1/20 scale Aluminum WW2 ELCO PT Boat

[ozzie-crawl]

plenty of room in side maybe some big low kv out runners or maybe some drill motors
not sure on scale boats but thinking you only want fairly slow prop speed
hopfully paul (785boats) will chime in as im sure he will know

[CornelP]

Actually Doby has a good point here... You could change gears to lower rpm and enable the motor to go full speed, but this would be also amp hungry... you're talking 60-90A continuous.
A Graupner Speed 820 will draw only 24A at maximum and could be powered from 16 to 24V.
I somehow think you could design an easy to change system for the motors... shaft diameter is pretty much the same for these big motors: 5mm. A small tray on two screws to carry motor and ESC, so it will be plug and play.

http://www.cornwallmodelboats.co.uk/acatalog/graupner_6375.html

[Gerwin Brommer]

or take the wipermotor out of your car .....................

[kenb]

Motor & controller

Hi guys,

Summer is coming fast, so I got back into researching the motor and controller choices for this boat again. I've been looking at the components listed below, and I wondered what you guys think of this stuff. I haven't made any decisions about where I'll buy any of it yet, I'm just evaluating what's out there at this point.

I'm looking at using the Graupner 900 BB TORQUE motor in the PT Boat, powered by sealed lead/acid wet cells ganged up to 12 or 24 or 36 volts, depending on whether I intend to go fast that day or not. If I'm spending the day at a scale model regatta, I'll gang them up to provide lots of 12v power for a day of slow running at a show, and then I can change the harness around to provide 24v or 36v with the same set of batteries for faster, but much shorter runs at the ponds.

Here's a link to the specs on the Graupner 900 BB TORQUE:

http://www.cornwallmodelboats.co.uk/acatalog/graupner_6373.html

Most of the controllers I see only deliver up to 12 volts, but here are a couple of them that deliver 28v & 36v

Graupner MOS 60

http://www.cornwallmodelboats.co.uk/acatalog/graupner_7176.html

and the SC480 (scroll all the way to the bottom, it's the last one on the list):

http://www.cornwallmodelboats.co.uk/acatalog/esc.html

Anyone have any comments or suggestions about the suitability of these components for a boat like this? The empty hull weighs 12 pounds, and I suspect the completed boat will weigh roughly 18-20 pounds before the batteries are installed.

Ken

[CornelP]

Welcome back, Ken.... I've been waiting to see this finally done.
The graupner unit is a very good piece of kit, you have to watercool it but it is very stable and solid. I have one that has been through some rough times and still works ok. BUT it has the problem that the SC480 was designed to fix: low speed control. I would say this is the best choice, as it also allows for speed by just moving a switch...

[kenb]

Welcome back, Ken.... I've been waiting to see this finally done.
The graupner unit is a very good piece of kit, you have to watercool it but it is very stable and solid. I have one that has been through some rough times and still works ok. BUT it has the problem that the SC480 was designed to fix: low speed control. I would say this is the best choice, as it also allows for speed by just moving a switch...

I was liking the looks of the SC480 myself, it's reassuring to see that someone agrees! It tough to tell how big it is in the picture with nothing for comparison, but judging by the size of the wires it's a pretty large unit.

I can only find a supplier for it in the UK so far, anybody know if they are available anywhere in the USA or Canada? I'll get back to googling for it in the meantime.

EDIT: I seem to be having trouble finding a brand name for this part, is SC480 a generic name for a part that is made by different manufacturers?

Ken

[CornelP]

I was also looking a bit around, but the manufacturer, Model Control Devices, seems to have disappeared... so maybe they do not have a good product support anymore?
They are still on various directories for Canada, but the website seems to be down...
http://www.modelcontrol.com

[ozzie-crawl]

i dont know much about scale boats but if you want a high torque slower spinning motor to push a large hull how about this sucker
http://hobbyking.com/hobbycity/store...ner_(eq:_70-55)

[Xfactor]

Scale speeds dont require all that technology its over kill. Although your beautiful work just begs for something extravagant your application doesnt call for all that. I know it isnt fair that a brushed motor gets such a nice home. They call that seniority dont they?lol

[kenb]

Batteries and controllers

Thanks for the comments and suggestions guys, it's been very helpful. I'm still undecided about which way to go, as I still have some serious learning to do about this electrical stuff.

I've been doing some more measuring within the hull, and it appears that my choice of using sealed lead/acid batteries for the power supply is going to be a non-starter. The 6 & 12v ones I'm looking at right now are quite big & tall, and they simply aren't going to fit through the hatches. The other problem is that lead/acid batteries weigh a ton, and I doubt I'll be able to cram enough floatation inside the remaining interior space to float the thing if it wants to go under.

So, that leaves me looking for other options for batteries. Would anybody be able to suggest an alternate battery type to run a power hog like the GraupnerBB 900 Torque in an aluminum boat? I'm guessing that whatever you recommend, I'm probably going to need quite a few of them! Bear in mind that this will mostly be a scale model regatta boat, with the odd trip to the pond to let her rip once in a while.


CornelP - With regards to the controller, I can't seem to locate the original supplier for the SC480 anywhere yet, so I might be back to looking at the Graupner MOS 60. You mentioned that there were low speed issues with this unit, I'd be very interested in hearing some more details about the problems you experienced.

Ken

[kenb]

i dont know much about scale boats but if you want a high torque slower spinning motor to push a large hull how about this sucker

Whew, that thing is positively scary, the spec sheet says that it produces power equivelant to that of a 60-80cc gas engine! I was originally going to put a stock 25cc Zenoah in the PT Boat, and I thought _that_ was going to risky. I've since decided I'm going to keep the PT Boat on the slow side, just to make sure I don't have any fender benders with it or anything.

Still though, it's nice to know that somebody out there is producing stuff like that, I may just end up designing a project around one of those one day. Retreival boat maybe? LOL.

Ken

[CornelP]

Well, the problem is in the first 10-15% of throttle. Most ESCs will work perfectly beyond that. On a scale boat you will need a lot these 15%... There are only a handful of ESCs that can perform at low speeds, and one option could be the ones designed for rock crawlers (the only ones I can think of where slow speed is a must).
My personal problem with the Graupners first appeared when I was getting back to shore my Baby Bootlegger, almost smashed it in the concrete bank... no real control . Initially I thought this is mainly the Tx, but even with a better quality one, the experience was the same.
As far as I can see, over at RCGroups (more scale oriented), they tend to use a lot the old astrofights and a lot of Traxxas... there has to be a reason for this...

[Hydromaniac]

Fantastic workmanship!!!!

[Xfactor]

Buy nickel/mh you can get them cheap now and for your app they would work.

[Xfactor]

If low speed is an issue you better stay with a brushed set up. These sensorless brushless motors are not all that smooth down low. If youre gonna go that route you better look at some sensored brushless power. Like the kind you see in the brushless car.05's. If you go the brushed route a 50 amp or so h-bridge esc will be plenty smooth down low.