DSM Excelsior re-furb

[Jeffrey Cottrell 2]

Hi All

Those following the 'To bec or not to bec' thread will know of my progress with the second hand DSM Excelsior.
However I have moved away from the original idea of converting to electric, so decided to start a new thread rather than contaminating the old one.

So, potted history:

Went to Wings & Wheels a few weeks ago, with the firm intention of not buying anything (yeah,right).
Always had a soft spot for the early Dave Smith models, so despite my best intentions I came away with two.
One was a Smart Move, but after having a good look inside, and the terrible way it was put together, decided it was not such a smart move (sorry) after all.
That's on the bench for a re-fit, read complete gut and start again.
Meanwhile the other was an Excelsior 188, with a Thunder Tiger Pro 120 pumper on the front.
Given my fleet has been all electric since can motors and seven cell nicads were state of the art, not sure buying a glow model was such a wise move.
Did look at going electric with that too, but after some help from a clubmate to get the motor going, I decided to stick with glow and get the necessary support gear.
So, this will be an occasional (very) thread posting what I find, and also asking for advice.
Bear in mind this will be my first foray into glow for a very long time, but also the biggest and most powerful model I have owned, so I'd rather check on things beforehand rather than ending up with (at best) a rather large hole in the ground.

More to follow

Jeff

[Jeffrey Cottrell 2]

Hi All, here we go.

Since I wanted to see if the engine would run reliably, first look was at the fuel system. Overall, pretty good.

Pulled the tank and found no gunge or gunk lurking inside. However, I did find the clunk tube was a little too long, meaning the clunk could suck itself to the back of the tank and cut off fuel flow. Shortened that a bit, and re-sited the fill and vent tubes. They had been fitted upright so were hard against the tank top. Again, not good for fuel low.

Replaced all the pipes. Probably not needed but the original builder must have had only short lengths available, so ally tube joiners all over the place. Firm believer in removing any potential sources of failure before they become an issue.

The model is RE with a pipe. The diameter of the manifold and that of the pipe differed, so the builder had used two bits of silicon tube, one inside the other. Ok so far, but where the two pipes sealed the tube was soft, so nothing for a cable tie to tighten against. Probably explains why, when it was running, seems more exhaust came down the outside of the pipe than through it. Found a short length of brass tube which fitted inside the inner tube, so cable tie can now get some purchase.

Also during testing the tube came completely off the pipe. Must admit it sounded good running open pipe, but probably wouldn't meet 82Db.

So, used the old trick of putting a couple of turns of thin wire round the pipe about an inch from the end, then coating with epoxy. The tube slides over this then the cable tie goes on the far side. That ain't coming loose anytime soon.

Now, first question.

As a matter of course I replaced the on/off switch. Not sure of the history of the old one, so £6 or so for peace of mind was a bargain.

To fit the new switch I had to enlarge the hole in the side of the fuz, and I was expecting to have a battle with the ply internal doublers.

No such issue, knife went straight through. As far as I can tell, the fuz does not have doublers at the nose end. For a model this size and weight, that seemed odd, but I'm not sure whether it should have.

Anyone put together an Excelsior 188 and can confirm yes/no?

That's all for now. Chapter two to follow

Jeff

[Jeffrey Cottrell 2]

Hi All
Had the model out again today. Lots of work still before it's flyable, so just playing with the engine, trying to refine the settings.
Looking pretty good so far. Starts readily, runs smooth, tickover fine and transition to full throttle without a hitch.
Seems still to be a little rich. Plenty of smoke coming out the pipe, but maybe that's supposed to be. At least ensures a good flow of lubricant. Using Prosynth 5% seems a good match.
With it running full chat, put the tacho on it and got 7300rpm. This on a 16 x 12 prop, how does that sound?
Have to say if that's sufficient to fly the model, tempted to leave it as is. Everything else looks so good, don't want to spoil it.
Meanwhile attention turned to the servos.
Model has 3003's all round. Probably perfectly serviceable but pretty old now, sure I can do better.
In the process of dismantling a couple of old helicopters which I no longer use, and that gives me a range of servos, all metal gear digital, and working fine.
Got a couple of JX PDI 4409 MG, which are low profile so perfect for the wings.
Mentioned these on the other thread, and Peter suggested I check the centering before I used them.
This I did, and they were pretty much perfect. Obviously lead wires were not long enough to reach the wing centre. I'm not a great fan of joining wires, so I pulled the servos apart and soldered longer wires direct to the board.
Doing it this way also meant I could change the layout so the wire came out the side rather than the end.
If I've got my measuring right, they should come out right opposite the hole in the core to carry the cable to the centre section.
Relieved to find the old cables could be slid out. On a lot of models they are glued in, so can't be removed for maintenance.
Only thing I found to rectify was on one servo the mounting holes came close to the edge of the ply plate, so the edge had split away. Hmmmm.
Would have thought that the obvious next step would be to cut the plate away and fit new. Not this guy.
Decided since the screws wouldn't hold he would glue them in instead.
What is is with gluing in wing servos?
The Smart Move also had both glued, did a bit of damage to the foam core getting them out.
At least this wasn't as bad.
Both servos are now out, but because I don't have to space the plates far enough to acommodate the lead wires, I will re-make all the mounts with just enough gap to allow the servos to slide in.
Works for me, now what's next?
Jeff

[Jeffrey Cottrell 2]

Hi All

Just a quickie this time.

Not sure how valid it is, given it's all based on estimates, but I found this.

On the bec thread, I looked at a possible electric set up. The one I chose gave theoretical figures of 6900rpm and 11 lb thrust on a 16 x 10 prop.

Having got the glow motor running pretty well, I have tacho'd it at 7300 on a 16 x 12 prop. Appreciate the higher pitch prop will take longer to come 'on song' but when it does should produce thrust north of 11 lb.

Not definite by any means, but encouraging nontheless.

Onward and upward

Jeff

[Jeffrey Cottrell 2]

Hi All

Question time, servos.

Replacing the 3003's on the Excelsior with something a bit more upmarket. Ailerons are sorted but I am thinking about rudder and elevator.

On an aerobatic model, which is more important, torque or speed?

Recently dismantled a couple of helicopters which are no longer required and left me with a selection of servos to choose from.

Couple that spring to mind are JX 6221 at 17.25Kg but only 0.16 transit or JX 6208 at 6.8Kg and better transit at 0.09.

Will bear in mind Peter's advice to check centering on those, but which would be more suitable?

Thanks

Jeff

[Peter Jenkins]

For F3A, "standard" speed servos appear fine.  For rudder, generally, higher torque servos are specified than for aileron or elevator servos ~ 11 kg cm seems standard.

[Nigel R]

12 hours ago, Jeffrey Cottrell 2 said:

On an aerobatic model, which is more important, torque or speed?

 

Neither; accuracy.

 

[Jeffrey Cottrell 2]

Hi Nigel, thanks

Short and to the point, but surely not quite right.

Understood, accuracy is important, hence in my post about checking centering, but you need enough torque to move the surface against wind resistance and enough speed to complete the manouevre when you want.

To my thinking, the correct servo for a particular purpose would combine all three.

Jeff

 

[Nigel R]

1 hour ago, Jeffrey Cottrell 2 said:

Short and to the point

 

as intended?

 

1 hour ago, Jeffrey Cottrell 2 said:

but surely not quite right.

Understood, accuracy is important, hence in my post about checking centering, but you need enough torque to move the surface against wind resistance and enough speed to complete the manouevre when you want.

 

You asked what was more important, from two choices. My take - accuracy is more important than both torque and speed.

 

Torque, yes, you need enough, plus a safety margin, this is a simple 'is it stong enough' question. Safety margin is your call.  How much is enough? Your old 3003 with 3kg/cm is enough torque for ailerons and elevator. As for rudder, something around 6kg/cm there. You may disagree - fit bigger, no problem, don't forget an appropriate RX power source.

 

Speed, any regular servo is quick enough, I think, even those plain old 3003s. As a disclaimer, however, I am not Jase Dussia doing an exhibition flight containing rifle rolls with course corrections, nor am I CPLR winning yet another first place, I cannot personally tell the difference in the air between a fast servo and a slow servo, especially if I am trying to fly smoothly and the sticks are not moving quickly.

 

I would say different on a 3d model. Fast and powerful is way more important than accuracy.

 

If you are the aforementioned top guns, you actually need all three.

[Jeffrey Cottrell 2]

Hi Nigel

Thanks for the quick reply and the clarification. Sorry, I misread your post. First thing in the morning, brain not firing on all cylinders.

Much clearer now

Jeff

[Bruce Collinson]

Lucky bunny, finding one of those.   Will watch progress with interest.

 

BTC

[Peter Jenkins]

Most servos are much faster than a FW aircraft that has inertia as well as aerodynamic damping to overcome.  At the slow speeds 3D 3D manoeuves are carried out speed is more of an issue than for precision aerobatics where centreing accuracy followed by torque are the key criteria.  Digital servos are preferred in precision aerobatics as they will actively hold the demanded position whereas an analogue, once it reaches the commanded position can suffer blow back which can distort the shape you are trying to fly.

 

OTOH, most pilots will distort the shape more than the servo!

[Jeffrey Cottrell 2]

Hi Guys

Bruce

More correct to say it found me!

Wandering down the trader line at W&W, passed a stand which had this huge glow aerobat front and centre. Took a glance, decided it was not for me and walked on.

On the way back had another look, and I heard a little voice saying 'buy me, buy me'.

After this happened a couple more times, went into the stand and made a silly offer, which they accepted. Struggling back to the car, saying 'what have I done'.

Having got into it, more and more looking forward to getting it in the air. Lots still to do, but mostly my preferences, like servos, but determined to see it through.

While researching DSM in general, came across a guy called Geoff Hodgson from Foam-Wings.co.uk. He was talking about putting the DSM kits back out.

Think he was starting with the Dalotel, and not sure if the big Excelsior was part of the plan, but you never know.

Peter

Mulling this over long enough now, all servo'ed out. I know what I want on the Excelsior, but it's complicated. The clubmate who helped me out with the motor, as a reward I offered him servos for his new build. Trouble is, I don't know what he's building or whether he'll take me up on the offer. Apart from being standard size, no idea what he needs. Need to keep some flexibility there.

Also, at some stage, got the Smart Move to think about.

Decisions, decisions

Jeff

P.S. Nigel

Never be a Top Gun, possibly at some stage a cap pistol  ?

[Jeffrey Cottrell 2]

Quick add on

Nigel mentioned 'appropriate power source'. Currently (ahem) using a 4cell 2500 NiMh pack. Is that ok, or could I do better?

Jeff

[Peter Jenkins]

I would steer clear of 4 cell NiMH packs as they are likely to lead to a potential brown out on your 2.4 Rx.  I'd use 2 cell LiFe cells (I think you can get 2,500 mah ones) or else use a 2 cell LiPo but use a Powerbox switch to drop the voltage to 6.0 V or else use HV servos and use the full voltage of the 2 Cell LiPo.  Best to use the voltage reduction feature of a Powerbox switch as this gives your servos a constant voltage so their performance stays constant.  

 

I have used 2S LiPos (850 mAh) packs on my electric 2 mtr and they are good for 4 or 5 flights.  Each flight is 8 mins.  With an IC engine banging around, I would expect a higher current draw from servos so maybe a larger capacity LiPo will be needed.  I carry a couple of cells charged up in case I fly more than 6 flights - which is very rare!

[Jeffrey Cottrell 2]

Hi Peter

I must be behind the times, I thought brownouts were a thing of the past.

Anyway, I plan to use a FrSky V8 receiver, and operating voltage on those is 3-16v. Don't think that'll be an issue.

2 cell LiFe, I believe, is nominal 6.6v, so that would be fine as well.

Did a google search for a Powerbox. Not sure if I was looking at the right thing, but the one I saw was £91. that's more than the model cost!

Am thinking about going to 5 cell NiMh for a bit more punch. All the figures I am using are for 4.8v.

Trouble is, although nominal 6v, hot off the charger a 5 cell pack is nearer 7.5v. I know the rx will be fine on that, not so sure about the servos.

Instinct tell me no problem, but I have a message in to JX office, just to confirm.

If they say ok on 8.4v then a 2s LiPo is back in the mix as well.

Waiting to hear

Jeff

 

[Nigel R]

6 hours ago, Jeffrey Cottrell 2 said:

Hi Nigel

Thanks for the quick reply and the clarification. Sorry, I misread your post. First thing in the morning, brain not firing on all cylinders.

Much clearer now

Jeff

No worries, I could have written something a bit longer and clearer in the first place ?

[Jeffrey Cottrell 2]

Hi again, Peter

Forgot to mention I read the reviews of your book. Didn't tell us anything more that we've already found out.

Well researched, well written, and a mine of information for those budding CPLR's out there.

Note I don't include myself in that throng.

Jeff

[Peter Jenkins]

Hi Jeff

 

Thanks for the kind words.  

 

It's important to remember that there is no substitute for practice and for practicing the right thing.  Even the "natural" pilot gets lucky by practicing a lot!

 

Look forward to seeing you at a competition soon Jeff!

 

Peter

[Jeffrey Cottrell 2]

Hi Guys

Peter

Quite right too. I believe it was a golfer, when asked about luck out on the course, who said 'the more I practice the luckier I get'.

Never a truer word spoken.

Not sure about meeting you in a competition. Let's get the model in the air first!

Meanwhile, general question.

Posted on RCGroups about max voltage for servos. Answer I got back I'm not entirely convinced by, but he also said LiFe is better. Why?

LiFe's are nominally 3.3v, but off the charger they are 3.6v, or 7.2 for 2s. Not far short of the top voltage on a 5 cell NiMh pack.

Main disadvantage of a LiFe pack is it has to be removable for charging. NiMh are basically fit and forget.

So, I'm missing something. Anyone enlighten me?

Jeff

 

[Nigel R]

14 hours ago, Jeffrey Cottrell 2 said:

I must be behind the times, I thought brownouts were a thing of the past

 

Brownouts, the myth that won't die...

 

4.8v / 60.v nimh are fit and forget. Slow charge overnight, easy. Voltage drop on AA Eneloops is well documented and they hold up well until around 5A. They are much maligned, I think. However, if you are fitting fancy dandy servos that can draw a lot of juice then AA might not be big enough; sub C are starting to get quite bulky.

 

[Peter Jenkins]

Brownouts may be a myth but I lost 2 aircraft, one a Wind S 110 to brownouts when using the JR/Spectrum kit.  Since moving to JR's own protocol in the XG series and using a 2S Lipo through a Digiswitch I've not experienced a problem.  

 

Jeff, you can charge LiFe cells in-situ.  LiFe cells are used in almost all laptops and there have been extremely few cases of problems experienced during charging.  I have used LiFe cells (2500 mah) in my petrol bird for both the ignition and Rx circuits and these are charged in-situ in the fuselage - I do have balance charge lead extensions on both so they are balanced on every charge.  LiFe's can be charged at 1C in an hour (although I usually only go to 95% capacity) which is a lot faster than the NiMHs used for Rx power.  Of course, a 5 cell Enelope is another very good solution as they don't lose charge after charging at least over a couple of months.

 

The JR servos that are rated for 4 cell NiMHs seem quite happy with the Digiswitch regulated voltage of 5.9 volts.  However, I found that with a 5 cell NiMH the voltage caused the servos to misbehave.  Futaba servos appear to be quite happy with 5 cell NiMHs.  My latest 2 mtr has HV Futaba Sbus servos (even though I don't have Sbus in JR) and they will take a 2 cell LiPo at full voltage - still seems odd to see 8.4 v as the Rx voltage compared with the 5.9 v I'm used to seeing.

 

Just my experience of course.

[Nigel R]

Quote

Since moving to JR's own protocol in the XG series and using a 2S Lipo through a Digiswitch I've not experienced a problem

 

Spektrum kit that is not the really early 1st gen stuff will also not have brownout problems, the voltage cutoff for their RX has been 3.5V for a very long time, lower than the practical limit for servo operation. This may not be the right place for the discussion but was it definitely a brownout? and not a loss of signal from interference or shielding? those early 2.4 protocols were technically quite poor from a robustness point of view. Also, a suitable power source would not have allowed the voltage to drop either. 

[Jeffrey Cottrell 2]

Hi Guys

Been racking my brains trying to find one distinct advantage of LiFe over NiMh, or vice versa. Can't seem to find one.

Didn't help when I wondered about a 3 cell LiPo running through a regulator like this, one of which I just happen to have.

I have a dartboard with three labels on it, LiFe, NiMh or LiPo, and a dart at the ready.

Might just make my decision that way.

Many more decisions to be made on this bird. If I take as long with those, might never see the light of day.

Help

Jeff

[Nigel R]

Only thing I would steer by, simple tends to be reliable. Feed the servos and RC with a battery that needs no complex kit betwixt it and said devices.

 

4 hours ago, Peter Jenkins said:

LiFe's can be charged at 1C in an hour (although I usually only go to 95% capacity) which is a lot faster than the NiMHs used for Rx power.

 

You can charge NiMhs at a 1C rate.