Another newbie, about batteries & wires, etc.

[erickkr]

I have several years experience flying models, (R/C power & soaring, and C/L), but electric, especially this small stuff, is somewhat of a mystery to me, and I don't know where, (other than here), to get the info. First question is: What do all the numbers mean in reference to batteries?? I get confused with the numbers, (other than the number of cells), that are talking about the mAH and voltage combinations. Can you substitute larger mA batteries for smaller ones?? It seems to me that the ESC should control how much current/voltage is getting to the receiver and motor. No? And I got a Great Planes Electrifly C-20 and the wires and connectors are HUGE. What's up with that??

Anyway, I think I need some basic info before I go to much further. Right now I'm putting the C-20, a DC5-2.4 geared at 8.3/1, with a 9x5 carbon prop, a Hitec Feather receiver, 2 Hitec HS-55 servos and a 7 cell NimH battery pak into a Dave's Model PF-5 park flyer. Is that a viable combination??
I got a Herr 'Starlite' and started building that for the equipment, but then decided that it was rather delicate for my undoubtably heavy-handed first flights, and went for the PF-5. I guess it would have been much better to have come in here BEFORE I did all of that, but I always have been somewhat impulsive ;-P 'Course, I didn't KNOW about this site before I got started :-(

Any help would be appreciated, (read 'needed').
Thanks, Ken :confused:

[ 08-11-2001: Message edited by: Ken ]

[flyingbuddy]

Ken, the ESC does control the voltage and current to the motor, and the BEC (battery eliminator circuit) part of it sends regulated voltage to the receiver.
Larger mAh cells mean more weight, and weight on an indoor plane is the enemy! Each cell chemistry type (NiCd, NiMH, LiMnO2, lead-acid, etc.) has a specific voltage output. Add cells to make a battery of a voltage you want. Capacity and current delivering capability are two more factors. Capacity of cells is measured in ampere hours (Ah), or how many amps of current a cell can put out for an hour. A typical car battery can put out about 50 amps for an hour. Marine batteries top 100Ah and usually show the Ah rating on the label. Smaller cells of less than 10Ah capacity are usually rated in mAh, or milli ampere hours where milli equals 1/1000th. Thus a 1200mAh cell is the same as 1.2Ah. Current delivering capability is how much the cell can put out right now, without destroying itself. Can a 12V NiCd pack start your car? The answer is yes, provided the cells are large enough to deliver that kind of current. A car starter motor needs from 50 to 200 amps to turn over an engine (little four cylinder, 50A; big V-8, 200A.) Ever notice the "CCA" rating on car batteries? That's what we're talking about now. CCA means Cold Cranking Amps. It means that a battery can deliver, say 750 amps in zero degree weather. There are many factors that affect this, mainly, chemistry and type of construction. Smaller cells generally don't have the surface area of the plates to deliver as many electrons as larger cells. Cell specification sheets sometimes rate a cell with a nominal discharge rate. If the rating is, say 10mA (0.010 amps,) there's no way it can deliver a full amp, even if you short the negative terminal to the positive. Size for size, NiMH cells cannot deliver as much current as NiCd. 110mAh NiCd cells can easily put out more current without damage than 120mAh NiMH cells. Is this clear as mud? Just to clear things up, or baffle you completely, check out these links: http://www.batteriesamerica.com/newpage3.htm http://www.gpbatteries.com/industrial/batteries/NiMH/NiMHspecs.htm http://www.sonnenschein-lithium.de/Products/lrbatt/tadiran/tadirBt.htm click on "download product data…"
For more confusion, see: http://personal.lig.bellsouth.net/lig/r/e/redscho/

Back to your question, your model might fly, but not very well. The DC5-2.4 draws 1 amp at 8 volts, so you need an 8 or 9cell 120mAh NiMH pack. See: http://www.flyifo.com/ordermini.html
Dave rates the plane at 120g with an 8 cell NiCd pack, two 7g servos, and a 3g receiver (SHR-72) and a 2g ESC. Your equipment would add about
26 grams, or 22% to the designed weight of the plane, the major culprit being the ESC at 17g. Speaking of which, The C-20 is a fine ESC, but it is overkill at a 20 amp rating. You only need 1 amp for that motor. The DC5-2.4 is a coreless design, so although a conventional high rate ESC will work, you are better off with a JMP HF-9 ESC, or wait for Castle Creations to come out with their new ESC for coreless motors. See: http://www.toddsmodels.com/esc.htm
With a GWS flight pack, the receiver and servos would save you about 10g, not as big a deal for the money. If you're going to build lightweight models, you need an electronic balance. See the topic: "Scales" in the Indoor RC Microflight forum, which you can access from the Hop To box at the bottom of the page.

I hope that I've been more help than hindrance.

[flyingbuddy]

More on the battery thing.
As I said before, weight is the enemy. The problem is, capacity in mAh determines flight time, but more capacity means more weight and degraded performance. So the compromise is to get the biggest capacity that will afford an acceptable flight time without adding so much weight that performance suffers. New battery technology helps this situation, so do more efficient motors and speed controls which extract the most power out of your battery. The DC5-2.4 motor is one of the most efficient small motors available. Good choice, Ken! NiMH and Lithium Metal cells are the newest technology. See the topic: "CR-2/li-ion/li-metal" in the Indoor RC Microflight forum.
To estimate flight time, you need to know the capacity of the cells and the motor current that they will be running at. The equation is: Capacity in Ah (not mAh)/motor current in ampsX60=minutes.
Using your example, 120mAh =0.12A, motor current = 1.0A (from http://www.toddsmodels.com/dc5.htm)
So, 0.12Ah/1.0AX60=7.2min. flight time.
Play with this a little. If motor current goes up, flight time goes down. If cell/battery capacity goes up, flight time goes up, but don't forget about the weight penalty.
As the old axiom says, "To improve performance, add lightness." Are we clear on that?

[flyingbuddy]

Wires! I forgot about wires!
According to the chart in David Lewis' catalog (http://www.homefly.com/), for 1 amp you need a wire that is 28 or 30AWG.
28AWG is safer, especially if you add in a couple hundred milliamps for the servos.
John Worth (http://www.rcmicroflight.com/cloud9rc/) sells some 24AWG wire that weighs only 0.9g per foot. 24AWG is good for 3.5-5 amps! Keep the wire lead from the ESC to the motor as short as possible. Mike Blott solders the Sirius GFS ESC directly to his motors! Keep the lead from the
ESC to the battery as short as practical, since you usually need the battery to establish the plane's CG. Shorten the battery lead as much as you can, or replace it altogether with thinner wire, like the 24 gauge, which will handle up to a Speed 280 motor. While you are replacing the battery wires, why not save a gram or ten and replace that heavy heat shrink wrap with the Clearly Superior stuff from Gabe Baltaian (http://www.nyblimp.com/)
It goes on and on.

[erickkr]

Thanks, that does clear up some things. I guess I should have been more specific about the battery packs. They are: a 7 cell NIMH, 8.4 V, 600 mAh, and/or an 8 cell NIMH, 9.6 V, 600 mAh pack, but if I understand what you are saying, they are both along the same problem as the ESC, shooting squirrels with an elephant gun, (and too heavy to boot). I was thinking, (HA!!), that the voltage would be OK, and 600 mAh would be a LOT more flight time without much penalty in weight, but I guess a little weight turns into quite a few grams :( Bummer dude. So it looks like I have about $100 worth of batteries that I can't use and will be replacing both battery packs and ESC in the near future.
Ken

[flyingbuddy]

Ken, now that you have a scale, I'm curious what the 7 cell and 8 cell NiMH packs weigh. Are the cells the size and shape of AAA cells? They would be Perfect in a plane like Joe's Elipstik!
A 9 cell 120mAh pack would weigh about 35g.
Your next step up in batteries for the PF-5 would be the 9 cell 220mAh NiMH pack at about 55g, or better yet, a 3 cell 430mAh Tadiran pack at 37g! Of course, you would need the WES charger for lithium cells, but you could get at least 15 minutes of flight time with little increase in weight.
See the topic: CR-2/li-ion/li-metal in the Indoor R/C Microflight forum, and http://www.ezonemag.com/disc/Forum5/HTML/003111.html
Save the C-20 ESC for a 280 to 500 powered plane, or replace the wires and use it on something smaller.
If you think that you may start doing a lot of soldering, which if you really get into this stuff you will, I recommend that you invest in a decent adjustable soldering iron, like a Weller or Hakko. I picked up a Hakko 936 (http://www.hakko.com/itnl/products/936.html) for $90 on sale ($10 off) at Fry's electronics. The iron heats up ready for use in about 30 seconds! Do a search on Google for decent prices.
;)

[gjohnson]

John,
Now you've got me curious. When I first got back into all this I bought a soldering iron at the LHS. It died not much later. Then I bought a Heller pistol grip model and a Heller pen style unit from Home Depot, but wasn't happy with either one. Now I'm using a Radio Shack pen style that can be set to either 15 or 30w. Will a unit like you've just mentioned make soldering much easier? Also, since you sound like you know what you are doing, which setting would you recommend (15 or 30) for most soldering like wires to small Deans connectors, wires to motors and capacitors to motors? I'm getting better at soldering, but always worry that I may be about to melt something while I'm doing it.
--Gordon

[flyingbuddy]

Gordon, I'm glad that it SOUNDS like I know what I'm doing. I often wonder.
I've used Radio Shack pencil irons at home for years, and a decent Weller soldering station at work.
I'm very happy with the Hakko 936-9. Will it make soldering MUCH easier? No, but it will make it faster, safer and easier in that the unit is more flexible. It's rated at 50W and is like having a ½" drill in a pencil sized handle. What you need in soldering are the proper temperature and heat transfer. For soldering small wires and printed circuit boards (PCB,) 15W at 600-650 degrees F is fine. Sometimes I crank it up to 750 for tougher jobs. I know that they're tougher because 650 ain't enough. What you get with a soldering station is temperature regulation, among other things. For soldering to metal sheet, like small motor housings, 30W should do, just make sure that the surface is prepared by roughing it up with sandpaper or a Dremel wire wheel, then tinning it a bit. I also tin Deans connectors before applying the wire to be soldered. As a matter of fact, if it doesn't already have solder on it, I tin it, whatever it is. BTW, did you get my email?