Beginner Revell Kit Conversion

I am attempting to use a Revell 1/72 scale Type IX kit as the basis for an (initially) surface running submarine. It will have to be surface running initially as I only have 2.4 Ghz radio (model aircraft for years) and 40mHz sets seem to be 'hens teeth' currently. I read the section on LRS but lack the soldering skills (and the little grey cells) to tackle the modifications required. I looked at the Hobbyking website and couldn't find the 3.3 volt dongle that was referred to, though the tx and rx seem to be available, though I didn't think that 100mw power output was allowed in the UK.

I will use an acrylic cylinder (3mm wall thickness) as the watertight section and make the end caps using a 3d printer. Probably ABS or PETG with a O ring seal.

I will try to get working planes as well as the rudder(s) and lock them in place initially. I think that I may have to depart from scale for the rudders and aft planes as there is very little clearance and support in the stern. Possibly a single large rudder and move the planes up to a wider part of the hull to get a space with more room for support and a servo arm. Or a servo arm outside the keel through a hull bottom slot to the planes.

From reading on here I think that I will use bellows for the servo rods, though so far I haven't discovered where they come from. One of my old aircraft modelling friends said that he used to run in buggy motors in water. I know that a brushless motor will (attempt) to run in water (overturned floatplane) so I wonder if anyone on this forum has experience of running the motor in the wet section? Otherwise I suppose its another sealing problem round the prop shaft. As most surface running boats don't seem to have a leak problem I assume that standard shaft tube seal reasonably well.

Welcome to the fascinating world of R/C submarines. So far,you have mentioned several items as problems, but almost all have been solved for awhile.
Using bellows for pushrods is used a lot. I am sure on of these guys can speak up on that. I use an o-ring and have several successful subs.
A power shaft can use another seal, called a cup seal.
You do not list where you are from, so I am not sure where to help. I am across the pond.
This site has a couple of gentlemen using 433MHz. Check out postings on that.
Enjoy and see if someone lives near you. You can learn a lot from visiting.

Hi Rob,

I agree with Tom's reply and so some information on 458 Mhz.

The 3.3v Dongle is available from Sparkfun:

https://www.sparkfun.com/products/9873

I wouldn't give up on openLRS. The equipment is quite cheap and very compact (with no soldering required) so buy it and have a play with it over the winter. You do need a PC or laptop and to be reasonably confident with them.

Remember that the equipment will work "out of the box" (On 433Mhz with an earlier version of openLRS) so have a play with it before you upload the more up to date software and set it for the UK legal frequency of 458 Mhz.

The guy that started the whole openLRS thing for model submarines (Tim S) has just posted a useful guide on Youtube.

Concerning control rod seals. I use bellows and I got about 6 on eBay which have lasted me a number of years. As Tom says you are best using proper oil, cup seals "Simrit" etc. for shaft seals. Lots more info on this Forum. (Surface boats don't have to resist any significant water pressure so grease filled tubes etc aren't really up to the job.)

I use brushless motors exclusively now, but I have never got one running in water! Best kept dry, I think.

You don't say what other sources of information you use. A little list:

SubCommittee - Forum and good online magazine for a modest subscription.

Facebook  - Our own AMS site and the Dive-In (the latter is very chatty.)

Events - Keep an eye on events posted on here. Big enthusiast gatherings at Papplewick, Bournville and Norwich. I see that you are from Buxton and so the exhibitions at Haydock Park (August 2018) and Poynton (You've just missed it!) could be useful for you.

Enjoy and let us know how you are getting on.

David

Hi Rob

I am a newcomer to submarines, and I shall soon be building a Type VIIC U-Boat in 1:72

I am afraid that I am completely clueless when it comes to RC systems, besides radio sets, servos and speed controllers, I have little experience with such things.

You're far more educated than me on the subject, so maybe we could share information as our builds unfold?

I look forward to seeing your progress

All the best

Sam

Some of this might be useful as you cobble together your Revell 1/72 Type-7 kit:

https://support.caswellplating.com/index.php?/Knowledgebase/List/Index/33/revell-vii-cabal-reports

... and the pretty pictures:








David

K80 wrote:Hi Rob

I am a newcomer to submarines, and I shall soon be building a Type VIIC U-Boat in 1:72

I am afraid that I am completely clueless when it comes to RC systems, besides radio sets, servos and speed controllers, I have little experience with such things.

You're far more educated than me on the subject, so maybe we could share information as our builds unfold?

I look forward to seeing your progress

All the best

Sam

I doubt that I am significantly better informed (if at all) than you K80, but will update you with my progress.

I have obtained a 50mm OD length of extruded acrylic tube and am in the process of trying to design a 3d printable set of end caps, motor and servo mounts. I have a single 385 brushed motor and a speed controller with BEC for the same plus some prop shafts and a pair of handed 25mm diameter 3 blade props. I have also obtained some servo rod bellows (don't know what else to call them) and some O rings for motor shaft seals and end cap seals. Some experimentation will be needed to get the appropriate depth of groove for the O rings in the end caps. I have decided to take a leap into the unknown with openLRS radio and have ordered a tx module and rx from Hobbyking (unfortunately only the global warehouse stocks these items apparently, so delivery time and final cost due to possible tax and handling charges remain unknown). As the first iteration of the design will be surface running (or possibly dynamic dive, depending on rate of progress) I have not addressed a ballast system at all. I suspect I should have gone for a bigger diameter tube to accommodate this in future, but lets get the mark 1 working first.

I have the following design decisions/questions which I would like some suggestions for if anyone can help;
- Do I need a reduction ratio between the motor and the props? One internet item suggests 2:1 reduction.
- As I am running a pair of handed props from a single motor, am I better with the gearing inside the WTC (requires two shaft seal) or in the wet section (has the gearing running in water, which might be good for wear, but bad for friction loss)?
- As the twin rudders are positioned well outboard, can I implement twin rudders or depart from scale to a single central rudder?
- Will a 3D printed endcap be sufficiently waterproof? Acetone smoothed ABS is supposed to work for bowls and vases, but will it take any pressure? If not, what do I do without a lathe?
- What problems have I not yet realised?

david f wrote:Hi Rob,

I agree with Tom's reply and so some information on 458 Mhz.

The 3.3v Dongle is available from Sparkfun:

https://www.sparkfun.com/products/9873

I wouldn't give up on openLRS. The equipment is quite cheap and very compact (with no soldering required) so buy it and have a play with it over the winter. You do need a PC or laptop and to be reasonably confident with them.

Remember that the equipment will work "out of the box" (On 433Mhz with an earlier version of openLRS) so have a play with it before you upload the more up to date software and set it for the UK legal frequency of 458 Mhz.

I use b
David

Decided to give 458 MHz a try. Bought a Hobbyking 433Mhz module and matching rx and a Turnigy tx to accept the module. Order the 3,3 dongle.

HobbyKing module and rx arrived. Can't find any manual, jus spec sheets. Can't get two of the little screws holding the cover on out. Shifted two but the others are just burring over (damn little crosshead screws).

What is an FDTI cable? The Sparkfun gizmo doesn't come with one and I can't find a definition, just a reference to an electronics company company with the same initials. Amazon have some cables listed (at a higher price than the Sparkfun gizmo) with various plug options. If the modules are based on chips similar to the arduino, why is programming at 3.3 volts needed? the Arduino boards all seem to accept standard usb connections?

Getting confused.

The Youtube video seems to be using a different tx/rx combination, though I expect the basic flow would be the same.

Rob,

the need for the FTDI cable (not FDTI) is to plug into the HobbyKing TX module and RX... they don't have USB ports like arduinos do.  the FTDI "Cable" is not really a cable.  it IS the dongle that the sparkfun link points to.

basic OpenLRS equipment (which is what the HobbyKing stuff is) requires a 3.3v setup, not the usual 5v setup that arduinos use because the RF chip that the OpenLRS original designers based their work on is a 3.3v part, with no safety measures.  you need to buy a 3.3v FTDI specific dongle, or you will destroy your HobbyKing devices.

the dongle connects to the TX and RX circuit boards on specific pins, and has a usb port to connect to the PC.

I agree that a lot of shortcuts were taken when designing the entry level parts like what hobbyking sells, adding a layer of confusion to an already confusing situation.

I have personally stopped buying the HobbyKing equipment, but my favorite manufacturer of better equipment no longer sells OpenLRS equipment, so i am at a loss for buying new hardware...

Give me a ring, Rob. (I have just pm'd you my phone number.)

Tim's videos and descriptions are excellent but "Technology Transfer" is never easy at the best of times. The ability to ask questions by the pond side is probably the best way forward but failing that maybe I can talk you through a bit of the learning curve to openLRS.

David

Thanks David. It was a useful conversation and will get me further along the (hopefully not too rocky) road to openLRS success.

openLRS module installed in TX and connecting to rx in 433MHz mode. Can't wait for the sparkfun gizmo to arrive.

Will keep the forum posted on whether I get 3d printed parts to work.

Hope to see you at one of the events this year. I intend to get to at least one even if I haven't got a boat running.