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Member postings for David Hepworth 1

Here is a list of all the postings David Hepworth 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Fairmile D - help needed
17/06/2020 15:53:35

Hi Charles

No. Not upset. I never get upset over what is said on the internet. I save that for real lfe. I was worried that I had upset someone else.

I agree about 4 motors but the previous owner of the hull had already fitted 4 prop tubes...and, as the original Fairmile had 4 props, that's what i'll go with. More importantly will be the props. The current 3 blade brass ones will be rubbish, I know, but they look the part, so i'll live with them for now.

The batteries i'm using are fine for heavy current and deep discharge (I use them in my work).

The effective current is nothing like 25Amps, as i'm running the motors at 12v, and nowhere near full power. I reckon closer to 12Amps effective.

Hi Malcolm

Not ideal for the application, true, but i'll use them to get the boat in the water. I reckon i'll get about 20mins use before a battery change. I have a few different boats and, when I can drag myself to the pond, I like to give them all an airing so 20 mins would be fine. If I find I'm happy with the boat and i'm using it more then I'll change them out for a Lithium battery.

17/06/2020 11:36:13
Posted by Dave Milbourn on 17/06/2020 11:09:37:

I'm not saying you're wrong - you're probably right but no harm in having a bit play about, is there?

Yeah - whatever.....



Have I upset you in some way?

17/06/2020 09:32:21

Hi John

Motors are Graupner 600 ECO, with 30mm 3 blade brass props.

I'm driving at 12v (2 x 6v 12Ah AGM) and nowhere near max power as the scale speed would be stupid fast.

Yup - I'm expecting to have to buy a second ESC but...

As well as current limiting, my ESC has thermal limiting too (they're more usually used for robotics applications).

The batteries i'm fitting arrived today so I should be able to get the hull in the bath.

Static water is worst case. If it works in static water, it'll be fine on the pond.

If it goes into current limit, or thermal limit, i'll have my answer.

17/06/2020 08:39:58
Posted by Dave Milbourn on 16/06/2020 18:44:03:

DC electricity isn't very tricky stuff, whatever connotations and complications the digital revolution might have brought us. However 25A is still only 25A, while those particular motors are best running at 12A each. Restricting the current to 50% is like selecting the wrong gear in a car or on a bike. No doubt your laptop knows better, so good luck.

Dave M

Hi Dave

As ESCs use PWM, is 25A at 50% duty is the same as constant 25A?

What is the difference between a purely resistive load and a high frequency reactive load?

My laptop doesn't know better, it's just a tool.

I'm not saying you're wrong - you're probably right but no harm in having a bit play about, is there?

16/06/2020 17:10:38

Thanks John, very useful.

I agree, I think 4 x 600s will be over powered but that's what came with the hull so they're getting used.

As mentioned above, I can program my ESC for whatever max power I like to give a reasonable max scale speed.

That'll be me at the pond with my laptop plugged into the boat wink

16/06/2020 11:23:01

I'm using one of these ESCs. Has anyone used one of these before?


Its more usually used for robotics but accepts RC servo inputs so why not?.

Good for 25A continuous without heatsink and runs at 22khz so no ESC 'squeal'.

I've been playing about with it on the bench and It's a cracking piece of kit. Fully programmable for max speed, acceleration, current, temperature etc.

I'll set the current limit at max (25A) and see how the boat behaves in the pond. If it's too sluggish, i'll add another ESC and split the motors port/starboard.

16/06/2020 10:30:14

Hi Ray, Yes, it's about 60". 1/24 scale.

It has to have its own shelf in my workshop and gets put away before I can do anything else.

I bought the hull (fibreglass) years ago from a pal, and have only just got around to doing anything with it.

The motors, shafts, props and A frames came with it.

I chickened out of doing a scratch build superstructure. I'm using Russel Wilson's kit. So far it's coming together quite well.

It's upside down at the moment getting a coat of paint on the hull. I tried acrylic paint...and its rubbish. Just not binding with the filbreglass. So, thats coming off. Must remember... do a test patch first... do a test patch first.

16/06/2020 08:46:06

Next thing...

I'm running with 4 props & 4 motors (brushed Graupner 600 Eco).

I currently have them all on a single ESC. This works fine on the bench but i'm reading about folk that split port & starboard motors off different ESCs, and using differential throttle to help with slow speed steering.

Would I see much benefit from this or is it over the top?

If so, would you recommend just doing it off two joysticks or using a 'rudder mixer'?



16/06/2020 08:23:15

I'm thinking an 'aft' deck hatch is the way to go.

Thanks for the advice

-Ray Wood " planking joints are so bad you couldn't see the join" smiley

-Dave Cooper "I wouldn't worry too much about deck joins etc showing as once it's out on the water you won't be able to see them !" wise words.

15/06/2020 01:35:38

Hi all

I'm building a 1/24 scale Fairmile D.

Everything going fine so far but i've hit a snag which, hopefully, the more experienced can advise me on.

The Fairmile D superstructure is quite a modest affair and therefore the hole in the deck it conceals is quite small and gives limited access when removed. There's enough access to change batteries and get at the electronics but, if I needed to replace a motor, i'd be snookered.

Question you folk ever fit the deck and hope nothing fails, or is there a more cunning way of retaining access. Is there a practical way of making the whole deck removable and, if so, how do you make the 'seam' invisible?

Thanks in advance


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