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Author Topic: RAF Range Safety launch electric drive options  (Read 6237 times)

rayna

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RAF Range Safety launch electric drive options
« on: October 26, 2009, 12:27:17 am »

Hi team ,
I have just purchased a good secondhand model of the 43 foot range safety launch built 1 inch to the foot (1:12) and at 43 inches long she is a nice size of model.
I have no information on how it performed on the water but I understand that these planing hulls are not that simple to set up for a reasonable performance on the water.
She is fitted with twin 6V Decaperms and the sliding resistance type speed controls but only battery positions for 4 x D type cells. This I am sure will be VERY limited in speed and duration. The props are 25mm diam three blade brass, chrome plated with maybe 35 degrees of pitch with generous blade width.
I am figuring i will need to set up with new batteries and maybe motors so am asking for some drive/battery advice from any who have the same or similar models on the water that have a good performance speed wise (on occasion) and a reasonable duration.
thanks all
Ray
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HS93 (RIP)

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Re: RAF Range Safety launch electric drive options
« Reply #1 on: October 26, 2009, 08:36:01 am »

go for a Pair of 700bbs  9.6v the decaperms are a nice but old slow revving motor as in one of your other posts you use Li polys use a min of 12v and you can happiley go up to 19.2 if you put the extra coil around them to watercool, you will have to play props but there are plenty of set ups about as they have been used for some time and are about 19 each  you can up the volts from 12v to get more speed, but two on 12v should be a good starting point and you only have to add batteries .there is a chart on the fire boat web site that people have posted there set ups and as the ranger is similar to the 12th scale firetender for should find a set up that suits.

http://modelfireboats.com/rc/setups.php

peter
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rayna

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Re: RAF Range Safety launch electric drive options
« Reply #2 on: October 26, 2009, 09:12:33 am »

 ;)
Thank you Peter. I need to weigh this beast as I think I might have a real problem with weight.
Will locate a scale and do that tomorrow and get back.
thanks
Ray
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andyn

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Re: RAF Range Safety launch electric drive options
« Reply #3 on: October 26, 2009, 10:55:56 am »

Sell the Deca's on ebay, that'll make you enough money hopefully to buy a MMB 900 and an ESC for it :-))

http://www.marksmodelbits.com/
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rayna

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Re: RAF Range Safety launch electric drive options
« Reply #4 on: October 26, 2009, 08:52:16 pm »

Hi again,
Well I weighed the beast and it is around 18 lbs without batteries so I guess I do have some problem.
Maybe TWO BB700s or MMB900s with suitable batteries and up the prop size to 30mm or change to a two blade fast fizz boat style.
The "fireboat" web page table had a few at my length ~43" but they all had single shafts.
I will get 4 "D"s today and just see what it does do with those. We have an Armistice Day celebration at a local park, which has a temporary set up pond for the day which is limited in size so a slow speed might be appreciated for that.
thanks all
Ray
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HS93 (RIP)

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Re: RAF Range Safety launch electric drive options
« Reply #5 on: October 26, 2009, 09:43:25 pm »

D cells are a waist of money and are not up to it  dry D cells will last 5 min  and rechargeable ones even the 7000 wont give it up fast enough and I am not shore if you can get them in fast charge .  borrow an alarm battery 12v and run the motors in series it will save you money as the decoperms are not going to get it flying so you may as well have duration then think about what you want speed or run time and how much you want to spend..

Peter
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rayna

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Re: RAF Range Safety launch electric drive options
« Reply #6 on: November 09, 2009, 12:28:57 am »

 ;)
hi all Well we had two days on the weekend and i tried her out with the decaperms linked to TWO 6v 12 AH gell cells but speed and duration were not good.
Unfortunately one decaperm has been overheated so has had it anyway so now need to consider the suggestions made ie TWO 700bbs with lipols 14.2 volt so thats TWO 2 packs. Will see if can finance it all and take another look. My resistance type SCs will be no good I suspect as well.
cheers for moment
Raynor J
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FullLeatherJacket

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Re: RAF Range Safety launch electric drive options
« Reply #7 on: November 09, 2009, 08:54:26 am »

Raynor

Bullet-biting time.

25mm props are way too small for this power train. I run that  size prop on a Speed 400 in a 20" all-balsa Swordsman. With the weight of two 6v 12AH gel-cells as well (2 Kg each) then your model will do little better than sit there and slowly whisk the pond-water. The Decaperms are geared motors, so you would probably do better with something like 45mm-50mm 3-blade props.

Using two SLA batteries connected in parallel there's every possibiilty that one is discharging into the other and so starving your motors of power and slowly damaging both batteries.

Steer clear of LiPo batteries unless you fully understand the correct way to operate them - they are NOT fit-and-forget items. Be aware that, at best, you'll only get betwen 100 and 150 charge/discharge cycles out of them, whereas you'll get nearer 1000 cycles from NiMH cells. The only real advantage of LiPos over NiHM cells is weight, but there's no need to worry about that too much once you've removed those heavy SLA bricks. 4600 mAH NiMH Sub-C packs is probably the best option here.

The best place for resistive speed controllers like those you have is in the bin - or maybe the Science Museum. They waste power like nothing else I know, apart from supermarkets who insist on fully lighting their stores all night.

Suit yourself, but change the props, speed controllers and batteries at the very least.

FLJ
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tony52

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Re: RAF Range Safety launch electric drive options
« Reply #8 on: November 09, 2009, 06:59:40 pm »

Have you read the item by Hugh Bright in MMI Nov 2009? re: Brushed vs Brushless motor comparison?

A 37" single screw Perkasa is tested with brushed and brushless motors. The results are in favour of brushless, showing a 35% increase in speed, a 30% reduction in power and less heat. The motors and speed controllers used are very realistically priced.

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rayna

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Re: RAF Range Safety launch electric drive options
« Reply #9 on: November 09, 2009, 08:01:55 pm »

 O0
Thanks FLJ and Tony.
A couple of things . i made a mistake on the twin screw prop size's they are actually 50mm 3 blade.
The 6v gel cells were brand new but not sure of the charge condition. I did put them on charge first but only for ~12 hours.
Already have decided the motors are to be changed. One as previously stated is definitely kaput.
Can get the following Graupner items here
Speed 700 bb 12v,
700 8.4v and 12v,
700 RACE 9.6v
600 7.2v
can get all the Viper ESCs Electronise have to be bought from UK, Nothing else locally except car helio and aircraft stuff.
FLJ would you have a suggestion amongst that lot to use your NiMH 4600aH suggested set up. thanks on that.
TONY I will find that article and take a look see thank you.
Raynor J
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DickyD

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Re: RAF Range Safety launch electric drive options
« Reply #10 on: November 09, 2009, 08:28:54 pm »

Come on FLJ put on one of your diagrams, you know you want to. ok2
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rayna

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Re: RAF Range Safety launch electric drive options
« Reply #11 on: November 16, 2009, 12:06:54 am »

 :o
Tony . Just visited our local model shop and MMI for November is not here yet so I will have to wait about a month i am told. So shall probably twiddle thumbs and work on other things till I get a look at that article.
cheers
Raynor
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rayna

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Re: RAF Range Safety launch electric drive options
« Reply #12 on: November 20, 2009, 09:21:45 pm »

 %)
Thanks all. one of the forum members has set me the article so now have a bit more to go on. Thanks for all the help
Raynor
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