Quadrocopter advertises that the CS8 with a 2-axis gimbal will fly approximately 25 minutes with a GoPro camera ("Max Flight Time (GoPro HD): ~25 min."). Flying time was a big deal for us in determining which copter to get. At the time they, claimed to get ~25 min flying time with a 6200mAh battery. (Oddly, they have changed the battery to 8000mAh, but the flying time has remained the same.) Anyway, after reading many threads discussing flying time it became apparent that this flying time is a fantasy. I need to know exactly how much of a fantasy. So I flew the CS8 with a 2-axis gimbal and a GoPro camera in-doors (so there was no wind), just hovering, and draining the 6200mAh 4S Quadropower battery to it's limit (12V). So this is the most optimistic flying time you could possible get with the configuration in their advertisement. And the flying time I got was nine minutes. That is not even close to half of 25 minutes. Bah! Anyway, I also tested a dual Turnigy 5S 5000mAh set up and got 17 minutes flying time. Interestingly, the two Turnigy batteries combined cost less than the single Quadropower battery. We are not flush with capital so an important figure for us is minutes of flying time per dollar.
With batteries, my experience is that you get what you pay for. All batteries, even the cheapest, work well new. As they age is where you see the difference, the cheap ones will not have near the same number of cycles. The other bad habit of cheap batteries is to fail suddenly whereas the expensive ones just very slowly fade away. Plenty of exceptions to that, but on the whole that has been our experience.
Yeah...my experience, limited as it is, is that the Second Law of Thermodynamics holds true: You gets what you pays for. The top quality/capacity batteries that I've seen so far are the QC6200, QC8000, and the MaxAmps 10900/120C's. I've not tested the Turnigy's though so take what I say with a grain of salt -- my sample size is not statistically significant. So there seem to be several variables: 1. Capacity. 2. Actual real world discharge rate (closely related to internal resistance). 3. Voltage sag with respect to discharge rate (which is what did in the Maxamps 11000 for me). 4. Number of lifetime battery cycles. 5. Decay of capacity with respect to time. 6. Price. Andy.
It may be that it flies 25 minutes without the gimbal, but there is no way you could construe the product description to get that meaning. Essentially, they would have to be saying, "in some other configuration then the one we are talking about here and pictured above, we can get a 25 minute flight time." It's a really misleading statement, and it really stinks to find out after I bought the thing. But it's OK. The 17 minute flight time is pretty good and I think I can close in on 25 minutes if I use a pair of 8000mAh 5S batteries.
We fly a CS8, with a 2-axis CS gimbal, a 9.5 oz camera, and 4 - 5450 4S batteries. We are about 20 minutes on the nose.
Four? That's impressive. Did you mount the batteries on the booms around the hub or did you stack them on the battery plate? I have considered trying three batteries (as that is what can find nicely on the battery plate), but for each battery I would add I would get closer to the thermal barrier which is a problem. (That, and I would have to make yet another cable. ugh!)
They are around the hub. We limit our batteries at ~21800 mAh (4S) because we are running the Mikrokopter BLs and our comfort level for running current through them, granted we have a generous margin of error, is right about at this weight. YMMV. There is more time aloft to be had by running bigger props. And we haven't tested the 4S vs 5S - I heard that not much is gained without going to a lower KV motor - just hearsay though.
I was staring at the image, going "What on earth is that big box out on the end of boom #3" then I realized it was on the table. I'd love to see an image of the central hub with the batteries removed -- did you make up custom battery plates? Andy.
I did make them. Little squares of G-10. They Velcro to center plate on the sides and the use the boom screws in the front. I don't have a machine here, but I'll grab a close-up photo later.
I should try that then. Rather than using bigger booms I was wondering if I might get away with inverting every other motor. I would have to move the legs so that they wouldn't be in the way. It might work.
I think you would need a custom control algorithm for that, since the props would no longer be in the same plane. Who knows.. maybe it would work fine though. If you were going that route I might suggest an X8 config.
There are a couple guys testing an overlap config in the other forums with good results. Prop overlap is approx 2.5 - 3 inches. Supposedly better efficiency over coax config. Advantage is slightly small diameter octo/hexa.