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Over powering motor in my Tailwind..

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Cyclicscooby26/05/2011 15:04:00
874 forum posts
531 photos
Hi guys...

First, I've finished my tailwind at last...32" with A.U.W 21.7 oz with 3s 850, or an ounce less with the 450mAh batt..
When I get to a pc, I'll upload pics....

But.. I've just tested my new watt meter and I have more power than expected...

Spec -
E-flite park 370 BL - 150w 12/15A cont/max
3S 850mAh lipo - 25c / 35c 21A / 29A

Using suggested prop (in motor specs) - 8 x 8.3

It's drawing 175W @ 16.5A full chat and 90W @ 8A half stick

So batt and esc within specs, but motor overpowered.

I presume a 2s batt would lower it, but Cud I down size the prop.. and if so, to what...? I haven't a clue, so you'd save me buying 15 props n guessing....

Any help or advice gratefully received..
Luv Chrisie xx
Richard Wood26/05/2011 16:07:18
1094 forum posts
164 photos
Hi Chrisie,
The easiest & cheapest way to reduce current draw & power
is to use a smaller prop - so try something like an APC E 7 x 4
for starters. This could well bring the current down sufficiently.
Your little 450mAH battery will struggle to provide the current though -
it'll be working at about 33C to provide 15A - a bit too much.
Tim Mackey26/05/2011 16:14:57
20920 forum posts
304 photos
15 articles
Id leave it TBH - it will unload in the air anyway.
Agree on the battery issue though

Edited By Tim Mackey - Administrator on 26/05/2011 16:15:24

Richard Wood26/05/2011 16:47:58
1094 forum posts
164 photos
Yep, good point - and you'll probably find that you use full throttle very
little & only in short bursts anyway.
Cyclicscooby26/05/2011 17:49:59
874 forum posts
531 photos
Cheers guys

Yeah, id realised the 450 wud probably explode

It just so happens, I bought a 7 x 4 prop yesterday to build the edge 540 shockie that's in the June RC Model World..
I also got a 3s 1300 batt, that might get called upon, as I've just done the C of G and found she needs 28g in the nose, with the 850 batt as far forward as it'll go.. I'll go and weigh it in a bit...

Ur probably right about the current setup being ok tho, its no stunt flyer, so full throttle shuddering be a rare occurrence...

So, I'm off to glue 7 pennies and a 5p inside the nose...

Luv Chrisie xx
Cyclicscooby26/05/2011 17:52:09
874 forum posts
531 photos
Sorry about the spelling, I'm lacking internet so I'm using my phone...
Chris Bott - Moderator26/05/2011 18:13:37
6707 forum posts
1392 photos
1 articles
Chrisie is it really an 8x8.3 prop? or was that yr phone adding it's own thoughts to the post?
It just sounds a very odd size. If it is, or if it's an 8x8, then an 8x6 would help the situation.
Also, is it an APC-E electric prop? If it's an I/C prop the swapping to an APC-E will be more efficient and could reduce the current.
Cyclicscooby26/05/2011 22:42:03
874 forum posts
531 photos
Doh... ! You're right Chris.. It's meant to say 8 x 3.8e..
I wish I could blame the phone, but its my fopar..

Luv Chrisie xx
Frank Skilbeck27/05/2011 10:17:00
4568 forum posts
101 photos
Changing to a 2s battery would probably drop the wattts down to around 80w which might be a bit on the low side.
Rather than buy lots of props, get a copy, free, of drivecalc, www, you select your motor (or one near it if its not listed, i.e. same kv) and change the props and check the effect.
Chris Bott - Moderator27/05/2011 14:00:47
6707 forum posts
1392 photos
1 articles
Just another thought Chrisie.

8x3.8 sounds to me like a slow fly prop.
Now, I have no experience of these, but does anyone else on here know if 175W is OK for one of these? Don't want it to shed a blade on you.
The APC website says the slow fly props should be run at no more than 65000/ prop diameter RPM. So thats 65000/8 that's 8125 RPM.

Edited By Chris Bott on 27/05/2011 14:01:05

Cyclicscooby28/05/2011 00:10:32
874 forum posts
531 photos
Hi Chris..
Correct, it is a slow fly... I didn't realise there would be an issue with rpm, so thanks for that.. iirc the motor is 9k- 13k rpm.. that is full chat, but even so...
I'll have to give the 4 x 8e a go on the watt meter..
I'm gonna try an angling shop tomorrow, for a set of hanging scales, to measure the static thrust...

Thanks for all the replies..

Luv Chrisie xx
Peter Miller31/05/2011 08:19:43
10478 forum posts
1246 photos
10 articles
Just one comment. Mine was quite aerobatic. Have fun.

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