Slo mo Shun

[Bob Abell 2Participant @bobabell2]

Hello Phil……………Just got back……………Where`s that tomato sauce?

 

All the latest mods made absolutely no improvement!

 

In fact from a cruising speed to the maximum power made very little difference in speed.

It feels as though the hull is stuck to the water.

 

The rear elevators just sent the nose down!

 

There`s plenty of motor power available, as the props fling the water backwards with some velocity

 

Need a brainwave at the moment………….Bob

 

PS Thanks for the battery info…….I`m still charging at 2 amps

[Phil Winks 1Participant @philwinks1]

Hi Bob sorry to hear that.

 

I think straight of the top of my head that it’s time to take a deep breath and consider some fairly drastic action.

 

But before that lets look at the balance issue. You need to be sure she’s perfectly balanced about 1/2″ max forward of the rear of the sponsons. do what the originals’ designer did get her in a sling and shift what you can to achieve the balance.

 

Your elevator thingy’s need, I would say, no more than a 5 degree down angle.

 

The mod between the sponsons may need to be removed and the planning area of the sponsons builtup by app 1″ max, make this cover the area between formers 6 to 8. At full height between 6 and 7 then blended back to original line forward of there (I assume that your formers are spaced as in the kit and numbered rear to front)

 

Finally get those fans seriously reduced as they are prob what is sapping the extra revs you want above1/2 throttle. (I’d suggest about 10mm bigger than the motor dia)

 

Phil

[Phil Winks 1Participant @philwinks1]

One further point Bob have chat with Dave about the possibility of taking out one pair of bty’s and running both motors off the same set, that would lose a huge chunk of weight. ok it would shorten the run time  too, but no pain no gain as they say, and you would have the second set to change too mid sail as it were. (good excuse for a coffee break)

 

The good news on mine is my best guess on the empty weight of the hull will be in the 500g region so the 1Kg target may be just achievable.

 

 

Phil

[Bob Abell 2Participant @bobabell2]

I`m beginning to think that the props are too small now!

 

There`s too much water being pushed back effortlessly and I`m guessing we need more resistance to the water

 

Since this little mod would cost about £30.00 to try…….I`m open to anybody`s comments

 

Anybody out there using the MMB 900 motors?

 

Bob

[Len OchiltreeParticipant @lenochiltree67043]

Hi Bob,

Crikey Page 61 of this Thread and still it doesent go as wanted.

As you are altering the underneath of the hull and not keeping to the Plan, what about fitting a Wing beneath the Bow to give added lift ?. This will not add much weight.

 

Regards to all,

 

Len.

[Bob Abell 2Participant @bobabell2]

Hello LEN

 

I have already given that idea some thought……..But not got enough speed at the moment.

 

If I manage to crack it…………….I`ll try the wing idea, just out of curiosity!

 

It`ll look like one of those Russian contraptions!

 

Bob

[Phil Winks 1Participant @philwinks1]

Hi Bob without reliable data on the amps being drawn by those motors when on full power I really wouldn’t like to comment on the idea of bigger props. 

 

What sort of running time are you getting on a full bty?

Are they warm, very warm or hot when you recover her?

Same question on the motors

How many Mah does your charger put into the bty’s after a run?

 

The answers should give me some clues as to whether it’s safe to “prop up”

 

Best way to get this data (apart from telemetry) is to:

 

Fully charge bty’s;

Run un-relentlessly on or close to full for 5 Min’s (or till esc shuts down on low voltage. (unlikely) whichever is shorter) Time this accurately ie: within 10sec;

Check bty/motor temp;

Charge bty’s and note the final Mah figure.

Get back to me and I’ll figure out what it all means!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

An alternative to the full bore run is to keep it steady at 3/4 throttle for the 5 Min’s just a little harder to hold steady unless your throttle channel doesn’t have a spring to neutral.

 

 

Phil

 

 

[Bob Abell 2Participant @bobabell2]

Thanks for your advice there, Phil

 

That sounds a bit risky to me……..Don`t fancy running the motors for five mins, until I`ve proved the cooling fans are doing a safe job. The motors are very hot after a few short bursts of speed…….It runs ok just as a motor boat, but it`s got more potential than just a sluggish speedboat!

 

If this is of any use, the batteries are loaded up to 14.5 volts on full charge

 

Is there some risk of trying out the bigger props…….for about two mins for instance?

 

To repeat myself………………Today, I noticed there was hardly any increase in speed going from half throttle to full throttle……..The boat just seemed to dig itself into the water and build up a forward bow wave.

 

There seems to be plenty of power available, especially when doing roaring sharp turns

 

Should I get an ammeter from Maplins and do something with it?

 

Thanks my M8……Bob

[Phil Winks 1Participant @philwinks1]

Hi Bob as the motors are getting hot I’d suggest  bigger props are only going to make them hotter. (Potentially smokers)

 

On the Ammeter it really is only good for checking that the alignment is good unless it can record details over a time period and display them later (so you can record details during a run)

 

The voltage when charged isn’t the figure I need. a bty’s ability to deliver current is measured in Amps/Milliamps A/Mah this figure tells you how much gas is in the tank so to speak. your charger should tell you how many Mah it put into the bty during a charge. comparing this with how long it was run for at a set throttle setting will tell you how many Amps (Ampere/ Amps per hour) the motors took out.  that will give us a good guide as to how close to the motor/esc/bty limits she’s at.

 

If your nervous about an extended run try it for say about 2 Min’s (almost any length will do just time the run accurately) do not use the bty before or after the run and charge asap before and  after (allow to cool before and after use obviously) I think I’ll ring you on this one! prob tomorrow late pm (3 ish) if that’s OK.

 

 

Phil

Edited By Phil Winks 1 on 30/03/2010 20:06:12

[Dave MilbournParticipant @davemilbourn48782]

PLEASE ditch those ruddy fans, Bob. They might be making a nice roaring noise (and how much energy is that using up?) but all they’re doing is sucking a gentle breeze past the smooth motor casings. These would really need some serious finned heat-sinks to increase the surface area enough for any significant air-cooling. Water-cooling brings the cooling medium more or less into direct contact with the motor casings and so has to be more efficient thermally – conduction vs convection.

 

And then there’s the power being wasted by the fans……. am I getting boring here? Go buy some copper brake pipe and get bending. Seven or eight turns should do the job.

 

You said in one of your earlier posts that it had actually got up onto the plane at one point, so you’re not far off that milestone.

 

DM

 

[Phil Winks 1Participant @philwinks1]

Got to agree with Dave there Bob.

 

while your about Dave how much would it take to reduce the bty count. or do you feel it needs all 4600Mah on each motor.

 

I’m thinking 2 packs in series running both motors giving it 24v but sharing the bty over both motors so obviously increasing load on the bty and reducing max run time to about 1/2 of present, but it would create a significant weight loss.

 

Phil

[Bob Abell 2Participant @bobabell2]

So your still out there , Dave………Lurking in the shadows, waiting for a titbit to pounce on………lol!

 

I`ll finally ditch the fans now, having reached, almost the length of my tether.

 

But, can you tell me what the max prop size, these motors can live with?…….What size does Stavross use etc.

 

It did get on the plane on the last outing……just as we were down the lake for another return power run……..and it just gallopped away!……….I noticed the wind was behind it at the time!

 

Up till now, we`ve not decided where the C of G should be…….But we`ll get the slings out and see where it is at the moment.

 

Dave…….Thanks for the techie stuff…….but most of it is going over my head!

 

Geezzzzzzzz!…………..I loved those fans!………….Bob

[Phil Winks 1Participant @philwinks1]

On the subject of the balance point I,ve been looking elsewhere “Rum runner fast electric forum” and  the thinking seems to be start at 10% of the aft plane (the sect from transome to sponson) behind the sponson then gradually shift forward to a max of 10% of aft plane forward of the rear of the sponson, till the optimum is found.

 

 

Phil

[Phil Winks 1Participant @philwinks1]

Oh and one other thing the corner between the lower sponson surface and its transome should be 90 degrees and as sharp as possible to prevent water following the curve and dragging it back

 

same goes for the transome bottom of hull intersection

 

 

just thought you’d like to know that

 

 

 

Phil

[Dave MilbournParticipant @davemilbourn48782]

Ref reducing number of batteries and the prop size – it’s suck-it-and-see time, chaps. Bob is the pacesetter on this type of model at this size; all we can do is interfere (hopefully) in a helpful sort of way.

I think Stavros uses an X55 2-blade, but my Aussie mate John Darke would probably say to use a Raboesch Type A 3-blader. I would hesitate to go beyond 55mm dia at 24volts, although the motor will happily swing a 110mm 4-blader on 12v – but not in a three-point hydro!

Dave M

[Bob Abell 2Participant @bobabell2]

Just when you all thought Barmy Bob was fast asleep……….Up he comes bright and cheerful……………………..Note the time!….btw

 

Thanks chappies!……..For your contributions to the thread!

 

Ah! Ah!…………..You`ve said it there Dave………”The motor will happily swing a 110 mm -4 blader”!

 

So I`ll think I`ll try a bigger prop now?…………………What`s 30 smackers between friends anyway?

 

If I don`t make drastic changes…………………….I couldn`t really face next Tuesday!…lol

 

So!………………Next Tuesday………No fans!………bigger props!………20 sec burst of optimism!………………………..Then…………………Have another think!

 

G`Nite chapz………………………….Bob

[Bob Abell 2Participant @bobabell2]

Phil…………..To get the balance at the step point…….All four batteries need to be forward of this point…………..I`m thinking this might have a chance?…….Say`s Bob the Optimist!

 

As it was, all the weight was at the back……..No wonder the back was down!………If I was trying to achieve the destroyer simulation, we don`t want the rear end down, do we?

 

I`ll get two bigger props today, just to see the effect they produceon speed etc………Just to put my mind at rest!

 

All I need now is another hat!……..Having eaten the last one!………………..Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob , what size was the prop shaft again?   I strongly suggested experimenting with props, and ditch the fancy hydro props for some “ordinary” jobs…I would have though members at your pond-side would have a selection to try out?

 

I have a large plastic carry-all thingy with compartments that I always carry. Has ALL my bits and bobs in, including a good selection of props from various experiments and ex-boats.

 

On more that one occasion at the pond I have doubled the speed of chaps boats simply by trying out a few different props….

 

General question for an expert.. Is there a rule of thumb on closeness of twin props before bad  interference sets in?   ie especially on “fast” jobs 

 

Ashley 

[Bob Abell 2Participant @bobabell2]

Hello Ashley……………….The more I think about it, the prop is a good source of improvement potential!

 

There is only one club member who could advise me on big speedboats……..But he is hard to track down.

He runs the crazy club 500 races but he`s available on Wednesday evenings now that we`ve got the extra hour

 

The back end of the boat is quite narrow compared to the bulbous front end and can`t help but sag down at the back…………………The batteries at the front end hardly affect the floatation……………….More optimism again

 

I wondered about prop spacing, early on, when deciding the pitch…….But who knows about this?…….Suppose Paul would have had an input

 

My selection of props start at 40mm and go smaller…….No hope there of course

 

Bob

[Len OchiltreeParticipant @lenochiltree67043]

You can make Props , Bob.

[Bob Abell 2Participant @bobabell2]

Hello Len………Thanks for your confidence!

 

I`ve made a few unimportant ones in the past, but really can`t make these high rev ving, high tech types!

 

What are you up to these days?

 

Bob

[Bob Abell 2Participant @bobabell2]

Fitted the running boards

They might help to keep her tail up?
If not, they look nice anyway!

 

Bob

[Phil Winks 1Participant @philwinks1]

Quite a good asthetic improvement in my view Bob and yes they should help esp now her tail  is lighter.

 

 

Phil

[ashley needhamParticipant @ashleyneedham69188]

Yes, now the running boards have been veneered they look fairly “original”.. good job.

 

A flat bottom is the way to keep the rear end up methinks. I know I know all that veneer…but..

 

Make a filler box or something to alter the rear end profile and try it (temporary box that is).

Hey, you could make one out of perspex to use while in the water (so its invisible) and then have it removable to display !  (assuming it works)

 

AFTER you have ditched the fans and tried some cheap X50s or something!

 

Note for boat builders everywhere…try unusual machines out on the water before finishing the paintwork!!  

Ashley 

[ashley needhamParticipant @ashleyneedham69188]

Yes, now the running boards have been veneered they look fairly “original”.. good job.

 

A flat bottom is the way to keep the rear end up methinks. I know I know all that veneer…but..

 

Make a filler box or something to alter the rear end profile and try it (temporary box that is).

Hey, you could make one out of perspex to use while in the water (so its invisible) and then have it removable to display !  (assuming it works)

 

AFTER you have ditched the fans and tried some cheap X50s or something!

 

Note for boat builders everywhere…try unusual machines out on the water before finishing the paintwork!!  

Ashley 

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