| Image Comments |
| SteveM | 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 | 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). |
| Heinrich Dorfmann | 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 | 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. |
| SteveM | 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. |
