you need a bigger pack - I was running the same combo as you but with a 4000mAH pack and it has enough to get me through (just) I was still hitting 75% of the pack capicity  - so I think your 3000 is to small for this application

I had advise from Mike Palko about using a larger pack for more "head" at the end of the pattern- seems like he is right.

Jim

Wynn is correct. You are running out of adequate reserve in the battery. The Rhino 3700 4s will also work well and get you thru the pattern. I saw this last year with the original setup in my T-REx and ran into it again this year. The 3000 mah 4S packs while able to do the job early in the pattern just could not sustain the rpm for the entire pattern and you see the lap times climb near the end and run out of power in the final maneuvers. Rick Sawicki proved it to me by plugging a Rhino 3700 4S into my plane and changing nothing else proving it. He seems to always be right. We both find the 3700 mah rhino 4S to be a very nice pack. I'd like it if it were shorter but it is what it is. And it lasts. His are in their third season of stunt use. I just ordered 4 more and use them in the T-Rex and the sv-11. The issue you uncovered is not just the total amount you are taking from the pack but the voltage fall off when you are near the end. Having the larger pack gives you the capacity you need to apparently not run into the voltage fall off.



bob branch

My Electron weighs 1820 grams (64 oz.) and I use  the MVVS 6,5/910 motor with an APC 12 x 6 E prop, on a 4-cell 3300 Lipo. This use 2200 mAh up here at 5000 ft. ASL for the 5:30 flight, and 2400 mAh down at sea level. I fly on 66 ft (eyelet to eyelt) of PAW Staystrate 14 thou lines with a lap time of around 5,1 to 5,2 secs. The Electron is to heavy at this weight, so I always try to buy Lipos that are as light as possible. I have some X-Powers and Dersire Power Lipos that weigh around 320 grams, but my model is o.k. up to 350 grams. The Electron is a full take-apart model with 2-piece wings and split fuselage etc., so it's hard to make this light. My target weight for my latest design is 1650 grams.

If your model is losing that much at the end of the flight, then all the above advice is correct. If you can't get the weight and drag down, then your only alternative is to use bigger capacity batteries. The wonderful thing for me about electric stunt, is the way that we can measure the performance so easily with gadgets like the data recorders. Just changing the flying line thickness can be seen on the amount of power used. For prop experimenting, this is just too wonderful for words. I've tried all kinds of props, and the neat thing is that APC are such a good price. If you just consider what it cost before to buy the competition carbon props. Good stunting has never been easier....or cheaper!

Keith R

Thanks for the info all. I figured it was a lack of battery capacity but thougt maybe one could program around it. Good thing I only bought two batteries to experiment with! Now to order more capacity.

My brother Ron, myself and one other flyer at our field all have experienced slow down at the end of the flight using 4000 mah 4S 20C batteries.  These batteries were using 70% or less of capacity but they still had some drop off toward the end of each flight.  We changed over to 4000 mah 5S 20C batteries and the drop off went away.  Total power used is about the same but the higher voltage eliminated the slow down at the end of flights.  My brother has now tried 3000 mah 5S 20C batteries in his Brodak T-Rex and he is using about 85% capacity and he does not experience any drop off toward the end of the flight. I can't speak for anyone else but as I said, all three of us flying electric at our field have experienced this same thing.  It appears to us that the higher voltage gives a more consistant performance.

That's a sign that you're 'asking' the system for too much RPM for the motor/battery combination.  A permanent magnet motor needs enough voltage to turn a certain RPM, if you're too close to the top end at the beginning of a flight then at the end when the battery sags you won't have enough overhead.

The reason that changing the battery voltage worked was because you changed the amount of voltage overhead you had available.  You could have also done this by changing to a motor with a higher Kv.  You may have been able to do this by changing to a higher pitch prop and programming for lower RPM -- but I'm not a good enough prop-swapper to predict what other things this would have done for you, good or bad.

Note that this probably isn't an answer to Jim's problem, because he's pulling his battery down by 85% -- he needs to sacrifice some lightness to get more battery capacity, or he needs to lower the power through the whole run in hopes of getting more oomph at the end.  In theory he could jigger the prop pitch and lower RPMs to suck the battery down even further -- but then his batteries aren't going to enjoy long lives.