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Member postings for Malcolm Frary

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

Thread: Size of a typical mast
02/04/2021 15:18:20

If going for carbon tube, here is a pointer from the DF65 rules -

G.3 Mast Construction To avoid the mast tubes splitting it is permitted, and recommended, to glue in the Mast Top Plug and glue the mast section joints. Boats supplied from 2015 onwards come with metal mast and jib boom bands to reinforce the tube ends. These rings are available as accessories and may be used on older boats.

Taken from -

https://dfracingdotworld.files.wordpress.com/2017/03/dragonforce-65-restricted-class-rules-v1-61.pdf

The inference is that carbon fibre tube, while incredibly strong and stiff, is inclined to split at the ends, and needs a bit of help.

Thread: Rigging
31/03/2021 09:27:53

Local club if available. Not seeing them at your local lake doesn't mean they are not there - their sailing times might not coincide with your visit times. When chatting with passers by ay my lake I often get told that they didn't know such things happened, because they had never seen it in 30 or 40 years. I've been playing boats there for 30 years.

Alternatively, sites like this or one of the many others with like, or more focussed, interests. I did a lot of learning reading racing reports (and looking at the pictures) in model boat magazines. What works for a top racer is good enough for casual sailers like me.

Catalogs give a lot of information, even if some of it is unintentional. You spot names of parts which need a web search for an explanation, but its all part of the journey along the learning curve.

Thread: What material is used to make yacht Sails.
30/03/2021 10:57:27

A word with one of the model boat sail makers, Nylet, HouseMartin, Sails etc, PJ, and no doubt others, will show that they already do suitable sails for your boat. They will cost rather more than DIY sails, but they will be better made and have a better chance of working as required.

Material? Take your pick. Poly cotton from a dead shirt, bin liners, shower curtains, florists cellophane, drafting film, rip stop nylon, all have been used successfully.

Thread: Size of a typical mast
30/03/2021 10:39:40

What Ray said.

Just measured the mast on my Victoria, a slightly bigger yacht. 9mm diameter, aluminium tube. So 6mm carbon would sound OK. Although tube might be preferable. Competing or not, you still want the boat to behave well in a range of conditions, racing boats do this and it is a good idea to grab as many of their tricks as is feasible.

And, when another yacht appears, a race is going on.

Thread: Modav Huntsman 34? fittings
24/03/2021 10:30:29

In the model boat world, many fittings go by size rather than scale since in the real world, larger fittings follow the same design.

1:11 is a very odd scale, probably determined by something that the designer had available. More common scales are 1:12 (1 inch to the foot) or 1:10 (handily metric). The difference for fittings either way is probably small enough that nobody will notice. Smaller scale fittings usually fit better, more room to position them easily.

Thread: Bending 5mm brass rods to make driveshaft
24/03/2021 10:23:47

If the original used 5mm brass, fair enough. I would be tempted to look at stainless bike spokes. About 2mm diameter, much easier to get a 90 degree bend in, probably as durable as 5mm brass. They come in packs of 10, but unused ones tend to find uses very easily.

Thread: Mixing paint
20/03/2021 10:51:57

Nearest match to a shop-bought tin any time. The only exception to that was back when Humbrol were ruining their reputation having out sourced to foreign parts where it seems that the paint mixing department was using the local colour blind. It's taken them a long time to live that down.

Using a catalogue colour gives a much better chance of getting a later match when the inevitable touching in is needed after a bit of real life weathering.

Oil based varnishes tend to oxidise over time, which causes them to gain colour, usually yellow-ish. Acrylics don't.

Thread: kms bismark
16/03/2021 09:53:38

Finally found a datasheet for A4988.

https://www.pololu.com/file/0J450/a4988_DMOS_microstepping_driver_with_translator.pdf

Still having trouble seeing the need for an 18 volt supply, given that the A4988 uses a load supply voltage down to 8 from a max of 35, and the stepper that it is driving rates at 12volts.

15/03/2021 10:24:02

A link to a datasheet for the chosen circuit would be useful. A good data sheet can answer many questions, and might highlight some otherwise unforseen problems.

The few that I have seen for stepper controllers all indicate a need for cooling, either a heatsink or a fan or both. Stepper motors do have a reputation for speed and precision, but at the cost of being very thirsty for the work done, hence the need for cooling. Possibly the reason for the need for cooling. Not an issue with devices with external power (i'e; running of the mains) but definitely an issue in self powered portable equipment.

Thread: Motors/prop for model warship
15/03/2021 09:11:46

Rather than buy a combo that you might not be able to get extra receivers for, something like a HK-T4A V2 is not much more, but you can get extra receivers at modest cost.

In the days of AM/FM radios, all that was needed to ensure compatibility between transmitters and receivers in the same band was the correct crystals. Different makers ensure that you stick with their range by making sure that only their receivers will bind with their transmitters.

Again in the old days, when you bought a transmitter, you got all that you needed apart from batteries, today you get a transmitter, a bound receiver and the box they came in. Battery and ESC are needed.  Servos are fairly universal, but some might need a bit of trimming of the plug body to fit the hole in the receiver case. Not usually a problem, because most modellers have a knife somewhere. Care needs to be taken plugging in a trimmed lead - black/brown needs to be on the pin nearest the receiver circuit board. From experience, it also needs to be on its row of pins, rather than between two.

Although a shallow, long, narrow hull can be tender, the main problem with warships is the low freeboard.  A short tubby boat will ride over waves.  Or try to.  A long, low hull might well be longer that the wave spacing, so water will go over the decks when waves are higher than the freeboard.  Good edge sealing is important to allow draining to the outside, rather than the inside, of the boat.  Since there is no 100% certain way of totally keeping water out of this type of hull, sealing all of the surfaces inside and out is needed.

Edited By Malcolm Frary on 15/03/2021 09:41:40

Thread: kms bismark
14/03/2021 09:27:57

i was going to use some arduino mega pro or nano v3, i was going to couple a potentiometer to the rudders control, so when i deemed that i was going hard to port or starboard, i would reverse the appropriate motor so i could turn quicker, i also thought of choreographing the gun controls as the data flow using lora between the boat and me would be incredible but i am still interested in trying that out.

Differential steering. Look for "Mixer". Either hardware in the boat between radio and ESC or done by the transmitter. Many transmitters do mixing. No point re-inventing something that is already on the market unless it is either going to work much better or cost a lot less, or both. Or do something extra that well established hardware cannot.

hence my question about needing a higher voltage and regulating it so the stepper controllers have 12v

5 volts will be needed, probably at very low current, for the control circuits. The control circuits will, if properly designed, be quite happy controlling any voltage. If a stepper motor control circuit requires the full motor voltage to provide the control signals, it comes down to a question of designing the right interface between the stepper control input and the arduino output.

 

Quick check of my car battery height - 175mm.  I didn't check the weight.

Edited By Malcolm Frary on 14/03/2021 09:40:05

13/03/2021 11:24:30

For 12 volt motors, a 12 volt battery is the most efficient answer. A model that size could carry a much, much bigger battery than a 7AH one. A 1:96 Bismark, done as a full hull model rather than a shallow draft representation, will weigh about 112 pounds floating at waterline. Plenty of space for real, full size, car batteries if proper precautions regarding ventilation and acid proofing the battery compartment are made.

No point in using a higher voltage and regulating it down using a linear heat generator - UBEC regulators are available, but probably not easy to come by for the power levels needed. If odd items need higher voltages, circuits are available to step up voltage. Google for "step up voltage regulator".

A total of 15A needed for scale performance gives a theoretical 4 hours off a 70AH battery, probably a lot longer if cruising rather than escaping the attentions of the Home Fleet. A set of 3 of12v7AH batteries, one powering each ESC plus another to power the non-esc items, will work and give plenty of run time.

12/03/2021 09:43:17

The ESC will often have a BEC that eliminates he need for a separate supply for the radio itself and other items that plug into it.

As Ashley says, go for NiMH. A pair of 5 cell packs allows you to position them more easily than a Lead Acid lump. They are also much easier to look after than either SLA (need fairly constant attention to ensure long life) or Lithium which do have a charge cycle limit and very careful attention. Being lighter than SLA, you get to position the batteries where they are convenient to you. This allows you to position any ballast where you need it to be - preferably out at the ends to give a more realistic looking ride through waves.

What scale Bismark? I am assuming not a 1:350 one, since that size doesn't really lend itself to any SLA. Unless totally inappropriate motors are used, 4500mAH should give a very full afternoon's cruising.

Thread: JIF 65
10/03/2021 09:43:29
Posted by carl brotherton on 09/03/2021 17:09:05:

Being Sad, I went to sleep thinking, hmm, going down wind there is definitely no airfoil.

Just as you say, a bit of Newtons physics, of action and reaction (is that Law 3 and all the rest 1,2 &3 at work).

I am now thinking that is why the mast can be moved, backwards and forwards (if you know what you are doing) to get that handling balance.

Newton, Bernoulli, and probably a bunch of guys in ancient Egypt who had figured out sailing upwind with fore and aft rigs while our locals were still figuring out that keeping your thumb out of the way while banging rocks together was a good idea.

09/03/2021 10:26:52

A bit of "why".*

Balance is everything in a windy boat. The forces acting on the sails apply force towards the front and back depending on the relative areas, and where they are. Too much at the front, the centre of effort being the average of the sails, the boat goes downwind, too much at the back, it points into the wind like a weather cock, and sits there. Or goes backwards.

The boat tries to move in the direction that the difference in air pressure on the faces of the sails determines. Downwind, obvious. The sails just block the wind.

Across the wind, the sails are angled to cause airflow across themselves, which, if they have the right curve, causes a difference in air speed and therefore pressure between the two sides, and puts a force into the rig. Left to itself, the boat will go sideways, but having a shape underwater resisting the sideways motion, the boat goes forward. Just how much of the sideways force is translated into forward and not left to sideways motion (leeway) depends on how the boat is set up and whoever is driving.

Heading into wind, trigonometry says that up to a point, you still get the resulting forward motion, and you do. After getting to that point, typically 45 degrees off the wind, you get steadily less forward motion until the boat stalls.

Finless boats tend to be better at straight running and are reluctant to turn which makes tacking one across the wind a bit of an art. Boats with fins usually turn easily, and as long as they have got enough inertia, can get through the dead bit between not getting forward drive and having their sails presenting their other faces to the wind before coming to a stop.

Since every action has its corresponding reaction, the wind on the sails needs something the react to. This is provided by the hull in the water. This resists the sideways push. On a deep hulled boat with no fin but a long lengthways keel, the centre of this action is where it is according to the side area. On a shallow hulled boat with a long fin, the fin is the main component in deciding where the CLR is, and its position becomes critical.

*Probably true enough.

08/03/2021 11:12:46

A pre-made fin will likely be easier to mount than a home build. It will* come with a moulded in fixing rod that goes far enough down the length of the blade to spread its load, and long enough to go through the deck of its DF65, again, spreading the load. With home made, either there is the problem of fixing the rod down the inside of the blade, or extending the blade upwards into a fin box far enough.

I have been tempted in the past to try a helicopter blade, since some have spoken well of them, but haven't plucked up the will to try. Not knowing if they are, or are not, symmetrical or if they vary between types, is one off-put. Understanding the strange techno-babble of heli-folk is another.

* just looked on the ripmax spares page - the fin says "complete with screws" but I take that to mean the ones that fit the weight to the bottom end. No way can a fin just bolt to the boat bottom, it needs more support, either a rod going far enough down the inside of the fin and up through the deck, or a substantial tab at the top sitting in a fin box, with a screw bolt holding it in place from above.

Thread: Bristol Channel Pilot Cutter
07/03/2021 16:59:58
Posted by Dave Cooper 6 on 04/03/2021 23:26:53:

Just pondering main mast positions as most line drawings don't show it. I want to get this right as I think the deck-supporting frames in this area will need to be quite close in to carry the longitudinal and lateral sail loads.

From various photos I've studied, a figure of 5/13ths of deck length back from the stem head seems about right ?

I think this will mean frames at around the 4/13th and 6/13th 'datums' thus enclosing a fairly stout keel box for the mast step. This may be over-kill as the standing rigging will probably take most of the loads in tension (my usual tendency to over-engineer here !). Anyway, I'll try it out on the mock-up and see how it looks.

Any thoughts welcome...

A very rough and ready way is to draw your sail plan on card, and see where it balances. Do the same for the side profile of the submerged part of the hull. The first indicates the probable centre of effort, the other the probable centre of lateral resistance. On a 40" boat, having the sail plan centre about 1" or so forward of the hull centre seems to work.

If going for internal ballast, lead. Anything else lets the centre of gravity rise too much, and in a scale hull, there just isn't the space available low down for anything much lighter than lead. Cast ingots if that can be managed, a wide variation of shot sizes if not.

Thread: JIF 65
06/03/2021 10:23:11

I am also wrestling with the aluminum keel, how thick should it be for both performance and normal, rough and tumble use.

If the plan suggests 1/16", 1/16" it should be. Or 2mm.

The really important parameter is that it should be rigid. Clamp one end, put your weight on the other, Any flex should be minimal. At a Laser meet a few years back, we tried two stock Laser fins against each other using a step and the ground as mount and reference. One drooped considerably more than the other. Use of the more rigid one gave a faster boat. The same applies with any other fin.

Even if not racing, with any sailboat you need to get the best performance you can. It can make the difference between getting the boat back and sailing again, or not. I expect that "real" RG65s would use carbon fibre to get the thinnest profile combined with the stiffness needed.

Thread: Dave Milbourn RIP
06/03/2021 10:07:03

The hobby and model boating community has lost a giant.

Deepest condolences to Liz.

Thread: Newbie
04/03/2021 17:28:20

Assuming that they are intended to go like fishing boats, something like a 540LM, or a 545, run on about 3/4 the volts on the label driving a prop about the same diameter as the motor can.

A heavy SLA battery helps with ballast, on the other hand a lighter battery such as a NiMh lets you put the ballast where it is needed and gives more opportunity to choose the voltage that you prefer.

Building heavy is not always the best option - there was a case in one of the magazines many years ago where the builder had a fixation with ultimate strength. He was upset when he found that it floated below water line before any working bits were added, and that rather than a working model, he had a rather nice display only one.

Edited By Malcolm Frary on 04/03/2021 17:29:28

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