jsr1017

THANK YOU for the pointer to the 2.4 Radio Clinic!! I'm at work and can't really watch the trailer now, but that looks exactly like what I was hoping for when I started this thread. As the website text for the video download says, "This is not like FM, where you can chuck a receiver and a 5 year old niCd pack in the fuselage and go flying." so I'm hoping to educate myself on the ins and outs of the new tech as deeply as I can.

BarracudaHockey

My Feedback: (11)

Its a fantastic video, I reviewed it a while back for this site and my comments at the time were something like "this is something any modeler converting to 2.4ghz systems will gain a ton of useful information from"

Give or take.

Gray Beard

My Feedback: (-1)

Any of my planes has five servos, some are all digital and a digital draws a lot of power. Now think of a snap roll and figure the power draw, you just about went down below the 4 volt range. Back when Spektrum hit the market you bought a radio that came with your choice of servos and it didn't mater if you got analog or digital, the system came with a 4.8 volt battery pack. See the problem now, fly twice and on the third flight do a snap roll, brown out!!
Today we know better and use 6 volt or LIFE packs or Lipo and we now have some serious voltage so even if you had an old system you would be pretty safe. Things still happen but it isn't anything like it used to be.
BUy the brand you think you like best and don't worry about it, just use at least 6 volts with any system you buy.

rcjetflyer0718-RCU

My Feedback: (1)

Some months back Cal Orr (former radio columnist for RCM Magazine) gave a talk and demonstration, at our club meeting. on 2.4 radios mostly Spectrums. He showed {using an oscilloscope) that even running one digital servo can cause your voltage can drop. Cal said 90% of radio problems are caused by batteries. His solution was to run dual batteries.

Gray Beard

My Feedback: (-1)

I run two packs in all my big planes and any of the smaller ones I'm in love with and one for the ignition. That was also with 72, just a habit I got into.

jsr1017

So this talk about batteries has made me realize that I can't even remember what capacity I used to run in my old planes. My first project is a scratch built Clancy Speedy Bee - 40" wingspan, total weight around 42 oz (according to the plan), wing loading around 12.7 oz/sqft. I'll be powering it with an OS FS 26S and am planning on five micro servos (rudder, elevator, throttle, dual aileron). I'm guessing that for this project I'd want an on-board pack around 2000 mAh? Something like this one if I want to go NiMH or this one in LiPo?

I'm guessing the receiver's current draw will be constant and pretty minimal, but I don't see any specs on current draw for the servos - and I suppose that makes sense since their draw is going to be highly dependent on flight speed, control surface deflection and so on. Got any rule-of-thumb guidelines for pack capacity on glow-powered planes?

EDIT: I had originally mentioned Spektrum A2020s as an example servo, but then realized that's the one I had been researching for the electric glider I plan to build and re-orient my brain and thumbs before putting the Speedy Bee in the air. Not sure which servo I'll be using in the Bee yet.

jester_s1

You don't need anywhere near that much battery for a plane that small. I use a 950 mah LiFe in my .40 and .60 size sport planes. They average 100-130 mah per 10 minute flight, even with my Kaos which has all digital servos. A 3D plane that size would use more because you do so many more big surface movements with them, but for my sport and aerobatic flying these batteries are fine. I fly 5 times and recharge, knowing that I still have plenty of reserve. Your Speedy Bee will do just fine with a quality built 6v pack anywhere in the 600-1000 mah range. And by quality built, I mean a pack built with Sanyo cells and welded together instead of soldered. It's probably hard to find commercially made packs that aren't welded these days, but there are plenty that are built with Tenergy or other cheap cells that won't last as long and can't deliver the amp draw that the Sanyos can.

Gray Beard

My Feedback: (-1)

But you can get AA cell packs with 2200 mah so why fool with the little ones. I buy Enellope type and have the packs made up at Batteries plus for a couple bucks. Only thing about the Enellope type is they don't self discharge very much so you can charge them today and fly with the pack next year without charging again. Great for people like me that don't like to charge the packs all the time to keep them from going bad.
You don't need the high mah but why not get a bigger one? They cost the same.

jester_s1

More capacity = more weight. I don't know much about the plane he's planning, but if weight is an issue a AA size pack may be too much.

jsr1017

I guess the main takeaway for me re. capacity is that something around 1000 mAh will be more than enough capacity for a relatively simple fun-flyer or sport-scale model with five servos and that was my most important question - woulda sucked big time if I had started out with a drastically undersized receiver pack and crashed on the first flight after running out of juice!

In my research I've seen A123 cells mentioned quite a lot (for LiFe/LiPo), and radicalrc.com as a good source - any direct experience witth them? On this page I see an 1100 mAh 2S pack for 27 bucks, weight 2.7 oz. Or here there's a 1000 mAh NiMH AAA pack for $21 at about the same weight, or I could bump up to a 1500 mAh 2/3A pack which comes in about two ounces heavier at 4.4 oz. I guess once I get closer to completing the airframe I can evaluate whether to trade off a little extra weight for a little more capacity. The Bee I built ten years ago flew great with a 4.8v NiMH AA pack (I'm pretty sure) and I'd bet that those were a good bit heavier than today's cells, so I'm guessing an ounce or two isn't going to make or break the flight characteristics.

The 2S LiFe packs are rated at max 7.3v, but I've only ever seen receiver/servo specs mention 4.8v or 6v. The radicalrc page says they "Replaces Ni-type 5 cell battery packs with lithium technology without the need for voltage regulation." I could just take them at their word ... or I could ask if I need to worry if the pack has a slightly higher voltage than the receiver specs really want. I guess if guys are flying with 2S LiFe packs it must be okay, or do you all have an additional voltage regulator on board? Man, things have changed since the days when NiMH was the brand-spanking new battery tech.

And as long as I have your ears ... got any recommendations for chargers? I'm going to be building and flying an electric glider before the Bee takes to the air, so I'm going to need a charger that will support LiPos. Been looking at the HiTec X4 series, seems like a good mid- to high-end system.

jester_s1

There are a couple of things to know about LiFe batteries. First, there are 2 varieties of them. The A123 brand packs are metal cylinders that look like long NiCds. The manufacturing technology they use gives you incredible amp capacity and a very durable battery. Standard LiFes are soft and flat cells that look like lipos. They aren't as durable, especially against vibration and crashes, and can't deliver the ridiculous amp draws that A123 packs can. Amp capacity won't be a factor in what you're doing, because you won't come anywhere near the limits of either kind of battery. Lipos are different. A 2 cell lipo puts out 8.4v hot off the charger, which is too much for most servos. So guys who want to use a Lipo have to regulate it down.

On voltage: A NiCd or Nimh hot off the charger puts out 7.2v. So any system designed to be used with a 5 cell NiCd can handle that much voltage just fine. A hot off the charger LiFe puts out 7.4v. Both fall below 7v fairly quickly as you discharge them. So unless you are using a very high performance servo (like in a helicopter tail) where the manufacturer specifically says to never go above a certain voltage, you have no worries.

jsr1017

This isn't really a radio "tech" question, but I'll throw it in here anyway. I'm just about ready to pull the trigger on a DX-9 black edition - I sold off a bunch of gear from my motorcycle racing days so there a wad of cash burning a giant hole in my pocket. What I'm wondering is this: ever since I placed a ~$50 order from Tower (for a motor mount, tank, pushrods etc.) I get emails from them with monthly coupon codes offering around $70 or $80 off of an order of $599 or more ... but of course Tower doesn't sell Spektrum radios. Anyone ordered direct from Horizon and gotten similar coupons? If I place a smaller order with them first and can then save $70 on the radio, that'd pay for, say, the Coverite for the Speedy Bee, or a field box, or servos, or any of the dozens of other things I'm gonna need. There's currently a promo on the horizon site for $30 off after placing and order for $200, but it expired on January 31. Maybe the best thing to do is just get it from one of the local hobby shops (I know of two that have them in stock), and it certainly wouldn't hurt to support local business, but if I could save that much that would trump my civic duty.

BarracudaHockey

My Feedback: (11)

Horizon sends out specials now and then. Of course, if you're waiting to buy something it won't show up till right AFTER you order it

jsr1017

Sweet, I found out that one of the shops here in the Twin Cities is offering the DX9 Black Edition for $559, that's $40 less than I could find anywhere else online. So I'll give them my business for the radio, even though I'll have to pay sales tax that'll satisfy my desire to support a local business. I'll order the rest of the stuff from Tower and use their coupon, it's basically 11% off and their prices beat most other online sources I've found. After selling off even more of my old racing gear I've got quite a shopping list going!

I've decided that I'm going to make my first flights with an electric sailplane from one of my favorite manufacturers from my old R/C days in Germany - the R.E.S.olution from Stefan Hoellein. They make CNC- and laser-cut kits that are works of art. It's a two-meter balsa-and-ply kit with a carbon fiber main spar, rudder/elevator (and spoilers for some optional fun at landing). Has plenty of dihedral so it'll be nice and stable to get me used to flying again.



She will be powered by a Hacker A20-22L with a Hacker X30-Pro BEC. The kit, motor, BEC, and prop hub, blades and spinner were ordered a few days ago and should be here tomorrow. For the rudder and elevator servos I'm thinking Hitec 5055 digital featherweights, for the spoilers HS-40 nanos - those match up with the specs of Graupner/Robbe servos that Hoellein recommends. I'll talk to the guys at the local shop when I go down to pick up the DX9 tomorrow and pick out a lightweight Spektrum Rx.

Once I'm comfortable flying again I'll put the Clancy Aviation Speedy Bee that I've been working on up in the air. I have a build log thread with tons of photos running over in the scratch builder's subforum, it's coming along nicely. The Bee will be powered by an OS FS 26S four stroke that I got new-in-box for a really good price on eBay. I'll go ahead and put the Rx that comes with the DX9 in her, for now at least. Servos will likely be:

-- Hitec 5085mg digital micros for the rudder and elevator
-- Dual Hitec 5125mg digital wing servos for the ailerons
-- Hitec 5055mg digital featherweight for the throttle

That leaves batteries and a charger. I'm liking the Hitec X4 plus AC/DC for a charger, and I think I'll order the batteries from Radical RC - their RRC K6 1800 2s LiPo for the glider, and a Reedy 2S LiFe Rx pack for the Bee, most likely 1700 mAh since it's only a 0.6 oz heavier than the 1300. It probably makes sense to get two of the LiPos for the sailplane, so I can fly out one pack and be charging it while I'm flying on the other one.

Have I forgotten anything, electronics-wise? What do you guys think of my servo and battery choices?

jester_s1

There's no need for digital metal gear servos for the throttle. Actually, there are some negatives with going that route. Metal gear servos experience more wear in a high vibration environment than nylon servos do, so it will get sloppy faster. And digitals will burn themselves up pushing against a hard stop if you are a little off in your end point adjustments while analog servos won't. And, of course, there is the cost consideration between analog and digital.

If you plan to go and spend an afternoon at a time flying, get 3-4 lipos. A flight will probably be 10 minutes, then you'll have usually 45 minutes of charging to get back up to 95%. With 3 batteries, you'll finish the last one just about the time the first one is ready to fly with again. The Hitec x4 is a great charger

jsr1017

Had a very good experience at the hobby shop today and got a great deal. R/Cers in the Twin Cities (MN) area that don't know about the Hobby Warehouse at 71st and Chicago in Richfield should definitely check them out! Came away with a DX9 (transmitter only instead of the black edition), two Spektrum AR610 receivers, two generic receiver switch harnesses, the Hitec X4 Plus charger, plus a Hobbico 1300 mAh LiFe pack and Hitec HS82mg servo to play with, for $789 including sales tax. The best combination of prices I could find online for the same gear was $808, with shipping costs on top of that, so I call it a win.



Playing around on the kitchen table I got as far as binding one of the receivers and seeing the servo move in response to the sticks, I know it's a very simple thing but it was pretty dang cool to see that again after ten years. Also did a simple test with the X4 and the Rx pack to get at least the basics down, that worked perfectly as well. Now I gotta clear off the building board and get the plane finished!