[JamesBC]

I have been shopping for new batteries for my Multi, and now going to need them for the one I bought from rchelicanada.com the Spacewalk 550 FPV.

Now the one I am flying right now is a tri copter with 6 motors and with camera and tx it weights in at 1500g with its 6 motors, ESC's, just no battery. So using my 3S 2800mah 25-50C (that is the batteries I fly in my 450's Heli's) I get 6 minutes flight, most times on the ground just after 5 minutes as that is what my timer is set for and batteries are down to 3.74 or so, and they are warm, not hot. Motor's and ESC's are still cold.

So my question is, what C rating for the multi should I be looking at in the 4s packs?

Also, is it better to have a 4s pack rather than two 2s packs?

Well sun is out, no wind time to go putter around with the multi.

Jim

[Max]

Ah.. the beauty of watts!!!

Ok, some simple math

From your information above, A 2.8Amp (Battery) over 5 minutes is about 25A of current.

Watts is VxA
12.0V (Im gonna use this as nominal Voltage) X 25A Current = 300W

So we now know that your heli pulls 300W to stay airborne.


Now if we calculate current from a 4S pack that needs to give up 300W, we need to work backwards

If W= VxA, then A = W/V

300Watts(We know from your quad) / 16V (again, I use this avg for 4s) = 18.75A

So we figure that using a 4s, to get 300W of power that we know flies your quad, we will only need 18.75A

So if you have a 2200 4S pack, 20C = 44A that you can safely full from the pack. 18A falls well below the safe limit, but we are assuming you arent goosing the throttle at all for the duration of the flight

This would be the lowest C rating I would use.
Personally, I prefer the highest C rating that is most cost effective. A 25C pack wont cost that much more but will give you a longer lasting pack (IMHO)

If you used a 28004s, then a 20C would give you a maximum of 56A. Again, we know you will only pull 18 A, so you are again safe with a 20C pack,

Cheers!

[Max]

Originally Posted by JamesBC

Also, is it better to have a 4s pack rather than two 2s packs?

Oh yeah. I forgot to mention.

If you are using 2200's or 3000's, then its much easier to use a single 4S pack. 2 2S for such relatively small batteries is a pain in the butt.

The only time that is an advantage is in the case of a quad where you want to spread the weight around the quad rather than in one spot. But a 4S pack isn't much thicker than a 3S pack so I dont think that really makes much of a difference.

[JamesBC]

Ahh the pain in not fully understanding batteries...

Ok so best to go with 25c from what you said, or even a 30c, never hurts to be to high, only two low.

I guess the next thing to look at is Mah of the batteries, that will depend on how much weight I want to add. I tend to fly slowly around, so speed is not a considertion and at present the tri-copter is flying at half throttle. So I might play with using a smaller prop and adding a small amount of weight to see how it handles it. I am using the Naza and think I can use the throttle curve to bring rpm up with a smaller prop.

Thanks Max

Jim

[buffythesaint]

Originally Posted by JamesBC

Ahh the pain in not fully understanding batteries...

Ok so best to go with 25c from what you said, or even a 30c, never hurts to be to high, only two low.

I guess the next thing to look at is Mah of the batteries, that will depend on how much weight I want to add. I tend to fly slowly around, so speed is not a considertion and at present the tri-copter is flying at half throttle. So I might play with using a smaller prop and adding a small amount of weight to see how it handles it. I am using the Naza and think I can use the throttle curve to bring rpm up with a smaller prop.

Thanks Max

Jim

If your using the naza, no need for a throttle curve, in atti at least. It will bring up the rpms enough to hold a hover. In manual, you can play with the throttle curve, depending where your hover stick position is in manual. If it's mid point, no need for a thottle curve, if you switch back and forth with atti and manual. Adjust the curve for manual if hover is above or below mid stick. As battery voltage goes down, your hover stck position, in manual, will be slightly higher. Adjust for a bumpless transfer.

As for bats, a 4s setup will give longer flight times. I would go with a 4s 4000-5000 mah pack. Should get 10mins or more flight time.