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Member postings for Dave Milbourn

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

Thread: Prototype build of ELLIE
21/02/2019 17:39:02

I am looking forward to seeing how the Ellie version performs with twin motors.

I would imagine that it will perform pretty much the same as Sea Spray, Paul, although it will look different.

I reckon Sea Spray needs 9.6v to get it up and running properly with those motors. Either that or fit some of Harrikin's maniac brushless inrunners! surprise

Dave M

21/02/2019 15:25:31

Also keen to see how the Ellie version works with twin motors,

Sorry to interrupt, Doc, but don't forget that the Sea Spray version I left with you has twin [Speed 600 Eco] motors. You could always throw that into the oggin and see for yourself. IMHO it went OK but I reckon it needed more than 7.2v.

DM

Thread: Increasing model top speed
19/02/2019 16:58:30

Paul

The problem is almost certainly because the geared motors aren't spinning the props fast enough to give the speed you're looking for. The #6317 Graupner 70BB 12v is quoted at 11,600 RPM at its nominal voltage of 12v. Check this link again **LINK**

There were several different types of Speed 700BB at one time - all with markedly different specifications. This seems to be the only type still on the market after the demise of Graupner, although you might actually be supplied with a differently-labelled motor, albeit with the same spec. I agree whole-heartedly with Malcolm about SLA batteries. I use them only as weights in the workshop these days.

The current drain at maximum efficiency is exactly what it says, and the difference between the two figures quoted hardly seems significant in the context of a P94, which will happily handle 20A for each motor all day. No need to search the web for verification of that - I've been making P94's since 2008.

DM

19/02/2019 13:50:23

Sorry, pardon - I missed the bit in the OP about not having room for bigger props. I still reckon 22,000RPM is way too fast for those 38mm props. Drumbeat is at best a semi-displacement hull and not a fully planing type like the Trent. The 700BB 12v motors would probably be OK but 12v might be a bit too much. Still, you always have the throttle stick to slow it down!

DM

Edited By Dave Milbourn on 19/02/2019 13:52:32

19/02/2019 10:07:50

Model Slipway always used to recommend 2.5:1 gearboxes for use on 6v and 6:1 on 12v, but that always seemed to me to be a bit on the conservative side [small 'c']. Granted that my Envoy sailed very nicely using the 6:1 ratio gearbox with 12v, but that was turning a 70mm 4-blade prop. If your motors are 2.5:1 - and there's a label on top of the mounting plate which tells you which it is - then first try bigger props e.g. 45 or even 50mm. They'll still only be turning at 5800RPM with no load, whereas the sugested 6:1 ratio would produce a mere 2400, which is very slow indeed.

Gliders of Newark have the 700BB #6317 motors in stock **LINK** but you'll see that the speed on 12v is over 11000RPM.

Dave M

Edited By Dave Milbourn on 19/02/2019 10:08:21

Thread: Build the Bismarck
17/02/2019 23:09:19

Let's not forget this is a commercial enterprise, pure and simple, nothing really to do with our hobby in the slightest.

A sobering thought, Ray, and very true.

Dave M

Thread: Batteries
17/02/2019 17:37:15

Bryan

Before you do that, you might discharge each pack until the total voltage is about 6.6v - no less. Use a car bulb or similar as a load. Once the voltage gets below 7.2v it starts to drop quite rapidly, so do keep an eye on it! Then slow-charge the pack as described.

Dave

17/02/2019 16:15:02

Bryan

Some cells will be OK while others may not. A lot depends on the state of charge you left them in and under what conditions they've been stored. I'd advise a slow-charge and then, if you can, check the voltage across each individual cell. If you push a pin through the heat-shrink you can find a contact where the cells join. Any cell showing much below 1.2v should be regarded as suspect.

If all seems OK then several slow discharge/recharge cycles will do them good. By "slow" I mean less than C; C being the capacity without the H bit e.g. a 3300mAH pack has a C rate of 3300mA. I usually charge my NiMH packs at approx C/10 for 14-16 hours.

Glad to hear you're out and about again.

Dave M

Thread: Geared motors
17/02/2019 14:00:31

I drilled a small hole in the plastic cover, just large enough to allow me to insert the plastic tube on an aerosol can of light machine oil. The occasional squirt while the motor is running seems to do the trick without the need even to remove the cover.
Works for me.

DM

Thread: Build the Bismarck
16/02/2019 09:47:19

They should have asked me and I would have advised them of the RIGHT materials to make it from....

Aha! This looks like a job for...

hardboard.jpg

Thread: Graupner Jumbo 550 maximum current
15/02/2019 12:34:58

Yes - what he said! I can find no relevant data on 't internet but it seems there were three different versions of this motor (which is long since out of production): a direct-drive one, a 1.5:1 gearbox and a 3:1 gearbox. The geared ones will take less current than the direct drive version, but if you're looking for a suitable ESC then I'd suggest a 20A one. As Malcolm says, if it gets too hot to touch then it's being overloaded.

Dave M

Edited By Dave Milbourn on 15/02/2019 12:35:32

Thread: Riva Aquarama Windscreen
14/02/2019 18:57:17

Keith

This is the stuff I use and can recommend **LINK**

Dave M

Thread: Fairey Swordsman 33
07/02/2019 18:06:26

I cheat these days and use square-section bass, then I sand them to a D section when the glue has dried. It works fine on the water. Not strictly scale, I know, but in that respect my models have flat decks anyway!

Just today finished the 1/16 scale Swordsman kit drawings, CNC parts CAD files, photos, instructions etc. No idea when it will be out there - that's in the lap of Ian Hull at SLEC. Here's the cover of the Manuals -

cover image.jpg

Dave M

Thread: brushless clarification
05/02/2019 09:44:55

Kevin

A workboat could mean quite a lot of different types, but generally I would imagine it has a displacement hull and is fairly slow-moving with a large diameter 3 or 4-blade prop and relatively low revs. If so then you really need a larger diameter motor with more torque and less kv. Perhaps a 35mm diameter motor of no more than 750kv would be a reasonable place to start from.
This might be a good one on a 3S pack **LINK**

Dave M

Thread: Water cooling brushless motor
03/02/2019 23:04:13

MFA 540/1 3-pole brushed motor on 7.2v = 9,000 RPM

XYZ 3500kv brushless on 3S LiPo = 38,850 RPM

QED?

DM

03/02/2019 17:50:20

Chris

Is the model being built from a plan? If so, what motor/prop combination did the designer use? That's usually a good place to start.
And build a surface-piercing prop?? Really?? Sorry to say it, m'duck, but this all sounds like an awful lot to aim for unless you really know what' you're doing and have some remarkable workshop skills and equipment.

Dave M

Thread: lifepop4 batterys
02/02/2019 10:42:00

If you Google "B6AC pro professional balance Charger/Discharger" you'll find a number of informative videos on You Tube. They are totally free of charge and you can always go back to them for reference. I use an X200 Touch Screen charger but it's sadly no longer available.

DM

30/01/2019 12:43:06

I completely agree with Malcolm about using a 10v battery on a 6v motor i.e. don't.
As regards Gary's Tx battery, LiFe and LiFEPo4 are quite different chemistries. Check out the specifications of the latter on a website like Hobby King and you'll find maximum discharge rates much higher than 1C. Here's one at random **LINK**

Sorry about the typos these days, but Firefox has decided that underlining spelling errors is apparently no longer nessurserry.

Dave M

Edited By Dave Milbourn on 30/01/2019 12:46:14

30/01/2019 09:23:18

Hutch

Without knowing what the current drawn by the motors is I can't say for sure, but I'd personally steer clear of servo connectors for anything except devices which plug directly into the receiver. For restricted space and/or light weight I'd go for something like 2mm gold bullet connectors **LINK**

...and it's Dave, please...or I'll think Mum's come back to shout at me!

Dave M

30/01/2019 08:27:45

**LINK**

Seems to be OK and definitely safer than LiPO batteries. The two things to watch for are the maximum charge rate and maximum discharge rate - both usually expressed as a multiple of the C rate. This is simply the "amps" part of the capacity e.g. a 3600mAH battery has a C rate of 3600mA. I would say that you'll be fine as lomg as you don't want to run a brushless inrunner at some iunearthly speed or fast charge the pack in ten minutes! Also make sure that your charger is designed to charge them.

Dave M

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