. Now the charger is all happy and everything works great. Good thing I have a boat that needs a new battery, or I would have just wasted that $110 on a really pretty yellow battery that's too big for my motorcycle.

I've got it all ready to fly and decide to weigh it all. Comes out to 11lbs., 4 oz. That just doesn't seem right. As I look into the situation, I find out that I'm not alone. The Impact design tends to be heavier with the methods that are used to build it. Others, including some of the "big boys", had to resort to using smaller batteries to make legal weight. When I first weighed it all, it was around ten ounces or so too heavy, so I put it on a diet. I got rid of pretty much everything I could live without, took dremel tool to different items and ground away all excesses. Including the spinner mods, I've so far got it down to the above weight. I've figured out some other items to change, but will wait as I start flying and trimming, to see if some of the requirements to make it fly right are going to change. I believe that I can get the weight down to legal parameters, but 4 ounces is a lot when there isn't but a couple items I can change. Maybe a carbon fiber spinner and changing to a lighter speed controller. I have been researching controller weights and have found over six ounces difference between viable controllers I could use. But, it all comes down to whether or not the individual controller has all the bells and whistles needed to do the task. They are not all created equal... I've still got some work to do!

This has been a very interesting experience. I have completed the plane and have begun to fly it for trimming purposes. You can't tell it, but I still have a big smile. My face is starting to hurt. Pretty much all the rumors on power and need for rudder control are true. It is definitely different. It's still new to me, and I don't have it all trimmed up yet. The wind has been way too bad for any serious efforts as of late. Maybe I can come up with more as I learn it....

There is a lot going on with batteries and power consumption rates that have recently been posted on RCU. It is very good, useful info for all who may wish to jump in to the electron pool. There's a lot of comparison on motor efficiency from brand to brand, and the power requirements involved. Just some small examples I will throw out there, is the fact that flying Masters vs FAI has different requirement as far as batteries go. Flying times for each sequence is different, by about 2 minutes. Thus, the mAh used from the battery is different. What this means to some is that a flier in Masters may be able to use the 4200mAh pack instead of the larger 5300 mAh pack. At present time, this would save around 8 oz. in total weight and around $65 per flight pack. Now, I realize that as of yet, we don't have foolproof information on battery longevity and such, but we're getting there. After this season, we will be flooded with useful data. The fact that this info is starting to come in is a real help to those that are contemplating the jump.

The learning curve to electrics is no harder than using all the different components in fuel planes. It's just different. Some aspects make it easier. Just plug the battery in, and move the stick. The drawbacks? Moving the stick might create a little too much heat, if you've screwed up along the way. You've got to realize that you are dealing with enough juice to weld with, and it will if you short it out! I for one am excited about the advancements made in the electric scene, and would like to thank all those who helped me through this build with their advice and sources for acquiring the parts and pieces. Electrics are just one more viable alternative to provide a broader spectrum of available power sources for use in our great hobby. Is it for everyone? Probably not... For some, they like 2 strokes, some 4 strokes. They like the sounds, the smells. For me, I'm looking for a good duster...

Thanks Rex for this nice article and sharing your experience. I would like to add a observation of my own. Rex came to visit and I was fortunate to be a part of the maiden flight of his Impact. This same weekend I also flew my new OS 1.60 powered Temptation for the first time. On our first trip to the field Rex was able to complete 5 flights with little to no technical problems. It was a pretty impressive outing. It was pretty cool! Very quite and incredible power, I was very surprised at the level of performance. Rex was able to fly the full Masters routine with capacity left for a little more flying.

Here is some additional data provided by Scott Covey from D7 on his setup and costs:

When I decided to convert to electric from Gas last year.. I flew a electric Venus 40 in 3-4 contests in Advanced and Masters, and won all contests with the Venus 40. This total Electric cost was approx:

-Venus kit $150

-Hacker B40-10L motor, $260

-Hacker 770 Speed controller, $220 - I wanted this for my next 2M plane. Did not need to spend this much to get into electric.

-Radio / servos I had

-Batteries (2) - $275 x 2 = $550

-Astroflight 109 charger, $100

-Deep cycle battery, $100

-Watt meter, $55

-Misc, $95

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$800 - and selling my YS / old pattern stuff was about $500, so out of pocket was maybe $300

I sold the Venus for $1000 with servos after about 200 flights. It was in excellent shape.

Below is a discussion about li-poly batteries from Chad Northeast:

The resting voltage is of paramount importance for good pack life. A 1C discharge with a 3V/cell cutoff will leave you with a very low resting voltage, as compared to a 15C discharge with the same cutoff. Recently there has been a number of discussions about increasing safe cutoff values as the C rates go up since most of the current packs hold voltage so well up until then end when they simply dump everything they have....so 3 v/cell now equals to a much deeper discharge than in the past. Then there is the problem that the ESC is only seeing average pack voltage and not cell voltage...so its entirely possible while under discharge to have a pair of cells at 3.2v (6.4 total) and the third at 9-6.4....or 2.6V, and now your ESC will cut properly...but that one cell is being damaged. If you run a bit higher cutoff (3.1-3.2) and fly so that your open circuit resting voltage is 3.75-3.8 you will have very happy batteries. I agree...there is not enough of this information available without a lot of online reading. There is a lot of this on RC Groups...although it can take a significant amount of time to wade through the BS and gather what is useful.