Which has more torque 5 or 7 “

[Chris PearceParticipant @chrispearce30862]

Morning all,

Which shaft has more torque if any, will it be a 5 " or a 7" shaft fitted to a 500 engine.

any answers will be greatly received.

ChrisP

[Bob Abell 2Participant @bobabell2]

Hello Chris

Torque is FORCE multiplied by the radius the force is acting on.

ie…………….3lb force X  2 inch radius  =  6 lb. ins

So  a ,,,,,,,,,5" or 7" shaft will have no effect

Bob

[Chris PearceParticipant @chrispearce30862]

Hello Bob,

So if I use a 40mm brass prop will I get more torque than a 35mm Brass..!

ChrisP

[Bob Abell 2Participant @bobabell2]

Hello Chris

You will get less torque with a bigger prop by calculation…………….but it also depends on the pitch of the prop……………..a fine pitch prop will have more torque than a coarse pitch prop………like a screw thread

A fine pitch prop will have more thrust than a coarse pitch prop…………..but a coarse pitch prop will eventually go faster than a fine pitch prop………………like a loco with big wheels……..it will set off slowly but will gradually speed up.

It`s really a matter of experimentation……………..hmmmmmmmmmmmm!

Bob

[ashley needhamParticipant @ashleyneedham69188]

CP. Torque is wots generated by yer engine. Thrust is all you get from a prop…HOWEVER there is a "torque reaction" whereby the turning effect of the prop twists the hull. The issue facting a 500 motor is one of gearing…..no gearing and a 30/35mm prop is possibly the ballpark size, but (say) up to 50mm may be turned adequately by a 500 on 2.5:1 gear ratio, for use on (say again) …..my model icebreaker !!!!  (hopefully) …. I am using a geared setup to turn, in actual fact, a 55mm prop as I want lots of pushing power, and so a larger prop is required, turning at a slower speed that a small one. I will start with a plastic prop, but these are not as corse pitched as the brass ones, so i will eventually get a brass one….these work much better in reverse than the plastic ones, and I might need this to get of the ice floes (as if)    555   Ash

[60wattParticipant @60watt]

Now you’ve done it Ashley.     Bob’s 2nd post is  there for eternity and he’s just pm’d me to say he got it round the wrong way

Chris,To answer your question,the shaft length has no effect other than there is more chance of vibration at high revs as the shaft will resonate at a lower frequency.

The 40mm prop will indeed exert more torque on the motor than the 35mm prop but whether that gives more or less thrust & speed depends if you have exceeded half the motor stall figure. 

 click here and then start the flash presentation.You will see that peak motor power occurs with a prop big and coarse enough to slow the motor down to half its free running rpm and no more. The efficiency is 47% and current drain is half the stall figure.

[Mike DavidsonParticipant @mikedavidson22772]

 Gentlemen I am able to bring tyou the benefit of years spent in the submarine world. You may know that Submariners spend a large proportion of their time listening to the sounds in the water around them on their sonar setsEvery vessel including yours has a distinctive sound in the water (a the motor with its brush noise  (b The prop shaft with its bearings at each end (c The propeller itself with its three four or five blades each getting a bite at the water in turn. Each of your servos will radiate noise into the water when it is running. The professionals astound me regularly by saying things like that is the Isle of Wight ferry, because she has two five bladed props and one blade cavitates. Cavitation is not good, because the blade thrashes at the water, and creates a whirlpool of bubbles in the water around the prop. This has a devastating effect on the vessel as the ship’s engines put their power into making bubbles in the water which kills the thrust, so if youm have a 45000RPM brushless motor that makes a lot of noise and don’t go nowhere, it is probably cavitatingWhen you put the boat in the water and press the loud pedal, is there a stream of bubbles stretching aft under the stern? I expect that the boat will still motor along but not as fast as you calculated. I think the answer lies in a gearbox and a bigger prop that will push a lot of water astern, and the boat will be like a tug, Next time you see a tug in dry dock take a sneaky peek underneath , it will have a very big ducted prop, I am currently looking at a model ducted hydrojet, to get an idea of prop efficiency, so experiment with prop sizes gearboxes amd motor RPM the answer lies in therfe somewhere……………………………………………………..Mike ….D

[Mike DavidsonParticipant @mikedavidson22772]

 Gentlemen I am able to bring tyou the benefit of years spent in the submarine world. You may know that Submariners spend a large proportion of their time listening to the sounds in the water around them on their sonar setsEvery vessel including yours has a distinctive sound in the water (a the motor with its brush noise  (b The prop shaft with its bearings at each end (c The propeller itself with its three four or five blades each getting a bite at the water in turn. Each of your servos will radiate noise into the water when it is running. The professionals astound me regularly by saying things like that is the Isle of Wight ferry, because she has two five bladed props and one blade cavitates. Cavitation is not good, because the blade thrashes at the water, and creates a whirlpool of bubbles in the water around the prop. This has a devastating effect on the vessel as the ship’s engines put their power into making bubbles in the water which kills the thrust, so if youm have a 45000RPM brushless motor that makes a lot of noise and don’t go nowhere, it is probably cavitatingWhen you put the boat in the water and press the loud pedal, is there a stream of bubbles stretching aft under the stern? I expect that the boat will still motor along but not as fast as you calculated. I think the answer lies in a gearbox and a bigger prop that will push a lot of water astern, and the boat will be like a tug, Next time you see a tug in dry dock take a sneaky peek underneath , it will have a very big ducted prop, I am currently looking at a model ducted hydrojet, to get an idea of prop efficiency, so experiment with prop sizes gearboxes amd motor RPM the answer lies in there somewhere……………………………………………………..Mike ….D

[Chris PearceParticipant @chrispearce30862]

AH yes,

So using my figures on the box I should be able to sort out my prop size, I will speak with her ladyship on the morrow.

Ash your ice breaker will be great when the ice returns..!

The lifeboat with 385s pulled nicely the sea commander today in the windy weather more like a tug now..!

CP

[Mike DavidsonParticipant @mikedavidson22772]

 Chris, I have just run your question past a retired Chief engineering artificer in the Royal Navy, and he reminded me of something I had forgotten, He said if you have a particularly stubborn screw that is too hard to screw in, you get a longer screwdriver, the reason for this is that the shaft of the screwdriver  torques up and provides a greater torque at the driven end, so the answer to your question is that the longer shaft may well give you greater torque at the screwtorque is a much misunderstood animal all about moments about an axis,or force, so if you look at the equation, youwould go for a larger diameter motor, or a gear ratio to amplify the force available from a smaller motor. The diameter of your prop will simply increase the load on your motor / shaft combinationrequiring greater torque to turn it. Finally, taking this thread from the silly to the cor,blimeythere is another factor to take into account, which is the pitch of the propeller, so, taking a leaf from aero modelling, the prop size is given by the diameter and the distance fofward it would move for each revolution, I don’t know a lot about model boat props , but I do know that pitches do vary,so the greater the pitch, the greater thereactance to the motor. If there is a greater resistance to turning, you would require more power from your motor traditionally provided by more volts from the battery or stronger magnets in the motor body. These days, motor manufacturers are only too keen to provide torque figures for their products, so if you wantbetter performance, go for a greater pitch prop, and a more torquey motor, choose your shaft length to set the propeller angle close to horizontal, and fit the deflector plates to the transom to keep the boats nose downso steps in the hull profile can keep the boat planingbecause the less there is in contact with the water, the lower the resistance will be to forward motion. and the best of luck………………………….Mike ….D

[Len OchiltreeParticipant @lenochiltree67043]

Hi Guys,

If you re read the original Question,it could be a 5" or 7" Length or Diameter Shaft.

And is it a 500 Electric motor or a 500cc Engine

Len.the confused.

Chris Pearce wrote (see)

Morning all,

Which shaft has more torque if any, will it be a 5 " or a 7" shaft fitted to a 500 engine.

any answers will be greatly received.

ChrisP

[Chris PearceParticipant @chrispearce30862]

Hello all,

The shaft is or 5 or 7 " in length on a speed 500.

 Mike,

Yes i remember the old screw driver tip, I use to use a 8 " on the visor screws on the flying helmets, when someone used to much loctite. Ex SE makes good.

I will be speaking to a top racing engineer on the prop side.

I suppose I could add in a step just before the start of the shaft as it comes out.

CP

[Mike DavidsonParticipant @mikedavidson22772]

 Yes Chris Safety Equipment section, the destination for all bods wantinganything sewn together, and, I can’t get enough loctite these days for my spectacles, but a final comment on the torque businessfoot pounds or ounce /inches is a measure of the amount of force transmitted down the prop shaft to the screw by the motor, so, the more water pushed astern by the screw whilst it is rotating,is a ball park figure for working out how much force the motor needs to provide, so anything that helps is what we modellers need like more volts,or  stronger magnets(both of which give us more magnetic lines of forceon the motor stator for the rotor to push against……………………………….Mike….D

[Mike DavidsonParticipant @mikedavidson22772]

Len, I was not confused until I read your thread, and now I’m ready for the short basket weaving course,

I would love to see a model boat with a 500cc engine, but don’t show it to Paul

[Chris PearceParticipant @chrispearce30862]

Len,

Yes a squipper…! I done my sewing cse at Halton No1 school of tech training, 2 weeks…?

A model boat with a fiat 500cc engine mmm , there was a 1:3 Mersey with twin electric wheel chair engine.

[Mike DavidsonParticipant @mikedavidson22772]

 Len my mind just strayed to a wheelchair with a caterpiller Deisel engine from a lifeboat, you’d have no trouble picking up the shopping in that You should see a Tamar class boat on a shout, then watch it when the cox gives it helm, now that is impressive, there might be a video on the RNLI website, have a peek.

[Len OchiltreeParticipant @lenochiltree67043]

Hi Guys,

It’s nice when the old Grey Matter goes off on a Tangent isn’t it ?.

I am thinking of when I get to be an " Old Fart " I will get one of those Electric Buggies fitted with a V8 or bigger Sound System and frighten the living daylights out of Hells Grannies/Bikers when I open it up!.What do you think?.

Mike,

Paul is after something a bit on the large size to fit his barrel back monster,so maybe!!.

Len

[Mike DavidsonParticipant @mikedavidson22772]

I just mentioned Paul because at one time he was having a go at his local authorities because they had decreed no infernal combustion engine boats on the lake. I’ve got a Vauxhall corsa windscreen wiper motor in minethat has so much torque it will drive three props through a gearbox I was thinking of suggesting to Ashley that we asked for an olympus engine out of one ofthe scrapped concordes for our Ekranoplan, Ah roast duck coming off the pond at 1500 MPH, it won’t just be you they call the menace

[Chris PearceParticipant @chrispearce30862]

Mike,

How big is this motor from the corsa, I might have a scrap electric fan, those ones used in the summer i think!

Need to rush down to the bin area,first. it was turning 3 props 8 " each….mmm, I wonder….

Roast duck sounds good but burnt Avgas flavour…nah.

[ashley needhamParticipant @ashleyneedham69188]

CP. Norty, burning ducks to a crisp will get the parks plod on to u….no wot i mean ?????    Ash

NB choose a shaft size to join the motor at its chosen location and the prop, at ITS chosen location (allowing for couplings etc) nothing else comes in to it really.

[Paul TParticipant @pault84577]

Oh Bug*er

Now you have got me thinking of fitting IC engines to the barrel back and sailing it on the canal rather than electric on Runcorn boating lake.

I would love to fit a 500cc unit and have spent some time today looking for a flat 4 or 2 cylinder unit (without success) but I do have a matched pair of 75cc strimmer engines that would fit in the present hull if I installed them backwards, i.e with the shaft pointing to the bow and then using a chain to connect to the propshafts.

The boat would fly along and with the right size of copper expansion boxes the exhaust note would be sweet.

I didn’t need this as I was quite happy fitting a triple electric setup…………….but now???? perhaps I might go duck hunting as well

Paul

[Paul TParticipant @pault84577]

Yes Len it is amazing how the old grey matter can have a senior moment and come up with wild ideas that seem perfectly rational, I blame the new medication……..that’s my excuse…. 

Having spent the night thinking about an impressive twin IC installation I got up this morning and did some basic power to weight calcs and found that twin IC would produce less speed that a single unit and that a single 75cc unit was at least 50% overpowered.

So I either fit a 32cc single unit or go back to an electric set up or I build a bigger boat…..the calcs indicate that a hull length of 2.2m would work very well with the twin 75cc units. But its hardly an easy model to transport and I wouldn’t need radio control as I could just get in it to drive it.

I said it was a bug*er.

Paul (fed up now and looking for a boat trailer to tow behind the Trooper)

[Chris PearceParticipant @chrispearce30862]

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