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| SteveM, Image # 8764 | 23 Jun 08 15:51 |
Big and little Enos Burdett. |
| SteveM, Image # 8763 | 23 Jun 08 15:49 |
These benches make it a lot easier to work on the larger planes. Unfortunately I have to have the wing off in order to adjust linkages, check motor power, and RPM. |
| SteveM, Image # 8726 | 18 Jun 08 16:26 |
My new battery charger is a battery, kind of like a chicken and egg problem I guess. About 20' of 18 AWG wire connects the Pb-Acid to the LiFe in order to limit current. Then 11.8" of 10AWG makes up my shunt ammeter, 1 mV = 1 A. |
| SteveM, Image # 8695 | 16 Jun 08 03:56 |
I need to tidy this mess and cut a hole in the firewall for the motor wires, then it is on to covering. Weight is 6.78 lbs so AUW should be that plus the weight of a Monokote covering. It's also a touch nose heavy so I'll move the batteries or motor aft. |
| SteveM, Image # 8690 | 15 Jun 08 01:46 |
Gluing on the tail feathers. I suppose I could have used a cardboard box as a jig, but this all should work ok. |
| SteveM, Comment for image # 8685 | 15 Jun 08 01:13 |
| My understanding is that even fuel/glo engines took a while before they became fairly standardized. Part of the chaos with electrics comes from little standardization and the ability for an electric motor to operate efficiently over a wide range of RPMs.
Part of the reason I chose this motor is that E-Flite reckons it to be equivalent to a size 90 glo engine. By only running it at 20 volts (it can do up to 32) and using a 14-15" prop I only use about 400-500 watts, so there will be no aerobatics for now. But if I drop in another battery pack just like these two and size the prop to make the motor draw 50 amps (about a 16x10) then it'll be in the 1500-1600 watt range! So unlike a glo, there is a lot that goes into picking the system and there are interdependencies to be considered. And like I have done here, you can run it in a size 40 or you could put it in a 60 or a 90.
It also allows you to pick a scale prop then select a motor and battery pack to give a suitable performance with that prop. |
| poppy, Comment for image # 8685 | 14 Jun 08 23:39 |
| Wow! I know electrics are quiter and cleaner, but with a glo engine, just install proper size, add receiver and servos with battery pack and go. However, I am betting that what you have will give some nice aerobatics. |
| SteveM, Comment for image # 8685 | 14 Jun 08 22:04 |
| The motor is rated 325 Kv but I had to set Motocalc to use 290 Kv then it was spot on. I bumped the ESC timing advance to "high" and it now does 350 watts with the 14x10, which is equivalent to about 300 Kv using Motocalc numbers. I don't know what kind of tolerance these motors have so I guess I'll have to ask around on RCGroups. |
| SteveM, Comment for image # 8685 | 14 Jun 08 20:49 |
| Motocalc is a lot more accurate with the Tyro power numbers so I may have some issues with the motor not being accurately modeled.
The bones weigh 6.5 lbs so AUW could be around 7.5 lbs. With the 14x10 that is ~40 W/lb and on the 15" it is ~50 W/lb. I flew the Tyro on those power numbers so I'm not worried about getting into the air. If you consider that the electric motor that I have on here weighs as much as a size 40 engine and that the batteries weigh 2 lbs then a AUW of 7.5 lbs is right where I would expect since the kit estimates a 5-5.5 lbs AUW. |
| SteveM, Image # 8685 | 14 Jun 08 20:41 |
Testing the motor on the fuselage with 15x10 prop. I only got 380 watts but Motocalc estimated 540 watts. With the 14x10 I got 325 W and Motocalc said 420 W. The 14" barely clears and the 15" hits the floor so I may have to swap wheels. |
| SteveM, Comment for image # 8588 | 14 Jun 08 17:51 |
| The correct size motor mount arrived today along with the required 10mm prop reamer so I have been able to get on with building the firewall. While the epoxy dries I just had to try this out with a 14x10 prop. I chickened out at about 1/2 throttle (200 watts/20 volts/10 amps) as I was holding the thing in my hands and it was about to start dragging me across the floor. |
| SteveM, Comment for image # 8588 | 07 Jun 08 15:49 |
| The plane has a 62" wingspan (size 40 trainer) with a designed AUW in the 5-5.5 lb range.
I have multiple reasons for separating the packs into 3 cell in series. My Cellpro 4S charger can only charge 4 cells or fewer, a 3 cell pack can be charged from a 12 volt battery with nothing more than 10' of lamp cord, the BEC can be connected across just one battery pack, and future planes will use 9S so 3 of the packs will work just nicely. As far as safety goes, I plan to put a fuse on the ESC and in each servo lead, only the radio will not have a fuse. |
| Heinrich Dorfmann, Comment for image # 8588 | 07 Jun 08 11:10 |
| That's a lot of weight ... What is the wing span of this plane? Why are you using two battery packs? Safety reasons ? |
| SteveM, Comment for image # 8588 | 07 Jun 08 01:44 |
| It seems that when the disconnect is removed the ESC passes the voltage from the left pack through its positive lead and out onto its ground lead, putting a reverse voltage on the BEC and allowing enough current to flow to turn on the micro controller in the ESC. For now I will use a diode on the negative lead of the BEC but am considering using a separate switch for the BEC.
Each battery pack weighs 483 grams for a combined weight of 966 grams (2.13 lbs!). A LiPo of same capacity and similar voltage weighs 571 grams (611 grams if you scale the weight to compensate for the slight voltage difference). |
| SteveM, Image # 8588 | 06 Jun 08 20:32 |
The power train is nearly finished. The battery packs are 3S2P of 2300 mAh A123 cells with a CC BEC across just one of the packs. Only problem is even with the disconnect removed the pack on the left is powering the ESC by way of the BEC somehow. |
| SteveM, Image # 8576 | 05 Jun 08 00:35 |
View of the right wing before the sheeting goes on. The spars are 1/4" sq. spruce but everything else is balsa. It's almost embarrassing to admit this, but other than trimming a few of the webs and one sheet to fit, I haven't had to sand or cut anything. |
| SteveM, Comment for image # 8562 | 03 Jun 08 17:54 |
| These are LiFe cells by A123 and are the the big brother of what I have been using in the Tyro. When abused they do not go into an exothermic reaction like LiPo, and they can be charged at 5C and discharged at over 30C. The Tyro batteries charge faster than I can drain them by flying.
I got two used DeWalt battery packs but one had some sort of Sony cell in them. The fella that sold them to me is sending another with A123 cells but I am going to give the Sony cells a try as a 5S2P pack is nearly identical to a 6S2P pack of the A123 cells. But the Sony cells are only good for 10C discharge and I have yet to find out how fast they can be charged. |
| jgood, Comment for image # 8562 | 03 Jun 08 16:51 |
| What kind of cells are they Steve? LiPo? |
| SteveM, Image # 8565 | 03 Jun 08 03:21 |
The left wing is nearly finished. At just under 5 ounces it is lighter than I thought it would be. Very little of what you see required any cutting or sanding, it's a lot easier than what I am used to a "kit" being. |
| SteveM, Comment for image # 8562 | 02 Jun 08 17:44 |
| This system is far more than what is required for the size 40 Aero-Star. But the battery and prop choices I have made (14" to 15") should produce 400-500 watts which should be appropriate. Later on I can add more battery cells in series to get 1000 watts or more for a size 60 or 90 warbird. |
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