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Member postings for Nigel R

Here is a list of all the postings Nigel R has made in our forums. Click on a thread name to jump to the thread.

Thread: engine refurb
24/01/2020 08:54:16

You buy stove glass cleaner?

Newspaper, make wet, pick up some ash on it - removes crud from the glass almost instantly.

As per Don's post, I've used washing powder in an old saucepan before - seems to work ok.

Thread: SWEET & SMART Acronyms meaning??
23/01/2020 10:31:38

Switch on, yep, still relevant.

Model selected, I have to pick the right model before going any further on my TX(s). Meter, my meter is digital, so what, I check it.

Aerials, one of mine has an external aerial, could be damaged etc etc. No aerial? Lucky you.

Rates, I use rate switches for several models. Flight modes, use them? Pretty much an equivalent. Arming switch? another modern equivalent. They're all switches. Want to add those to the list, fine. "rates and switches" works for me. How detailed do you want?

Trims, funnily enough, a visual check to make sure no trims are applied. If I had to dial in a load of trim last flight, and I forgot, because I was busy flying, then something might be amiss with the model. As I always try to adjust linkages back to zero trim then the trims should always be zero (at most a couple of ticks one way or other, see e.g. snakes and temperature).

 

Edited By Nigel R on 23/01/2020 10:32:41

Edited By Nigel R on 23/01/2020 10:34:08

Thread: Capacity checker accuracy?
23/01/2020 10:18:56

Checker says 95%, I know I've charged the battery and I fly with it.

Checker says much anything else, battery goes home for charging, I don't fly it.

If it consistently reads <25% when I land, I decrease my flight timer a bit.

These things are just voltmeters, really. And quite cheap ones at that.

Capacity can only be rated at a particular discharge rate (usually something quite low) from fully charged to fully discharged. Manufacturer's idea of fully charged and fully discharged is likely to vary from yours. The temperature affects matters, too. An exercise for your normal charger to perform, if you want. You probably know this already.

Thread: Dereck Woodward Bigga Bit
23/01/2020 09:39:11

The fuselage as pictured above weighs 7oz. It is about as strong as a Challenger tank.

I think a large chunk of that weight comes from the 3mm liteply sides. If I was going with liteply again on this size fuselage, I'd go down a thickness to 2mm. One problem for the thicker stuff is that there isn't much scope to cut big holes in it, on something this size.

Not sure where else the weight could be shaved off, there isn't that much structure in something this big. All the balsa in the fuselage has already been thinned down a bit, to 3/32, from the 1/8 called out on the plan.

I've obviously added a good few oz's in the U/C. But you can't do touch and gos without a set of wheels.

On a slightly different note, I think I'm about two thirds complete now. Main (more small stuff) jobs remaining before covering - sort out the lipo mount and access hatch, the wing tips, elevon bevels, and then I am covering. Errors and omissions, etc.

23/01/2020 09:25:08

I think I've reached the point where the major woodwork is done, and all the jobs now are 'not much to see' type stuff.

20200123_081728.jpg

That said, the small jobs done last night were

the fin separated from the rudder

the fin aligned with fuselage / wing

the fin stuck on

rudder bevelled

1/32 ply added to rudder to reinforce the horn area

the top rear sheeting sorted and attached (made up from a few offcuts of 3/32 scrounged from the scrapbox)

Thread: 6 Turning 4 Burning
22/01/2020 13:12:19

Answered here

**LINK**

which states the same fuel used for both. Would make a lot of sense to run a common fuel pool.

The wikipedia entry suggests the jets were for improving takeoff performance, and for high altitude cruise / dash, and with all 10 going it was more maneuverable at height than most contemporary fighter aircraft!

22/01/2020 10:14:45

"It would prevent having to plan flying several days ahead of time and then being left with piles of batteries to discharge if you didnt go."

I think you're overthinking this electric business Jon. Down in the small end of the pool, it doesn't need that much pre-planing.

I leave my packs charged all the time. Yes, lifespan is reduced - a tiny bit. If I didn't have them ready to go, I wouldn't bother with the electrics. This is a no brainer for me with the small cheap 3S3000 kind of size.

A charger with a couple of parallel boards could do all 10 packs in one go, especially in the 3S 3000mA sort of size which would equate to the 30 four stroke level of power.

I use a reasonably priced Hobbyking Reaktor which will do 20A and that would charge up one flight's worth of small packs in one hit - yes that's probably a 90 minute charge but if you double up (or more) on chargers then you're properly cooking on gas.

It wouldn't sound the same as 6 four strokes though!

Thread: First generation acrowot tail fin
22/01/2020 09:29:26

I would use epoxy to stick the fin on. Then some soft block to fill the missing area on the one side of the fuselage.

Thread: Dereck Woodward Bigga Bit
21/01/2020 22:51:51

Fin and rudder structure tonight - just a bit of foamboard with some laminations of 1/16 around the edge. Dead easy. will need reinforcement around where the control horn will go because that foamboard is, how to say, squashy.

21/01/2020 22:43:18

20200121_213009.jpg

Thread: Flat plane wing question
21/01/2020 21:09:04

have a feeling there was a chris foss glider with a wing made from two lengths of 1/4" thick wood, for 6' total span.

still used a very narrow chord, only a few inches (4"?) mind, so very high aspect ratio, sort of 15:1 type ratio.

Thread: 6 Turning 4 Burning
21/01/2020 16:46:07

That you are!

Sounds interesting - not much around with that configuration.

Thread: Theory of the operation of a servo
21/01/2020 15:02:11
Posted by Peter Christy on 21/01/2020 14:34:42:

Its actually not too difficult to apply a crude form of velocity damping to a conventional "analogue" servo by feeding some of the back emf from the motor (during the "off" period) to the pulse stretchers, and most amplifiers do this. It helps in controlling overshoots on light loads.

every day is a school day - fine points of analogue circuitry was/is not my strong suit

21/01/2020 13:52:44

"I stand to be corrected, but this is my interpretation of how a digital servo works"

You can see the digital PWM in effect quite clearly around 10:50 in the video linked above.

It is exactly like analogue PWM, but at a higher frequency.

As Pete has explained quite well, either analogue or digital can output anywhere between 0% and 100% power.

However, I would say this again, the most important difference is that the digital controller can drive the motor with more power and accuracy, when the error between desired position and actual position is very very small, the main reason for this is that the digital amp can implement more complex feedback processing, beyond just the simple 'proportional to error' that an analogue will do. It can also add rotation speed, and acceleration into the mix*. This gets better accuracy at low errors. You can't really see that stuff on the scope trace. All you can see is the PWM implementation.

* you can do it with analogue, but, more components needed, with tighter tolerances, more cost, etc.

Edited By Nigel R on 21/01/2020 13:59:48

21/01/2020 10:13:51

**LINK**

Bruce provides a pretty good overview of servo operation here.

21/01/2020 10:11:41

"Average these pulses out and the voltage would be much higher than the analogue equivalent"

I'm not sure you understand the control theory behind analogue and digital difference amplifiers. And nor does the guy in that video, it's 13 minutes of red herring talking about the PWM rate. Which is the least important aspect of the servo.

It would be perfectly possible to make an power equivalent digital version of an analogue servo.

It would be perfectly possible to make an analogue servo that had 300Hz PWM output.

Analogue servos ran at 50Hz because - traditionally - they were hung on the end of the 35mhz decoder, which (guess what) had a frame rate of 50H; the servo ran at the same speed to minimise complexity.

In a digital servo, the control signal is processed differently. This opens up some possibilities over and above the analogue servos.

The major difference in the digital servo is that the difference amp - being software - can be programmed however the manufacturer likes, and it can put out very high power much quicker than the analogue. In engineering terms, the digital amp can implement a higher order difference algorithm to figure out the drive voltage.

(none of this is visible from looking at a scope trace of the motor drive signal).

The implementation of the difference amp is what is responsible for determining how good a servo is at holding a position under load, any overshoot it suffers, and centering accuracy. An analogue circuit, there are less elements to play with to get this right, all the elements are physical components, so component tolerances affect its performance and that has to be factored into the design. With a digital amp, more accurate control is possible, their can be more simulated elements in the control algorithm, and none of them suffer from tolerance or lifespan issues.

It has little to none to do with the PWM frequency.

Thread: 7 Day challenge Nigel Hawes 30" Tucano...............
21/01/2020 09:49:10

well done!

Thread: DX9 Tx Battery Warning, Warning!
21/01/2020 06:47:25

It wasn't 95% discharged.

Figure on charging efficiency of 80% or so. I forget the exact figure.

Ie you put 3000mah back in the pack. Or thereabouts.

Gives 25% remaining. Assuming the 4000mah rating is honest.

The warning is there to avoid battery damage IIRC. Instant damage starts around 3v per cell. This is much lower than "flat" or fully discharged to 3.4v - which is a nominal figure trading off capacity per use against pack life of course.

During high discharge you could easily see 3v terminal voltage which instantly recovers when the discharge stops.

Thread: DB Hurricane paint and finish.
20/01/2020 17:10:35
Posted by Don Fry on 19/01/2020 17:36:49:

That point in a build where there is a months worth of bits to do. Nothing much to show. I am amused when someone is selling a bare airframe, not fitted together, no bits done, and the say 80% complete. That is still a nice colour scheme.

To be fair (and I have kept some fairly OCD logs to back this up), if I have a bare airframe, ready to cover, I'm about three quarters done.

Note, my 'ready to cover' also means I have installed (and removed) all the electrical and motive power already. Other definitions of 'ready to cover' are possible!

The above may apply very badly to scale masterpieces with a fistful of finishing work and detail stuff.

Thread: Recommendations please
20/01/2020 16:04:43

If you're looking at charging at the field in that kind of time, I'd use a single charger, do them one at a time at a 'one hour' charge rate. Any of the 4 button jobs should do it.

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