KD Perkasa help

sybercottage · 19-02-2008

Hi all
I have only just joined the group and am looking for some help. I recently removed my 1/32nd scale fibreglass hulled KD Perkasa from my mothers shed, where it has been sitting for the last 8 years. Everything is in the box and appears in good condition. Also in the box was the MFA marlin motor and mechanical speed controller which I purchased at the same time. In the box was a tin of Isopon P40.

Now I haven’t built a boat for about 8 years so am a bit rusty. Excuse me if the following questions seem basic but I need a refresher. Could anyone advise a suitable adhesive to use on the woodwork build which is either ply or balsa. Also as technology has moved on could you recommend a suitable adhesive to bond the wood to the fibreglass hull?

I am not sure about the speed controller and power plant. Again technology has moved on. Would an electronic controller be better and what type of battery would be best with this setup. The motor and controller came as a matched pair. Any help would be most appreciated.

Best regards

Alan

**Bunkerbarge** · 20-02-2008

Firstly a warm welcome to the forum Alan, I hope you find us informative and interesting.

Firstly wood glue, I always use a PVA based wood glue, which can be purchased from B&Q under thier own name or the good old "Resin W" brand. It is the thick white stuff which can be obtained in a waterproof version. The great beauty is that is soaks into the wood and forms a joint far stronger than the wood, can be watered down and brushed on for detail and intricate work and dries clear. I also use it for making deck caulking because it is tremendously versatile.

As for bonding the wood to the fibreglass, you could use cyano, gell would be better to fill in the undulations and surface imperfections but I would use a two part epoxy such as araldite. The rapis stuff isn't supposed to be waterproof but I think when covered with paint, resin or varnish it will do the job. the safer option is the normal cure stuff but you will have to leave it at least overnight to get a good bond.

As for speed controllers I would definately go for an electronic one. They are lighter, more reliable and can be purchased with built in thermal protection. Two popular varieties are Mtronics solid state ones or Electronise which are supposed to be repairable. I have both and the deciding factor is quite often how much room you have in the boat.

As for batteries, you will have to tailor it to your model and motor. A higher voltage will give you more speed etc but it depends on the motor, prop etc. as to what suits best. The biggest dictating factor will be ballast so when you have decided on what voltage you want, 12v, 9.6 or 7.2 depending on number of cells you will then want to experiment to see how big a battery you need to give you the right ballast whilst giving you the maximum duration.

There is never a quick fix easy answer to these questions, you will have to experiment and make your own decisions. Put the hull and propulsion together and experiment in the bath with differrent voltages. Don't forget these boats were fast and you will need to get up enough speed for it to plane correctly, so that has to be part of the ballast thinking. I've seen a lot of pondside experiments with these models over the years and they are not easy to set up correctly but keep trying, leave your interior with enough space to give yourself options and be prepared to mess around for a while until you get it how you want it.

bogstandard · 20-02-2008

Alan,

Having built a couple of these in my lifetime, both the wooden and f/g version, the first advice before anything else is KEEP IT LIGHT. Anywhere you can put a lightening hole without it showing on the finished model, do it. Just a massive weight reducing exercise. Resin, rather than white metal fittings, it all helps in the long run.

As Bunk said, it is a rather difficult process to get them running really well and onto the plane. They were designed for ic engines which means that to run them on electric takes them into a different ball park. Ic engines gave you a very good power to weight ratio, so they went like stink from the start, but electric propulsion is only just now beginning to catch up with cheaper versions of brushless motors and their related battery packs and controllers.
Rather expensive at the moment.
To keep things light, I personally would go for racing packs rather than gel cells, and say graupner BB motors for the power and put up with the limited run times of about 10 to 15 mins. Get a couple of packs and a pondside charger and you should, if timed right be able to sail, and have a pondside chat while preparing for the next run.

Just to reiterate, if you want it to plane, you will have to get some decent power into it and keep the weight as low as possible.

John

sybercottage · 20-02-2008

Thanks guys for the reply, it is appreciated. A trip to the local model shop and I came away with Zap Z-Epoxy 30min for bonding the hull, and 5min epoxy for the shaft ect. He did recommend balsa glue for the guns etc.

As I mentioned I bought the MFA marlin motor and mechanical speed controller at the same time I bought the boat. I think I will stay with the motor, which is 12v but loose the controller in favour of an electronic one. Comments noted about battery weight, so I think gel will be out of the question in favour of an inline pack and field charger. I have not tried to find any fittings yet but I will try and go for plastic or resin if I can find any.

If anyone knows of a supplier of fittings for the Perkasa, I would be grateful for the contact details.

Once again, thanks for the information already given.

Best regards

Alan

Broomstick · 20-02-2008

Action are another excellent manufacterer of speed controllers and other electrical goodies as fro batts one of the cheapest if not is Component shop excellent service.I have no connection wiht either of these companies only a satisfied customer.I fi had to choose a speec controller I would go either Mtronics or Action as if you send an Electronise speed controller back fro repair you wopnt see it for MONTHS,a sad TRUE fact!!!!!!!!!!!!!!!!! BUYER BEWARE

Dave

bogstandard · 20-02-2008

Alan,
If I remember correctly, the Marlin motor supplied with the mechanical speed controller is a very power greedy thing. I think a few years ago MFA changed the spec of the Marlin, so I would contact them and ask for the running specs of the old motor you have. It might save you from burning out a speed controller, as if you ask for one for a Marlin, they might supply one for the newer spec motor, and it won't have enough grunt to run the older spec motor.

John

IainM · 21-02-2008

Hi Alan,
Don't know whether it will help or hinder, but there are some pictures of my Brave Class (1:35 scale) build on the Galleries (IainM's Gallery).
As has been said ...... keep things as light as possible otherwise getting realistic performance on the water will be difficult.

I opted to make and install a tooth belt drive with a ball race shaft to enable me to play around with speed reduction ratios and also to easily change over motors. The current setting is 2.5:1 reduction and it performs pretty well on 9.6V NiMH's with a 40mm racing prop. There are drawings for this on the gallery.
The motor is an MFA Stingray 600. The MFA Torpedo 500 I tried first was underpowered at anything less than 12 volts and was much more power hungry.
Of course none of this applies if you are going for three screws!!

Couple of things to be aware of ....
None of the fast cure epoxy adhesives is truly water proof. 24 hour stuff is OK. I used chemical metal repair compound to fix the prop shaft sleeve into the hull.
Secondly it is really worth making the transom flap adjustable since small changes in setting can have a dramatic effect on performance. (see pikkies)

Best of luck with your build. If you get it right the KD's can look really good on the water.

Iain

sybercottage · 21-02-2008

Thanks Ian for the photo link, it looks great and very well built.

John the information on the side of the Marlin is as follows:

Voltage 12v D C

RPM 5100

Torque 253 M.N.M

Power Output 68W

Current Draw 0.97A No Load
5.0A typ load

Current consumption stalled 26 amps

Static thrust: 45mm prop: 0.5kg (3.5amps), 50mm prop: 0.55 kg (4.5 amps)

I don't know if anyone could advise me of the ampage for a controller based on the above.

Thanks again for all your replies. It is appreciated.

Best regards

Alan

dynamite25 · 21-02-2008

In mine I am fitting two MFA 850 motors and they also have a water cooling jacket fitted,and they will be controlled by two Electronic Speed Controllers one for each motor and power will be by two 12v flight packs which cost about £50 each unless they have gone down in price.

I will have two brass props fitted with twin brass rudders.

Spec on the MFA 850 motor.

I also have the Huntsman 31 46" 1/2 Wood Hull Version which will have a similar setup.

bogstandard · 21-02-2008

Alan,
Using that information, you would drive the prop direct, of a size around 50 to 55mm. Don't go for a fancy prop, just a standard x type racing plastic prop (keep the money in your pocket while playing about). According to the motor info you have, in theory, with a 12 volt 3 amp hour racing pack, you should get about 30 mins sailing, but with experience expect a little less.
For speed controller, I would go 50% up on stall current (about 35amp or above) and use 25 amp fuses in the power lines.

All this can only be guestimation on the info provided, the only real way to do it is get it in the water (not the porcelain test tank) and play about with prop settings and sizes, you might even find that going down to a smaller prop sometimes gives more speed, and extended running times, because the motor is running in a more efficient power band.

I hope this helps

John