Nicad alternatives – part 4

It would appear that the publishing of details on Lithium rechargeable cells in this column as well as in other ‘conventional’ modeling publications has sparked a lot of interest. For many years now, the venerable nicad has provided sterling service in the many and varied applications that we modelers continually throw at it. With the rapid growth of portable equipment, the demand for reliable portable power sources has grown at an incredible rate. This demand has promoted extensive research into primary and secondary cell technology, as well as the development of new cells in all shapes and sizes.

These are two different NiMh cells that I have in my collection for "normal" electric flight. They help to illustrate the sizes and configurations available amongst the nicad alternatives.

A number of you have designed chargers, or gone looking for charger details for the Tadiran rechargeable Lithium cells I published details for.

BobSelman <bselman(at)clandjop.com> is one such designer. You should check out Bob’s charger design and description on his pages at http://www.janics.com/~bselman. The schematic has recently been updated to cater for the variation in Q1 (needed a trimpot to adjust out). Bob has also added a calibration procedure. Thanks Bob.

I picked up another charger circuit off the net (from the SlowFly list I think), but unfortunately, I lost the details of the designer/originator. As best I can recall, it solicited some comment as to the suitability for Lithium Manganese cells, but appeared OK for lithium ion cells. I’ll pursue more info. and hopefully present it next month.

Another source for charger circuits and components that I have located is MAXON – packed in one of the many boxes surrounding me at the moment is design notes and test circuits for several IC’s from Maxon that appear to be ideal. They even have one IC that can form the heart of an automatic charger capable of handling nicads, NiMh and lithiums!? Again, more next month.

The Dutch SlowFly Scene

I am pleased to present the second half of Harold van Berk’s <hvberk(at)gironet.nl> article, with a look at some of the SlowFly ‘goodies’ that were at the Dortmund trade fair earlier this year.

Simprop indoor motor, ESC and Rx. Kontronic indoor ESC Graupner indoor ESC. This is re-engineerd schulze stuff. Ikarus Taube. Made from foam. Bit heavier than the Bleriot (330g), but with the same gear. Close up of the 1717 motor. In the display area: a very light slowflyer build like the 'stubbefliege'. 5 x 50mAh. 50cm span. The "Johnny bee" is a simple slowflyer with a moter like the pusteblume, an 8 x 110mAh, 100 cm span, 180g. The Simprop 'Taube'. - Comes as ARF. Build from wood. Same size as Ikarus bleriot. The Simprop team gave demo's with 3 of these things at a rather small area. They used 500mAh cells for flights over 15 minutes. Normally you use 250mAh cells just like the Bleriot. Note the prop - It is from the new APC indoor line.

Aerobatics ‘Down Under’

Eric Parsonage <ericpa(at)mpx.com.au> and Scott Gage <sgage(at)chariot.net.au> both live in Adelaide, South Australia. They have been instrumental in promoting SlowFly in Adelaide, such that they now have two regular get-to-gethers a month attended by up to twenty flyers. Scott is fascinated by the real tiny stuff while Eric is bored wittless by anything that can’t fly inverted, roll or climb vertically.

All this has lead to some impressive developments in indoor aerobatics over a very short period of time. The guys sent me a CD of digitised video of some of the Adelaide events. Being pushed for time, I’ve only extracted these pictures to wet your appetites. Next column will have more details and plenty more pictures.

Some of the models awaiting their opportunity to fly at one of the Adelaide SlowFly get-to-gethers. Top left is delta by Eric Parsonage – 25" span, 2 x DC5-2.4 at 6.7:1 driving single 23x12 prop, 3 x Tadiran Li. cells or 8 x 110mah nicads, Lower right is a "Micro Step" designed by Eric Parsonage – 900mm span, 4 x 9g servos (rudder, elevator, ailerons, flaps), mass 320g   A Cap21 look-a-like. Very aerobatic and capable of loops, rolls, inverted, cuban eights, running eights, knife edge, etc., etc. This one is by John Tonks. Another is flown by Peter Smythe. Power – Speed 300, HY42 g/box 4.2:1 with standard HY prop by VL products. 34" wingspan, mass 384g 4 x GWS naro servos (9g) and 7 x 500 mah NiMh or 7 x 550 mah Nicad   Erics’s delta

DC5-2.4 Repairs

I have mentioned several times in previous columns about the ‘problem’ of burning out the brushes in the WES DC5-2.4 motor (including my own efforts) when operating them on high voltages. The DC5-2.4 motor is a stirling performer that will give amazing performance for its size and mass. However, in the quest for even greater performance, many modellers have resorted to higher voltage packs, which have lead to ‘fried’ brushes. There is hope - here are details on how to repair them, should your quest cook your motor!? The R&D for this comes from Jacques Wakae <jacques(at)vision.net.au> in Tasmania (that’s Australia again folks!!)

 

From: Jacques Wakae <jacques(at)vision.net.au> Hello to the 'burned brushes fraternity'! I was pleased to notice the large number of people with this not-so-unique problem, now I don't feel like such a dork anymore, my DC5-2.4 burned its brushes after about 1 hour flight time. If you have patience, willpower and an eagle eye (a magnifying lens will do) it is possible to recondition the motor by installing a new set of homemade brushes. The motor will most probably loose some of its peak efficiency but I consider the end-result worthwhile. Here follows; Take the motor and clamp it with the backplate facing up (if it screams, you have clamped it too tight!) remove and discard the little center backplate -make a locating mark on rim of backplate and motor housing drill out (1-2 mm deep) the 4 plastic fixing points on the housing circumference. -gently lever-out backplate unscrew both brush holders and remove them and their attached power leads reinstall the backplate, with the brushholder cavities facing up and with the location marks 180 degrees opposed. – fix the backplate in position with whatever at hand, I used the points of toothpicks and a drop of Zap. locate some brush type material, I used the brushspring from a servo motor grind one of the original brushes from its brush holder arc weld the new brush material to the brush holder, what no arc welder! well in that case just use a low temperature silver solder ( I used; Comweld 965 Silver Solder) and flux. bend and cut he new brush to conform in shape and length with the remaining original brush repeat previous 3 steps with the other brush install the new brushes apply a small voltage(1.5V-3V) to the unloaded motor whilst monitoring the current tune the brush tension to achieve the lowest no-load current, but ensure that all segments of the commutator still make contact. You are now the proud owner of a reconditioned 'DC5-2.4' motor with 'al fresco' brushes. This reconditioning can be repeated until the commutator wears out.(or your eyesight fails) Lest I forget: remove the clamp before flying! Best of luck Jacques

 

Further enquiries to Jacques yielded the following additional information….

 

From: Jacques Wakae <jacques(at)vision.net.au> Dear Wayne, Here are some answers to your questions, (or is it questions to my answers?, I forget!) Joke aside, the repairs have held-up pretty well so far. I have flown about 5 times in front of the house and about 15 to 20 flights for the last 3 indoor meets. (4minute flights) I have not dared to look at the brushes or commutator and I am just waiting for it to fail. The only problems I can see are these; because I used a round piece of phosphor-bronze as the new brushes, the wear on the commutator must be fairly high at the center point until the brush material starts to wear flat, a solution to this would be to flatten the new brush material before installation (the size of the hammer is not important) Also due to the motor only having a front bearing it is important that both brushes apply an approximate equal tension to the commutator and as such both brushes must be made from identical material. The only perceived change in efficiency was that I could not match the original unloaded current (not that I checked it first of when the motor was new) As for flying, my 'WESPE' still climbs at about 35 degrees at full throttle on 6 x 50ma nicads for a total flying weight of 107 grams and cruises at about half throttle. I have now build another wing with an extra rib/panel and covered it with the 2.2 gram condenser foil instead of the 7 gram, end result is +/- 11 % more wing area for an identical wing mass of 15 grams. I did originally only burn-out 1 brush but needed both brush holders to affect the repairs, if however you would have 2 motors with 1 burned brush each, then you can recondition 1 motor with the 2 remaining good brushes and make new brushes for the other one. Repair time is really dependant on the sharpness of your eyesight, the steadiness of your hands and the composition of the floor in your workshop, you would not believe how long it takes to find a small screw on a chinese slate floor. I fly a "Wespe" as previously mentioned and am the only one so far in Launceston with a true RC slow fly, there is one Bleriot II, but at 250 grams it is more like a "divine wind' plane (Kamikaze, baka, etc... ) There are however a few more people interested (there are about 150 RC fliers in 2 power clubs and 1 glider club) and next winter could be quite interesting. My next project is an all CF version of the Bleriot II, I should be able to bring the weight down to about 170 grams. As for slow fly experiences so far, I used to get a lot of glitches (using a Simprop Piko 2000 and GWS naro servos). I have installed a 4R7 resistor in-line between the servo amplifier and the servo motor and all glitches have dissapeared, this really proves that the stall current of a Naro is too much for 50 Ma nicads.(the blue one) Glad to hear from you, your articles in E-zone are great, the only problem I have with e-mail information is that I cannot figure-out where people are geographically and as such information given or received can be pointless. (took me awhile to figure-out what KRC meant) Best Regards, Jacques

 

So, if you have a burnt out DC5-2.4, you now have no excuse not to try and fix it – let me know how you get on. Thanks again Jacques!!

Surfers Succeed (catch a wave??) in Internet Land!!

Here again, for another month is some of the ‘electro-spondence’ I have received (and sorted!!) that I know will interest you. Remember to tell us what you have been up to (or what you would like to get up to - as long as it relates to SlowFly that is !?!?!).

First off this month is a series of emails from Dmitry Marukh <dmitry(at)hcl.com> with a simple but clever idea for you to try….

 

From: Dmitry Marukh <dmitry(at)hcl.com> Hi, Wayne If you ever wanted to know charge state of the battery pack instantly, you'll probably like following solution. New Duracell alkalines have built-in PowerCheck strip. Carefully take battery cover off, trim it. Before covering your new battery pack with shrink tubing put the strip over any cell joint in such a way that negative contact lays on one cell and positive "button" located on the other. Make a small cut and a round hole in the shrink insulation, right above the scale and a button point. Shrinking the tube make sure it presses negative end firmly, making permanent contact with cell. The same works for big models or sailplanes, even better. PowerCheck can be glued to any curved surface, e.g. leading edge near root chord. Put small piece of aluminum foil underneath as positive contact. Battery pack must be modified to have a third terminal, or small separate connector. Those indicators operate by displaying temperature of thin foil resistor. That's why they would mislead you if battery pack is getting warm or model exposed to hot weather. Anyway, they weigh nothing and are good for quick shelf inspection. Mounted externally on indoor model they provide accurate readings. Regards, Dmitry

 

 

David Whitten <davew(at)senet.com.au> , flies with Eric Parsonage and Scott Gage in Adelaide (yet another Australian!!)

 

From: David Whitten <davew(at)senet.com.au> Dear Wayne, My name is Dave & I fly mainly electric power,( for 20 years or so) I was just brousing on the net & found your page. My models are varied--pylon aero ,glider,&indoor The indoor model is a facetmobile from the Neil Hardiman plan. Powered with a Speed 300 ,Schultze be25 control & 7-500ar cells. At 350 gr it has plenty of power to spare. Electric indoor is becoming quite popular in Adelaide at the moment. Regards, Dave Dave’s "Facet Mobile"

 

I have had an ongoing discussion with David Lewis <dlewis(at)usginteriors.com> on a number of SlowFly subjects. As usual, David has lots of good information to share with us.

 

From: David Lewis <dlewis(at)usginteriors.com> I have thought more about lithium/DC5 combo & believe there are couple of items to be mindful of: 1. The ESC delivers full battery pack voltage to the motor - no matter what the throttle setting. The lower the motor rpm, the lower the motor impedance. The armature resistance is very low, probably an ohm. For that reason, the motor looks like a short circuit when it starts up. As the motor spins up, however, it behaves like a generator, creating a voltage which opposes the supply voltage. Ergo, at high rpm, the battery sees enormous impedance looking into the motor terminals & only a small current flows. So my hypothesis is when the ESC sends a full voltage pulse to the commutator while the motor is just leisurely ticking over, you get a lot of current flowing through the commutator and armature. High current through the commutator by itself is not particularly harmful. The problem is that a strong magnetic field is now created by the armature poles (flux density proportional to current) and this distorts the field flux. How does distorted field flux cause trouble? Because we want the brush to short two commutator segments together only during the brief time interval when there is no voltage difference between those two segments. This occurs when the windings are moving parallel with lines of field flux. As long as the armature coils are not cutting lines of magnetic force, they do not generate any voltage -- the perfect time for commutator switching to take place. But this can occur at one current only. Any other current value, the field flux assumes a new pattern due to aforementioned armature reaction, throws the timing off, and you wind up with commutator sparking. Technically there are two other phenomena that prevent clean commutation at high current: armature self inductance and mutual inductance of the windings, but these have a lot in common with armature reaction, and are cured by similar techniques in most cases, so not necessary to delve into. Put these phenomena in conjunction & it's easy to understand why flying around on 200mA for hours with a 9v pack can do damage. Solutions: 1. Go to higher voltage motor: DC1717, DC6-8.5, or use two DC5s in series. 2. Use lower voltage (6v max) battery. My DC5 has lasted many, many hours on 6v with absolutely no diminution in performance. The 6v pack is two Duracell DLCR2 (11.1g, 3v, 750mAh each) These are the smallest hi-rates (1A continuous) available at low cost. One of my customers, George Young has reported that his Wespe flies OK on 6v. Not much of a climb rate, but viable. 3. Optimize commutator timing to suit cruising current. Rapid commutator deterioration will still occur at any other current, though. The commutators in coreless motors are relatively delicate because of their low impedance design. Brushes are usually made out of silver or platinum alloy as opposed to graphite. Getting the most out of your lithium batteries is important when you use primaries (throw away). Have noticed the voltage goes down as the capacity is used up. For a 6v pack, the initial open circuit is 6.6v, and goes down to 6.2v near the end of it's life. I'm using a very cheapy volt meter, so not a perfect measure, but corresponds well with real life performance & gives an idea of how much energy has been used up (unlike NiCd). The first sign you're running low shows up in aircraft ROC (rate of climb). Also, I never use auto cutoff. I disable it no matter what, since it could (& has) cause(d) trouble. (I don't think you can disable AC on Heino Jung. For JMP, simply put a solder drop between pins 1 & 2 on the processor. Kontronik I don't know anything about.) The airplane will indicate low battery by the way it flies. Tadiran unofficially lowered min voltage to 2.0v on their TLR 7103 cells which gives us another 50mAh to play with (total 850mAh). Pretty good for 3v @ 17g rechargeable. I do have these on sale for U.S. customers that happen to be interested. – price $15. each. The old Soviet government put a lot of resources into model airplanes, point of national pride. Which reminds me, I sent a catalog to a comrade in Russia last week. Perhaps he'll be the point man for Russian SF. Did you know aeromodelling classes were mandatory for schoolchildren in Mussolini's Italy? Not a bad reflection on model airplanes, they simply thought it was educational. And if a few fighter designers resulted from the program, they didn't complain either. Just got done flying my Little Bee. There were some soccer games in the park so big audience. The crowd liked the fly bys & touch and gos. Also flew in our large conference room at work this week several times with no problem. I practiced first on the weekend to make sure it was feasible. It was, and coworkers were fascinated. This may be of interest: A while back I took out the downthrust in an attempt to improve climb rate. I couldn't get out of ground effect with zero downthrust. My theory is propwash hits the wing at lower angle of attack without it. The prop is close to wing LE and diameter is large in comparison to wingspan. What seems to work best is, with the aircraft putting along at slow cruise, the propshaft should be approx horizontal. This translates into around 5 degrees of downthrust. Another thing that improved STOL performance was to mount a nice, low friction tailwheel on a long strut. This holds the fuse @ the best ROC (rate of climb) ground angle & the plane pops off the ground right away. Since I use a 6v pack, climb performance is critical. Plans for the tailwheel are in my catalog & the design has proven to hold up well under all kinds of abuse. On the main gear legs, somehow I'm getting away with just sticks of balsa glued to the fuse(!) You can't beat that for light weight & simplicity. Cheerio, David

 

Alan Perrin <alan(at)trident-uk.co.uk> is organising a SlowFly event in England. Unfortunately, its a bit far for me to go, but those closer should make an effort to attend!?!

 

From: Alan Perrin <alan(at)trident-uk.co.uk> INDOOR RC SLOW-FLY EVENING September 19th 1998 at The Warwick School Noke Drive, Redhill Surrey, RH1 4AD 2:00pm until 8:00pm All types of indoor flying model are welcome..(no i.c.) Freeflight, Radio control, Slow-fly sport or scale.. Cost of session will be £5.00 per flyer If you have ever been interested in flying indoors with R.C. or freeflight, or even control line then come along. Spectators welcome.. The school operates a strict non-smoking policy on the site Non-marking shoes must be worn in the gymnasium (or bare feet) For any enquiries please contact the event organiser direct. DO NOT contact the school, as they will not be able to answer your questions.. Event Organiser: Alan Perrin 01737 213533 (evenings) Proof of insurance must be shown before flying. The event organiser reserves the right to refuse entry. E&OE

 

Jim Moffat <jmoffatt(at)lucent.com> sent in some info. on suppliers he has tracked down – thanks Jim.

 

From: Jim Moffat <jmoffatt(at)lucent.com> Here is some of the information you requested on motors, batteries and other related supplies. Motors and related supplies are available from: Hobby Lobby 5614 Franklin Pike Circle Brentwood, TN 37027 Kenway P.O. Box 889 Hackettstown, NJ 07840 HiLine P.O. Box 1158 Goldsboro, NC 27532 Windsor Propellor Company 3219 Monier Circle Rancho Cordova, CA 95742 Lowest prices on individual cells are usually available from: Great Planes/ Tower Hobbies P.O. Box 9021 Champaign, IL 61826 Complete custom made battery packs are available from: SR Batteries Inc. P.O. Box 287 Bellport, NY 11713 I will send you another e-mail about my electric control line plane. It is my favorite project and I have already sent pictures of it to the E-Zone electronic FTP Incomming folder. I'll send more later. Best Regards Jim Moffatt

 

Helmut Felderer <helmut.felderer(at)sea.ericsson.se> is a lateral thinking SlowFlyer who has been able to earn some ‘pocket money’ using his Bleriot to tow advertising banners – here are some details.

 

From: Helmut Felderer <helmut.felderer(at)sea.ericsson.se> Ok Wayne, I think here in Austria I am alone with this business, and I am this just for fun, so: the banners have a length of 3-4 meters and made off stripes off plastic shopping bags with the logo of the advertising companies and shops, strenghtend with carbon-rods (up to down) in different locations and equipped with something not to heavy ( like small balls of ballbearings) on the lower edge.the bags have to be provided from the advertising companies and the banners take about 15min to be ready... a string to the fuselage of the slowflyer (In my case the bleriot III) and lets go... no especially security-measures to be taken (because of the slow speed and low weight) and not much place needed ( a pingpong table is anough to start and land) flying is not very difficult, just need more power as without banner, reduces flighttime about 1 min. compared to flight without banner. this fun give me 500 ATS per hour extra-budget for my hobby:) bye for now! h. Helmut’s Bleriot towing a banner during a "practise" session before going public.