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[Rhodeislander]

Hi all,
 New to boat building(models anyway) I will do a photo load of the box opening and build. Getting some tools together currently and has a few questions after reviewing the kit contents.
 The hull and deck are fiberglass, but motor mount and bulkheads look like 3/16 balsa drawn out on one full sheet, no die cuts.



 
 Glue:
 I have worked with West System on big boats. I assume its the same with models? Microballons 404? as filler to gusset?
 Curious about hull shape while bulkheads cure with epoxy? Anyway to retain shape? Was thinking making a temp bracket to hold hull deck joint area while curing?
 I will take a pic of that sheet later tonight.
 Bud

[Rhodeislander]

Parts, etc.

[RST]

Hi, you're already a bit further in to this aren't you according to RCgroups?  You're asking questions you asked there a month back but you progressed since???  It might be easier to keep the same threads running at the same time if you need feedback on the same thing?

https://www.rcgroups.com/forums/showthread.php?3984015-New-build-MFA-Spear-Police-boat/page2


...don't be shy you're already on to cutting the hull for drive train a few days ago, so bring us up to speed please.

Rich

[Rhodeislander]

Rst,I decided to move the build here as this forum seems more active. I actually excluded questions that have been answered. In reality, I have not put anything together. I will update this forum today.
Bud

[Rhodeislander]

The mount was built for the gas motor option, I was going to mount a flat thin ply plate ontop. The fit is just not very good and big gaps between mount and hull.

[Rhodeislander]

I have the motor and esc finally. I went with the 2300KV to keep rpms down.
 I found a coupling that allowed 3mmto 5mm. Need to grind a flat on the shaft for the grub screw. Not sure what to do with the nut on the shaft on the coupling side?
 I thought maybe another thin nut as a jamb nut? Adjust coupling then lock that nut against coupling?
 What have you all done in this situation?I also wonder is a nylon washer closest to the shaft tube at each end might be a benefit?
 Bud

[Rhodeislander]

The hull slot has been cut to 1", once the prop has been slide forward to its location, the angle for the electric motor has to be dealt with. I'm thinking of scrapping the gas style mount. The kit has a bulkhead template for an electric motor I may use. It would be a bulkhead with a hole in it, then if I connect the shaft coupler the angle transfers. The bulk would be tilted at that point, and just epoxy in place? If I use the gas style mount, I have some thin sheet metal to make a L bracket, but it may flex too much.

[RST]

Rst,I decided to move the build here as this forum seems more active. I actually excluded questions that have been answered. In reality, I have not put anything together. I will update this forum today.
Bud

No worries "Bud" -it's also OK to call me Rich or Richard when I sign-off as it on posts!!!  But it helps on a new forum if you keep up to date with the posts otherwise it's not fair on us new folk.


"I have the motor and esc finally. I went with the 2300KV to keep rpms down" ....that's not usually what I hear of sensible brushless motors (very high rpm on otrunners and lower torque) but some folk such as Backerther make high rpm inrunners work so I will bow-over to anyone else like that are far more knowledgeble from now.  If I'm not mistaken your propshaft seems a very steep angle though, you may want to lengthen the hole in your hull by 6-7-10 times or much more to have the propshaft at a more reasonable angle and fit a support / strut in just before the prop also.


Good luck with your build,

Rich

[Dave_S.]

I am also surprised at the idea of 2300 KV as 'keeping the revs down' - what battery are you planning to use? I am restoring and re-motoring a 46" Crash Tender I bought recently, and for that have chosen a 500KV motor which I will run on 6S Lipo packs - shaft RPM should be in the 10,000 RPM are which I expect to result in a good speed on the water when required.


Even using a 2S pack with your 2300KV motor will give a shaft RPM of about 16,000 - which seems very high to me. The motor will also be drawing a large current to turn any meaningful propeller, whereas a lower KV & higher voltage will result in lower current draw and the ability to use a reasonable size of prop.


I'd be interested to read why you have chosen the high RPM route as it may well be that I have missed something in going the high voltage/low KV route - I'm always open to being educated!

[Rhodeislander]

Hi dave,My theory was if the KV number was lower, it would result less rpms once multiplied by voltage. I have a dozen 7.4v packs from cars laying around, so figured I would make use of them. I chose the 3650 configuration (36 in the 3650 meaning 36mm case.)as it seemed substantial in size for this type boat. I did not see lesser Kv offered, I did see much higher Kv in this type motor which would result in higher rpms. The boat and prop were designed for up to .60 size gas. It looks like the rpms would match that configuration?I see my prop is threaded inside the hub, anyone know where to buy this type? I see the dog style used now. Maybe I should switch the shaft over to a more modern style?Thanks
Bud

[Dave_S.]

I can see the logic in that, but it will only be able to turn a relatively small prop. A fairly ordinary .60 glow or gas should be producing at least one BHP, which is roughly 750 watts, which with a single 7.4 pack means a drain of over 100 amps, which in turn means lots of heat and very short run time. Not many battery packs are capable of delivering that much power without damage.


If you used a lower Kv motor with two of those packs in series, then the current to produce 750 watts would be only 50 amps, still high but not unreasonably so. That's why I chose to use a low Kv (500) motor in my Crash Tender which has a similar power requirement, so I can use a 6 cell LiPo pack (22.2 volts) meaning a current draw of about 33 amps for 1 BHP at about 11,000 RPM. I haven't installed the motor in the boat as yet, but have used the same logic to determine the motor KV and battery voltage for several boats that I sail fairly regularly.


That's my way of looking at it, there are several ways of going about it. I start from what sort of RPM the model needs and what power would be required to turn the chosen prop at that RPM.

[Rhodeislander]

Rich, the angle was too much as you noted. I opened the slot a little more and brought the shaft down. The supplied support gave me the angle to shoot for. Now the prop sits closer to the hull and looks better.Picture is before the slot was opened up.
Bud

[Rhodeislander]

Dave,The instruction says .29-.40 for normal operation, and .60 for performance. I'm looking for more of scale speed.Here is a picture of the supplied prop. Again no idea of its spec.
Just going to run with what I bought and see what happens.
I spent all day trying to figure out a way to mount the motor low enough to match the new lower angle, the old gas mount was too high. I used a contour gauge to make a new support. I have an whole new issue now. Its seems the coupler is too large on the shaft side. Its has too much play with shaft inserted, it really never centers. I tightened the two grub screws and spun the prop, the motor and mount move up and down as I spin it. I'm sure this will cause loads of vibration if I dont cure it. Looking for a new coupler. I cant use 2 nuts on the motor side either as the shaft is not long enough. I was going to grind flats in the shaft for the two grub screws and then tighten the nut against the coupler. I can then adjust shaft end play with prop and nut at that end.I feel like im going in circles.I thought may get a kick out of my make shift workshop on the back of my golf cart.
Bud

[Rhodeislander]

So,The shaft fit too loose in the coupler I bought. I measured it with calipers and came up with the reading 4.6mm or .18 inch. The coupler is 5mm. I think I need a 3.5 mm for the motor and a 3/16 for the shaft side....To be continued...Bud

[Dave_S.]

I think our entire house would fit into your workshop! I have to make do with a spare bedroom too small for an actual bed.


There's a lot of trial and error in getting things lined up and running smoothly. Mostly error, in my case! Looks like you're doing it right and getting the drive train lined up and running smoothly before putting the deck on. My last few boats have been 'rescued' from e Bay and I had to get my far from tiny hands into some very awkward spaces to get motors in and out repeatedly.

[Rhodeislander]

Sorry for not responding but life gets in the way.My 84 year old independent mother fell down her stairs. I have spent the last couple months getting her into rehab, and then thru a covid infection.I stopped by my local hobby shop that really sells trucks and cars, and asked for a motor shaft universal. He asked what I was working on, and he pulled out a Traxxas Blast missing several parts. I bought the coupler and he handed me the Blast for free. Off topic I know, but I will post a pic when I have more time.I was running into another state on business and had to wait before the meeting. I pulled up the online service for selling used items and typed in RC boat. I see a listing for a Proboat Sonic wake 36" raceboat.I figured well I was in the area...The boat used once, rtr was maybe worth 400.00 It had a spectrum smart charger that will charge 2 big lipos at once. Maybe 150.00 4 Lipo packs 100.00 each. The package was a good 900.00 dollars US. The guy was a RC plane guy as I could see by his shop, and all monster planes. He says he will take 250.00 for all the boat stuff. So, of course I bought it. he then says a friend is a CA glue rep and fills my pockets with CA gel glue, 8 bottles in all.I figured you would all get a kick out of my RC boat addiction. Im packing the Spear, and my shop, into my truck and heading south to Florida. I will setup a second build area in the Florida house for my winter stay. Hopefully get some pictures of what those guys are up to, and the work as it moves along on the Spear.Merry Christmas!Bud