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Member postings for Jonathan M

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

Thread: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
03/06/2020 18:37:37

Now taken delivery of a 2nd 700mAh NiMH, so a question on 'best practice' with a new battery. Just charge and go fly, or cycle up, down and back up again, then go fly?

Thread: Walnut Scale Mr Mulligan
01/06/2020 22:25:53

Button is back to front. As the model is bound to need a good deal of nose-weight, might as well beef up the inside of the front cowling with balsa, then bore out to accept the parallel part of the button behind the flange for a snug fit. Also, unless the wire is long enough so that the hook protrudes properly out the back of the bayonet-former, I'd open up that hole a decent amount.

Re balance, things will be a lot easier (as with flying R/C) if you go for a slightly forward CG - obviously balance as per plan initially and then add weight during test-glides. Light lead fishing-weights pressed into blue-tak or clay will be useful, maybe form an opening at the base of the rear cowling former so you can load the lead in well forward.

Don't know how you'd start to add side- and down-thrust... given the bayonet system of attaching the cowl.

Maybe fit one of Derek Knight's adjustable nose-buttons?  third photo from the bottom

Edited By Jonathan M on 01/06/2020 22:38:45

Thread: The Lockdown Restrictions Have Been Relaxed. Who's Been Flying?
01/06/2020 09:34:10

Flying the Ahi lots in this settled weather of easterlies on various slopes within a 40 minute driving radius... but this one yesterday was an hour's walk from home!

The bowl isn't very steep or clean - lots of rolling 'moguls' to give the breeze random twist as it winds up the valley - but excellent and relaxing fun.

ahi may 2020.jpg

Edited By Jonathan M on 01/06/2020 09:36:18

Thread: Walnut Scale Mr Mulligan
01/06/2020 09:05:48

Very neat job on the VMC Cessna George!

We used Eze-Dope on my son's Sparrowhawk... my brain might have been shot as a kid sniffing dope and diesel, but his is still fresh! It obviously works well enough if you thin it with water etc, but I prefer non-shrinking dope thinned to 25% and given 2 coats if indoor model, 3 if outdoors.

01/06/2020 08:56:44
Posted by Dwain Dibley. on 31/05/2020 23:35:46:

I watched a video about "braiding " the motor, the rubber in this one is 2 X the length of prop to peg and when the winds fall off the prop drops down. do I need to braid, shorten, or just double up the rubber?

If the prop falls off at the end, that's because the nose-block or button is too sloppy a fit - thicken things slightly with CA... but let dry properly before re-inserting!!

Braiding isn't essential but it is neat and shortens the length nicely. Shortening the rubber length will just shorten the duration. Doubling it will double the power (disasterously) and halve the duration (irrelevant after the aforementioned disaster).

The videos used to confuse me, here's the simple method for small models:

  1. before tying the knot, double a short piece of masking-tape over one end and press the winder's hook through it,
  2. tape the rubber half way down it's length to a table,
  3. wind clockwise (i.e. normally) about 100-120 winds (that's 10-12 times on your 1:10 winder) will do for Mr M,
  4. remove the masking-tape bits and tie the ends (Don's method),
  5. starting at the knot, work the braids smoothly with your fingers towards the other end, then back the other way.

I normally smooth the braids after I've rubbed a little bit of silicone lube into the rubber - makes it all slip nicely - doesn't have to be perfect, and tends to improve after winding properly in the model a few times.

Then pre-stretch the rubber - all in Don's book.

Jon

Edited By Jonathan M on 01/06/2020 08:58:50

31/05/2020 22:42:21

Mr M looking very good!

Thread: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
31/05/2020 22:34:40
Posted by Martin McIntosh on 31/05/2020 21:14:35:

I am now gradually changing to LiFe packs and even a tiny 700 will happily supply digi mini servos or none digi standard size with ease and they seem to last for ever.

Are you using a voltage-regulator for the servos? Mine are rated for 4.5/6.0v only.

31/05/2020 22:32:44

Had another sesh with the Ahi this afternoon on a more local slope (five mile round-trip walk from home) but only marginal lift so a much gentler, more careful half-hour's flying: only 170mAh used, half that of the active aerobatics in the same timeframe previously.

31/05/2020 11:51:02

You've hit the nail on the head ED. There's clearly a world of difference between nudging a large soarer around bigger skies with 2000mAh for nose-weight and constantly whipping something like the Ahi with a third of the battery capacity close in to the slope.... although I'd add that the video link isn't of me flying (for a few years yet), that's Steve Lange on the US Pacific coast !!

Slope Aerobatics

Thread: Walnut Scale Mr Mulligan
31/05/2020 08:34:34

Ours was 2016. The airframe and prop weighed 21.5g, rubber was a 20.5" loop (twice length of hook to peg) of 3/16" weighing 4.8g, needed 5.0g nose-weight, total 31.3g so a wing-loading of 0.70g/sq in - just right for calm outdoor conditions.

The max breaking winds of this rubber motor was calculated as 1700, so a safe repeatable 80% was 1360, but even on 1000 winds (60%) it was doing 45 secs!

Jon's Record Keeping Dept

PS Just checked the dust-covered surfaces - it has a 1/64" shim for right-thrust, a 30mm wide card down-tab two-thirds down the left wing and a similar left-tab on the rudder.  The Kid is now too 'cool' to play any more and is at his mum's, but the first calm day we get I'm off with it to my local field!

Edited By Jonathan M on 31/05/2020 08:42:52

Thread: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
31/05/2020 08:21:12

How would I check the current draw of the servos?

They are quite hefty units for the light weight and small size of the Ahi, but it's got relatively big control surfaces and I'm running big travels with lots of expo.

This is how they tend to be flown (I'm scrappier on the sticks and have been flying on trickier slopes in gustier conditions): surfimp

Dream Flight DFFA009 12.4g Specifications
Body dimensions 23.4 mm wide x 9.4 mm thick x 26.2 mm high  
Max dimensions 32.1 mm wide x 9.4 mm thick x 31.5 mm high  
Stall torque (4.8V) 2.40 kg.cm  
Weight 11.5 g  
Lead length 15 cm  
Operating voltage 4.8V to 6.0V
Bearings 2 Ball Bearings
Gear material Metal
Case material Plastic
Motor type DC motor
Digital Yes
Programmable No
Supplied accessories 2 Plastic output arms, 2 Arm retaining screws, 4 Mounting screws.

 

Edited By Jonathan M on 31/05/2020 08:22:03

31/05/2020 08:02:06

Thx Peter...and now I can start working on the 'safety margin' of the Ahi's foam airframe itself!! laugh

Thread: Walnut Scale Mr Mulligan
30/05/2020 21:35:37

The Sparrowhawk is a lovely little kit, all the VMC wood and laser-cutting is spot on! Helped my kid build one as his first model about three years ago, flies extremely well - even took it to a SAM 1066 meeting on Salisbury Plain and played with the big boys!

Thread: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
30/05/2020 21:30:30

Back earlier from a session on Beacon Hill and just re-charged the 700mAh NiMh: 330mAh or half its total capacity was put back in return for half an hour's very active flying (11mAh per minute, exactly the same as Peter's LiPo above). I'll therefore leave the countdown timer at 30mins, with safe allowance for a bit of over-run. Just ordered another 700mAh of the same, so any given session can safely run for an hour... with lots of breaks and tea from the flask between flights!

Thread: Walnut Scale Mr Mulligan
30/05/2020 21:11:53

Sorry about the dicky stringers Dwain. Scalpel some 1/32 or 1/20 wide lengths off 1/16 sheet and use a smidge of thin CA to 'double' the cheese from the inside - will obviously involve stripping and re-covering the bottom tissue.

I almost never wet tissue anymore to shrink it - just waving the fuse or over a kettle for 30-60 secs gives an even, less fierce shrink.

Yay to the Don Ross book - for lubing the rubber use silicone lubricant from a tube rather than messy caster oil.

Thread: Aileron-rudder mixing
30/05/2020 14:03:24

Just read your last post Tim - maybe the massive mix on thermal is just based on his personal flying style rather than the model's requirements?

I always understood that - generally - one needs a bit of rudder to co-ordinate with ailerons to enter a turn, but then a bit of opposite aileron to flatten the wings for optimal lift while still using the rudder to maintain the turn. If there's already a CAR mix in place, then the second part is going to require a lot of "opposite" rudder so to speak.

30/05/2020 13:55:47

I know its not directly relevant to full-house thermal gliders, but since I've stopped mixing rudder to ailerons on everything (power, slope and thermal DLG), my flying got initially harder but gradually better.

The biggest thing that has helped me train my left thumb has been flying a bungee-launched 2mRES recently. The rudder is primarily on the left stick, albeit with a switch programmed to activate right stick also until I got used to using just the left one. I now leave the switch off all the time and happily nudge the model around with just my left thumb.

Moving back to the slope, now with a highly manoeuvrable Ahi, I'm suddenly able to start achieving basic knife-edge flight etc - all because my left-thumb has become better wired to my brain! Funny that.

Thread: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
30/05/2020 13:38:51

Those 2/3 AA look just the ticket Steve - never soldered up my own packs but can't be that hard really!

In the meantime the totally flat battery charged back up to full in 94mins, putting in 784mA at a new higher charge rate of 0.7C. It got nicely warm towards the end (showed 6.09v at 85mins) then settled to 5.90v initially after the lower peak-detect of 5mV stopped the charging altogether.

The discharge then took 81mins at the same 0.5A as the charge rate, pulling out 676mA until the voltage was 0.9v/cell then settled at 4.88v, i.e. Paul's "4.9v is flat".

The second re-charge has just now taken 90mins, put in 746mA, settled back down at 5.75v.

Off flying later... with countdown timer programmed in! wink

Edited By Jonathan M on 30/05/2020 13:42:04

30/05/2020 08:48:00

Thx for the suggestion but the Overlander AAA pack would be too long. The easiest solution is just carry a spare 700 exactly the same as existing, for which the cavity in the foam nose is designed to fit.

500mA is 0.7C, so will try that with 5mV peak detect, then discharge to 3.9v and repeat charge to help recondition.

Good idea to not play below the half-way mark! Now programmed a countdown timer into the model memory: say stop after 30 mins active flying, swap to fresh battery if want to continue flying, then measure amps put back in later.

30/05/2020 08:02:26

Frank, my charger can't go lower than 100mA on charge; seven hours at this equals 700mAh. On the discharge cycle I see you suggest a cut-off of 0.9v per cell; I've been doing 1.1v on my NiMhs as I was previously worried about damaging the packs?

LiFe is an option, which my charger can handle, but can I safely do this on servos rated up to 6.0v without extra gubbins?

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