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Member postings for Chris E

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

Thread: Balsa Shortage
30/09/2020 11:35:53
Posted by Charles Oates on 30/09/2020 10:55:40:

Chris, my comment, re breathing, was out of order, I'm sorry. The point was that if you waterproof the inside of a model, it will help prevent de lamination with lite ply, and as balsa is prone to swelling when wet, it will help the model be stable for a long time. I'm certain that there are un sealed models out there that are also decades old, that's probably due to good maintainence, storage and infrequent use.

Chas

Agreed. I think that Cascamite & real wood bread & butter construction helped as well.

30/09/2020 10:20:55

Dave

This discussion has somehow gone wrong.

Yes I am a modeller but I have not used knowingly used LitPly. I have read some very dismissive reports on Litply and I was just trying to full understand its characteristics and how you use it with success whereas as others fail miserably.

I realise that no wood is waterproof but some are more resilient to water damage than others. I am now seeing Liteply as more like balsa than birch ply (in need of a high level of protection).

I have read what you have written about fibreglass covering & that is the way to go as well as what I do. I am, however also aware of various finishing methods suggested by others and I have known of modellers who don't do anything to the inside of their hulls to let the wood "breath". They seem to get away with this but they would not do so with LitePly. They seemed to manage to breath without great difficulty.

 

 

Edited By Chris E on 30/09/2020 10:38:58

30/09/2020 08:53:20

Dave M

That is a useful summary.

The thing that I note most strongly is the need to have a very durable and totally waterproof finish inside & out as the liteply isn't waterproof and compared to birch ply is impact damage prone.

Thread: MFA385 - A Story of Confusion
29/09/2020 14:41:41

Yes knowledge & testing are a great help.

29/09/2020 11:56:40
Posted by Richard Simpson on 28/09/2020 10:38:23:

........................... My choice of motor, to date, has simply been based on size......................

Um.................. You have been very lucky if you have been successful using this method of selection.

I have also read the thread from the gent with the barge. It is the sort of thing that an experienced modeller would sort out very easily (probably by avoiding the problem in the first place) but I guess that there is nobody to help. Unfortunately forums are not ideal for sorting it out.

Thread: Balsa Shortage
29/09/2020 11:48:01

Charles

Thanks for that. When you said "a bit of practice" I thought that there might be something specific.

Thread: MFA385 - A Story of Confusion
28/09/2020 11:19:55

Richard Simpson

I don't think that the MFA motors were designed for specific model boat use at all. They are general small dc motors that can be used for pretty well anything that requires a small dc motor. I agree that you could put a larger prop on the LN motor.

If we look at the next range up – the 540 – the situation becomes even more confused. These are just 5 examples but there are many more out there with wildly varying specifications.

Mtronics 500 which gives at maximum efficiency 12v /4700rpm /2.7A

MFA list the 540.1 and the 540LN. The 540LN is a 5 pole motor which gives 12v /5258rpm/1.42A. The 540.1 is a 3 pole motor giving 12v/ 6180rpm/2.1A.

Component Shop used to list a 540 giving 12v /13360rpm / 2.85A

Hobby King list the Mabushi 540 – 6527 which gives 9.6v/ 20040rpm(!!!) /6.8A

 

Add to this the tendency of beginners to look for the “free” motor that came out of a power tool and about which they know nothing.

 

Edited By Chris E on 28/09/2020 11:36:06

Thread: Balsa Shortage
27/09/2020 09:32:15

I will repeat something that I said some time ago. A tutorial on successfully using Lite Ply would be very welcome. There seem to be lots of misapprehensions and simple ignorance around (including mine).

Charles Oates

What did you learn ?

26/09/2020 18:59:40

Balsa has been used as a core material for a very long time. When I was involved with expensive full size yachts in the 1970's Balsa was often used as a core material between the skins of decks to make them light & rigid. I guess that foam is used now. It was available a balsa plywood.

I had also heard (apparently wrongly) that Lite Ply contained Balsa.

I agree that growing balsa is preferable to clearing the traditional forest for crops but I suspect that if demand increases greatly it will be "as well" as rather than "instead of". I doubt that modelling use makes much difference but I can imagine that the quantities that you could use in Wind Turbines would be enormous.

26/09/2020 09:34:04

I seem to remember that Solarbo have their own plantation (in Indonesia?????) so there is likely to be some availability but at what price I don't know..

Tragically this all sounds like another reason to cut down some tropical forest.

A lot of model aircraft are now now made of foam and even that has problems as the favourite foam for amateurs was Depron & you cannot get it any more.

25/09/2020 18:06:48

The first time that I saw this reported was about 6 months ago. The potential problem is that I can't see it being resolved in a hurry. I wonder how long new Balsa forests take to grow?

Thread: todays boating
25/09/2020 10:01:13

Great. smile d

You have managed a nice finish on the foam.

Thread: MFA385 - A Story of Confusion
24/09/2020 16:01:12

Colin

I am not sure of the real world difference but I would be surprised if it wasn't significant. I don't build planing hulls so I always prefer to run my motors lightly loaded. The maximum efficiency spec means something to me.

I note that at maximum efficiency the base motor is turning at 9280rpm or 9869rpm (depending on where you look) whilst the LN motor is turning at 5950rpm. Both are just under 1A which suggests a considerable difference in the size of a suitable prop. With the 6v/7.2v favoured by many beginners around 3000-3250rpm for the LN doesn't sound a lot when connected to a small prop. Fit a larger prop and you could end up with around 2000rpm

I suspect that the 2 different specs for the base 385 are due to a change in spec, or at least a change in what is stated, by MFA.. I doubt that 9280rpm / 0.85A is very different to 9869rpm / 0.99A.

I suggested the beginner buy from Component Shop.

24/09/2020 12:45:17

The humble 385 motor is the basis of many models and is often recommended to beginners but when one asked me which 385 motor to get I was surprised as I had assumed there was one and that it would be obvious.

MFA actually list 3 different 385 motors but we can probably forget the 24v version for now.

The RE385 is a 66gm motor spec 4.5-15v (although it says 6-15 on the motor) that has maximum efficiency at 12v 9869rpm 0.99A

The RE385LN is a 110gm motor spec 6-12v with max efficiency at 12v 5950rpm 0.9A

Now lets look at the retailers:

Component Shop list both and show the same specs as MFA !!!! Congratulations Component Shop.

Model Boat Bits list both the RE385 and the RE385LN but then give them both the same spec, which is different to either MFA spec, 6-15v max efficiency 12v 9280rpm 0.85A. They do give you the opportunity to pay £2 more for it as the LN version however. I guess that the LN spec might be a mistake but the RE385.....?.

Cornwall and Howes list the RE385 using approximately the same spec as Model Boat bits. Has MFA changed the spec of the RE385 motor?

My local model shop, Pegasus Models, list the 385 motor but when you decode the model number you find it is the LN version with its very different spec, rather than the base RE385.

As an experienced modeller I can see my way through this but a beginner cannot. I do not understand how something so simple can be made so confusing. I wonder how many beginners have not got the motor that was recommended to them.

Thread: Discussion on Motors and Props
18/09/2020 19:53:05
Posted by ashley needham on 18/09/2020 18:05:30:

.......................................Ashley

Very few of my boats are of any use for such an article as most of them are specials and thus the combinations I used are of no practical use for anyone.

Ashley

I would have thought that you Landers, Mintanic & Sans Pareil (+possibly others) were good candidates. No example will ever be identical to all models of the same size.

Edited By Chris E on 18/09/2020 19:53:23

18/09/2020 17:32:02

Lots of pictures and very litte information seems to be the rule these days.

What I would like to see is a simple comparison between different props but all the same size. Take any size of prop (lets say 40mm) and connect it to a motor with plenty of power then give us the watts consumed and the thrust delivered for a range of props - 2 blade plastic "S" & "X" and 3 blade plastic and, 2, 3, 4 & 5 blade brass (all 4 being one make & model).

I have never seen that done but it would be so useful and increase the value of any examples enormously as we could see that if the example worked well with say a 40mm 3 blade brass it would/wouldn't work well with a much cheaper "X" plastic .

I realize that this makes a whole load of assumptions but I am convinced it would be useful and might debunk some of the odd statements that are made here & elsewhere.

 

 

Edited By Chris E on 18/09/2020 17:53:34

18/09/2020 13:58:38

Mark

Nice as it would be I wasn't really proposing developing an all inclusive modelling programme for model boats but rather observing that some real data for props would make drive examples that were posted much more useful in a wider sense. The motor data is already available.

Edited By Colin Bishop on 18/09/2020 14:07:36

18/09/2020 11:03:13

Colin

Brushless Motors

My experience of brushless motors in aircraft is that specifying them is simple. There is very little difference in the performance of different brands of motor that have the same specification although the more you pay the better the marginal performance. Indeed the same motor can often be purchased in many colours with many different labels and for many different prices. Better quality expensive motors do have advantages but they are beyond the scope of what I am saying here.

What matters is the kv of the motor and its ability to dissipate heat. Test data is available for brushless motors that tells you exactly how many watts of power they use if loaded to any particular rpm ,With model aircraft I know for any propeller exactly how many watts is required to turn it at any given rpm and how much thrust will be achieved. It is thus easy to match motor and prop.

With model boat props it is guesswork but see my previous post above. For model aircraft I work on around 3W per gramme of motor weight but that is with a nice big cooling fan. For model boat use I would go less - particularly if I didn't use a cooled motor mount.

Moved from Data topic. Colin

Edited By Colin Bishop on 18/09/2020 11:18:05

18/09/2020 10:46:26

Colin

Firstly let me say that I regard a wattmeter as essential so that you know what is going on as soon as you deviate from a few well trusted combinations.

Propellers

To be useful you need rather more propeller data that you have asked for. The make and model of propeller makes a large difference to its performance and loading. With model aircraft props the data is available to compare any 2 propellers and be very precise about what they will do.. With model boats it is alchemy.

Take the simple example of a 40mm 3 blade propeller. The Raboesch list above lists pitches of 41mm, Proteus Design (Propshop) are 45mm, Graupner Plastic are 21mm, etc. These differences are enormous and haven't started to include the effects of the different blade designs that are out there.

Even with basic 2Bl plastic props there are large differences between P and X types.

Without good propeller identification I would find the results of very little value.

Edited By Chris E on 18/09/2020 11:08:47

Moved from data topic. Colin

Edited By Colin Bishop on 18/09/2020 11:18:26

Thread: ESC ratings for brushed motors.
12/09/2020 17:02:37

All motors have a kv value regardless of whether brushed or brushless. It is just that brushless buyers want to know what they are buying which doesn't appear to worry many brushed buyers who often buy from a very restricted range of motors that they are familiar with. (ducks ready for the assault). Not knowing the kv works if you know the motor anyway and what it will do ie MFA 385 or 540.

Your watt meter is a very useful bit of kit. You can connect it between that battery and any user of power - motor - servo etc to see what is happening. I generally connect it between the battery and the esc. It should have connectors marked "in" (battery) and "out" (esc/motor etc). You will obviously need to have plugs/sockets on the leads that make this possible. It will then tell you the battery voltage and the amps/watts that you are using. This not only tells you about the motor but also tells you about how happy your battery is.

The optical tachometer reads revolutions.

If I have an unidentified motor the way that I use mine is to attach, using sticky tape, a piece of dark (brown, black etc) card to the output shaft of the motor when it is out of the model. It should look like a narrow 2 blade prop. You then use the tachometer to look through the spinning blades at a bright source of natural light. This will tell you how many revs the motor is giving from the battery that you have connected. The only thing to bear in mind is if it wasn't meant for model use it will read double the revs because two blades pass the sensor each revolution. I suggest wearing glasses for obvious reasons.

The reason for natural light is that mains electricity runs at 50Hz and, particularly with fluorescent tubes, that can crate havoc.

To use the tachometer in the model I just use a piece of white card wrapped around the coupling. I stop the card falling off with a strip of black dark tape in line with the motor and propshaft that also stops the coupling rotating inside the card. You need the card sleeve to rotate at the same speed as the propshaft!  You need as much natural light as possible falling onto the card. Your tachometer will now read the revs correctly as there is only one black line per revolution.

If you combine the wattmeter & tachometer readings you are now well on the way to understanding what is going on with any motor/battery/prop combination.

Edited By Chris E on 12/09/2020 17:08:34

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We welcome well written contributions from Website members on almost any aspect of Model Boating with a particular emphasis on practical hints, tips, experience and builds.

In order to maintain a consistent standard and format, all suggestions should first be sent to me by Personal Message for approval in principle. Only a very limited amount of time is available for editing contributions into a suitable format for placing on the website so it is important that the material is well presented, lucid and free from obvious spelling errors. I think it goes without saying that contributions should be illustrated by appropriate photos. I shall be happy to give advice on this.

The Member Contribution area offers space for short informative mini articles which would not normally find a place in Model Boats magazine. It is an opportunity for Website Members to freely share their  expertise and experience but I am afraid that virtue is its own reward as there is no budget to offer more material recompense!

I look forward to receiving your suggestions.

Colin Bishop - Website Editor