Slo mo Shun

[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 

[Bob Abell 2Participant @bobabell2]

You don`t have to tell me FOUR times!…….I heard you the first time!

 

What are you on about, Ashley?…………..It has got a flat bottom at the back!

 

I suggested a float box at the back……..Weeks ago!

 

Bob

[Bob Abell 2Participant @bobabell2]

Just look at this chaps……..What I thought was a cover, when seen on a small photo….turns out to be a gaping hole each side of the hull!

 

Hmmmm………Am I brave enough to copy this?

 

Will need top consult my floatation  tests pix before I get the saw out!

 

I`m tempted!…………………..Bob

[Colin BishopModerator @colinbishop34627]

So why aren’t we seeing smoe of those excellent pics in the photo competition Bob?

 

Colin

[Bob Abell 2Participant @bobabell2]

Thank you, Colin

 

It`s all in hand……………..Bob

 

PS………….Really hoping for a good action shot…..soon!

[Bob Abell 2Participant @bobabell2]

The will be very handy for getting the batteries in too!

 

Bob

[Phil Winks 1Participant @philwinks1]

I believe that in use that hole has a cover on it and this has been left of in the museum to allow a view of the structure in side. As you point out very handy for bty acess I’m seriously considering it on mine if the bty’s will fit through. doubt it though !

 

 

Phil

[Bob Abell 2Participant @bobabell2]

Hello Phil

 

I`ll sandwich a black plastic cover between the ali ring and the hull wall.

 

Next time we sail, I`ll see if it really needs covering

 

Bob

[Phil Winks 1Participant @philwinks1]

I’d lay money on it Bob looks like the quickest way to turn it into a submarine to me

 

 

“Periscope depth if you please No1”   

 

Phil

[Paul TParticipant @pault84577]

Good Morning Captain Bob

 

I have been following the twists and turns of your build from a hospital bed (again…..got my own parking space now) and found myself waiting for each installment with bated breath…will it work…will it plane….will it sink. but unable to offer any support as I could only view.

 

It seems to me that your problem all along has been one of simple power to weight ratio so why not try a simple calc to work out just how much power is required, with this question answered you would then know what size prop to use.

 

The basic information required is the dry weight of the model and its point of centre of gravity (dont forget to add the suction effect of the water when working out the wet weight, I would suggest adding 40 – 50% due to the huge wetted area)

Do a static bollard pull test to see how much trust you are getting from the present set up…a length of string to a set of fishermans spring scales…the scale fixed to the bank and the string to the rear of the boat and set her off under full power and you will get a reading of thrust in lbs (convert that into metric or better still Kn)

You would also need the angle of prop attack and the pitch of the current props.

 

Chuck the lot into a computer and it will spit out the answer…………..a 32cc 2 stroke unit driving a single 60mm racing prop.

 

Back home now.

 

Paul

 

 

[Bob Abell 2Participant @bobabell2]

Good morning, Paul

 

Nice to see you again……….The wonders of modern medicine,eh?

 

We`ve had our ups and downs over the past few weeks…….And so have you, I reckon

 

I`ll do the test, next time out………….and give you the figures!……….The main problem, will be to guess the suction effect of the water!

 

Have now got a 68mm prop………The original was 54mm……………..Can we have your theoretical  predictions before we sail on Tuesday?…….just for fun, you understand…….I fancy a nice trilby this time with BBQ sauce!

 

The turbo fan is still installed!…….I`ve changed the handing of the fan blades, so that it is blowing directly on the motor casing……………..Ran it for 15 mins and it barely got warm!

Wifey terminated the test, she couldn`t stand the din!

 

The wave splitter has now been removed………another great idea……in the skip!

 

Anyway, Paul my mate and you too, Phil……………..and all my readers, where ever you are!………Have a nice Easter

 

Bob

[Phil Winks 1Participant @philwinks1]

Thanks Bob I did although no time for any eggs!!!! Till now that is now where did they get to  our fun sail yesterday in support of a local charity egg-hunt went better than my wildest dreams 300 + spectators and more boats on the water than our club’s seen in many a moon. And the weather was just superb.

 

Any way I digress just popped in to wish you all the best for your next outing with Daddy Slo-Mo, here’s hoping for some improvement.

 

Welcome back Paul sorry to hear off your recent stay in hospital. I hope they’ve made some progress for you and that you’ll soon be dazzling us with your next creation

 

Phil.

[Bob Abell 2Participant @bobabell2]

The 4th Test

 

Slight improvement, but still stuck like Gorilla Glue to the water surface!

The boat lay in the water nicely, now that the balance was adjusted correctly.

 

Next mod would be something to break up the suction effect……..Any ideas chaps?

 

Did an anchor test, with the boat connected to a fishermans spring balance and we got exactly 8lb……………………How`s that, Paul and Phil?

Looking nice waiting for the off!

Just coming round for a fly by!

There`s plenty of fire and brimstone available………..How about a few “steps” to reduce the suction effect?

 

Still got too much water squirting out at back!

 

Bob

 

PS…..Many thanks to Keith for taking the pictures!

Edited By Bob Abell on 06/04/2010 13:11:36

[Bob Abell 2Participant @bobabell2]

I`ve just had a word finally, with the club`s Speed Freak………John G`…………….And he put his finger on the problem, straight away!

 

He says that the MMB 900 motors are “Torque motors” as opposed to “Speed motors”

And they work best with coarse pitch props

 

The latest props are on the limit of max pitch…..(100mm)………………So the next step would be to gear the props up by……..2 to 1…….because the motors can live with this!

 

The motors run at…….9000 rpm, so by gearing them up, I could get 18000 rpm and using a smaller prop……………She will fly!!!!!!!!!……………Where have we heard that before?

 

What does the team think?

 

Bob

[Phil Winks 1Participant @philwinks1]

That Bob is exactly what they did with the real one.

  

A high tourque motor with a geared up small prop! Why did we not think of this earlier?????

 

So if the motors can take it which they prob can, and if you’ve room, then yes why not try it.

 

Have you changed the mod you inserted between the sponsons yet? As i think there’s possibly some advantage to, increasing the volume of the sponsons, and re-instating the tunnel. To let the “film of air” as ted johnson called it, get under the aft plane reducing drag significantly.

 

The volume of spray in the air behind her will, by the way, always be there I reckon.

 

Out of interest how warm where the Bty’s & Motors after a run and how long was that run? and finally how many Mah went in to the Bty’s on the post run charge?

 

Phil

[Bob Abell 2Participant @bobabell2]

Hello Phil

 

We ran for about 20 mins on and off……..the motors got too hot to touch but the batteries were hardly warm

 

There was a figure on the charger, but it didn`t say what the units were, the book called it….”charged capacity”…..and I think the figure was about 2000?

 

I`ll be taking the boat to Bury this Sunday and see what their experts have to say about it

 

Should I remove the tunnel cover then?……………The boat would sink lower if the cover is removed!

 

Bob

[Phil Winks 1Participant @philwinks1]

ok Bob that suggests 2000MMah so bty’s less than half empty.

 

Motors are working hard possibly to hard  are they water cooled yet or are the fans still in residence?

 

bty’s barely warm suggests no worries in  that direction so the idea for using just one pair of bty’s instead of all 4 is an option. and 10 to 15 mins continuos high (ish) throttle runs still achievable  LiPo’s will be the way eventually.

 

the  motor load issue may well be addressed by the gearbox/smaller prop idea.

 

If the hull mod is removed your  right! it will sink the boat lower! But with 3.5lbs less in bty’s and if you add 12 to 15 mm in depth to each sponson over the aft 50% then taper them to original line over the next 25% the balance should be maintained. try to make the addition hollow if possible

 

Final score  3

                      1

                      1

 

So I reckon on average you should be somewhere between  &  

but definately not

 

Phil (hoping this all helps)

[Phil Winks 1Participant @philwinks1]

Actually Bob if you mod the sponsons without removing the tunnel cover you may have a good result without reducing bty’s.

 

Remember to rebalance afterwards though the idea is as she gets up on deeper sponsons a tunnel will appear letting the air in and bingo

 

Phil

 

 

[ashley needhamParticipant @ashleyneedham69188]

OO er..so near yet so far!

 

The power is simply not being applied into the water judging by all that white stuff out the back…and the white stuff is concentrating in a single column as well..? how about a fence separating the props as a try out to see if interaction is hindering max.performance?

 

please please try some boring 3 blade brass ones, out of sheer curiosity!

 

This, or at least the original underside of Slo-mo reminds me of some ancient Italian torpedo boat someone found an article on a while ago (cant remember what it was called) whereby it was a semi-hovercraft, or at least a sidewall job..it had hard sides but a lip at the front to contain the AIR. it strikes me that, with the faired in hollow once again restored to normal, some of that 80watts of fan air could be ducted into this space to de-wet this area and provide lift or at least cut down stickion/suction/whatever..as a radical idea?

 

Looks dead good though, coming on, as one might say

 

Ashley

 

[ashley needhamParticipant @ashleyneedham69188]

OO er..so near yet so far!

 

The power is simply not being applied into the water judging by all that white stuff out the back…and the white stuff is concentrating in a single column as well..? how about a fence separating the props as a try out to see if interaction is hindering max.performance?

 

please please try some boring 3 blade brass ones, out of sheer curiosity!

 

This, or at least the original underside of Slo-mo reminds me of some ancient Italian torpedo boat someone found an article on a while ago (cant remember what it was called) whereby it was a semi-hovercraft, or at least a sidewall job..it had hard sides but a lip at the front to contain the AIR. it strikes me that, with the faired in hollow once again restored to normal, some of that 80watts of fan air could be ducted into this space to de-wet this area and provide lift or at least cut down stickion/suction/whatever..as a radical idea?

 

Looks dead good though, coming on, as one might say

 

Ashley    sorry the notebook is playing up and enters stuff if the cursor is left hovering hence the two posts and 4 posts earlier!….can i remove this post?

 

Edited By ashley needham on 06/04/2010 19:20:24

[Bob Abell 2Participant @bobabell2]

Thanks Phil and Ashley for your contributions

 

I like the idea of a speed up…………and I`ve got the room……….need some nylon gears…. 20 pcdia and 40 pcdia………….and a 30mm packer and it`s practically done

 

Also, as Ashley has been saying, all along…………….. A multi bladed prop would have nearly the desired effect…………..or even a bigger prop altogether

 

So, before I get the hammer and chisel out…………..A trip to Bury this Sunday may be worthwhile……………They are THE experts………..So I`m told

 

All good fun and it keeps us off the streets!……….Bob

[DuckyParticipant @ducky]

I admire your perseverance Bob and your abellness to carry on with this demanding build. I’m sure you will surmount all these problems as always and come out at the end with a great model! .

[Bob Abell 2Participant @bobabell2]

Thank you, Duckie

 

I`m perservering because a sort of success is just around the corner……..I think!

 

Need two pairs of nylon gears……..Have a look in your secret skip!

 

3/4″ and 1 1/2″ dia x 1.2″ wide…………….or there abouts

 

Bob

[Phil Winks 1Participant @philwinks1]

Hi Bob I’ve just had some feed back on the fast electric forum I went to for motor/prop advce and this is what the guy has sai

 

quote:

I built the Slo-Mo kit several years ago. You should know that it has some flaws. The most egregious being the shape of the rear sponsons. You will notice that on your picture five, the shape of the sponson angle actually reverses between the second to last and last station. This will make the boat run wet which will not only cause the boat to run slower but, also result in a drag on the motor and ESC. You will need to lower the rear sponson station to correct the plan flaw. A three degree angle will be about right.
end quote

 

This kinda supports my theory that some build up is  required on the bottom of the sponsons.

 

Phil (just being helpfull)

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