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'[EE] Connector for high current'
2008\06\16@193555 by Zik Saleeba

face picon face
I'm designing a small VTOL UAV which runs on brushless DC motors. The
maximum current draw at the LiPo battery is 210A (at 22.2V). Normally R/C
applications like this use Deans Ultra plugs but they're not rated for this
kind of current (info is scarces but some sites claim they're rated at 60A).

http://www.wsdeans.com/products/plugs/ultra_plug.html

I was wondering if anyone had a suggestion of a good polarised 200+ amp
power connector which is light in weight and reasonably easily attached and
detached. Any ideas?

Thanks,
Zik

2008\06\16@195044 by Richard Prosser

picon face
Zik,

There's an Anderson power pole connector rated at 350A. I wouldn't say
it's easy to connect/disconnect but probably reasonable considering -
especially if one side is fixed to something moderately immovable.

<http://www.andersonpower.com/products/multipole-sb.html>

RP


2008/6/17 Zik Saleeba <spam_OUTzikTakeThisOuTspamzikzak.net>:
{Quote hidden}

> -

2008\06\16@195822 by Marcel Duchamp

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I don't have the connector info you asked for but am curious about your
design.  Are there any websites with info on this particular plane? My
calcs show that to be 4.66 kw. Wow. I'm impressed!  I'd like to see it.
 Will you use a pic to control any parts of it?

Zik Saleeba wrote:
{Quote hidden}

2008\06\16@201958 by Zik Saleeba

face picon face
Thanks Richard. That looks like a nice connector but maybe a little large
and heavy for my application. The plane will have a total weight of about
4.5kg. The total weight budget for the airframe and payload is less than 2kg
on a 2m wingspan plane. That means every gram counts (or oz if you're
American). The total assembly there is 18cm long which is about 17cm longer
than the Deans plugs. That's going to be a size and weight issue for me.
Thanks for the pointer though.

Cheers,
Zik

On Tue, Jun 17, 2008 at 9:50 AM, Richard Prosser <.....rhprosserKILLspamspam@spam@gmail.com>
wrote:

{Quote hidden}

2008\06\16@203100 by Zik Saleeba

face picon face
On Tue, Jun 17, 2008 at 9:57 AM, Marcel Duchamp <
.....marcel.duchampKILLspamspam.....sbcglobal.net> wrote:

> I don't have the connector info you asked for but am curious about your
> design.  Are there any websites with info on this particular plane? My
> calcs show that to be 4.66 kw. Wow. I'm impressed!  I'd like to see it.
>  Will you use a pic to control any parts of it?


I'm designing it as a demonstrator of my UAV autopilot. The autopilot is
based on an AT91SAM7 processor, but it does have an auxiliary PIC16F687 to
help with some of the I/O. The autopilot is pretty close to completion.

The plane itself is an unusual design with a swept-forward wing and three
ducted fans providing approximately 6kg of thrust. At the moment it's just a
concept. I'm making a smaller scale R/C version to test the idea first.

Cheers,
Zik

2008\06\16@225945 by Steve Smith

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face
Try Anderson power products... The SBS50 is about 3" long as an assembled
pair and are rated at 50A continuously and during mating. The copper mating
surface is about 5x the area of a deans plug and burst mode they are good
for 250+A total weight is about 2 oz and most of that is copper. The
termination pins accept either 6mm or 16mm cable depending on which one you
go for... I know they are bigger than deans but they are well up to the job
. The power pole 30A (PP30) are used for racing cars and are ok to about
100A peak they are about equivalent to the deans plugs but a bit bigger they
could be parallel connected as they stack...


Steve

{Original Message removed}

2008\06\17@071813 by olin piclist

face picon face
Zik Saleeba wrote:
> providing approximately 6kg of thrust.

Not likely since Kg is not a measure of force.

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\17@082809 by Apptech

face
flavicon
face
> Zik Saleeba wrote:
>> providing approximately 6kg of thrust.

> Not likely since Kg is not a measure of force.

PICy picky :-).
While that is strictly true, there are many exceptions to
such general usage that allow such nominally "lazy"
statements to be made in polite and even informed company.

eg the pound mass is not a valid unit but is embedded in the
psyche of the US and UK community. What Y'All think is a
pound is actually 1/g th of a slug, but slugs never caught
on. Slugs are to pounds force what Kilograms are to Newtons,
which is Olin's point.

And, properly, one should ask for sold-by-weight material by
it's force value rather than it's mass. Which the lbf is.
But I am not aware of anywhere in the world (though such
perverse places may exist) where eg dead fish is sold by the
Newton.

And even steely eyed rocket men have haggled for countless
thousands of hours over many many decades over the
proprietary of mixing force and mass units in certain
classical instances. eg the unit of merit of a rocket motor
and propellant combination is Isp = "specific impulse".
Some, indeed many, declare the units thereof to be "seconds"
as it is eg the number of seconds that a pound mass of
propellant will produce a pound force of thrust, OR,
pertinent here, the amount of time for which a kgm or
propellant will produce a kgf of thrust. Cancel the units of
eg kgm/kgf and you get seconds. Many argue volubly, as
would, perhaps, Olin,  about the impropriety of such a
cancellation of mixed units. But seconds is "easier" than
saying lbm/lbf or kgm/kgf.

So, mass units as force units is a time honoured aberration
in the thrust using community and, interestingly, more
understood by the general public than the use of the
"correct" units. If Zik had said that his UAV would produce
about 60 Newton of thrust fewer would have understood the
order of force involved. Or, that to be VTOL capable that it
would probably need to "weigh" less than 6 kilogram (even
though kilogram is NOT a valid weight unit :-) * ).

* "It masses about xxx kg" is one way around this.
I haven't met anything being said to eg "mass under 0.4
slug", as Zik's UAV will.

       Russell




2008\06\17@085638 by Wouter van Ooijen

face picon face
Apptech wrote:
>> Zik Saleeba wrote:
>>> providing approximately 6kg of thrust.
>
>> Not likely since Kg is not a measure of force.
>
> PICy picky :-).
> While that is strictly true, there are many exceptions to
> such general usage that allow such nominally "lazy"
> statements to be made in polite and even informed company.

Made yes, and hanging someone for making such statements would be out of
bounds, but criticism is certainly justified. IM(H?)O criticizing such
criticism is [self-censorship kicks in].

> And, properly, one should ask for sold-by-weight material by
> it's force value rather than it's mass.

no, definitely by its mass. weighting instruments used are calibrated to
read the mass *at the place they were calibrated*, so nothing wrong with
asking for mass. It even prepares for interstellar trade.

Glimpse from my 6-y old son trying to understand our sometimes confusing
world: kilo is a synonym for 1000, as in km. but it is also a synonym
for 1000g. He is (rightly?) blaming the world for being illogical. He is
in for an interesting life.

--

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu

2008\06\17@092412 by olin piclist

face picon face
Apptech wrote:
>> Not likely since Kg is not a measure of force.
>
> PICy picky :-).

Not that picky.  Sloppiness and inattention to detail are the source of many
problems in firmware and electronics.  If he'd said "Kg force" as a short
form of "the weight of 1 Kg at nominal earth gravity", that would have been
fine.  There is enough confusion about physical measures and units that
errors should be stomped on quickly and hard when they pop up.  Ask Nasa
about that satellite...

> eg the pound mass is not a valid unit but is embedded in the
> psyche of the US and UK community.

As long as you say "pound mass", it's clear enough what you mean and it
shows you're not confused about the physics.  "Pound mass" as short for "the
mass of something that weighs 1 pound at nominal earth gravity" is
acceptable.  But saying "pound" when referring to mass is wrong.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\17@093047 by Tomás Ó hÉilidhe

picon face

> Glimpse from my 6-y old son trying to understand our sometimes confusing
> world: kilo is a synonym for 1000, as in km. but it is also a synonym
> for 1000g. He is (rightly?) blaming the world for being illogical. He is
> in for an interesting life.

To be honest I don't see this as any different from saying:

   Give money to the poor

instead of:

   Give money to the poor people

Adjectives being used as nouns, stuff getting shortened, redundant stuff
removed. Plus it helps for newspaper headings:

KILO OF HEROIN SEIZED

:-P

2008\06\17@093438 by Jake Anderson

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face
Wouter van Ooijen wrote:
> Apptech wrote:
>  
>>> Zik Saleeba wrote:
>>>      
>>>> providing approximately 6kg of thrust.
>>>>        
>>> Not likely since Kg is not a measure of force.
>>>      
>> PICy picky :-).
>> While that is strictly true, there are many exceptions to
>> such general usage that allow such nominally "lazy"
>> statements to be made in polite and even informed company.
>>    
>
> Made yes, and hanging someone for making such statements would be out of
> bounds, but criticism is certainly justified. IM(H?)O criticizing such
> criticism is [self-censorship kicks in].
>  
I dunno, in terms of giving a ball park figure that's understandable Kg
force seems pretty good to me.
First thing I do when judging the "force" of something in that size
region is mentally divide by 10 to get kilograms and compare that to
cartons of milk. (which works out to a buttload of thrust for a model
sized contraption, its gonna be zippy)

If the OP was making a post about the physics of something then I'd
expect to see it in newtons.

> Glimpse from my 6-y old son trying to understand our sometimes confusing
> world: kilo is a synonym for 1000, as in km. but it is also a synonym
> for 1000g. He is (rightly?) blaming the world for being illogical. He is
> in for an interesting life.
>
>  
The Kilo Gram is an odd unit of measurement, it is actually 1000 grams,
but it "works" better than measuring everything in grams.


2008\06\17@101321 by Apptech

face
flavicon
face
>>> Not likely since Kg is not a measure of force.

>> PICy picky :-).
>> While that is strictly true, there are many exceptions to
>> such general usage that allow such nominally "lazy"
>> statements to be made in polite and even informed
>> company.

> Made yes, and hanging someone for making such statements
> would be out of
> bounds, but criticism is certainly justified. IM(H?)O
> criticizing such
> criticism is [self-censorship kicks in].

You are being, for you, unusually inconsistent :-). I KNOW
you know what you are talking about and I understand your
point. But it is in practice violated in everyday use in
much of the world to the extent that people are unaware of
the "correct" usage at almost all levels. Weighing units
whose mechanism works by measuring force MAY be calibrated
in mass units on their scale (although a vast number are not
*) but they MEASURE force, as you know. One could argue that
a mass/mass balance is a mass measurer as the two masses
generate forces which are related by the (almost) common
gravity field that they reside in, as I know you know. A
rare example of a true mass measurer is the Space Shuttle's
astronaut weigher which uses AFAIR period of oscillation of
an arm to determine mass. * Pounds are not, as I know you
know, units of mass. Even pounds-mass are not a real unit
(he said dangerously). The real unit is, as I said and as I
know you know, the slug which is the mass which "weighs" g
pounds or about 32 pounds. I have yet to see a mass
measuring device, or a force measuring device, calibrated in
slugs, but there are countless many calibrated in the force
unit pounds, which is the force exerted in a one g field by
the non existent 1 pound mass. ie in the imperial system the
overwhelming common usage is to use force units to represent
both mass and force, and only a scientist, an engineer or a
pedant does otherwise. (I being all 3 ... ;-) ).
For the mksa / SI system the opposite everyday convention
applies and the norm is for both mass and force to be
commonly represented by mass units, leaving poor old Sir
Isaac to the realm of aforesaid scientists, engineers and
pedants. (I being all 3 ...). Which is where we came in.

>> And, properly, one should ask for sold-by-weight material
>> by
>> it's force value rather than it's mass.

> no, definitely by its mass. weighting instruments used are
> calibrated to
> read the mass *at the place they were calibrated*, so
> nothing wrong with
> asking for mass. It even prepares for interstellar trade.

As above.
Slugs just don't cut it.

And re my discourse on Isp. That argument really has gone on
for decades and is unlikely to ever be resolved. In that
case it's almost only the pedants who get it "correct". Some
give up, multiply Isp by g and call it exhaust velocity.
Which it sort of is, but it is far less evocative.

> Glimpse from my 6-y old son trying to understand our
> sometimes confusing
> world: kilo is a synonym for 1000, as in km. but it is
> also a synonym
> for 1000g. He is (rightly?) blaming the world for being
> illogical. He is
> in for an interesting life.

Indeed :-)


       Russell

2008\06\17@104957 by Martin

face
flavicon
face
Zik Saleeba wrote:
> I'm designing a small VTOL UAV which runs on brushless DC motors. The
> maximum current draw at the LiPo battery is 210A (at 22.2V). Normally R/C
> applications like this use Deans Ultra plugs but they're not rated for this
> kind of current (info is scarces but some sites claim they're rated at 60A).
>
> www.wsdeans.com/products/plugs/ultra_plug.html
>
> I was wondering if anyone had a suggestion of a good polarised 200+ amp
> power connector which is light in weight and reasonably easily attached and
> detached. Any ideas?
>
> Thanks,
> Zik

I doubt you'll be drawing 200 amps for very long, right? A minute or
two? You should be fine with something like a powerpole connector. There
are no light-weight easily-attached connectors that are rated for 200
amps. Electric vehicles routinely use Anderson connectors rated for a
few hundred amps, at very high peak currents.

-
Martin

2008\06\17@132818 by Gerhard Fiedler

picon face
Jake Anderson wrote:

> Wouter van Ooijen wrote:
>> Glimpse from my 6-y old son trying to understand our sometimes confusing
>> world: kilo is a synonym for 1000, as in km. but it is also a synonym
>> for 1000g.

Only a "synonym", as in "everyday language", otherwise it would be
something like "kilogram". I think he's probably old enough to start
understanding the difference between exact definitions and "normal"
language.

> The Kilo Gram is an odd unit of measurement, it is actually 1000 grams,
> but it "works" better than measuring everything in grams.

That has historical reasons, because the units meter and gram (and many
others) were there before the SI and its precursors like CGS were formed.
They picked the base units among what was already there, considering
convenience over consistency.
<http://physics.nist.gov/cuu/Units/history.html>

Gerhard

2008\06\17@185942 by Zik Saleeba

face picon face
Thanks guys - powerpoles seem to definitely be the favored choice. I'll have
to look into just how far I can reasonably push the specs to get as small
and light a version as possible into my plane.

Cheers,
Zik

On Wed, Jun 18, 2008 at 12:49 AM, Martin <EraseMEmartinspam_OUTspamTakeThisOuTnnytech.net> wrote:

{Quote hidden}

> -

2008\06\17@192104 by Zik Saleeba

face picon face
Who'd have thought that I'd wake up this morning to a nice flame war on the
piclist which apparently I started by simply referring to thrust in units of
kg. Now I know why I love this place.

Incidentally the manufacturer of the ducted fan I'm using themselves quote
the thrust in grams:

http://oos.modelengines.com.au/command/servlet/Command?command=display_item_pub&pkey=meng&itemid=HIM-DF96

Sloppy use of units is pretty common in the R/C world. I'm not going to try
to justify it. In the end it's all about the most effective form of
communication for the medium. Let's face it - even Olin knew what I meant
and he's the one who made the fuss in the first place. If I'd given the
thrust in Newtons how many people would have taken the time to think it
through? Of course if I'd been writing a formal spec rather than a casual
email I'd probably have expressed it differently.

Cheers,
Zik
PS. I bet James is glad he un-moderated Olin

2008\06\18@045348 by Apptech

face
flavicon
face
> I'm designing a small VTOL UAV which runs on brushless DC
> motors. The
> maximum current draw at the LiPo battery is 210A (at
> 22.2V). Normally R/C
> applications like this use Deans Ultra plugs but they're
> not rated for this
> kind of current (info is scarces but some sites claim
> they're rated at 60A).
>
> http://www.wsdeans.com/products/plugs/ultra_plug.html


Coanda effect UAV.
I could imagine building something like that. Not that I'd
ever get to it, but a REAL flying saucer ...


       http://jlnlabs.online.fr/gfsuav/index.htm



           R


2008\06\18@060741 by Zik Saleeba

face picon face
Very interesting project! Thanks for that.

Cheers,
Zik

On Wed, Jun 18, 2008 at 6:49 PM, Apptech <apptechspamspam_OUTparadise.net.nz> wrote:

{Quote hidden}

> -

2008\06\18@064602 by Jake Anderson

flavicon
face
Zik Saleeba wrote:
> I'm designing a small VTOL UAV which runs on brushless DC motors. The
> maximum current draw at the LiPo battery is 210A (at 22.2V). Normally R/C
> applications like this use Deans Ultra plugs but they're not rated for this
> kind of current (info is scarces but some sites claim they're rated at 60A).
>
> http://www.wsdeans.com/products/plugs/ultra_plug.html
>
> I was wondering if anyone had a suggestion of a good polarised 200+ amp
> power connector which is light in weight and reasonably easily attached and
> detached. Any ideas?
>
> Thanks,
> Zik
>  
The small Anderson power poles are good for a bunch of amps. I think
people use the 25A ones at > 100A or so in robot wars.
We always use ring terminals in our bots, they seem much more secure.

2008\06\19@130402 by Clint Sharp

picon face
In message
<@spam@d02e69350806161650i66d491ddk1df6a3af338f62faKILLspamspammail.gmail.com>, Richard
Prosser <KILLspamrhprosserKILLspamspamgmail.com> writes
>Zik,
>
>There's an Anderson power pole connector rated at 350A. I wouldn't say
>it's easy to connect/disconnect but probably reasonable considering -
>especially if one side is fixed to something moderately immovable.
>
><http://www.andersonpower.com/products/multipole-sb.html>
>
>RP
>
Seconded on that, commonly used on APC UPS's. Very handy connectors and
relatively easy to remove give the contact pressure they need to carry
the current. Not cheap though if you buy the tooling to suit.

--
Clint Sharp


'[EE] Connector for high current'
2008\07\07@082230 by Zik Saleeba
face picon face
A couple of weeks ago I asked about ultra light weight power connectors
capable of carrying 200A. I had plenty of great suggestions. I thought you
might be interested in the outcome. I ended up using some 6mm gold bullet
connectors which worked out lighter and smaller for the same current
carrying capacity than the equivalent PowerPoles.

These connectors aren't polarised so I set them up in a way to prevent
reverse polarisation and short circuiting.

[image: http://www.zikzak.net/~zik/vtol/power.jpg]

http://www.zikzak.net/~zik/vtol/power.jpg

Thanks to everyone who helped with suggestions.

Cheers,
Zik

On Tue, Jun 17, 2008 at 9:35 AM, Zik Saleeba <RemoveMEzikTakeThisOuTspamzikzak.net> wrote:

{Quote hidden}

2008\07\07@093353 by olin piclist

face picon face
Zik Saleeba wrote:
> A couple of weeks ago I asked about ultra light weight power
> connectors capable of carrying 200A. ...
>
> http://www.zikzak.net/~zik/vtol/power.jpg

What's the point of a 200A connector if what it is connected can't handle
200A.  That wire doesn't look like it's capable of anywhere near 200A.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\07\07@125306 by Bob Ammerman

picon face
Olin opined:
> What's the point of a 200A connector if what it is connected can't handle
> 200A.  That wire doesn't look like it's capable of anywhere near 200A.


IIRC this involves a low-duty cycle requirement. Even AWG 30 wire can handle
200A, for a short while :-)

-- Bob Ammerman
RAm Systems

2008\07\07@132117 by M. Adam Davis

face picon face
I don't see anything in that picture that gives away the size of the
wire.  The side cutters could actually be a large pair, and the other
connector might be available in several sizes.  Also the wire
insulation might be very thin.

Still, I agree that it doesn't _look_ like 1 AWG wire - if it was then
the side cutters are indeed huge...

Looking a bit more closely, looks like the black heat shrink tube is
labeled 0.40 - ostensibly 0.40" (could be something else, but this a a
common size).  This means the wire with the insulation is likely to be
around 0.25" assuming 50% shrinkage.  With very thin insulation this
indicates 2 to 4 gauge wire.

The current carrying capacity of a wire (apart from regulations such
as NEC) is dependant on the heat rise above ambient that the wire and
insulation can stand without breakdown.  Given high end insulation,
200A from 2 AWG wire is perfectly acceptable.  Further, I doubt the
duty cycle is 100%, and chances are this is meant for proof of concept
and will only be used for very short durations over several tests,
rather than continuous use for months/years.

Depending on the length of the wire, and the environment in the
airframe, this could be extended (especially with active cooling).

So... yes, it's ambiguous, but it would be interesting (and
instructive!) to know what gauge wire is being used, the insulation
surrounding it, and how it was determined that this should be safe
given then operating parameters.

-Adam

On 7/7/08, Olin Lathrop <spamBeGoneolin_piclistspamBeGonespamembedinc.com> wrote:
{Quote hidden}

> -

2008\07\07@141445 by Sean Breheny

face picon face
Hi Zik,

I know I am coming in late but I can't resist.

Looks like a very cool design. However, there are a few things I don't
understand:

1) 4.6kW seems like a LOT of power to produce 6kg of thrust. In grad
school, I built a four-rotor helicopter which weighed 6kg and needed
only 1.6kW to hover. We used four 18 inch diameter unshrouded props. I
suppose that your considerably smaller diameter fans (look to be about
6 inch) are probably the reason for the higher power usage but it
seems like a huge discrepancy.

2) Can your battery pack really supply 210A? How long do you expect to
pull 210A for?

3) We used some of the original LiPos (around 2002-2003) in a 7 cell
series by 2 cell parallel configuration, drawing about 10 to 15 amps.
There was one of these packs per motor. Even this was pushing the
packs to the point where they would get very warm. I know that newer
LiPos can handle higher currents but 210A seems huge!

Sean



On Mon, Jun 16, 2008 at 7:35 PM, Zik Saleeba <TakeThisOuTzikEraseMEspamspam_OUTzikzak.net> wrote:
{Quote hidden}

> -

2008\07\07@170050 by Tomás Ó hÉilidhe

picon face


Sean Breheny wrote:
> 1) 4.6kW seems like a LOT of power to produce 6kg of thrust.

We talking 58.86 newtons of thrust?   ;-P

2008\07\08@014857 by Zik Saleeba

face picon face
On Tue, Jul 8, 2008 at 7:00 AM, Tomás Ó hÉilidhe <RemoveMEtoespamTakeThisOuTlavabit.com> wrote:

>
>
> Sean Breheny wrote:
> > 1) 4.6kW seems like a LOT of power to produce 6kg of thrust.
>
> We talking 58.86 newtons of thrust?   ;-P


Oh please don't start that again :)

Cheers,
Zik

2008\07\08@020040 by Zik Saleeba

face picon face
Radio control applications routinely push specs beyond their usual limits to
achieve acceptable flying weight. (Ok, mass if you prefer... Gimme a break -
I'm a hobbyist!)

The wires you see on the lower left are the flying leads coming from the
large Lithium Polymer battery I mentioned. The battery's rated at 40C-50C
"burst" - ie. for less than 30s, and 20C continuous. I don't have the
battery with me so I can't check the wire gauge but it's thick for R/C gear,
probably thin for normal engineering practice. The "burst" 400+ amps might
heat up the wires a little but that's ok in this application. It should be
able to handle the standard 180A without too much fuss (you'd hope).

It's an interesting point though - I might do some voltage drop tests on the
leads under load to see what happens.

Cheers,
Zik

On Mon, Jul 7, 2008 at 11:35 PM, Olin Lathrop <olin_piclistEraseMEspam.....embedinc.com>
wrote:

{Quote hidden}

> -

2008\07\08@020853 by Zik Saleeba

face picon face
On Tue, Jul 8, 2008 at 4:14 AM, Sean Breheny <EraseMEshb7spamcornell.edu> wrote:

> 1) 4.6kW seems like a LOT of power to produce 6kg of thrust.


Due to the constraint of having to make the thing aerodynamic for forward
flight I'm using multiple smaller sized ducted fans for vertical mode. The
downside is that they're less efficient than a larger fan would be. They're
only used for a few seconds at takeoff and landing and then the plane
transitions to more efficient forward flight using wings for lift.

2) Can your battery pack really supply 210A? How long do you expect to
> pull 210A for?


Here's a web page with some info:
http://www.rctoys.com/rc-toys-and-parts/TP-9000-6S2PX/RC-PARTS-THUNDER-POWER-6-CELL-LITHIUM-BATTERIES.html

It's meant to handle 180A continuous or 400+A burst. In practice I'd be
using ~210A for a few seconds at takeoff and landing and flying at ~10A the
rest of the time.

Cheers,
Zik

2008\07\08@032519 by Tamas Rudnai

face picon face
Zik,

> Due to the constraint of having to make the thing aerodynamic for forward
> flight I'm using multiple smaller sized ducted fans for vertical mode. The
> downside is that they're less efficient than a larger fan would be.

What is the diameter and pitch of this fan? If that is 6" then I think it's
round 18k rpm (without doing the maths) and the prop reach the speed of
sound - which means less efficient than it at that speed plus very noisy. As
far as I remember that size of fan was driven with a 400 brussless outrunner
without a problem using around 12V@15A at max. That made around 15k prm.
Anyway, that fan looks a high pitch prop made for fast forward flying, and a
low pitch prop with a higher diameter would give you a better statical
thrust in my opinion. Have you ever considered of helicopters? They are
fairly good at hovering and efficient on forwad flying as well :-)

Tamas


On Tue, Jul 8, 2008 at 7:08 AM, Zik Saleeba <RemoveMEzikEraseMEspamEraseMEzikzak.net> wrote:

{Quote hidden}

> -

2008\07\08@034506 by Zik Saleeba

face picon face
On Tue, Jul 8, 2008 at 5:25 PM, Tamas Rudnai <RemoveMEtamas.rudnaiTakeThisOuTspamspamgmail.com> wrote:

> What is the diameter and pitch of this fan?


For this prototype it's three off-the-shelf 96mm fans running at up to
40,000 rpm. Here are the details:

http://oos.modelengines.com.au/command/servlet/Command?command=display_item_pub&pkey=meng&f_id=[INVALID%20FORM%20VAR]&itemid=HIBMB36-34-1850
http://oos.modelengines.com.au/command/servlet/Command?command=display_item_pub&pkey=meng&f_id=[INVALID%20FORM%20VAR]&itemid=HIM-DF96

They're not really ideal for this application but they're good enough for a
quick prototype. If the prototype is successful I might consider fabricating
some purpose-built ducted fans.

Have you ever considered of helicopters? They are
> fairly good at hovering and efficient on forwad flying as well :-)


Helicopters aren't nearly efficient enough in forward flight for my
application (aerial survey). I don't have much of a choice about
takeoff/landing locations hence the VTOL requirement - yet I need as much
flight duration as possible to take as many photos as possible, hence the
preference for a winged craft.

Cheers,
Zik

2008\07\08@072858 by olin piclist

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Zik Saleeba wrote:
> Radio control applications routinely push specs beyond their usual
> limits to achieve acceptable flying weight.
> (Ok, mass if you prefer... Gimme a break -
> I'm a hobbyist!)

Actually you were right the first time.  In this case the relevant measure
of what you have to lift is weight, since you're trying to work against the
earth's gravity.  If you were doing this on some other planet with the same
surface atmosphere but half the gravity, you would still need to keep below
the same weight but your craft could have twice the mass.  If you can
produce 60N thrust, your craft had better weigh less than 60N.  That would
allow its mass to be about 6Kg on earth, but 12Kg on this other planet.

If you were flying your craft on the space station, then any amount of mass
would let it fly.  The thurst to mass ratio only dictates how fast it can
accellerate on its own.

And no, physics doesn't take a break for hobbyist.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\07\08@084724 by Tamas Rudnai

face picon face
> For this prototype it's three off-the-shelf 96mm fans running at up to
> 40,000 rpm. Here are the details:

96mm is around 3 3/4 inch so that makes sense, the velocity of the outer
circle of the propeller would not reach sound speed with 40k rpm.

> I don't have much of a choice about
> takeoff/landing locations hence the VTOL requirement - yet I need as much
> flight duration as possible to take as many photos as possible, hence the
> preference for a winged craft.

You can use a blimp: VTOL, very long time in the air :-) Just kidding.

There was an UAV model airplane flying over the ocean, not long time ago.
The flight time was incredible, and they was taking off and landing using a
remote, otherwise it was UAV. They used a relatively slow air speed to
maintain laminar airflow over the plane to keep the drag as low as possible.
They said the drag was less than for the Spitfire.

http://www.progressiveengineer.com/profiles/maynardHill.htm

Tamas



On Tue, Jul 8, 2008 at 8:44 AM, Zik Saleeba <EraseMEzikspamspamspamBeGonezikzak.net> wrote:

{Quote hidden}

> -

2008\07\08@091250 by Alan B. Pearce

face picon face
>You can use a blimp: VTOL, very long time in the air :-) Just kidding.

One of my colleagues was involved in flying balloon platforms from North
Africa to USA to study near space atmospherics and radiation. Used to take
several days for a flight.

Incidentally his speciality is closed loop servo control, and he had the
responsibility for keeping the balloon platform stable so that star
sightings could be maintained for latitude/longitude sensing to be included
in the telemetry (this was well before the GPS functions became available).
He had the development platform swinging from a crane in a warehouse type
area that he used as a lab. Working late one night, the security guard came
around on his inspection, and got all upset about him being there. I forget
the exact cause of the guards displeasure, but it didn't include the 2 ton
weight object that could have potentially damaged my colleague in a far more
serious way.

2008\07\08@111941 by Rolf

face picon face
Actually, both matter.... but mass more than weight...

mass is more important because flying straight is not much fun, and the
forces required to alter the direction of flight are related to mass,
not weight (whether in space or not).

As it happens, sometimes you do want to fly straight (and on earth), at
which point weight is important, because that is the force (well, it is
a measure of the force) that you need to overcome to accomplish straight
and *level* flight.

Since weight is related to both gravity and mass, it happens that mass
is important in every situation while flying (in 'stable' flight as well
as 'aerobatics').

Essentially, with model planes it is all about changing directions, and,
the less mass, the less force is required, which means all sorts of
things for modellers....

Rolf



Olin Lathrop wrote:
{Quote hidden}

2008\07\09@111623 by John Ferrell

face picon face
The world of RC electric flight presents an extreme set of conditions. We
push the equipment to the breaking point very often. It is the norm to use a
30 amp (or higher) speed controller on an airplane with a 2100MAH LiPo pack.
We experience about 100 flights of 8 minutes or so before the batteries are
trashed. A 3 cell 2100 mah Lipo pack costs from $50 to $90 in the US at this
time with most users agreeing the more expensive batteries are "better".

Often the criteria becomes "how hot is it going to get" and "how many times
can I do it before I need to replace it".
So far the airplanes I fly are only using the 3 cell 2100 mah packs as I
gain experience. I measure the pack temperature on landing and try not to
exceed 115 degrees F measured with an IR device. A LiPo battery pushed too
hard in charging or discharging burns like a road flare!

Electronic Speed controls for brushless motors are expensive, fragile and
very scarce as a DIY project. The folks at Castle Creations seem to have the
best and most expensive IMHO.

LiPo batteries still win out in competition but the A123 technology looks
like it will soon dominate the less demanding market due to cost and safety
issues.

BTW, many bigger models use 36 volts at 80 amps .

There may be a business opportunity in the industry!

John Ferrell    W8CCW

"All that is necessary for the triumph of evil is for good men to do
nothing." -- Edmund Burke
http://DixieNC.US

{Original Message removed}

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