| Image Comments |
| SteveM | 23-Apr-08 20:21 |
| The Tyro is repaired and ready to fly again. Based on the wind forecast very early Friday morning might be a good time to sneak out to the field to try again. |
| SteveM | 24-Apr-08 21:08 |
| I finally purchased an essential "Watt's Up" meter so I know what kind of current and voltage the motor is actually seeing. With this 8x6 prop and the 2 cell 640 mAh LiPo battery at full throttle (static, not in flight) draws 7.8 Amps at 7.21 volts for a power of 56 watts. I have no idea if that is a lot or a little power, but at least I have real numbers to work with now. |
| SteveM | 24-Apr-08 21:49 |
| I saw a recommendation on RCGroups that at least 75 watts should be used and 100 watts or more would give a sportier performance. Looks like I am underpowered on account of the small capacity battery borrowed from the Hellcat, hopefully my Tanic A123 packs get here soon. |
| jgood | 24-Apr-08 22:11 |
| Steve, I've been trying to find my meter so I can tell you what mine produces. I think you might be a little under prop'd, what do you think? Maybe try a 9070 prop, that's what I use. I think that battery should be OK, although obviously it will run out much quicker than the 2 cell 1320 batteries I use usually (I actually use a 3 cell battery with the camera on board - lots more power, although it wears out the motors quicker!). Power should be the same though - it's still 7.4V. Sometimes I use 870mAh 2 cells, and they have the same power available as the 2 cell 1320, it just runs for less time. The aircraft is nice and light with those small batteries though. What gearing are you using? |
| jgood | 24-Apr-08 22:23 |
| OK, found my meter. 6A / 40W with the 2 cell 1320mAh battery. About the same with the 870mAh. The 3 cell 1320mAh was crazy though - no wonder it takes off like a rocket with it! 10.5A / 100W! This is all with the 9070 GWS prop. |
| jgood | 24-Apr-08 22:27 |
| 40W really flies it OK - I can still loft the camera with that. I think many r/c flyers like their aircraft to be VERY overpowered. I kinda like having to actually use a runway, rather than a rocket launch pad. :) BTW, my batteries are Thunder Power packs, some of them are 4 years old, and still working acceptably. |
| SteveM | 24-Apr-08 22:32 |
| 6A and 40W?! That seems like so little. I did try the EP9070 but the ESC was tripping on low voltage at WOT (I assume so as I had no meter at the time). I have a 4.5:1 gearbox and the 15C battery means 9.6A max. But even at 7.8A the voltage on a fresh battery drooped to 7.2 volts.
My motor and ESC are rated at 10A so the only way I'll get close to 100W is through max current and 10 volts or more. The 1100 mAh A123 packs are nominally 9.9 volts and can source 30C, so I should have no trouble swinging a 9070. I also ordered a Cobri gearbox with two pinion and three spur gears so I can play with prop speed too.
Tomorrow bright and early I am going to try to fly again as the forecast is 0-1 MPH winds in the morning. |
| jgood | 24-Apr-08 22:51 |
| I wish my weather chart looked like yours. My ESC (a GWS ICS300E) is rated to 8A, with 15A burst. I know I'm pushing the motor and ESC with the 3 cell - I usually hang the ESC in the air flow, to help it cool, otherwise I sometimes get cutouts. My gearbox is a 5.33:1 (C gearing). Good luck tomorrow! Get her up high nice and fast, to give yourself some time if you get into trouble. Does your field have plenty of room? |
| SteveM | 24-Apr-08 22:54 |
| Update: The EP9070 prop provides 10.48 Amps at 6.89 volts and 72 watts. Looks like I was tripping the current and not the voltage! The bigger batteries will cure the voltage droop and a higher gear ratio will bring the current down below 10 Amps. Good thing I got the meter, it was all guess work (and wrong guesses) prior to now. |
| SteveM | 24-Apr-08 22:56 |
| The field is about 300' wide and 700' long with the runway near the middle. |
| jgood | 24-Apr-08 22:58 |
| Looks like a good place. |
| jgood | 24-Apr-08 22:59 |
| The repair job looks very good, BTW. |
