PopularRC

I know this has all been covered (somewhere in vastness of the internet) but I wrote a super simple application to write my Date and Time TAG.txt file for me. I thought I would share it for those that are interested.

I have had the Spy Gum camera since the early days and still use it. However a good friend of mine game me a brand new Keychain camera (green tinge to the lens) and I am thrilled — so much easier to place on the planes. Anyway, after dinking around with different Date Time files (none worked including the one in the instructions that came with it). I found one that worked:

TAG.txt

[date]
2010/05/26
23:07:10

You can download the app here: http://popularrc.com/KeyChainDateTime.zip

Source:

Imports System.Text
Imports System.IO

Public Class KCCDateTime

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim text As StringBuilder
Dim dt As DateTime
Try
dt = DateTime.Now
text = New StringBuilder()
With text
.AppendLine("[date]")
.AppendLine(dt.ToString("yyyy/MM/dd"))
.AppendLine(dt.AddMinutes(1D).ToString("HH:mm:ss"))
End With

If File.Exists("TAG.txt") Then
File.Delete("TAG.txt")
End If

File.WriteAllText("TAG.txt", text.ToString().Trim())
MessageBox.Show("Created TAG.txt File" + Environment.NewLine + Environment.NewLine + text.ToString())

Catch ex As Exception
MessageBox.Show("Error: " + ex.ToString())
End Try
Me.Close()
End Sub
End Class

Safety Considerations When Flying RC Aircraft at Nichols Park

1. Flying should always occur west of the concrete divider at the top of the hill.

2.  Spectators and stashed gear at the top of the hill should always be on the east side of that concrete divider.

3. All take-offs , Landings , Low Passes and Walk Ons should be announced loudly by the pilot to alert other pilots and spectators.

4. When landing from the west, plan on stopping several feet in front of the concrete divider.

5. High velocity low passes should be at least 15 feet from the concrete divider.

6. The maximum number of planes in the air ,  being flown from the top of the hill , should be 4.

7. Before maiden flights and after rebuilding or modifying an aircraft:

…..a.  Have a fellow pilot double check the setup and structural integrity of your plane.

…..b.  Take off from the bottom of the basin.

8. Fly within the boundaries of Nichols Park.

9. Do not fly over people, houses, automobiles or streets.

I noticed a series of links to video clips today showing up on my Twitter feed from the AMA — Burt Rutan at the 2010 AMA Expo — Cool!   I was riveted by his home video and photos of his research and development.  As well as some of his RC building and testing.

Read more…

A few days ago HobbyKing indicated they are experimenting with a Soft Magnetic Composite (SMC) alloy as a brushless motor stator material.

The following is a twitter feed from the HobbyKing blog.

“17/02/2010 11:30:41 AM
SMC Somaloy material for stator builds. No other R/C motor producer has ever used such an advanced and efficient material for producing stators. We’re currently prototyping the new material for solid stator production which greatly increases motor efficiency. The stators are extruded from molten Somaloy material to create a material with iron losses far lower than a standard Stator motor and with less wire for the same Kv and voltage. Our initial tests have shown amp draw to be far lower than is needed with a standard stator motor. We wont have the exact numbers until March when we dyno test motors side by side, but from looking at propeller size differences we are calculating around a 20% increase on an already very efficient motor. THIS COULD POSSIBLY BE THE MOST EFFICIENT R/C MOTOR EVER BUILT.”

………………………………….

Here’s a link to an article from Hoganas, the producer of Somaloy materials which offers some insight into using these materials as motor components.

http://www.hoganas.com/en/News-Center/Published-Articles/Advances-in-Soft-Magnetic-Composites—Materials-and-Applications/

The results of HobbyKing’s comparison should be interesting and potentially marks a significant step in brushless  motor development.

The following two quotes are from the FMA LIPO Handbook, Volume two, page 8.

…the determinant of (LIPO) cell life and performance is the temperature the battery cells reach during discharge.

A (LIPO) cell run continuously at the maximum C rating will lose capacity to 80% in as little as 25 charge cycles. The same cell with maximum current bursts less than 10 seconds and average current of half the maximum allowable discharge rate can last 500 cycles.

…………………………………………………..
Battery life  (number of cycles until capacity degrades to 80% of  rated capacity)  is important to electric aircraft pilots:

A $35 battery that only lasts 25 cycles results in a cost of $1.40 for each flight, while the same battery at reduced temperature during flight could result in a cost of only seven cents per flight.

Every battery will have a ‘final flight’. It’s better to have fewer of these.

Although it’s important to provide maximum battery cooling during flight, it’s more important to reduce the heat being generated during flight.

Factors contributing to temperature increase during discharge are many, but include:
Ambient temperature
Air flow rate over the battery.
Battery shape.
Power being delivered by the battery.
Physical and chemical design of the battery.

Some of these factors relate to removing heat from the cell, others relate to the generation of the heat energy within each cell.

Let’s use a simplified circuit model and describe each cell as consisting of a ‘perfect LIPO battery’ in series with a lumped resistance represented by a single resistor we will call ‘Internal Resistance’. (At the low discharge frequencies involved let’s consider reactive components to produce lower order effects.)

So every electron delivered by the ‘perfect battery’ must flow thru the series ‘Internal Resistance’ resistor and as this current flows, energy is dissipated in the form of heat. If we know the value of the internal resistance we can make an estimate of how much power is ‘lost’ in the form of heat during the discharge of each battery cell.    It turns out that the value of  ’Internal Resistance’ is easily determined.    Application of ohms law under two discharge conditions is all that’s required.

There are a couple of ways to measure d.c. internal resistance: (both are applications of ohms law)

1. Measure the voltage of a battery with no load, then connect a resistor of known value and measure the current flow thru the load resistor.

InternalResistance = (noloadbatteryvoltage / currentinampswithresistorattached) minus the value of the load resistor in ohms.

Here’s a video of measuring Internal Resistance using this method.

I.R. Measurement

2. Measure the battery voltage and battery current under two different load conditions.
InternalResistance = (Voltage1 minus Voltage2) / (currentinamps1 minus currentinamps2)

Even simpler, a couple of readily available commercial battery chargers measure and display Internal Resistance.

If we use a 3 cell LIPO battery with an internal resistance of 8 milliohms per cell, the overall internal resistance is 24 milli ohms (.024 ohms). Let’s say the current supplied by the perfect battery is 40 amps. Power lost to generating heat is I^2*R and equals 38.4 watts. That’s a lot of heat generated inside the battery. (Some soldering irons use only 15-20 watts of power). That 38.4 watts will never get to your motor.

That ‘perfect LIPO battery’ inside each cell maintains the same output voltage over the life of the battery, but we know that Internal Resistance increases during the battery’s lifetime. As the battery grows older, more and more power is lost inside the battery due to the increasing value of the internal resistor until only 80% of the capacity of the battery can be delivered to it’s terminals, the rest is lost as heat. Monitoring cell internal resistance levels over the life of a battery can be a useful tool as an indicator of electrical age, which may also differ from cell to cell.

We also know that as batteries are made smaller and lighter, the internal resistance tends to go up due to fewer and smaller parallel circuit paths.

When we buy a battery we look at size, weight, number of cells, capacity and something called C rating. C rating is the manufacturer’s estimate of maximum amperage before the battery reaches some temperature that results in loss of lifetime recharge cycles at some unknown rate. That’s close to meaningless and in almost all cases it is not verifiable. We are expected to accept the word of the battery sellers  and in most cases it’s not clear what they are claiming. Even if all the C parameters were defined, you would come close to destroying the battery trying to verify the sellers claims.

Internal Resistance measurement is not destructive and the resulting value relates directly and easily to the power lost as heat within each battery cell. Being an easily verifiable battery parameter the use of Internal Resistance as a quality and aging indicator could put in perspective the many exorbitant and close to meaningless “C” ratings advertised today.

Internal Resistance is easily measured and easily used to determine heat in watts generated within the battery during discharge at any current level.

Internal Resistance can be reduced by making the battery heavier and larger, but small size and light weight are two attributes that are highly valued in any battery used to power a model aircraft.   Internal resistance can also be reduced during the chemical and physical design phase of LIPO battery development and if the manufacturing process consistantly reproduces the design, a battery that loses less power to that always present Internal Resistor can be produced.

When buying a LIPO battery , some Quality Factors to consider that don’t make a lot of sense include:

1. Manufacturer’s/Packager’s poorly defined C rating claims.
2. Claims of lifetime in terms of number of cycles, without extraordinary data to support them.
3. Price
4. Generally, any recommendation that’s not verifiable.

Consider  instead:   size, weight, capacity,  verifiable data,   internal resistance  and expected cost per flight.

“…the determinant of (LIPO) cell life and performance is the temperature the battery cells reach during discharge.”

I have had the good fortune of attending all 6 of the annual Arizona Electric Festivals held at the Arizona Model Aviators AMA field in Mesa.  It is something we all look forward too each year.  I have had the pleasure to see some of the same faces coming back year after year from all over.

The festival has evolved a little over the years.  It is as large as ever, but we seem to see less and less of the kit plane vendors and designers each year.  In years past we would always see Pat Tritle, Charlie Mansano, Mountain Models, and a few model kit inovators — none of which were with us this year at the AEF.  We still have JTechLaser who had an awesome display of their laser works and products.  It was awesome to see Steven’s Aero there with several new kits including some control line planes that would be interesting as RC planes.

Though there was tons of good looking planes, awesome pilots, and  smoking deals by many of the vendors, there was nothing that jumped out at me this year as something I had to have or drew great interest for me.

I compiled a video of some of my photos and video clips.   I loved the noon-time demo — the Yellow SU29 and the Red Yak 54 (flown by Ryan Archer) were highlights for sure.   The green jet near the end was clocked at 162 mph the day before by radar in their speed run compilation.   Overall, it was awesome and would not trade it for the world.   I am already looking forward to the next.

2010 Arizona Electric Festival – HUGE RC Event from Qrome on Vimeo.

Hyperion Yak 55 SP with a Scorpion 3020-14 flown by Michael Tribe.  Great flying Michael!