DSM Excelsior re-furb

[Jeffrey Cottrell 2]

Ok, done it again, but now showing 80% and 6.7v. May have this wrong, but I thought a fully charged LiFe should show 7.2v.

Using a small GT Power charger (only one with 2s capability) which has never been used on LiFe before, so it could be the charger behaving strangely.

Not sure

Jeff

This could get silly.

Now cutting off every couple of minutes. Charge level is building up slowly but only by a few percent each time. Could be time for a new charger.

Jeff

[Peter Jenkins]

Do you know anyone close to you who has a LiFe charger that works?  Ask them to charge your battery and see what happens.

 

Yes, fully charged LiFe is 7.2 v.  Strangely, the JR provided Tx pack of a 2S LiFe, with a balance charger pack held in place with shrink wrap -( which is why they charge £75+!) won't charge beyond 6.9 v.  I bought 2 x 18650 LiFe cells of 3,600 mAh capacity that recorded 7.2 v  on delivery and soldered the charger onto them and shrink wrapped the whole caboodle.  The system will not start charging till it sees 6.7 v but will only get to 7.1 v.  Why?  Who knows!

[Jeffrey Cottrell 2]

Hi Peter, thanks.

Looks like I'm where I want to be.

Been recording the pack voltage on the charger. Seemed to go up by a few tens every few minutes, Last I recorded was 6.84v. Then, a matter of minutes later, the pack voltage had jumped to 7.2v and the charge current started to decrease.

Wonder if this jump in pack voltage when near full is a characteristic of LiFe's in general.

Couple of minutes later, the charger switched itself off, this time saying 'pack full'. On the cell checker terminal voltage was 7.2v and showing 97% full.

After a few more minutes this had relaxed to 6.88v and 91% full. Again, to be expected off charge.

So, we're there.

Not sure if this indicates a new charger is needed. The one I have is pretty old technology, so probably needing updating anyway.

either way, I sure have a lot to learn.

Old dog, new tricks etc.

Jeff

[Jeffrey Cottrell 2]

Hi Guys

Changing the subject, but might give you a chuckle.

Back to the undercarriage leg question.

Put a question on Google 'Removing legs on OK retracts'.

First two answers I got were

Swelling of legs or genitals, and

Foreskin care questions

Oooh errr, missus

Jeff

 

[Peter Jenkins]

2 hours ago, Jeffrey Cottrell 2 said:

Hi Peter, thanks.

Looks like I'm where I want to be.

Been recording the pack voltage on the charger. Seemed to go up by a few tens every few minutes, Last I recorded was 6.84v. Then, a matter of minutes later, the pack voltage had jumped to 7.2v and the charge current started to decrease.

Wonder if this jump in pack voltage when near full is a characteristic of LiFe's in general.

Couple of minutes later, the charger switched itself off, this time saying 'pack full'. On the cell checker terminal voltage was 7.2v and showing 97% full.

After a few more minutes this had relaxed to 6.88v and 91% full. Again, to be expected off charge.

So, we're there.

Not sure if this indicates a new charger is needed. The one I have is pretty old technology, so probably needing updating anyway.

either way, I sure have a lot to learn.

Old dog, new tricks etc.

Jeff

New charger!

[Jeffrey Cottrell 2]

Hi Peter

Think you might be right, but which one?

I have the small GT power one, and also an Accucell 8 from HK. Both are working well, but the technology is stone age compared to modern ones.

Might be due an upgrade.

Meanwhile, do LiFe's have a storage voltage, same as LiPo's? Thought I might give the pack a couple of cycles before I condemn the charger.

Final resting voltage last night was 6.74v.Checked this morning, still the same, so happy with that.

So far,so good

Jeff

[Jeffrey Cottrell 2]

Drat and double drat.

Just putting some foam packing in the nose compartment to isolate the battery from vibration. Got some sheets of foam about 1" thick.

Found with one layer above and one below, the battery will slide firmly between.

Means the battery will be easily removable for charging, this just after I extended the balance lead so I could charge in situ.

Drat and double drat.

Jeff

[Nigel R]

19 hours ago, Jeffrey Cottrell 2 said:

Having said that, any idea how the legs are attached on OK units?

 

Somewhat sure it is just a grub screw, in the body of the mechanism.

 

As an alternative, what you may be able to do is to cut the existing leg off short, retaining just a stub, and use an oleo mechanism to replace the leg and axle entirely.

 

e.g.

 

https://hobbyking.com/en_us/alloy-115mm-straight-mains-oleo-strut-for-5mm-mounting-pin-2pc.html

Edited August 5, 2021 by Nigel R

[Bruce Collinson]

Blimey those oleos look cheap enough, saves your problem with axles and hub thicknesses ... oh you just solved it ... even if they are straight from the PR of C.   Might have to compromise my principles for my DSM Saphir which has electric retracts which will NOT stay straight, especially as the wires aren't handed so one unloads the coil spring and one compresses it (they came with the model, which flies really pleasantly).

 

Tell all when the wires come out Jeff as I couldn't fathom that either, having removed grub screws.

 

Batteries; also sorted out, once you get a charger (I have a GT Quad from 4-Max, all chemistry, mains or 12v input, charges 4 at once, but you will hedge at the price) but my clear recollection from multiple sources was that the over-arching advantage of LiFe over NiMh is that LiFe gives you fair warning when it's getting low and NiMh falls off a cliff  with little or no warning.   I suspect LiFe has slightly higher power density, hasn't it Martin, Peter and Nigel?   Just bought two, 2A, from Component Shop, for so little money I can't recall the exact amount; a lot smaller than the NiMh which was supposed to be in my Acrowot but wasn't when I went to charge it ...

 

Waiting for news re an Excelsior 188 and keeping all crossed!¬

 

BTC

[Jeffrey Cottrell 2]

Hi Guys, thanks

Nigel

Not going to take the legs off at the moment, got loads of other things going on. However, when (if) I do I'll post on here what I find.

Great idea with those oleos, but not sure how they will fit.

I can see the grub screws for holding the axles in place, but can't see anything at the top to hold the oleo to the stub. also the specs say the mounting pin is 5mm. I would need 4mm. Anyway, feasible solution, but on the back burner at the moment.

Bruce

Those new legs did look like the ideal answer, until you put a doubt in my mind with your Saphir. You have one coil going back and one going forward. Couldn't find the answer by looking at the pictures, so I bent up a temporary leg from solder, and sure enough I would end up with the same problem.

Maybe not an issue in operation, but the channels in the wing where the legs fit are very narrow, so the previous owner had cut semi- circulars out of the wing to take the coils.

Not sure if I want to start cutting more bits out of the wing.

All is not lost. 4-Max also do a leg with no bends in it here. If I can find a way to bend the right angle tight enough for the wheel, I could actually make a handed pair.

Got some feelers out for wheels with thin hubs, so if I can find those should be able to use the original axles.

Work in progress.

As you say, batteries sorted (almost). However I do have chargers for them. Mine are pretty old and thinking a more modern one, with up to date technology might be a worthwhile investment.

I say almost because I have decided to use a separate pack for the retracts. Main reason is if the retracts get hung up or jammed, won't suck all the juice out of the flight pack.

Still working on that one.

Finally thanks for the thoughts on NiMh/LiFe. Did read somewhere that LiFe's have a much flatter discharge curve. If so, that's an advantage, but so many people just saying LiFe is better than NiMh, but without any definite or measurable reason for it.

Did post the same question on RCGroups and all I got back was 'LiFe are fit and forget'. Not so unless you extend the balance lead, or make the pack removable. Also Nimh will blow up if you fast charge them. Never had this happen to me, so I can only assume they were being fast charged beyond their capacity.

Gave up on trying to convince the poster his facts were wrong.

Anyway, so far more questions than answers, but I'll keep plugging away

Jeff

 

[Jeffrey Cottrell 2]

Hi again Bruce

Not even sure those no-bend legs will work either. Text says legs are 230mm overall. Looks like the upper and lower sections are the same length, which would mean centre of coil to one end would be 115mm. Take off 25mm or so for the axle bend, and you're down to 90mm.

The current fitment is 100mm, coil to axle. Wonder how short I can go before running into prop clearance problems.

If it ever stops raining, might get model out on the grass and check, but so far not looking too good.

Ho hum

Jeff

[Bruce Collinson]

Jeff,

Batteries; the uber-electronic guru at my club replaced his fleet, took out MiMhs and installed LiFes, I recall for this exact reason, no cliff edge and the local Jeti retailer told me exactly the same (Jeti use Li-Ion, without balance leads, for both Tx and Rx).  Balance lead extensions are cheap as chips, Component Shop or indeed the local Precious Shop, MS Leeds.

 

4 Max replacement wires; they do not appear to be handed so good luck with those.   I asked George why not and he said not to worry about it, he has a plane which pre-dates 4 Max and the retracts need to be straightened after every flight ... quod erat demonstrandum, as they say in Leeds ... even I can make an adequate 90 deg axle bend in 4 mm wire, use a large engineer's vice and a hammer.   Not sure it solves the symmetry issue though.   I will find out if I ever  get the wires out of the Saphir.

 

Weather looks dire so might be going to look at the Exelsior tomorrow. We might be comparing notes!   Three of us were doing LMA Elvington tomorrow and UKCAAHuddersfield Sunday but tomorrow is Bohemian Rhapsody weather (thunderbolts and lightning .. etc) so might be Elvington sun instead.

 

BTC

[Jeffrey Cottrell 2]

Hi Bruce
Can someone tell me why nothing is ever simple in this game?
So, LiFe
Notice your guru said no cliff edge with these. Not quite sure if that's right. My internet enquiries say the LiFe maintains a constant voltage through most of its discharge, but this fall away rapidly toward the end.
Posted the same question on another thread, about chargers, and Martin Harris came back with a list of Pro's and Con's.
One of the Con's he had was faster voltage drop at the end of the discharge cycle. Sounds like a cliff edge to me.
Have to say I have grossly over specced my Life.
Peter says he uses 850Mah and gets four 8 minute flights. Mine is 2100Mah, so unlikely to go flat anytime soon, but it seems to be different from your information.
Wheels
Still waiting for the dimensions from 4-Max, but I found a very similar item on RCWorld. This states that the lower section is 130mm which is fine, even after allowing for the axle bend, but the upper section is only 90mm.
If I was to make a handed pair I would need to use the upper section on one side. Take away approx 25mm for the axle bend, that leg would end up at only 65mm, as opposed to 100mm for the other side.
Would have to practice my circular take off's for that one!
No matter, says I. Wheels arrived from B&H models this morning. Looking pretty good. Hub is only some 12mm deep, so plenty of room for the collet.
Fine, except I noticed that one wheel had already been drilled out for a larger axle. Looks like about 4.5mm, very sloppy on my 4mm axles, but also left very little meat on the hub to withstand my less than perfect landings with a 9 1/2 lb model.
That was the last set he had,so if I go that way I will have to order from somewhere else, and swallow their exorbitant shipping charges.
Ho hum.
Hope the weather co-operates tomorrow. If it is as your feared, say hello to Galileo for me (another BR reference).
Otherwise, which Excelsior are you going to see? If it turns out to be a 188, certainly we can compare notes. In fact, would welcome your input.
We'll see
Jeff
P.S. In his post on the other thread, Martin also mentioned LiFe terminal voltage as possibly being too high for some servos.
Valid point. I'm using JX servos, and yet to find the maximum voltage they will accept. Martin made the suggestion to put a diode in the feed, which would drop 0.7v or so and put the output into the safe zone.
Great idea, except he suggested a diode capable of passing 7a, or at least 5a.
Do you think I can find one? Tried all the usual suspects, no luck.
If you or anyone else has any thoughts on a source, I would love to know.
J

[Peter Jenkins]

These days, we have telemetry to give us our Rx voltage.  We can set an alarm to go off at a selected voltage.  A good safety measure.  If you start with a fully charged battery, of any chemistry, and take a voltage reading before every flight while on the ground, as the ANO requires you to do (can the flight be safely conducted?) getting into a steep or gradual drop off indicates that you are trying to stretch the capacity of the battery to an extreme.  

 

As I said earlier, you can find out how much you consume from the Rx battery by starting with a fully charged one, go fly, then re-charge fully and divide the charge replaced by the number of flights and you get an average of capacity consumed per flight.  Ally that to checking voltage and decide on a safe level of voltage you wish to stop at.  We really don't want to be in the scenario where the Rx battery is close to being exhausted and you still want to fly it!  Keep it simple.

 

A 2100 LiFe used for 50% of its capacity and assuming we use 100 mAh per flight, will allow 10-11 flights.  You are unlikely to be troubling the battery or relying on it's not a cliff edge decline at the bitter end!  Don't know about you, but I cannot recall when I flew 11 flights on the same model on the same day!  Come on guys, we're practical types and we apply safety criteria to all sorts of other things so why are we so wound up about batteries.

 

As far as I'm concerned, I don't use NiMhs in my aerobatic aircraft as they are heavier than a 2S LiPo.  I use a Powerbox Digiswitch to provide a regulated 5.9 v to my JR servos where they are fitted.  A regulated voltage also gives you constant performance from your servos as they are not coping with 8.4 v at the beginning and 7.6 v when you are about to stop.  (My latest aircraft has Futaba HV servos so the v  If you don't want the hassle of having to remove a LiPo to charge it then the LiFePO4 comes into its own - fit and forget although you need to remember to extend the balance lead so it can be used for on-board charging - easily done.

 

I still use LSD NiMHs in some of my aircraft - Tutor trainer and Wot 4 spring to mind.  NiMHs are also useful if you want weight for balance issues.

 

Finally, my current F3A model, which I bought second hand, came with an Optiguard fitted.  For those who don't know, this is a clever bit of electronics that plugs into a spare Rx channel that assess the voltage being supplied to your Rx when you switch on.  If it detects a sudden drop in the input voltage, it supplies the same voltage to your Rx from a 450 mAh 2S LiPo.  On landing you will see from the flashing lights on the unit that all is not well with your Rx battery.  The voltage sensing bit of the Optiguard means it's good for 4S and 5S NiMHs, LiFe cells and LiPos.   I wouldn't normally use an Optiguard its just that it came as part of the package so I use it.  My other F3A model does without an Optiguard and has, so far, been fine as regards not having a battery run down in flight!  I never take off with less than 50% capacity remaining.  Below that the pack is replaced - remember I use 850 mAh 2S LiPos.

 

Yes, a Powerbox Digiswitch costs more than a bog standard switch (£46 from Nexus) but it has no moving parts has an LED that gives battery condition as well as On/Off, the ones I've used over the past 10 years have never caused me a problem and, if they fail, they fail ON.  OK, so £10 for a standard switch might compare well with £46 but then you don't have to scrabble around for voltage dropping diodes and other such gizmos.  Fit and they work.  The latest version of the Digiswitch also allows you to select different voltages from unregulated to 5.9 v.  What's not to like?

[Jeffrey Cottrell 2]

Hi Peter
Thanks again for sharing your experience and expertise. It's a steep learning curve for me, nice to know there's someone at the bottom, holding the ladder.
Having said that, I don't think I'm explaining myself very well, so I think a little clearing up may be in order.
First, I am using a couple of old, but ultra reliable JR transmitters. These I have home converted to 2.4 using either FrSky or Lemon modules.
Working fault free, and everything I need, and nothing I don't. Only thing is they lack telemetry facilities.
Myself I've never felt the lack, but each to his own.
Second, my thoughts on the end of charge characteristics of LiFe was in response to Bruce's previous post.
He had been told that LiFe do not 'fall off a cliff'. From what I read I think they do. Anyway, all opinion based, so no certainties.
It is not, or ever will be, a worry for me. You have said you get 4 x 8 minute flights out of an 850 2s. I know I overspecced with a 2100 LiFe. Can't imagine me doing even 4 flights on the same day.
Even if I do, I always carry a cell checker with me, and would use it before each flight.
No, my worry is how the servos will respond to higher voltages. It's easy enough to find specs for torque and transit speed on 6v, but no-one will state whether the servos will actually be damaged by a higher voltage.
My thinking is they would be ok, but I don't want to find out I was wrong on the maiden flight.
Martin's suggestion of using a diode in series was because they typically have a forward voltage drop of around 0.7v, so 6.8v from the battery becomes 6v or so to the receiver and servos. Now, that's got to be safe. Good idea in theory, but can't seem to find any that will accept suitable current levels.
Work in progress, this one.
Not sure where your figures of 8.4v at the start and 7.6v at the end would apply to my set up. Fresh off the charger, my LiFe shows 7.2v, but with resting, this quickly settles down to 6.8 or so. Given I have a larger than necessary LiFe I would be surprised if after starting at 6.8v I read anything less that 6.7v at the end.
Not really an issue.
btw, I notice that HK now have their failover switches back in stock. Same as the Digiswitch.
However, if I can determine the servos will be safe at my voltages, really don't think my flying style will require a regulator at all.
Have to mention that at the start I did consider a 3s LiPo with a stand alone regulator, of which I have three. That idea was quickly shot down, someone even suggesting LiPo's were 'fussy and unreliable'.
Try saying that to the many thousands of people, myself included, using them for motive power as well as running the radio.
Anyway, hope that clears up some things. There's clearly a difference between what I want from my set up, and what you expect from yours, but then again, you're a competition flyer, I'm not.
Talk soon
Jeff
P.S. couple of other things. After the fun and games I had with first charge on the LiFe pack I discharged it to around 3v/cell, and then put it back on the charger, which then worked perfectly. I only charged at 1a, so it took a while but did not turn itself off with that voltage error message.
Did find it didn't balance too well, so I have an ISDT Q8 on the way.
Also I did extend the balance leads. However in fitting some foam in the battery compartment I did find out the pack will slide easily out between the layers.
So removing the pack to charge is a piece of cake, but found out after I extended the leads.
One day I'll get things in the right order. (some hope)
J

[Peter Jenkins]

Hi Jeff

Just trying to get a sense of perspective given that we shouldn't be aiming to run battery packs so there is a danger of the dnd of capacity characteristics to become an issue.

 

As a rule, JR servos, unless of the more modern HV types, are designed to work on 4S NiMH (so around 6.5 v) which, about 10 years ago were pretty standard at 750 mAh capacity.  Futaba servos, in my experience, have been perfectly happy on a 5S NiMH (7.5 v tops).  I've found that JR servos will work quite happily when fed by a 2S LiFe and that's 7.2v fully charged.  I've had a JR servo misbehsve on a 5S NiMH and heard others say they fry on that voltage.

 

The 8.4 v comes from a fully charged 2S LiPo. HV servos are designed to cope with this higher voltage and all 2.4 Rxs seem to be rated to that voltage as well.

 

The regulator switches now give the option for unregulated to regulated at 7.5 v or 6 v.  They can also be used with LiPo, LiFe or 5s NiMH.  True they are significantly more expensive than the traditionsl switch but they don't suffer wear and can last a very long time thus recouping their higher initial cost.

 

As regards the JX servos, you could ask Chris Bond what his views are as he sells them.

 

Good to hear a new charger is on its way.

 

Hope that helps.

 

Peter

 

[Jeffrey Cottrell 2]

Hi Peter

Interesting. Hadn't noticed Chris stocked JX servos. Have to say, judging by the other stuff he sells, JX servos must be good. I have used them in many helicopters, and never had an issue, but still consider them to be a budget item.

Mind you, I did notice he sells Turnigy Motors too. These are an HK item, and definitely in the budget category. I also have used these and found them very good.

I have the 5045 he sells, to go in the Smart move, if I ever get back to it. Something keeps getting in the way. Wonder what that is?

Also had a change of heart on the throttle servo, so got a cheap and cheerful E-Max in there now, so will need to talk to George as well.

As regards end of charge characteristics, got some news on that as well.

I charged my LiFe, yesterday. As expected came off the charger at 7.2v but quickly relaxed to just under 7V. This evening looked to be holding at 6.9v. Even this well above the 6v level for the servos.

Anyway, put it on my discharger and set the level to 2.75/cell. For some reason my discharger doesn't seem to like going below 3v/cell but doesn't really matter because getting down even to that level, at a discharge current of around 3a took 50 minutes.

Imagine flying for almost an hour continuously.  Don't think I'll ever see it 'drop off a cliff'. (unless I happen to be slope soaring at the time, ha ha).

I have been using LiPo's for many years now, and never had one misbehave. All the horror story's I hear about bursting into flames, I firmly believe, are down to misuse of some sort.

Having said that, I wouldn't like to spoil that record by having one go up inside my flagship model. Since it is so easy to remove, I probably think I will charge outside anyway.

So, if the need ever arises (it won't) I could always get another pack and swap if necessary. All in all, think I'm covered on that score.

I got the ISDT charger because someone on the other thread said they try hard to balance correctly. My current charger doesn't seem too good at that, but if the ISDT is better, expect even the above figures to be improved.

The pack is back on the charger now, but charging at 1c rather than 1a. As expected charging is much quicker, but, if the charger is to be believed, it has put back in 2097Ma. If correct the pack must have been pretty much exhausted, but if I set 3v/cell as my lower limit that still represents 50 minutes of continuous flying. Good enough for me.

Changing the subject slightly.

Bought the charger from HobbyRC. Ok, not the biggest or heaviest package but they only charged me £2.95 postage. Meanwhile, trying to find a pair of Perkins wheels. Featherlight foam and small enough to fit in a jiffy bag. Had a struggle to find anyone charging less that £3.99 for shipping. Go figure.

Eventually found a reasonable price at Wireless Madness. Never used them before. Has anyone, what's your thoughts?

Jeff

[Peter Jenkins]

Never heard of Wireless Madness I'm afraid.

[Jeffrey Cottrell 2]

Hi Guys

Few fiddly jobs still to do, but the Excelsior is nearing completion.

Main task now is to find where the c/g should be. No plans or instructions, obviously, but nothing on the plane either to help.

So, I have Peter's book which will optimise position, but I need a good safe starting point.

Anybody built a 188 and can help, or can it be calculated?

Your thoughts?

Jeff

[Peter Jenkins]

35% back from LE at the root should give you a save starting position Jeff.  You may end up moving it a good deal aft of there once flying it.  You should also check how it flies in Knife Edge at each CG position - that is sometimes a yardstick for the optimum CG position.  What you are looking for is the least amount of divergence in pitch and roll when in KE.

[Jeffrey Cottrell 2]

Hi Guys

Quick note on Wireless Madness.

Same here, never used them before, but so far, so good.

Order placed Friday, arrived this morning. Posted Royal Mail 2nd class, so RM must take some of the credit, but next day shipping over a weekend can't get better.

Best thing for me (cheapskate, moi?) was they only charged £1.69 shipping, where everybody else wanted £3.99 or so.

+1 in my book

Jeff

[Ron Gray]

I've used them a few times, no problems.

[Jeffrey Cottrell 2]

Hi Ron, thanks

Based on both Peter and myself never having heard of them. was a bit worried. However judging by this initial order I would be happy to use them again.

Jeff

[Nigel R]

I've also used them, would happily use again.

[Jeffrey Cottrell 2]

Thanks Nigel, me too

Jeff