Mr Krabs build

[Xzessperated]

Thanks, I wish I could partake in a little Jameson my self. I am having fun finishing three boats right now. Lots of sanding and dust making!

Ahh that dust will taste good with a little Jameson Randy. If it does not then have another Jameson and after a while another and another and another. Did you even notice how the ugly barmaids got more beautiful as the night went on when you were young?

[Xzessperated]

You are all right 15C cells are rubbish and should be avoided, when I used the 14.8V 20C cell Mr Krabs took off, and I mean planed big time with a lot of speed.

I am currently looking at spending a lot of money on an 18.5V 4000mah 30C with 50C burst current this should deliver 120A normal running and 200A burst current. The other option is a 14.8V 4000mah 30C with 50C burst, a bit cheaper £20 - £30 but not sure what the extra cell will do for the boat other than the potential rev difference, not sure about the torque.

The motor is currently only a 60A 3300rpv water cooled 540, but as mentioned in previous threads I am not going for the speed record, I am simply using cheep components to get her trimmed out before I start to spend the money and start to build up the speed. Now I realise I am tackling this the wrong way round – go mental with good components and trim it out to suit. The SC is a Mystery FM100A, (thought it was a 160 when I brought it) ok I probably should be using at least 120A so I have twice the design capability of the motor.

For the time being I will stick with the current setup just to keep the cost down this month and buy a good / hopefully future proof for a couple of months, battery for Mr Krabs. The other option is to buy 2 x 14.8V 20C 4000mah Lipos approximately the same cost and series them together to give more volts but less Amps, once again not sure what it will do to the torque.

I am going to get a 45.7mm 2 blade Octura M645 Prop – the 45 was faster than the 3 blade 42mm plastic one. Not sure if going bigger is better, but from what I have seen the bigger the better?

I enclose some photos of the rear setup with the CF addition to the rudder and a photo of the spare turn fin – not properly attached to the right sponson because the original lovely sanded and sharpened is sitting of the bottom of the pond, the one in the photos has been lightly and roughly super glued to the sponson just so you can see how it looked prior to the accident.

I tried to take a photo or 2 of the COG hope it is good enough, I have been told that a rigger needs as much weight forward but the COG should be a bit back from the rear of the sponsons, not sure.

Once again all comments welcome positive and more importantly negative – HELP!!!

Slim

Before I go into things have you done the maths with that motor? I really think 3s is about it's limit. No wonder it went so fast on 4s but it will not keep going for long if my maths are correct

[RandyatBBY]

Ahh that dust will taste good with a little Jameson Randy. If it does not then have another Jameson and after a while another and another and another. Did you even notice how the ugly barmaids got more beautiful as the night went on when you were young?

Well that is a whole another story, As a youth in the 60ties and 70ties I had a blast. Much sipp'in and dipping of everything I could.

[andym]

Chuck all I was trying to do is narrow the thrust cone, I agree that they are a PIA to work on but taking it slow and steady seems to work.
Paddy just a thought but can you try that prop with the 1521 1.5, I think that it is such a large prop with a lot of pitch that the less RPM and more torque will get the same speeds if not faster. I am busy cupping and testing props like a mad scientist and learning all the time. My best so far is a Pranther s230 with some tip cupping and edge roll on my DF33, went from 51mph standard to 55.5 mph worked witch is a huge difference and surprised me alot. The thrust cone was very concentrated and flat the boat looked slower to a few but the gps and the way I was going past them told a different story, less roost looks slower but it is not!
Now slim, that turn fin is totaly inadequate for a curcuit boat. Have a look at some of the hydro build threads and have a look at what works. The best I have found are the range of Taipan fins sold by Andrew G at Fastelectrics here in OZ. The small size he sells would be ideal on your rigger and your turning problems I bet London to a Brick will dissappear.
Paddy see if you can get some SAW sponsons for the xs3 and I think you will find it a lot looser and faster.
Cheers all

[egneg]

Ahh ... the 60's and the 70's - the memories are gone - I was in California for part of that and because of it much of the time period is a blur! Although I seem to remember that all the women were beautiful ... at least until the next morning.

Jeeez ... I really feel old now!

Paddy ... does the Jameson help to blur the present?

[andym]

Sory Slim I forgot this http://www.fastelectrics.com/hardware.asp scroll down till you get to the Taipan turn fins and you will see what I mean.
Now that motor is not suitable full stop!!! On 4s a good cheap motor would be a Feigao 8xl and 5s a 10 xl would be the go. That motor will not last on 4 or 5s. The best advice I can give on a budget.

[egneg]

. I am busy cupping and testing props like a mad scientist and learning all the time. My best so far is a Pranther s230 with some tip cupping and edge roll on my DF33, went from 51mph standard to 55.5 mph worked witch is a huge difference and surprised me alot.
Cheers all

I will have to try a bit of cupping on the P225 as this is what I found to be the fastest on the UL-1 to date. I have detongued and backcut it so far and have just picked up a set of doming balls.

[andym]

Chuck what is a P225? The S 225 does not need detounging realy. Can you send a link to a P series prop?

[egneg]

Here is the link.

http://www.offshoreelectrics.com/pro...i-prather-s225

I guess you we are both talking about the Prather props. I will email you a pick of the one I have modified.

[slimshady]

Hi, all and thanks for all your kind comments, I have decided to keep the current setup with a view to buying a new Lipo and prop ASAP.

Lipo – 18.5V 30C with 50C burst 4000mah
Prop – Octura M645

I will leave the rest till next month, theory being, although the cell is the most important part of the boat (hopefully purchased soon) the motor demands the work and therefore going back down the chain the motor is a measly 60A the ESC is 100A and the Lipo can supply 120A so bottom covered. 60A required and half the input, although 3300rpv = 61K RPM (not under load).

I am looking at a 90 - 140A motor and 200 - 250A ESC, all out of my budget at this time but the two components letting me down at the moment are the Lipo and the prop.

Actually the third is the turn fin, I have drawn some 3D plans for the turn fin to be laser cut, then bent out of Aluminium or stainless steel sheet and to fix to the right sponson, although the information from Andy and others is nearly adequate, thanks, I still cannot decide on the full size, the link you suggest has 3 sizes for Hydros, I have made my designs on the largest but I am not sure, how big?

Paddy, I noticed you have cut the sponson and resined a bit of CF into it, is this a stable way to fix the turn fin? I am really uneasy about making any holes into the sponsons, they have helped keep her upright after sinking. I was thinking about using self tapping screws through the internal sides after using a lot of resin, what do you think?

Sorry again for all the questions


Slim

[Ub Hauled]

hi Slim...
I was looking at your pictures/descriptions and noticed a couple of things...

1st - that turn fin will not stay in place w/o a couple of screws holding it mate! it'll rip the glue and/or the gel coat off and then the fin will be laying on the bottom next to the prop you lost. Find a website that has Krabs in oval trim and look at their turn fins, you'll get the proportions better.

2nd - 61k rpm is WAY too much, specially with that prop. the motor will not take the abuse nor will the ESC, then you'll have to spend more money to mend that. Stay around 24-27k for oval and 30-35k for SAW applications. Unless you are experimenting with new things.

3rd - why do you have such big rudder? There is no need for such... please do tell the idea behind it.

4th - 200amp ESC is great, expensive... but a good size. The Mistery ESC is named properly... it is a mistery how it works, hehehehe. But you are correct, at least 120 would be the norm... since you wanna place a bigger motor and ESC in her, you should optimize the setup you have now and run until you have the "mula" to get the new stuff, you can make her a nice fun boat.
CG looks ok for a sport setup, for SAW you'd wanna push that CG forward somewhat.

5th - Get good batteries! Don't skimp on those, it'll be the difference between a good boat and a great boat... besides, weak batteries will overheat your system more then a powerful set of batteries, may even ruin the ESC.

my 2.55 cents

[Flying Scotsman]

Slim, I do not know rigger setups, but I would listen to these guys and your motor/prop choices seem dubious. "A bigger prop is better" no, in most cases...boom.

Dougggie

[andym]

Douggie this thread is over 400 post's long and has great info, all the above has been covered several times for Slim but he seems to want to blow and spend for his learning curve. Just like we did i suppose!

[slimshady]

Ub – good advice m8 I am already on the case:

1) The turn fin was c^&p and did not work – now at the bottom of the pond – never to be seen again (good)

2) Yes 61Krpm sounds a lot and I perhaps should drop the revs – might save a prop or 2 although unsure what it will do to and how this would affect a brass one I have now purchased. I learnt that 42.5Krpm is apparently the absolute maximum you can put a plastic prop through – not sure if it’s true but I dose explain things.

3) I can not turn – hard to explain but even with the rubbish turn fin Mr Krabs did not turn and that is the width of the pond so drastic measures occurred and the CF addition was used, without the turn fin I can just turn in the pond – when I get the new fin on and test it the CF addition could be removed.

4) Yes I agree the Mysterys are a bit of a Mystery but they bizarrely work and work quite well – how many ESCs cans deliver 61Krpm with minimal heat build up (ok I must admit I have modified it with heatsink compound and lots of resin + extra wide insulation tape. Another sick note on the day I broke the turn fin off and wrecked 2 props my mate Dave took his smaller rigger out for a run and burnt out a very expensive (in comparison) ESC – and when I mean burnt out the plywood rigger was smoken.

5) Yes this is the point of my last message – the battery is defiantly the most important part of the boat, the higher the Volts and Amps the better you are – I talked to the old retired electrical designer, also a master of servo motors at work today and we are both in the opinion that as long as the driving component, in this case the motor is demanding less than the supply and the bit in-between, i.e. the esc can handle it the sky it the limit. In other words if for example the motor demands 60A max and the ESC can deliver 60A and the Battery can deliver 60A all is ok but very much on the edge, by doubling the safety factor each time you have a bit of room for error i.e. 60A motor, 120A ESC and 240A battery then you should be covered. The chances of purchasing the components is very rare and the reason to double the design factor is in the event that the prop leaves the water, taking the RPM over the design load and therefore killing the ESC because the motor suddenly wants more Amps to spin freely. We talked about using an RCD in line with the ESC but could not think of anyone that produced an RCD small and lightweight enough to protect against 120A blowout. This would obviously save the ESC from frying but at the same time cut the electrics to the boat and leave it a sitting duck. Although I am a mechanical design engineer I do work closely with electrical units but to me brushless motors worked on witchcraft and all I know is they are driven with frequency delivered by the ESC by pulse modulation from the MOSFET drivers in the ESC – in other words a frequency of volts coupled with amps to drive the motor – what I am trying to say is that as long as you can supply the correct Volts and Amps things should be fine. This however does not explain how so many people burn out ESCs???????? Engineer I am but boat expert I am not.

Andy – thanks this is a big learning curve to me, I have used 3D FMEA fluid analysis models (similar to that used by the McLaren F1 tem) and I still can’t get it right, that’s why I rely on you experienced chaps to help me out.

I have had thoughts on the turn fin today and how to fix it to the right hand sponson many times – the first is the use rivets and 2 part resin, the second is gun drill straight through the turn fin and both sides of the sponson, allowing me to use a nut on the other side before filling in the open sides of the sponson.

Once again thank you all for your help


Slim

[Viking]

Hold on there

Hi Slim;
Hold on there. back up to when you said --- "The chances of purchasing the components is very rare and the reason to double the design factor is in the event that the prop leaves the water, taking the RPM over the design load and therefore killing the ESC because the motor suddenly wants more Amps to spin freely. We "" ---When the prop leaves the water it is doing no work and spinns freely ( no load) so the Amps Drop sharply. I can see this in the data from my Eagle Tree data logger.
There is another senirao that may play out and it goes something like this.
You are in trouble, the boat is out of control. You let off the throttle completely. NOW The boat is moving through the water rapidly and forcing the Prop to spin backwards. The burshless motor is exactly the same design as a good old fashioned Automotive Generator. Spinning it in either direction creates current flow, blowing up the ESC.
They say the ESC is OPtically coupled, but just where is the opto coupler in the circuit?? What is there to be fried by this current coming in on the out put wires??
Feel free to find an Electrical Engineer and shoot holes in that.
Viking