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Author Topic: Fast electric deep vee monohull build  (Read 14000 times)

pompebled

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Re: Fast electric deep vee monohull build
« Reply #50 on: June 10, 2013, 09:37:31 PM »

Hi Mike,

Sorry to hear about your teething problems with your boat.

The motor you're using is a two pole, rather short for the size hull and prone to overheating; on top of that the motor only gets half cooled as there will be air trapped inside the jacket, the outlet needs to be at the highest point!

If the 120A ESC cuts out, you're drawing way too much current, this could be the blunt prop or it's simply too big for this setup.

I think it's safe to say you overheated the magnets, effectively killing the motor, it'll still turn, but have no torque to speak of, draw massive amounts of Amps and run (very) hot...

What settings did your ESC have, you don't want the timing to be off too much, the standard 15 of the T-120 does not agree with all motors, better start low.

I would not go for a 28 mm motor, you'll lack torque, the 3060Kv 3660 Leopard motor is much better, but do make sure it's a four pole motor, giving you the torque you need.

On 3S you'll get close to 30.000 rpm at the prop, which is right in the sweet spot.

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #51 on: June 11, 2013, 10:14:29 PM »

Hi Mike,

Sorry to hear about your teething problems with your boat.

The motor you're using is a two pole, rather short for the size hull and prone to overheating; on top of that the motor only gets half cooled as there will be air trapped inside the jacket, the outlet needs to be at the highest point!

If the 120A ESC cuts out, you're drawing way too much current, this could be the blunt prop or it's simply too big for this setup.

I think it's safe to say you overheated the magnets, effectively killing the motor, it'll still turn, but have no torque to speak of, draw massive amounts of Amps and run (very) hot...

What settings did your ESC have, you don't want the timing to be off too much, the standard 15 of the T-120 does not agree with all motors, better start low.

I would not go for a 28 mm motor, you'll lack torque, the 3060Kv 3660 Leopard motor is much better, but do make sure it's a four pole motor, giving you the torque you need.

On 3S you'll get close to 30.000 rpm at the prop, which is right in the sweet spot.

Regards, Jan.
Im suprised at the way the motor performed. I have seen good reviews for it yet mine was thoroughly disapointing. I first tried it on my catamaran and allthough it didnt overheat it was pretty slow. It was only a 40mm 1.4 prop on the cat. I put it in the mono with a 42mm thinking it would be fine. What gets me is that 2 years ago i bought a 3600kv tiny 2845 with a seaking 60a esc. On a 37.5k graupner recommended by yourself in runs practically cold on 3s, yet i get a larger motor with a lower kv up the prop size a few mills and that has a fit. 
Your theory on the weekened magnets seems to fit the bill as to what has happened. I did run the motor on 15 degrees, im never too sure what timing to use for my motors.
Anyway ive bought and installed a leopard 3660 2700kv 4 pole running on 4s. The temps are mild to warm but not hot, bearing in mind when i tested it the sun was raging down on the lake, and the boat is matt black. I ran the boat on a octura 1.4 42. The handling was good although i think it runs a little wet. I tested the centre of gravity when i got home and its a bit to far forward at 40%. Theres very little room to move the batteries back either but still it will help. Im going to try some different propellers. Im thinking a 1.4 40 1.6 40 and a 1.6 42. I think if i down the prop size from 42 to 40 ill get the revs up. I dont know yet i havent got them.
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pompebled

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Re: Fast electric deep vee monohull build
« Reply #52 on: June 15, 2013, 04:22:43 PM »

Hi Mike,

Does the Leopard rev out up to 36000 rpm under load?
The 42mm prop would make that hard I'd guess, better start smaller and see what you can get away with without overstressing the (relative) short canned motor.

Get the COG right before propping up!

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #53 on: June 15, 2013, 10:17:42 PM »

I can only presume it is. I have no means of measuring the prop speed either static or water born. I havent got the 'ear' for it yet. With the 4214 the motor runs relatively warm. So the motor is worked but not over worked.
I dont know how to adjust the COG, at least not without either adding ballast which isnt ideal or start chopping at stuff which i really dont want to do.
What effects does having the centre of gravity to far foward have?
thanks
Mike
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martno1fan

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Re: Fast electric deep vee monohull build
« Reply #54 on: June 15, 2013, 10:35:57 PM »

Too far forward the boat will struggle to plane which means the motors working harder,too far back the boat will become very flighty,thats why the cog is very important.Cog should be around 30% .
Mart
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #55 on: June 15, 2013, 11:24:40 PM »

I had a think about moving the motor to adjust the COG. I thought id experiment to see where the motor would roughly need to go to get the 30% so i put the batteries in as far back as they would go then put laid the motor in loose at the bottom. To get the COG to sit at 30% id have to mount the motor at the stern next to the steering servo!  >>:-(
Itl just have to stay at 40% unless i fit an outboard and ive spent enough money allready.
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martno1fan

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Re: Fast electric deep vee monohull build
« Reply #56 on: June 16, 2013, 08:06:21 AM »

Mike that doesn't sound right to me,i don't understand why you cant get the correct cog how about some pics of the inside to show the position of your gear see if we can help.
Mart
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #57 on: June 16, 2013, 10:22:58 AM »

All the parts arnt fitted in at the moment as ive been doing some hull repairs. I had a bit of a tiff with gravity last week and lost. Lesson of the day:
Dont try to find the centre of gravity by balancing the hull on your finger whilst standing on the kitchen floor.  :embarrassed:
Anyway these pics show the battery and motor positions. The batteries on the maiden run were an inch forward then though. The rest of the hardware is not installed, the esc goes forward of the motor which helps the COG even less but that is the only place room for it. The Paint side profile is taken from the original plan. The red circle shows the current COG and the green circle shows the desired point. The blue rectangle is the motor position and the green one is where it needs to be to balance the boat to the correct COG.
I think the COG is off due to the fact that the front of the boat is heavy, the forward section has the chine shelf and frame in it which cannot be removed.
 
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pompebled

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Re: Fast electric deep vee monohull build
« Reply #58 on: June 16, 2013, 10:46:16 AM »

Hi Mike,

Running with the CoG at 40% is like having taped a brick onto the nose; in time you'll fry everything...

Like Mart said, you'll have to rearrange the components in the hull, your major obstacle is the steering servo.

The picture is of a slightly smaller monohull, where I has issues getting the CoG right.
I ended up with the servo (red) close to the motor:



The hull has a floodchamber and is set up as a 3S mono 1, so the receiver sits on the other side of the shaft, but you can see there's room for a second lipo if the receiver was moved under the deck.

Receiver and servo are relative light compared to the motor and batteries, so it's easier to position them where it's convenient without upsetting the CoG.

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #59 on: June 16, 2013, 12:08:58 PM »

The servo isnt in an ideal position i know. Its the only place i could get it to fit. Theres no room under the deck sides due to the nature of the hull construction, even if there was, the profile is too low to fit the servo between the deck and the bottom.
I wonder if a 2.5kg metal mini servo would do it?
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grasshopper

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Re: Fast electric deep vee monohull build
« Reply #60 on: June 16, 2013, 12:41:54 PM »

Would it be possible to move the tiller arm on to the other side of the rudder, have a connecting rod running  straight through the hull space to the servo mounted forward of the motor, you could then move the battery packs rearward and closer to the propshaft making the weight lower and more central?
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #61 on: June 16, 2013, 01:21:13 PM »

I see what your saying but no. The sides are boxed in by deck formers. You can see them on the first pages off this thread. Theres nothing really i can do about it as the boat sits low at the stern as it is. The water line is only a 1/4 of inch below the deck level. If i put the COG back anymore itl sink  :((
Theres only one thing i can do. And thats remove the construction frame from the front section of the hull. Itl mean having to remove the front deck section and dremeling out the frame.
Which exactly what ill do  %% %%
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #62 on: June 16, 2013, 01:46:56 PM »

cant stop now.
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grasshopper

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Re: Fast electric deep vee monohull build
« Reply #63 on: June 16, 2013, 09:39:39 PM »

You don't hang about do you?


Even if the section under the side decks were in-accessible you could still manage running the control rod along the in board side of the boxed in section.


 As long as the hull is waterproof she only sits low in the water when she's static, after that she should up on the plane..
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #64 on: June 17, 2013, 11:15:39 PM »

I dont get enough time these days to do as much as i would like. But generally no i dont hang about, I like to be on I dont see the point in waiting and holding off otherwise things dont happen and what you say you intend to do becomes nothing more than talk.
I waited a few minutes before i stabbed a hole in my boat but in the end it was simply case of ' if your gonna do it, then do it!'
So I did.
Because where the rudder is mounted the throw of the steering arm enters into the boxed off section. If i moved the rudder mount over towards the centre the rudder blade would hit the propeller. I also wouldnt have been able to move the linkage over a hole on the steering arm either without the rod hitting the rudder hinge when turning to starboard.
Anyway im having some success with removing the weight from the front. I dremelled out the frame and reinforced the skin seams. Ive jsut started patching the hole back up. Im afraid i have no pictures at the minute though. Ive managed to take the COG down from 40% to 32.3% Which isnt perfect but definatly better.
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martno1fan

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Re: Fast electric deep vee monohull build
« Reply #65 on: June 18, 2013, 01:09:33 PM »

You should be ok at 32% mate its certainly a big difference from 40%  :-)) .
Mart
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pompebled

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Re: Fast electric deep vee monohull build
« Reply #66 on: June 18, 2013, 08:51:00 PM »

And you can always add a wee bit of lead in the rear to get the CoG further back if this should be neccesary...

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #67 on: June 18, 2013, 10:26:44 PM »

Progress is coming along slowly but surely. On the underside edge of the hole in the deck i put some small flat peices around the perimeter. Then using a peice of paper and a pencil i placed the paper over the hole and shaded the pencil over it. The outside edge came out as dark ridges in the shading. I drew a heavy live on the dark ridges and cut the paper out as a template. I then transfered the template to the same 1.5mm birch ply i originally made the deck from. The patch fits almost perfectly inside the hole, some trimming was needed in places but the peices i put on the underside makes the top of the deck flush. Some aliphatic resin was used to secure it and some epoxy with a bit of talc in it was used to fill in the gaps. The top has been rubbed down and now almost flush. It will need an another coat of epoxy and paint to seal the wood but with a bit of elbow grease I am confident the hole and the repair will be unoticeable.
Another further addition i could doto the COG possibly is move the esc. As it stands it is still in front of the motor. I could mount it on top of the propshaft with a bit of tweaking however in order to do this and clear the flex coupling i would need to extend the 3 motor/esc wires.
Im thinking though that if i were to extend the wires the additional length would have a higher resistance, affect the back emf readings from the motor to the esc and therefore cause the motor to run badly.
What are peoples oppinion on this?
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pompebled

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Re: Fast electric deep vee monohull build
« Reply #68 on: June 19, 2013, 08:48:14 AM »

Hi Mike,

Extending the wiring between motor and ESC up to 15 - 20 cm makes no difference in performance, you may want to braidle them to minimize interference.

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #69 on: June 19, 2013, 09:24:15 PM »

I realised that i can also possibly move the rudder back a bit so that it is inline with the prop. It isnt necessary for prop walk reasons but it wont hurt.
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pompebled

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Re: Fast electric deep vee monohull build
« Reply #70 on: June 19, 2013, 09:51:08 PM »

Hi Mike,

In fact, positioning the rudderblade next to the prop is a major factor against propwalk, a turnfin is another one, as is offsetting the drive train.

So, in addition to moving the CoG rearward, the running attitude will benefit.

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #71 on: June 20, 2013, 11:06:48 PM »

Ye I worded that wrong. What i meant was im moving the rudder for other reasons other than prop walk. I know moving the rudder is for countering prop walk, I just dont have any at the minute %%
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #72 on: June 23, 2013, 10:52:51 PM »

After cutting all insides out i repatched and painting the hole. Its pretty smooth, itl do for me anyway. Ive also extended the rudder back an inch or so to help with the COG. With all the hardware installed the final COG is about 32.4%. I dont want to add lead because the back is low enough as it is.
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pompebled

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Re: Fast electric deep vee monohull build
« Reply #73 on: June 24, 2013, 05:04:46 PM »

Hi Mike,

All looks good again, congrats!

Don't be affraid to add lead if required, our boats also lay half submerged when in rest (due to the floodchamber filling), once you hit the throtlle the boat will ride level again.

Regards, Jan.
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Mad_Mike

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Re: Fast electric deep vee monohull build
« Reply #74 on: June 29, 2013, 02:38:56 PM »

Took the boat out again today for another try. After all that pratting about with COG and stuff, its still pretty slow. I dont think im seeing 30 mph out of it. It was actually pretty boring  {:-{
I reckon maybe going up a prop size. perhaps a 43 or a 44mm. Im half tempted to shelve this hull a put this gear into my catamaran.
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