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Old Apr 19, 2007, 11:37 AM
Todays a good day to fly
Jam Rectified's Avatar
Joined Oct 2005
973 Posts
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Can someone help me out with some headspeed calcs for Xero G

Hi Guys,

I am putting together a Xero G frame that I want to run with 620 blades (Titan boom etc) and on 10S2P A123 Cells. I have a Z50A 800 motor and a Z50A 600 on the way but what I could really do with is some advice on what setup I should use for just putzing around. I got a selection of Swift Pinions that I can use from 9T upto 14T I believe. The Xero G frame is pretty much built for 10S A123 packs as they fit in the frame very easily.

So please correct me if I am wrong anywhere here but lets start with the 800 (780KV) motor:
For 10S2P A123 cells am I right in assuming a voltage of 3V per cell?
so 30 x 780 is giving me 23400 right
So...with the reduction on the "box" I divide that by 2 giving me 11700, using the 85T main gear and a 14T pinion that gives me head speed of 1927...(11700/(85/14)).
Is that correct?

So how would that compare to using the 600 motor (not sure the exact KV at the moment bust assuming 600 for calculation sake), without the box, and using the 85T main gear and a 9T pinion..that gives me just over 1900...

I hope I am on the right track here...so...which is a better set up or is it just down to my preference...either way I am aiming for a headspeed around 1950 and from what I read it is better to get there mechanically than electronically with the ESC (HV85 in this case). Are then any benefits in using / not using the "box" assuming that I can still fit the 2 10S A123 packs and balance the CofG with the motor in the alternative position..?
Would appreciate any thoughts or just someone to confirm my clacs are OK...I have tried..
Cheers
Jam R
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Last edited by Jam Rectified; Apr 19, 2007 at 11:45 AM.
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Old Apr 19, 2007, 12:34 PM
Das Universus Elektrikus
Albig's Avatar
NM, USA
Joined Mar 2002
3,309 Posts
Take advantage of the gearing and use the 800.

Also if you bolt the 600 from below you'll lose some sapce down there for the packs.


It should do just fine.
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Old Apr 19, 2007, 03:31 PM
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Tean's Avatar
Ross on Wye, UK
Joined Jan 2006
264 Posts
30V is too optimistic for the voltage of the A123 pack. Under load these can drop below 25V. If you pinion for 30V, which is only realistic under hovering loads, you'll end up with a boggy setup. I think it better to pinion for 25V and hold the off-load speed down with the ESC's governor.

The 800 is going to perform better. If you assume a motor rpm of about 20,000, you could run it with your 85 tooth maingear, the "box" and a 16 or 17 tooth pinion, or direct drive from below with 9 or 10 tooth pinion and a Raptor60 95 tooth maingear. This would be my option as I don't like the "box". If the motor is in the way of the packs it is possible, with some mods, to mount the motor at the rear of the frames. I have a Z50A mounted here.
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Old Apr 19, 2007, 04:17 PM
Das Universus Elektrikus
Albig's Avatar
NM, USA
Joined Mar 2002
3,309 Posts
I'm seeing about 2.7 to 2.8Vs on a 700 running 10s2p so he's probably not too far off.

Remember he is running 2P here.

It won't be the hottest setup but it should fly for a while and have plenty of power for anything you want to do.
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Old Apr 20, 2007, 12:21 AM
Todays a good day to fly
Jam Rectified's Avatar
Joined Oct 2005
973 Posts
Thanks guys for the advice - So I'll aim for using a voltage of 27V in my calculations then and the 800 motor is preference..Where could I get hold of a 16T or 17T pinion?

Thanks
Jam R
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Old Apr 22, 2007, 12:42 PM
Todays a good day to fly
Jam Rectified's Avatar
Joined Oct 2005
973 Posts
16T pinion?

Anyone point me in the right direction for a 16T pinion?
Thanks
Jam R
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