The Ampeer ON-LINE!
June 2006
The Club Newsletter of the Electric Flyers Only, Inc
AMA Charter 2354
Walled Lake, MI, USA
Editor: Ken Myers

Fly the Future - Fly Electric!

     The first tests are performed with the ohmmeter function of your DMM. For each step below, the ohmmeter is to be connected twice - i.e., do each test with normal and then reversed meter leads. (This means there are two resistance measurements for each step below.)

     Use the appropriate DC voltage range of your DMM to perform the following tests.

(1) Connect Source (+) to a 10 K resistor and the other resistor lead to wire 1. Connect Source (-) to wire 3. First note the actual 18V Source voltage and then measure the voltage from wire 3 to wire 1. This voltage is to be 28% +/- 3% of the Source value.

(2) Connect a 22K resistor to the Source (+). Connect the other resistor lead to wire B and Source (-) to wire A. Measure the voltage between wires A and B to be 2.75 to 2.95 volts.

(3) Move the Source (+) to wire C and Source (-) wire B. The voltage on each placement pair should be between 2.75 and 2.95 volts. Repeat for wires C and D. All three readings should be nearly equal to each other.

(4) Reverse the Source polarity in the above process by connecting the 22K resistor to wire A (then B, then C) and the battery negative lead to wire B (then C, then D). Voltage readings should fall between 1.0 and 1.15 volts and be nearly equal to each other.

(5) Repeat (only) step (3) substituting a 2.2K resistor for the 22K one. The corresponding voltmeter readings should be between 4.0 and 4.5 volts with the value between the A and B wires being about 5% higher than the voltages between the B - C and C - D combinations. This is actually a subtle check on circuit behavior so do note that approximate 5% distinction.

     Any discrepancies must be resolved before proceeding.

     It is time to do a real signal test of the LCDC. This test will use an actual transmitter and receiver (Tx / Rx) throttle signal and servo as test equipment.
     Power your Rx with an ordinary Rx battery and connect a servo to the throttle channel. Move the throttle stick over the normal full range and observe the servo direction and rotation limits. These servo indications will be your measurement standard for the following tests - note them well. (Think of the servo and its movement as being another "test meter".) Return the stick to low throttle position and turn off Rx and Tx power.
     Use the "Y" cable with mini-clips to connect the LCDC to the Rx throttle channel. Connect the servo to the LCDC output. Using a test clip lead jumper, connect the negative wire of the "Y" cable (wire 3) to wire A. This connection remains in place in all that follows. Making SURE that all this is correct, power up the Rx and Tx. The servo should move a bit further in the low direction but not be "pegged". The throttle stick will now have no influence on the servo position. Return it to low position.
     With all conditions above in place, connect Source (-) to wire A and Source (+) to wire D. The servo should move to its normal low throttle position and stick movement should result in normal servo movement. Return the stick to low position.
     BRIEFLY touch wire B to wire A. The servo should move past normal low position but not be pegged. The stick will have no effect.
     Repeat this for wire B touching wire C, and then for wire C touching wire D. Results should be the same. (NOTE - BRIEFLY touch ONLY two wires at a time.)
     If (and only if) all above is OK, proceed with this next test which will closely resemble (i.e., simulate) actual low cell detection / operation.
     Move the throttle stick full ON leaving all else "as is". The servo will be back at full "high" position. Solder clip wires to the middle and either outside terminal of the 500-ohm pot, and connect the voltmeter to these same pot terminals. Connect the pot wires to wires A and B, and rotate the pot knob. At some knob position the servo will respond going in the low throttle direction. This will occur suddenly and the pot will be very touchy. The voltmeter will indicate about 3 volts when this happens. Now carefully adjust the pot around this point and you should see proportional servo response - still very touchy - and the entire servo displacement will occur between 3.0 and 3.2 volts.
     Connect the pot wires to wires B and C, and then again on wires C and D. The procedure and results for each wire pair should be the same as above but at different locations on the pot rotation. Notice also that if you set the pot for the servo somewhere between it's normal limit throws, the throttle stick has effect from its low position up to where ever the servo position (as set by the pot) is.
     This completes the bench checkout of the LCDC and it's ready for installation in your system. Connect it in-line with you Rx-ESC cable, connect the balance (taps) connector of your Li-Po pack, and then do "final test". "Final Test" is how it works in your power system and can only be demonstrated as you discharge a Li-Po that does have some "low" cell. Not to worry - I've never seen one that doesn't!
     As you can tell from these last tests, it only takes about 10 millivolts to move the servo (and now the ESC) from full ON to full OFF, and surely there is some cell in your pack that will hit the "detect" level before all others during rundown - on the bench, or in flight. The trick is to know which cell it is if you want to verify LCDC operation in your system, and that is up to you to know before hand or to find out. In any case, for every system IÕve tried it in, the LCDC has prevented any cell from dropping below about 3 volts. The LCDC gives you battery protection and confidence you never had before, not to mention the fun associated with building and using your own device.
     As a final operational word, be sure to disconnect your LCDC from the pack when done flying since it does draw a few milliamps and would eventually deplete your pack to damage level.
     Good Luck with your own LCDC. If you have any questions, please feel free to inquire and I'll do my best to help.

Bob

PC Layout: LCDCBrd2.pdf
Schematic: LCDCsch1.pdf

     Bob Kopski's article in the April 2006 Ampeer about the LCDC sounded like just what I needed for in-flight protection of my Li-Po cells! Some recent announcements for low voltage cutoff circuits didn't sound good, as total cutoff of the motors for my 13-pound B-17, just to save the batteries, didn't sound very practical. Bob's LCDC, which retards the throttle and allows you to retain full control of your plane, with plenty of time to get down safely, sounded great!
     Bob Kopski has done a great job in providing the information needed to build your own LCDC and the testing equipment and procedure to be sure it is in working order before connecting it to that expensive pack you just bought.
     I just had to try to build a couple (I have two packs in the B-17) and see for myself. I was not disappointed. I have built one LCDC so far. It works just as described.
     Bob's drawings reminded me of the good old Heathkit days! I do believe, however, that if you do not have any experience building your own electronics circuits, you probably hadn't ought to start with this one. For soldering, I used an iron with a 1/8" chisel tip; this is the largest that I would recommend; a smaller tip wouldn't hurt. The suggested pc board is very good, and the traces, which are pre-tinned, shouldn't lift off with heat.
     An LCDC is not expensive to build. If the parts are ordered from Mouser, as Bob suggests, the cost is very low. Mouser is quick to deliver, and is a joy to order from on the Internet. They did not have a minimum order amount when I ordered my parts. The highest cost item is the pc hole board, but one of these is large enough to build several LCDCs when cut with a Dremel cutoff wheel.
     For that reason, I suggest that those of you, who want to build one, find a group that wants to get one too, and combine your order for parts.
     Be very careful in counting the holes on the board so you drill out the correct holes and get the parts in the right places. Check and double check. It sometimes helps to get someone else to check your work. First, finger twist drill the traces off where indicated on the drawings and then install the jumpers. They are harder to install after the other parts are on.
     Make sure the orientation of polarity sensitive parts is correct (the regulators, transistors, electrolytic capacitors and diodes). I made one mistake installing parts--put one in the wrong holes; old eyes, you know, and had to move it when my initial resistance checks didn't give the correct readings.

     I ran two motors in my B-17 that normally run off one 3S3P pack. I used an Astro Flight Whattmeter to monitor the pack volts and amps, and three separate DVMs (digital voltmeters) to monitor each of the three series cells. I connected an oscilloscope to look at the throttle signal. The pack was not quite at full charge, but that didn't matter since I was interested more in what the low end would do. At the start of the test, full throttle gave Whattmeter readings of 10.0V and 39.3A. Throttle pulse width was approximately 1.9 ms. At mid-discharge (about 5 minutes, down to 9.3V and 25A total current) it became obvious from the scope that the pulse width had begun to decrease (1.7-1.8 ms), and the lowest of the three cell DVMs had reached 3.13V, which is where the LCDC should begin to slow things down.
     There was not much indication of the slowdown. My stick still was working and full control could be had throughout almost all of the stick travel. As the discharge continued, the pulse kept narrowing, the total current and RPM kept dropping, but the lowest cell stayed right at 3.13V. It never went any lower, even after I had almost fully discharged the pack to a point where the plane would have long since come down. At the end, I didn't have much effective stick travel left, but I still did have some control. At the point where I stopped the test, RPM was just about idle, current was down to about 4A, but all the cells were still at or above 3.13V.
     One question you may ask, "What audible indication do you get when the LCDC is working?" The answer is none. You may see a faster than normal power decrease at some part in the discharge cycle, but my feeling is that this effect is going to depend a lot on the condition of your pack. A new pack that has a flat curve and a sharp knee at the end, with balanced cells, may not give much of any indication at all--it may never trip the LCDC until you exhaust your time setting or whatever you normally use to judge how long you should stay up. A pack that is beginning to have problems with a weak cell will probably trip the LCDC much sooner, and the power decrease will become apparent much sooner. I believe this effect will be more severe the worse the condition of the pack, but you should still have plenty of time to come down safely, and you shouldn't lose your plane.

Ken,

     Congrats on a successful maiden flight on your Fusion!! It looked and flew very well. I may have something in that 'performance league' in the next few months.

     It is a joy to fly. While it was extremely windy, as you said, it flew very well. More on it in future Ampeers. KM

     Anyway, I watched you guys having a lot of fun. It seemed a bit windy for my lightweights so I opted to observe.

Roger and His Lazy Bee - Note the AF05 Geared
Old AF brushed Motors are still excellent power

     I think Roger had the most flights with his Lazy Bee. I think he got in about 5 flights and had a ball doing rudder-rolls in all that wind.

Richard Utkan & His LT-25 - good flier in the wind!

     Rich had a successful maiden with his new SIG LT-25.
     Yep, it was Rich's successful maiden that gave me the courage to maiden the Fusion in that much wind. Rich's LT-25 flew very well indeed! KM

Tom's Mirage really moved out in the wind

     Too bad Toms' plane suffered a mid-air with the other EDF plane.
     I flew the next day at the UFO field, BTW, not much wind.
Regards,
JIM

     All of the photos were taken by Jim. Thank you Jim!

     Jim Young had new Li-Po batteries to try out in his Hughes & Mr. Mulligan

     Jim Young also flew and took photos and video for his report on the Ezone of Sig's new E-Force Built-Up 3D ARF (www.rcgroups.com/links/index.php?id=4995)

     Keith Shaw entered his new Stomo into the Toledo RC Expo static contest. It is an electrically powered sport model inspired by an eligent, efficient homebuilt designed by Hans Moeller in 1930's Germany.

Wing Span: 85 inches Wing area: 1050 sq.in.
Weight: 120 ounces w/Kokam 6S1P 3200mAh Li-Po
Weight: 128 ounces w/18 2000mAh SCR Sanyo Cells
ESC: Castle Creations Phoenix HV-45
Motor: Astro Flight Brushless Geared 40

     I had a phone call from Bob Boucher after the article using his motor as an example appeared in the May Ampeer. We discussed a lot of things and I have noted a few of Bob's comments here. I tried to take good notes during the conversation but much of the following is paraphrased and not direct quotes from Bob. The numbered items are Bob's comments.

1. The speed control has a tremendous affect on high wind motors causing a lot of inductance. This inductance acts as a brake on the motor because the voltage gets out of phase with the rotor. Low Kv motors have a lot of AC "running around" in the speed control. This inductance is not modeled well in all of the Calc type programs.
2. When testing motors at Astro Flight a large power supply capable of 80 amps and 40 volts is used.
3. A Castle Creations Phoenix 45 using default settings was used to create the expected performance stated on the Astro Flight Web site for AF 19 Direct Brushless motor.
4. Bob will now be using 7v, 10.5v, 14v, 17.5v, etc. as the voltage numbers for his expected performance data since good Li-Po cells should be able to sustain 3.5v at a reasonable amp draw.
5. Astro Flight is located at sea level.
6. APC "E" props are used for the testing, as they have become the "default" prop of choice for many efliers.
7. Amps, volts, and watts are measured by an Astro Flight Whattmeter in line with the speed control and power supply.
8. RPM is measured with a tach and confirmed with a scope.
9. The resistance given in the AF data is the actual measured resistance.
10. The Brushless 19 Direct can be propped to a little over 25 amps without a problem and can probably handle 30 amp bursts.

     I would like to thank Bob for taking the time to call and explain Astro Flight's procedures. As I stated in the May issue of the Ampeer, put this motor into a 15 to 19 glow airframe on a 3S Li-Po pack and have a ball!