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400 geared motor

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John Cooper 105/07/2015 15:00:23
22 forum posts

Hi. The plan calls for a 400 geared motor what is this in modern brushless terms please.

simon barr05/07/2015 18:06:31
1051 forum posts
16 photos

I would have thought it would be better to go on the size and weight of the model you are building... What is it?

eflightray05/07/2015 19:29:29
622 forum posts
132 photos

Also the required prop size, a preferred Lipo voltage, (2s, 3s, ?).

Steve Hargreaves - Moderator05/07/2015 19:40:34
6762 forum posts
197 photos

A 400 can motor is good for about 100-120 watts max & as this is input power you probably have around 60-70 watts of usable power.....the gearbox will possibly increase this slightly.

Much better to start from scratch with a brushles setup than try & replicate a brushed motor, so we need to know, model type & approx weight...oh & if you have a specific batteries you'd like to use in it....

John Cooper 106/07/2015 07:57:32
22 forum posts

Thanks, it´s Fokker Eindecker 1120mm span, weight 560 gm. Plan by Dale Tattam for 3ch.

It says it is for the Novice Builder-- It is the first I have attempted!

Dave Hopkin06/07/2015 08:07:49
3672 forum posts
294 photos

560g is about 1.2lb so you would be looking for around the 100w per Lb so something that gives you 120Watts (ish) - which ties in with Steves estimates of the 400 sized motor

To take you down to suggested motor levels we would need to know what sized Lipos you want to use and the prop size you want to fit

Edited By Dave Hopkin on 06/07/2015 08:08:17

John Cooper 106/07/2015 17:59:23
22 forum posts

I haven't a clue about batteries-- 3s?? nor props but I do have a watt meter ( which I believe I need).

We have no "club" but the other guys fly for 15-20mins with their shop boughts so I would like to be in this area.

Dave Hopkin06/07/2015 18:47:12
3672 forum posts
294 photos

Ok, time for you to do some reading I fear!

A basic explaination of LiPo Batteries here - **LINK**

and a intro to brushless motors here **LINK**

Clubs? Have you checked the BMFA Website, Club Finder here **LINK**

I am going to assume that you have not flown an RC Aircraft before? If thats correct, then starting off with a plan build may not be the bext way to go, apart from the difficulties of learning to fly, you will have to content with a model that potentially isnt rigged correctly, is unbalanced or has slight warps and twists in it, each of which will make it harder to fly.....

Personally I would advise starting off with a plane thats designed as a trainer not a scale fighter

John Cooper 107/07/2015 15:59:22
22 forum posts

David you are quite correct-- I have never flown RC only control line over 50 years ago. I will never fly now due to eyes but I have others to do that for me-- I build-- they crash!

I should also mention I live in rural Spain.

I have built from plans the last was Dawn Flier but the Eindecker has been requested with a Neiuport to fight with.

The problem with the Eindecker is it is an old plan & uses old electrics hence my question.

I have used your links & think I will go for a 250-300w at under 1000kv props will be a guess but the wattmeter should stop a conflagration!

Thank you all for your help. I am off to the strip now-- a newly surfaced stretch of Camino!

PS the thermometer is reading nearly 44!

Steve Hargreaves - Moderator07/07/2015 19:58:19
6762 forum posts
197 photos

Aaarrgghhh.....250watts in a 40" span 1 lb Eindekker will be a bit too much.....I think you'd probably tear the wings off......I'd aim for about half that..150 watts max....1000kv is about right...8-9" fine pitch prop on 3S should be good...

Remember what we measure is INPUT power.....brushed motors are notoriously inefficient....even as low as 50% so for every 100watts in you'd get 50-60 out. Brushless motors are much more efficient...up to 85% so more of the input watts are converted into usable effort in turning the prop....

I have a Mini Tyro which weighs about 1lb...32" span or so & I fly that on about 60-75 watts fact I spent a very pleasant summer evening once just stooging it around & got 30 mins out of a 1000mAh pack....running the numbers later on I worked out it had flown around for that 30 mins on just under 20 watts. A smaller/lighter motor & battery will allow for a much lighter build which will be reflected in the flight performance.....add lightness & simplify as a wise man once said...wink 2

Steve Hargreaves - Moderator07/07/2015 20:01:45
6762 forum posts
197 photos

Tim Hoopers Pix E Major is a similar size & weight to your Eindekker.....I bet his set up would work well....thumbs up

Tim Hooper07/07/2015 21:41:33
2899 forum posts
2406 photos
Posted by Steve Hargreaves - Moderator on 07/07/2015 20:01:45:

Tim Hoopers Pix E Major is a similar size & weight to your Eindekker.....I bet his set up would work well....thumbs up

I was just thinking the same thing.....


Wingman07/07/2015 21:52:46
1147 forum posts
405 photos

Yep - at 250 watts a one pound model will try to rotate round the prop and turn on its back as soon as the wheels leave the ground - I have learned this lessoncrying

PatMc08/07/2015 01:11:27
4405 forum posts
527 photos

The Eindecker plan is dated 1999 so would probably have used a 7 or 8 cell 600mAH nicad battery weighing about 160g & the motor+GB would have been about 90g . Compare this with about 90g for a 3s 1000 lipo & about 50g for a suitable outrunner & there's a potential saving of around 110g not to mention lighter modern servos & Rx.
I'd estimate an achievable AUW for the same model today at under a 1lb. That means the power would be increased the weight reduced by about 20% & the available energy doubled.

IMO the 100W/lb rule is over well the top for this model, 40 or a max of 60W/lb is more realistic.
I've got a video on Youtube taken from my vintage APS Frankenstien taking of from grass, flying around & performing a couple of loops & a roll - at the time it had a geared 480 brushed motor on 8 cell nimhs power to weight ratio was 28W/lb.

Edited By PatMc on 08/07/2015 01:12:31

Max Z08/07/2015 10:58:43
554 forum posts
248 photos

Remember that it is all about prop and rpm! You can fit a 1 kiloWatt motor up front, but if it produces 1000kV it will only use 150 Watts or so on a 3s lipo when you fit a 8x5 prop, and it will not "tear your wings off"(don't hang me on the number please).

Of course there is weight to consider, but you may need some anyway on a plane that was designed for a geared SP400.




Edited By Max Z on 08/07/2015 11:01:41

John Cooper 110/07/2015 20:27:12
22 forum posts

OK Guys problem solved--Dawn Flyer has been crashed! So as long as everything is re usable I will use the Axi motor etc for the Eindecker. & will let you know how we get on.

John Cooper 110/07/2015 20:27:13
22 forum posts

OK Guys problem solved--Dawn Flyer has been crashed! So as long as everything is re usable I will use the Axi motor etc for the Eindecker. & will let you know how we get on.

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