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Author Topic: Thimble...  (Read 8889 times)

colh107

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Re: Thimble...
« Reply #25 on: September 19, 2019, 07:17:28 PM »

Waaaayyy old thread, but I remember the Thimble article from my youth. I've just got hold of the original mag with article/plans [even have a spare copy if anyone is interested].
It's exactly how I remember, but I'm thinking some modern materials/techniques could work well - things like a 540 motor mount, and a rudder/servo box, could probably be 3D-printed? Carbon fibre turning fin?  ok2
Maybe even 3D-print the bows, rather than sanding blocks of balsa?
And with the better weights these days of RC and batteries, it ought to be a breeze to bring new life to the design?
Drop me a line if you have an interest and/or would like to talk over 'modernisation' concepts!


PS - Also have Zing Ray plans, recalled from my youth too. Am debating which one to have a crack at!

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kiwiazz74

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Re: Thimble...
« Reply #26 on: September 19, 2019, 08:11:22 PM »

colh107 you legend i was so surprised to see a reply to this thread  this morning
after alot of time searching i ended up finding my thimble plan, but then i found naviga and mini eco's,
being at the bottom of the world with no naviga here and no one to race against i ended up shrinking down the plans i downloaded for a 1kg boat the "weisel" to mini eco length and have started building that instead of the thimble, running 3000kv brushless and 3s batteries.
as usual with me its a long term project but its been a fun build so far, will have to post a pic of it finished in here.
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colh107

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Re: Thimble...
« Reply #27 on: September 19, 2019, 08:28:07 PM »

Hehe thanks  :-)
It's a pet/embryonic project idea at the mo. I've not built from scratch before, but it always seemed a pretty straight-forward design. And whilst not having built wooden boats from scratch, I reckon my woodworking/engineering skills are up to the challenge. (Winter here soon...)
I reckon modern materials/gear can keep it definitely light.
I like that it's a 'pocket rocket'. Zing Ray also always appealed to me as a kid though - also pretty simple to build (and a Vic Smeed design, so gotta be decent).

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rnli12

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Re: Thimble...
« Reply #28 on: September 19, 2019, 08:36:36 PM »

WoW- built one for my CSE Woodwork exam in 1978 ish passed with a grade 2 i think......

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Subculture

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Re: Thimble...
« Reply #29 on: September 19, 2019, 10:03:50 PM »

Francis Costin used to call wood 'Gods plastic'. Very difficult to beat for weight to strength.

If you built it as per plan, give the exterior surfaces a coat of epoxy resin and light glass tissue (25gm2) you'll have very light but strong hull that is waterproof.  Substitute the 500 size brushed motor for a brushless outrunner and lipo, a tiny 2.4ghz receiver with a 9 gram servo and  a forwards only esc the performance should be very lively.

colh107

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Re: Thimble...
« Reply #30 on: September 20, 2019, 03:34:43 PM »

Francis Costin used to call wood 'Gods plastic'. Very difficult to beat for weight to strength.

If you built it as per plan, give the exterior surfaces a coat of epoxy resin and light glass tissue (25gm2) you'll have very light but strong hull that is waterproof.  Substitute the 500 size brushed motor for a brushless outrunner and lipo, a tiny 2.4ghz receiver with a 9 gram servo and  a forwards only esc the performance should be very lively.


Definitely with you there - unless rotten, you can always repair wood. (And if there's rot, cut it out and fit a new section! I'd rather repair a wooden door frame than uPVC).
Real wood only, of course - weight/strength of MDF..... WoW who invented that.... I had a 60yr old wardrobe with 2x2 frame and 1/8 skins, joints never came loose and I could pick it up alone. Not like modern rubbish that falls apart after a couple of moves and takes two+ to shift. Rant over lol.....  >:-o


Not sure about going brushless - I don't mind if it's 'gentle'  :embarrassed:

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Martin [Admin]

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Re: Thimble...
« Reply #31 on: September 20, 2019, 05:19:50 PM »

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colh107

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Re: Thimble...
« Reply #32 on: September 20, 2019, 05:51:24 PM »

I managed to get hold of a copy of the '79 Model Boats mag - article and the plans too.
In fact, concern over reliability of the first vendor means I now have two copies!  %)

Scary that all the Ripmax/Graupner/SHG ads still seem sooooo familiar.... And o m g  - MacGregor RC too!!
2-channel txrx, with servos, for £82 - that was a fair amount for a hobby back then  {:-{



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colh107

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Re: Thimble...
« Reply #33 on: October 05, 2019, 06:21:46 PM »

Francis Costin used to call wood 'Gods plastic'. Very difficult to beat for weight to strength.

If you built it as per plan, give the exterior surfaces a coat of epoxy resin and light glass tissue (25gm2) you'll have very light but strong hull that is waterproof.  Substitute the 500 size brushed motor for a brushless outrunner and lipo, a tiny 2.4ghz receiver with a 9 gram servo and  a forwards only esc the performance should be very lively.


I should have paid more attention to my Dad when he reconstructed a Graduate in the 80s! Ive built much in wood but never combined with epoxy coating. Can you give some tips/links on how to go about that?
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Subculture

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Re: Thimble...
« Reply #34 on: October 06, 2019, 10:14:44 AM »

Have a look at this guide. You only need the lightest cloth 25gm2, as the strength will already be in the wood, maybe apply two or three layers on the balsa areas as that is softer than the ply.

https://www.bucks-composites.com/sites/bucks-composites.com/files/how-tos/Surface%20Finishing%20with%20Glass%20fibre%20Woven%20cloth%20%26%20Epoxy%20Resin_0.pdf

dreadnought72

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Re: Thimble...
« Reply #35 on: October 06, 2019, 10:34:37 AM »

.... And o m g  - MacGregor RC too!!
2-channel txrx, with servos, for £82 - that was a fair amount for a hobby back then  {:-{



Just shy of £410 in today's money!  :o


Andy
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colh107

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Re: Thimble...
« Reply #36 on: October 14, 2019, 05:01:27 PM »


Continuing (hopefully) some conversation that started here, wrt Thimble in particular:


Colin Bishop: "It's just that looking at the plan profile you have posted any sort of 540 would seem to be putting a lot of weight well up up front"
I understand the comment, but the design was originally for a Cyclone 15. Looking at back issues of Model Boats, those were 150g so about the same as a 540. C of G can be adjusted a bit of course to get it back in the 'right' place, though the plans don't unfortunately show where that should be...! (Maybe there's a 'rule of thumb' for that?)


Subculture: "Motor and speed controller can be had for under a tenner"
I may (more than likely) be looking at wrong vendors or wrong motors, but even smallish brushless seemed to me to be starting at more like 30 quid or so?
You suggested 'outrunner'. I ought to go trawling info myself but, as you know your stuff, any particular reason for out rather than in?


BTW, I'd be content and happy with 'fun performance' - 'very exciting' not necessarily needed!
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DaveM

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Re: Thimble...
« Reply #37 on: October 14, 2019, 05:43:51 PM »

Ive built much in wood but never combined with epoxy coating. Can you give some tips/links on how to go about that?
Here's a bit of relevant nonsense... https://www.modelboats.co.uk/news/article/finishing-and-sealing-of-wooden-hulls/18771
DaveM
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Colin Bishop

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Re: Thimble...
« Reply #38 on: October 14, 2019, 06:02:17 PM »

There is a useful article on Brushless on the Model Boats site:

https://www.modelboats.co.uk/news/article/going-brushless/8029

I have only recently got into brushless myself as a result of building the SLEC Huntsman kit last year. I used Dave Milbourn's recommendations for the power setup and the boat goes like a rocket. OK, it's a bit of a learning curve but not really difficult when you get down to it.

This little Turnigy motor produces an amazing amount of power for its size:

https://hobbyking.com/en_us/d2830-11-1000kv-brushless-motor.html?___store=en_us

Outrunners are usually recommended for boats as the design produces more torque than inrunners which is handy for marine props.

I did use a fairly pricey speed controller from Component Shop but there are cheaper options out there.

As far as weight is concerned, a brushless/LiPo setup will be much lighter but you can always add a bit of ballast if it turns out to be necessary so your options are open.

Having said all that I'm still happy with brushed motor/NiMH batteries for my scale models which only need to plod along.

Colin
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colh107

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Re: Thimble...
« Reply #39 on: October 14, 2019, 06:07:27 PM »

Ive built much in wood but never combined with epoxy coating. Can you give some tips/links on how to go about that?
Here's a bit of relevant nonsense... https://www.modelboats.co.uk/news/article/finishing-and-sealing-of-wooden-hulls/18771
DaveM


Thanks. WoW that article digs so much terminology from the depths of my memory! 'Sanding sealer', Eze Kote

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colh107

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Re: Thimble...
« Reply #40 on: October 14, 2019, 06:12:27 PM »

There is a useful article on Brushless on the Model Boats site:

https://www.modelboats.co.uk/news/article/going-brushless/8029

I have only recently got into brushless myself as a result of building the SLEC Huntsman kit last year. I used Dave Milbourn's recommendations for the power setup and the boat goes like a rocket. OK, it's a bit of a learning curve but not really difficult when you get down to it.

This little Turnigy motor produces an amazing amount of power for its size:

https://hobbyking.com/en_us/d2830-11-1000kv-brushless-motor.html?___store=en_us

Outrunners are usually recommended for boats as the design produces more torque than inrunners which is handy for marine props.



Thanks for that steer - I've been gazing at their site several times today without seeing that. I think I'm going 'motor blind'! Does look neat and well-priced, and might be enough for a Thimble for me. Though I see there's also a 2200kv version at similar price bracket.

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Colin Bishop

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Re: Thimble...
« Reply #42 on: October 14, 2019, 06:23:12 PM »

There are others more competent than I am to recommend a suitable setup for Thimble. I initially put a 3S LiPo in the Huntsman but it was a bit too fast for my current reflexes so I replaced it with a 2S which still gives a pretty brisk planing performance.
( Edit: Just seen Subculture's advice above)

Colin
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colh107

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Re: Thimble...
« Reply #43 on: October 14, 2019, 06:33:23 PM »

Thanks all. So, from Subculture's mention of it yesterday - at what point does supplemental cooling become necessary? I guess for an outrunner that doesn't have it built in, you'd only be able to sink the heat away through its mounting bracket(s)....?

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Subculture

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Re: Thimble...
« Reply #44 on: October 14, 2019, 07:23:07 PM »

These size brushless motors are good for about 100-150 watts. At about 70-80% efficiency, that means the potential for 20-45 watts being burnt off in heat, so some form of cooling is advised. I find just a small copper pipe with some thermal connection to the motor is adequate to keep things cool. A pick up just behind the prop draws in the water. Simple and cheap to implement. I use no heli or Simon K firmware escís, very cheap on eBay and super smooth throttle control. N- channel mosfet stages run very cool, and donít require any additional cooling.

colh107

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Re: Thimble...
« Reply #45 on: October 14, 2019, 07:31:31 PM »

These size brushless motors are good for about 100-150 watts. At about 70-80% efficiency, that means the potential for 20-45 watts being burnt off in heat, so some form of cooling is advised. I find just a small copper pipe with some thermal connection to the motor is adequate to keep things cool. A pick up just behind the prop draws in the water. Simple and cheap to implement. I use no heli or Simon K firmware escís, very cheap on eBay and super smooth throttle control. N- channel mosfet stages run very cool, and donít require any additional cooling.


Ah, some terminology I am familiar with  :-)  (N channel MOSFETs, firmware). I even know how to calculate theta JC's etc lol
Thanks guys. :-))

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Colin Bishop

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Re: Thimble...
« Reply #46 on: October 14, 2019, 07:42:32 PM »

I've not had any cooling issues with my Huntsman but I doubt if I am running the motor at anywhere near full power and not continuously for several minutes as you would under racing conditions.

Colin
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colh107

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Re: Thimble...
« Reply #47 on: October 14, 2019, 07:51:58 PM »

I've not had any cooling issues with my Huntsman but I doubt if I am running the motor at anywhere near full power and not continuously for several minutes as you would under racing conditions.

Colin


I guess you also have a larger air space in that compared with summat like a Thimble, which would help to some degree [no pun intended].

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Subculture

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Re: Thimble...
« Reply #48 on: October 14, 2019, 09:27:28 PM »

Unless you're winding a pretty large prop, a 1000kv motor at 7.4volts won't be working the motor very hard at all, so air cooling will more than suffice. Remember also  that with the extended running time lipo's allow, things have more time to get toasty. In the old days of nicads, five minute runs were the norm, now you can easily get fifteen to twenty minute runs.

BTW, my previous post should have said 'BL heli' esc instead of no heli. The auto correct on my phone struck again!
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