Replies to This Discussion

Permalink Reply by marshall scholz on August 14, 2010 at 7:53am

your whole ardupilot setup probably pulls under 500 ma, the 2 standard size servos are probably whats killing your current pulling around 2 amps when moving each, i suggest you get a 4A ubec like
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=...
this one and power your ardupilot off of battery power, you can find how in the ardupilot manual.
http://code.google.com/p/ardupilot/wiki/ArduPilot

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Permalink Reply by Iceberg73 on August 16, 2010 at 7:48am

I Have Ardupilot, ardushield, arduimu and a generic nmea gps working together. All the hardware drains about 200 mA. without servos. Hope it helps.

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Permalink Reply by Jim on August 16, 2010 at 8:35am

I guess an Xbee would add quite a lot to this, I think they are about 100ma for the Pro 2.4g. I'll check the Datasheet for that.

Thanks for the input guys.

Jim

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Permalink Reply by Rich on August 19, 2010 at 11:44am

Forgive me, I'm a complete newb to this, but I've been looking around and this is the closest relevant topic that I've found.....amperage is nice info to have, but so is voltage :P

Looking at the ardupilot google code page, I noticed that the recommended battery clocks in at 11.1 volts. So how forgiving is the system? Will 12 volts fry this thing? Do all systems, including the engine and servos run on 11.1 volts as a common standard?

Looking at the mA measurements that you guys have given, it doesn't seem very unlikely that solar cells could be used to provide an adequate amount of power for all systems here:

http://scientificsonline.com/product.asp?pn=3026810&cm_mmc=Merc...

If there was some kind of a table that included parts and volt/amp requirements, as well as weight measurements, I can actually build the system first and then find the plane to carry it.

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DeveloperPermalink Reply by Michael Smith on August 19, 2010 at 1:27pm

@Rich - power is expected to be regulated externally to 5V. This is normally done by the BEC in your speed controller, though many folks prefer to use a separate regulator (frequently referred to as a UBEC after one of the first commercially successful implementations).

The 11.1 number is the nominal voltage for a three-cell Lithium Polymer battery. (~12.4 fully charged, ~9 at full discharge). 3s (as it's referred to) is the dominant cell configuration for parkflyer-sized model aircraft, as it makes a good tradeoff between cost, efficiency and practicality.

Receivers and servos run on a nominal 5V (4.8-6V) as a standard, though there is a slow trend towards permitting ~9v so that two lithium cells can be used in series).

Solar is an interesting corner of the field, but as most of these airframes are carrying large flight batteries around, it usually makes more sense just to siphon a little power off the flight battery to power the autopilot.

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Permalink Reply by Rich on August 19, 2010 at 4:01pm

Yeah iceberg says he's only drawing 200mA, not including engine and servos. So if you're using a 2200 mA/hr battery such as this one:
http://hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=7635...

....then you're drawing 9.09% off of the main source. That means the other 90.91% goes to engine and servos. Not too shabby. But here's what I'm thinking:

When you regulate voltage like that, the bigger the difference between input and output voltage, the less efficient it is - meaning, you're bleeding off precious energy in the form of heat. We jolly well can't get a 5v battery and power those systems directly, because the battery wouldn't have to drain very much at all before it would be unable to power what it needs to.

However, with solar power, you're looking at a constant 5-6v (or whatever voltage you're aiming for), as long as the sun is up - so there's no need for a regulator in such a circuit. I don't even want to begin to imagine just how much of that 90.91% of the power gets lost in that regulator, but I would imagine that it's a huge enough chunk to explore ways to bypass this.


So here's what I'm thinking:

Larger wingspan = more surface area for solar panels. The Art Tech Diamond 2500, for example:

Wingspan: 98.4in
= area of 852.5 sq in
Weight: 59.26oz stock

http://scientificsonline.com/product.asp?pn=3026810&cm_mmc=Merc...

Each 6V panel = 23in sq
= room for 37 panels (in theory w/o measurements)
= .37oz
= 3700mA @ 6V


I imagine that 3700mA @ 6v would be enough to power this puppy directly for as long as the sun is up. With ardupilot installed and everything. Including lugging the whopping 6.7oz battery weight around as well.

Everything needs 5-6V, so, you simply place a relay that will automatically switch power sources when the voltage from the panels rises above 5.5V (for example) or drops below 5V. Keep in mind, we're talking about main power sources for the entire aircraft. If you're looking to power one system on battery and another on panels, then using the panels as a battery charger might be the better approach here.

Sorry if I got side-tracked from the topic - I'm just thinking out loud here.

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Permalink Reply by JOHN PIZZICARA on August 19, 2010 at 10:25pm

Hi Rich,

You must bring yourself up to speed with Switching Regulator technology. You are relating to 'back in the day' of linear regulators. Switching regulators typically have an efficiency of around 90% or slightly more for top of the line units across a wide input voltage range. Most modern UBEC's have switching circuitry. ESC's with built-in BEC are usually an inefficient linear regulator afterthought with limited current output and limit the input voltage range if used. Also, there is nothing constant about solar cell output throughout the sunrise to sunset cycle and varying cloud cover. I've seen some consumer grade solar panels (like Harbor Freight) that have low efficiency linear output regulators in them that have constant VOLTAGE output but the max CURRENT output varies widely throughout the day.

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DeveloperPermalink Reply by Michael Smith on August 19, 2010 at 10:52pm

@Rich - you will use more energy carrying the solar panels around than you will be able to extract and convert from them

I don't want to be a party-pooper, but ask yourself why nobody else is doing this. It's not because they're all stupid...

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