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Nov 05, 2017, 04:12 PM
Registered User
Discussion

This is turning into a


Very frustrating hobby!

Smoked out a new esc, First run round the pond, balance was way off, nose was plowing under the water, brought it in, re-positioned battery further back and sent it out again, still nose heavy so I powered up to see if it would lift up on the plane. It didn’t, it nose dived, completely submerging. Popped back up no problem. Started trying to bring it in and it cut out, and wouldn’t go. Whilst I was sorting out the rescue kit my boy calls out “daddy it’s smoking” I look up and indeed it is. While I was looking on helplessly it smoked harder then with an audible pop pressure popped the waterproof tape and clouds blew out. I thought the lipo had gone and I fully expected flames to follow, but fortunately not.

I think it was a plumbing fault, there wasn’t any water in the pipes, its got 2 pickups so I’m not sure why it wasn’t working.

I’ll try warrentying the esc, doubt I’ll have much luck.

This is way more frustrating than nitro heli flying, and that is very frustrating indeed!
Last edited by Mambawan; Nov 06, 2017 at 07:41 AM.
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Nov 05, 2017, 04:43 PM
AndyKunz's Avatar
I would have used a 90A ESC.

Andy
Nov 05, 2017, 04:51 PM
Registered User
yes, sorry to say, it can be a very frustrating hobby. I wonder, though, if more than just your ESC is a problem. While battery position will certainly contribute to, and even cause, the porpoising and nose diving, I would look for other possible causes as well. Such as, shaft angle, trim tab settings, and even the prop itself can contribute to excessive stern lift.
You did not describe your cooling system and H2O pick-up so it is hard to make comments there, but they could be related to your drive line set-up as well. If you know anyone who has run a similar boat before, you might ask them to once over yours, for constructive criticism.
Jonathan
Nov 05, 2017, 05:10 PM
Registered User
Wow, lucky it did not catch fire and burn to the waterline. With no water in the lines that would account for the heat.

With a new boat or setup you might want to do a 30 -45 second run, and bring it in a check temps and cooling lines for water. Back out for another minute or so and check again. A shake down run on a new boat is always a good idea.

While no water in the lines was the problem, I think the esc might be a bit small. In looking at the spec on the motor, it is rated for 600 watts and 40 amps max. Your esc is only rated for 30 amps. Even if the cooling was working, i think the esc is too small. A 50 or 60 amp esc would give you some extra headroom.

Don't get too frustrated. Once you sort out out the problems, it is a very fun hobby. Good luck.
Nov 05, 2017, 05:17 PM
Just Plane Nutts
AirDOGGe's Avatar
30A is too weak for that motor. You need at least 60A, as is fitted in some RTR boats running a similar size outrunner.


And finding proper balance is more than moving thing around and sending it back out on the lake. Did you pre-balance thecenter-of-gravity (C/G) sitting on a tabletop first? That's a critical step before getting a new speedboat wet for the first time. Any narrow object that doesn't roll around can be used to roughly find your current C/G <See image below>.

Once you have that set, make some test runs and THEN shift weight around in SMALL increments to fine-tune the boat balance, depending on your results. Big C/G changes can quickly cause handling problems, as you discovered.


If the bow was plowing, then the pick-ups may not have been submerged. Also a boat running at that attitude will create excessive drag, making the power system work even harder than usual.


Any chance we can see photos of the bottom of the boat and the current prop set-up/water pick-up? The more photos and the more angles of shooting taken, the better we may be able to help.
Last edited by AirDOGGe; Nov 05, 2017 at 11:03 PM.
Nov 05, 2017, 05:20 PM
Registered User
I thought it was a gonna that’s for sure!

Ok I’ll have to dish for a bigger esc, I know it’s teething issues, I’m not giving up just yet. I’ve got a bigger one half built upstairs too lol.

The water pickups are one in the rudder feeding the motor, and one I made myself out of copper pipe feeding the esc, each had its own separate pipes and there was no water in any of them. I think the problem was the copper pipe being too small, I used 4mm break pipe. I used the same pipe as connections through the hull for the feeds, and the exits.
Nov 05, 2017, 05:25 PM
Registered User
I have ripped most of the plumbing out now but you can see the pickup layout, and shaft / prop setup. The prop is 38mm it came with the China special prop shaft.
Nov 05, 2017, 06:10 PM
Steps? What steps?
zozer's Avatar
At least part of the problem is the angle of the prop shaft - it is angled sharply down. This causes the plowing plus it loads the propeller too much by running submerged. Your boat should run the prop shaft close to parallel to the hull bottom and half out of the water. It is no wonder you have overstressed your setup.

You may be able to improve performance by moving the CG ‘way back, perhaps 20-25% ahead of the transom. With that drive alignment you will be outside of what many here are familiar with.


.
Nov 05, 2017, 07:12 PM
Just Plane Nutts
AirDOGGe's Avatar
There is a LOT of down angle on your prop shaft. That's why it plows if you add power. Thrust is pushing the stern upwards. Under a boat wita smaller submerged prop like a crackerbox racer it might have worked, but positioned way behind the boat, the angled prop has more leverage to push the bow down.

Mount the motor as low as you can go, or consider going to a flex drive so that you can angle the prop straight back. Shifting the motor and shaft a bit more forward to put the prop 35-35mm from the transom may help too. Technically, you want the rudder next to or behind the propeller, not in front.


The copper water pickup tube is set too low. Shoot for about half that.


Also try a 34mm or 35mm prop. They are more suitable for that motor and hull size, and will reduce torque-roll & steering.
Nov 05, 2017, 09:16 PM
Registered User
I may be way off beam and totally wrong, I often am, however.......

From looking at the rudder it appears that this is the pick up point for cooling water.

The other pipe appears to be the discharge pipe. The pictures do not make it very clear but the discharge pipe appears to be cut off with the opening facing towards the water flow from the boat's progress through the water. See right hand pipe in the diagram below. If so, this would have the 'discharge' pipe acting as a 'pick up' pipe. Two pick-ups and no discharge equals no (or little) water flow to the engine cooling.

If the cut off was facing away from the water flow, see the left hand pipe in the diagram below, then it would act as a discharge pipe as per the Venturi self bailer on a yacht.

That's my five cents worth.

Cheers,

Terry
Nov 05, 2017, 11:00 PM
Steps? What steps?
zozer's Avatar
I’m afraid you’re a bit off base Terry, the OP has identified his two water pickups, the rudder and the copper tube on the transom (see post #6). He doesn’t show the discharges....


.
Nov 05, 2017, 11:58 PM
Registered User
Thanks Zozer, missed that bit.

Cheers,

Terry
Nov 06, 2017, 06:17 AM
Registered User
Thanks all, yeah the exit pipes were in the side, where that hole now is :-( Wood broke away when I removed them.

The motor is mounted pretty much as low as it could go, and the shaft is perpendicular to the bottom of the hull, but the hull is essentially triangular in profile. Should the shaft be in line with the bottom of the hull or the deck / water level?

Smaller prop, ok can do that.

Prop submerged or surface?

If you hadn't noticed already I built the boat from the plans on this thread - https://www.rcgroups.com/forums/show...-small-18-boat
Nov 06, 2017, 07:43 AM
Registered User
Oh and what size tubing / pipe would be best for the waterworks?
Nov 06, 2017, 01:22 PM
Just Plane Nutts
AirDOGGe's Avatar
Quote:
Originally Posted by Mambawan

If you hadn't noticed already I built the boat from the plans on this thread - https://www.rcgroups.com/forums/show...-small-18-boat


It would appear that the designer mounted his motor far more forward: https://img.rcgroups.com/http://www....HRo-0V_lMF_9gQ


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