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Radio DT aka RDT

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Guest

Gentlemen,

RDT systems are a good way of minimising a long retrieval or preventing an excursion into a cropped field, wood, lake or housing estate and I am on the point of buying/making one.

The BMFA Free Flight Rule Book para 3.1.1 suggests.....'that a single transmission for the purposes of DT is allowed for free flight models. The rules disallow transmission on 27/35/40MHz and recommends use of the 2.4GHz frequency'.

I might not be reading this correctly but as far as I am concerned this would allow me to rig up a free flight DT system for BMFA competition using the bones of a current 2.4Ghz RC system. This would be at a quarter of the cost of some of the current commercial RDT systems and would prevent me buying ever more kit to fill the workshop. I have not seen anyone at a competition using this method and am being cautious before I get stuck in.

Is this BMFA legal?

Has anybody done this?

Any other comment?

Regards Ian

 

 

 

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martynk

Hi Ian

I believe that Phil_G may be developing a 2.4GHz R/C DT system and he lurks here occasionally. It may be worth PM'ing him. He is a very competent engineer.

Can't comment on the legalities or practicalities of your solution as I am no longer a Fee Flighter (except in spirit).

 

 

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PeterT

Hello Ian

To the best of my knowledge RDT is legit for BMFA FF competitions and I've seen it used on a fair few occasions.

If you want further information on 2.4 'homebrew' RDTs have a word with Gordon Warburton the next time you see him (this weekend at Luffenham perhaps?). Also, if you go to the SAM 1066 website and look through the 2015 issues of the Clarion newsletter you'll find details of Gordon's outfit. From memory the Rx of choice is the Lemon and the Tx uses a standard 2.4 module plus an add on board to provide the DT pulse. It's all explained in the article and Gordon or a chum can provide the add on board for around ten to fifteen quid.

My only other comment about RDT is that I believe that it's NOT the answer to a maiden's prayer. I (and just about everyone I've spoken with) find it difficult to assess with any real accuracy whether the model is in front of, directly above, or beyond any trees/obstacles. This is particularly the case when you are peering through bins up at a 45 degree angle at a model. Nevertheless an RDT should be useful for trimming on small fields when the model isn't that far away.

Cheers

Peter

 

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PeterT

Ian

 

Over a cuppa I've ascertained that Gordon's article is in the July Clarion. If you are only interested in the airborne end, there's some information from Nick Pepiatt in the April edition

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Guest

Peter,

Many thanks for the links to the Clarion article on RDT systems. I was aware of Leo's stand alone but thought that the price was a bit stiff. I am taken with Gordon W's solution, nicely 'steam punk' . I will seek Gordon out at Luffenham this Sunday and attempt to extract the PIC chip and pcb necessary to get a system up and going. I have been tempted back to E30 By Rod B and will use the RDT system first on some resurrected models for Nats 2016 duty.

Best regards Ian

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PeterT

Hello Ian

 

I had hoped to see you at Luffenham for a chat, but now it's  been cancelled due to the poor weather forecast - I'll go to the pub instead.

I've been corresponding with Rod on E30 and he told me that he had goaded club members to fly E30 on the basis that if he could win the Nats, it must be easy. We have to watch out for that man Page the air picker though:D I suppose I ought to do some more testing and build a new model!

Cheers

Peter

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Guest

Hi Peter,

Rod has indeed tempted Mick Page (hlg) and Peter Gibbons (P30, Coupe) into the heady world of E30 FF electric. Both did well flying loaned models at the Luffenham 8th Area bash and are beavering away on new stuff for 2016 with Rod as mentor/provider. Peter Adams , also a rubber advocate is building an E30. I decided to join them in this endeavour, nothing like a decent team to spur things on.

Shame about Luffenham, will have to get to Gordon another way.

Best regards Ian

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Phil_G

Hi, where Gordon refers to the S/C enthusiast who does the conversion electronics, thats me.   I can do a very simple 1" square RDT encoder very cheaply.
Gordon has since moved into creating his own RDTs but his first few were mine, the photos in his article show the early version which was much larger and based on my single-channel emulation encoder - the current one is much smaller, see attached pics.

All you need to do is to take the red & black wires to a battery (via an on/off switch), take the 3-wire to the RF module (neg, pos, PPM) and wire the black & white pair to a button.  Very straightforward.  If anyone would like to follow this up just drop me an email,  philg@talk21.com  

Cheers
Phil 

PS thanks Martyn!

 

new_dt.jpg

remote-dt.jpg

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Guest

I prevailed on Phil for one of his trip encoders and ordered a 2.4GHz RF module and Lemon RX on Ebay. I slipped up and ordered a ‘DIY’ RF module which has a few more connections but has the added advantage of an external ‘bind’ switch. To my complete surprise the RX ‘bound’ to the TX first time and the servo duly rotated 90 degs on a button press.
First time electronic success does not often happen  and I am well chuffed at the outcome. TX cost is about £40 but the switches/enclosure/heat shrink and connectors came from stock….say £5 for the lot. The allegedly full range RX stands me £8 and I need to package the battery (50mah 1s) and servo onto a ply plate. I will range check it when the weather has calmed down but do not expect any issues. Well done to Phil and fellow ‘men in a shed’  for providing the wherewithal for a neat cheap BMFA legal RDT. Probably going on a FF dlg for next season to replace a  viscous timer which always plays me up.

 

2.4GHz_DT 003.jpg

2.4GHz_DT 002.jpg

Edited by Guest
typo

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Jef Ott

Just out of interest, Ian,

Am very suitably impressed, my success with electronics is somewhat rubbish, but as I am considering doing similar with small FF Cabin models...

1) what does the rx weigh?

2) is there a fail-safe function on the rx?

3) what servo is it, what does it weigh?

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Guest

Hi Jef,

The RX I used was 2.7gms but Lemon do one at 1.7gms without pins, if you fancy a bit of micro soldering.

Fail safe...not sure...I had no instructions with it and did not test for this condition.

Any servo would do I grabbed the first one out of the spares box...typically 2-3 gms but triggered on a mousetrap release. The Clarion articles in a previous post show a good installation. Choose a servo with a really bad plastic gearbox so that gear train friction keeps the stab in place. I suspect that the servo is not powered until DT is required. So probably not fail safe.

I can forsee the day when FF CD's will insist on RDT. The PMFC is active in this respect as our flying site is tree bound and close to the Nene.

Did you get the Kalper back?

Regards Ian

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Jef Ott

I had seen servos of 2.5g advertised but had not seen a pic of one. Thanks for that, and the advice re friction in the gears. Yes I always get the Kalper equipped Bantam back. I had felt awkward about using radio on the OW FF field, otherwise I would have used the rc that is in it! The little basic Tx you have is far less objectionable. :)

 

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PeterT

A belated response from me!

 

Ian, as usual you've done a very neat job with the RDT set-up, and I suppose I ought to get off my backside and cobble one together - note to self, contact Phil G to buy the encoder:rolleyes:

However, I feel I must sound a word of warning here, namely that an RDT isn't the answer to a maiden's prayer that some claim. You'll never put a model in a tree again, or land in the Thames (Port Meadow) are comments that have been made, which rather gloss over the practicalities - namely, it's very difficult to judge depth (distance), is the model in front of, directly above, or beyond the trees (or obstruction)?

Invariably I get it wrong, and thought it was me until the flying mates I discussed it with said they had exactly the same problems. It's very difficult to judge where the model is, especially peering through bins up at a 45 degree angle. Also there's the temptation to let the model fly a little longer - just one more glide circle, I have RDT - pas de probleme! A noted US FF glider flyer was bemoaning his fate on the SCAT website a few months ago - he thought he could achieve one more turn and still land on the field - wrong - in landed on a busy highway and he had a sense of humour failure because a motorist ran over it:).

By way of an example, here's a photo of a model of mine in a tree at a recent contest in Italy. This tree was sitting in the middle of a field with no others around for miles - le loi du sod. I thought the model was going to hit the tree, but both my mate and the official timekeeper considered that it would miss it. For once I was right, but wished I wasn't - luckily it was a smallish tree!

Keep up the good work

Coppa Fea 010.jpg

Coppa Fea 008.jpg

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PeterT

ps Sorry chaps, I note that I've already bent your ears regarding difficulty in judging distance. Please put it down to senile decay and I'm slapping my wrist now :blush:

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Guest

Peter,

I too have some reservations re RDT but intend to trial it on a FF dlg where after 60s, the thing might be  visible without binocs. Am going to see how I get on with it but its another set of actions to complete or forget to do in the heat of the launch into perfect(?) air.

Am most impressed at your ability to DT into the only tree for miles around (1000:1) and will seek to repeat  this event with some resolve. I have done cow pats in the past but lone trees have evaded me.

BTW PMFC E30's are amassing mentored by RB....be afraid?

Ian

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PeterT

Hello Ian

I'm sure that in many cases an RDT is good, especially for trimming on small fields, and I certainly intend to try it. It's just that some of the claims I've seen make it appear that it's infallible. Perhaps RDT is infallible (subject to usual electronic whoopsies) but the human element certainly isn't.

I wish that I had DT'd onto the tree as it would of meant I'd maxed - sadly the model flew 100 yards or so crosswind at which point the tree leaped up and grabbed it :rolleyes:

Glad to hear that Rod is galvanising people into E30 action. What timer is being used, as I know that Bert had cobbled together a model a year or so ago using the simple Peterborough timer? I'd best get building a new model then as mine are a bit long in the tooth.

Cheers

Peter

ps how's the animal?

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Guest

Peter,

Do have a try at  Phil_G's offering , the method is very easy to duplicate and only requires a bit of soldering.

I used the 'DIY' Orange RF module but the Futaba variant is probably easy to find.

I am trying a Pboro FET timer as a controller. It does have some limitations but is small, light, cheap and easy to make.

We lost Sky to cancer a little over a year ago, but Bonnie came to us a while ago. She has now grown in to her head and ears.

Regards Ian

12_weeks 003.jpg

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Phil_G
On 16/11/2015, 09:09:57, boffin said:

I suspect that the servo is not powered until DT is required. So probably not fail safe.

Failsafe depends on the particular receiver Ian, some dont have it at all, some have it only on the throttle channel, some eg most Frsky receivers have it on every channel.  The trend now is for failsafe on all channels but there are still receivers with only throttle failsafe, and some with none, eg the Frsky VD5M.

The servo is powered all the time the receiver is switched on, so it will resist any externally-applied force with all its torque.
This effort of course gobbles batteries so its as well to devise a trip mechanism that applies minimum force to the servo. Gordon uses a mousetrap idea, other than an insignificant amount of friction theres no transferred force from the DT. Note that the wire doesnt actually connect to the servo arm, it rests under the arm, just like a mousetrap trigger:

dt2.gif.0e258c320a3456f88025dd9b02c436e4

dt1.gif.420f4a082393be97f7c4986e6ef4a474

 

Cheers
Phil

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Guest

Phil,

Thanks for your post but I am afraid I have to disagree with you on one small point and that is on not powering the servo when it is doing nothing. The first pic shows an 0.9m FF dlg to BMFA HLG rules with a Russian electronic PIC based DT timer driven by a 50mah 1s LiPo. The servo is not powered until the timer signals a DT. I flew this in competition over the 2015 season and whilst the no load voltage was checked prior to a competition the battery was charged at the beginning of the season and halfway through.
It follows that there is no need to power the servo on a mouse trap release system as there is zero loading in the rotary direction. Friction in the gears keeps the servo arm in place and I choose a  cheap servo with plastic gears and a stiff gearbox. It has worked well throughout the season with no failure of any of the components. I suspect that a powered servo battery would outlast a day of competition but I do not have to take that risk.


The observant and those familiar with HLG design will see  that the model showcases a conventional rear end, unusual for a dlg where a Butterfly arrangement is  more common. Suffice to say that provided the fin has area above and below the fuselage centre line the launch and transition handling is much the same as a Butterfly arrangement.

 

FF_dlg 002.jpg

FF_dlg 001.jpg

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Phil_G

Hi Ian . 

Your RDT uses a conventional RC receiver, and a conventional RC servo, both of which are powered during flight.

Cheers

Phil

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