Topic: Vic Smeed Rorqual bulkhead drawings wanted (Read 8901 times)

Andy M · « **Reply #25 on:** March 28, 2021, 09:20:24 pm »

It was quite tight getting the motor in on its mounting plate and the coupling joined before I glued the plate in position. I will still be able to remove the motor easily, hopefully. The rest of the radio was fitted, then a test, not on water yet but still showed me what I needed to know...
Finally think I have a suitable setup for this little boat. Its a screamer, I actually thought it was going to explode at one point. I was making sure the prop was facing well away from my face, hands etc...
I have brushless planes, but this will be my first brushless boat. I am expecting it to be fast, judging by the test. Cant wait to try it, I might even try it in the bath for a idea of how much water it can shift.
I have my 2.4ghz radio in it, so the radio link should be solid for its next river outing.

Andy M · « **Reply #26 on:** March 28, 2021, 09:21:19 pm »

Short video here

https://youtu.be/NYWFrjAMtwA

Subculture · « **Reply #27 on:** March 29, 2021, 11:03:26 am »

Might be a bit overpowered now. Can always knock it down to 2s though. What's the KV of that motor?

Andy M · « **Reply #28 on:** March 29, 2021, 11:51:28 am »

The motors are 4 pole 2838 4500kv. They were midway down the kv range of the motors on the specification sheet that came with the motors.
It does sound (really) fast, it is my first brushless boat so no idea what kind of speed that equates to, I hope to do a bath test at some point today, still feeling a bit rough after my covid vaccine on Saturday, so will see how I feel later.

Subculture · « **Reply #29 on:** March 29, 2021, 12:16:51 pm »

2s for that kind of kv. 3s is too much IMO, you'll find it overpowered. Even on 2s you're pushing it for a little boat like that.

Andy M · « **Reply #30 on:** March 29, 2021, 12:36:02 pm »

Rorqual weighs around 460g with the 2100mah 3s pack, feels quite a lump.
Bath test shows waterline at rest. I knew it would sit a bit lower than it did with the geared quadcopter motor and a 2s 500mah pack and its lighter speed controller.

Andy M · « **Reply #31 on:** March 29, 2021, 12:36:51 pm »

Short bath test video here
https://youtu.be/ffqMXdENFPc

Andy M · « **Reply #32 on:** March 29, 2021, 12:42:03 pm »

No shortage of power now, I was surprised by just how much thrust it has on the 30mm medium pitch prop that came with the propshaft. I can drop to a 2s pack if its too wild.

Andy M · « **Reply #33 on:** March 29, 2021, 01:15:36 pm »

I think the thrust is exceeding the weight of the boat, not sure how that goes in boating but for aircraft, it means you can go vertical after you take off like an F15 eagle.

Subculture · « **Reply #34 on:** March 29, 2021, 01:47:06 pm »

You'll have a job keeping it upright on 3s. There is a limit for a boats power to weight, and with brushless and Lipo it's easy to overpower things. Was never really an issue in good(bad) old days with brushed motors and nicads.

Andy M · « **Reply #35 on:** April 01, 2021, 08:28:15 pm »

Ok, I underestimated the motor just a bit, I had far too much rudder movement as well, as it was pretty twitchy. I got up to about 1/4 throttle and was in a straight line so I gave it an extra bit, probably about 1/3 throttle and the whole boat rotated round the motor and ended up upside down in the river, socks and shoes off, and wading in to the bouldery freezing water, stubbing my toe but trying to intercept it before it headed off downstream.... I made it past a dead tree in the water and got to it just in time. Filled with water, so gear all needs airlined and dried properly before I test it.
I think 'going to need a bigger boat' applies here! 😁

Andy M · « **Reply #36 on:** April 01, 2021, 08:50:56 pm »

I have only used brushless motors on planes before, where a smallish motor can drag quite a large plane, but built from depron so they are super light compared to a similar sized, balsa glow plane.
My motors are about 380 brushed size, which is a good bit bigger than the brushless fan motor I have on my 2 metre span camera plane! It weighs about 2 pounds and has 2m wings to stop it torque rolling.
Rorqual's hull is only a matter of ounces, I think the motor just spun the hull around it. Its narrow too.
Far too much power, as warned.
Didnt listen, well I did, but decided to try a shot of a drag boat anyway. 😁😁😁
Its a Little Monster right enough.
If my radio still works, I am going to put it in a bag this time, and have another go on a 2s pack.

Subculture · « **Reply #37 on:** April 01, 2021, 09:01:53 pm »

It'll still be too hot IMO at full throttle. A motor around 2000-3000kv depending on whether 3s or 2s is desired, would be ideal. The emax cf2805 re superb motors for this type of boat. They're my main go to motor for planes and fast electric boats. https://www.4-max.co.uk/emax-cf2805-motor.html

About eight quid on ebay.

Andy M · « **Reply #38 on:** April 01, 2021, 09:54:57 pm »

I have something similar in a plane just now, it might be going in a boat for a try.

Andy M · « **Reply #39 on:** April 01, 2021, 11:33:58 pm »

Any hull size recommendations for my motors?

Andy M · « **Reply #40 on:** April 02, 2021, 12:22:29 am »

I just had a look on ebay to see if there were any boat size recommendations for these motors, found these 2 in jet drives, but it says suitable boat size under 15 inches? My Rorqual is longer than that. Unless the jet drives are really inefficient compared to my propped versions? Confused a bit, but will keep researching.

Andy M · « **Reply #41 on:** April 02, 2021, 12:23:09 am »

Forgot photos😁

Subculture · « **Reply #42 on:** April 02, 2021, 12:13:08 pm »

Probably using tiny props, plus with a jet you get negligible torque effects. Very high revving motors are best suited to surface piercing props. For a submerged mono hull you want lower RPM IMO.

I use the following equation for getting a rough idea of speed prop pitch(mm) x RPM x 0.000022= speed mph. That accounts for a lot of slip, as small model props are very inefficient.

Plugging the numbers in for your boat, assuming a 1.2x pitch on the 30mm prop and 3s-

36 x 49950 x 0.000022= 39.5mph(!!)

Even on 2s the figure equals 26.4mph. You could try a smaller prop if you find the speed too much.

Andy M · « **Reply #43 on:** April 03, 2021, 03:35:52 pm »

Jeezo, it was probably doing over 10mph when it flipped at 1/4 to 1/3 throttle.
Obviously too much for my tiny hull. I have already started on a bigger boat build. Lol

Subculture · « **Reply #44 on:** April 03, 2021, 04:55:01 pm »

Well torque roll is a likely factor- the Rorqual looks a fairly narrow hull. Fitting a torque wedge may help a bit along with some strategic positioning of components inside to counter the torque roll and experimenting with smaller diameter/pitch props.

Andy M · « **Reply #45 on:** April 03, 2021, 08:59:42 pm »

I have temporarily decommissioned Rorqual and will be using the motor in a bigger build, a 26 inch long hydro, and I will take your advice and try it on 2s pack to start with.

Andy M · « **Reply #46 on:** April 06, 2021, 12:13:30 am »

Here is Rorqual next to my 'bigger boat', hopefully this hull will handle the power a bit better, I will be going for 7.4v for initial tests.

Subculture · « **Reply #47 on:** April 06, 2021, 11:13:21 am »

That hull could probably handle a bit more power, but you certainly won't be overpowered now.

Andy M · « **Reply #48 on:** April 06, 2021, 12:04:40 pm »

Hopefully I will get a longer shot of this one, the Rorqual had about 15 seconds before I flipped it. I still think it will be fast as it is very light for its size.
I kind of like the uncertainty of testing a new model, adds to the excitement. Especially as I have not had any experience of brushless motors in boats, apart from Rorqual, which wasnt very successful. It did give me an idea of how much power they have, so not all bad.

Subculture · « **Reply #49 on:** April 06, 2021, 01:21:54 pm »

That Rorqual looks about 15-16" long? If you use the motor I listed earlier, it should be a really fun boat to run.

If you want to run 3s for the same performance look for a similar size motor around 1700-2000kv.

The power limit for a boat of that size and type is around 100 watts, perhaps a bit more. the small cd-rom type motors tend to max out around that figure.

The shovelnose should be very quick, but they're hopeless in a small pond, cause they need a wide radius to turn.

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Author Topic: Vic Smeed Rorqual bulkhead drawings wanted (Read 8901 times)