gear drive question.

[ken t.]

I'm just curious what is the reason behind the gear drive cmb's. Why would someone go through the trouble. <_<

 

[Brian MAhoney]

I'm just curious what is the reason behind the gear drive cmb's. Why would someone go through the trouble. <_<

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They are used primarily for FSRV racing. These monos use subsurface drive and race anti-clockwise for anything up to 30 minutes. With direct drive it is imposible to get the top end and drivability required for these boats.

They can be a good option for monos as well, Terry K runs one with some succes. I suspect that with a mono its possible to get better throtling and drivability, the down side is that there are a lot of very good props and expertise about for direct drive monos. With a 1.5:1 ration and x450/3 or x452/2 may be good starting points.

Brian

 

[ken t.]

I'm just curious what is the reason behind the gear drive cmb's. Why would someone go through the trouble. <_<

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They are used primarily for FSRV racing. These monos use subsurface drive and race anti-clockwise for anything up to 30 minutes. With direct drive it is imposible to get the top end and drivability required for these boats.

They can be a good option for monos as well, Terry K runs one with some succes. I suspect that with a mono its possible to get better throtling and drivability, the down side is that there are a lot of very good props and expertise about for direct drive monos. With a 1.5:1 ration and x450/3 or x452/2 may be good starting points.

Brian

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I have seen some sites on the fsrv but have no idea what it is.

 

[gil sonsino]

Hi ken

You won't go to trouble with gear engines at all.With the right gear ration you will be surprised to see what a small .21 can do!

Just for an example a geared 21 will turn props that a direct drive motor can't imagine like Brian well said.

I Remember a geared 21 KB in a FSR mono spinning a .60 direct drive prop here with no problems.

FSR are basically endurance races 15m,30min and two hour marathon(yes 2 hour) on a M format course.

see more at www.prestwich.ndirect.co.uk

Gill

 

[Terry Keeley]

I run 1.5:1 in a Speedmaster 20 mono and really like what I'm seeing. The 21's are making their HP at higher and higher revs and I think the slip factor is hurting us.

My older SD1 ran high 40's very loose on a X440/3, audio tach said the motor was turning about 32,000. I now run that all wetted down for heat racing with a X450/2 and the motor isn't turning that high. Loosened up with an X450/3 I've seen 56 but 52-53 is more common. There's more to be had though!

 

[ken t.]

I run 1.5:1 in a Speedmaster 20 mono and really like what I'm seeing.  The 21's are making their HP at higher and higher revs and I think the slip factor is hurting us. 
My older SD1 ran high 40's very loose on a X440/3, audio tach said the motor was turning about 32,000.  I now run that all wetted down for heat racing with a X450/2 and the motor isn't turning that high.  Loosened up with an X450/3 I've seen 56 but 52-53 is more common.  There's more to be had though! 

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Wow, thanks for the info So what is different about the motor. Do they must run in reverse no?? Is there any other differences??

 

[gil sonsino]

Any difference with engines once they are posicioned with the front plate towards the bowl of the boat and the second gear on the motor mount with keep the same shaft rotation that on direct drives. Actually you will have your pipe aligned with the center of the boat ....easier set up!

Gill

 

[Terry Keeley]

Here's what Gil said with pictures:

https://www.intlwaters.com/gallery/displayimage...album=70&pos=13

https://www.intlwaters.com/gallery/displayimage...album=70&pos=16

If you have a rear intake motor it has to turn opposite, a front intake gets turned around and runs normal direction.

 

[ken t.]

This idea is very intriguing. I may have to do some experimenting.

Where do you get the gears and stuff??

 

[Brian MAhoney]

This idea is very intriguing. I may have to do some experimenting.Where do you get the gears and stuff??

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If you want a gearbox for a cmb 21 take a look at Prestwich models Dave can give you more info on gear ratios available.

The smaller the engine the bigger the payoff for the gearbox, not seen one used on engines over 45.

Brian

 

[Bart Drieghe]

The smaller the engine the bigger the payoff for the gearbox, not seen one used on engines over 45.

We got everything in Europe ;

4th pic i think :

http://modelboatracing.co.uk/photos/poland/poland7.htm

and this baby rocks , i can tell u .

Bart

 

[HendricX]

Peter Inglof used UPgear.

The CMB .90 runs at the best torque of about 19000rpm ,(under load)

with the 1.4 ratio the prop turns almost 27000rpm.

 

[izitbrokeyet?]

And all this time...I thought you were gearing down to run bigger props around 13.5krpm

 

[Norm Doerr]

Anyone remember John Bridge with the twins geared together? Nothing like a 25 pound boat running 80.

 

[DJT]

There was a post on here some while back about gear drives that got me thinking and tinkering, here is what I came up with.

https://www.intlwaters.com/gallery/displayimage...10032&pos=-2691

 

[izitbrokeyet?]

Great looking Gear Drive Unit.

is it made of 7075?

what size did you end up making the shaft bearings?

great looking work,

 

[ken t.]

There was a post on here some while back about gear drives that got me thinking and tinkering, here is what I came up with.
https://www.intlwaters.com/gallery/displayimage...10032&pos=-2691

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Dude that is awesome.I wished i'd thought of it <_< I was going to cut my car engine head down but i never thought to mill the sides...DOH!!

What are you going to put it in, do you have a boat in mind.

I think you have opened up a world of posabilities here...

 

[Jay Boyd]

Gear wine......mmmmmm!

 

[Ian Folkson]

I have found over the years that running gears especially on a 3.5 lets the engine rev out with good torque at the prop and more power to throttle up from low. On a standard 2 to 1 gearbox the motor will do 33000 but your prop is only doing half that. In non surface prop type boats. The props are not efficient at high revs.

In Europe more 3.5 and 7.5 circuit boats are going to gearing with good effect.

http://www.iansboats.co.uk/GEARS%20&%20BOXES.htm

Ian

 

[DaveMarles]

There was a post on here some while back about gear drives that got me thinking and tinkering, here is what I came up with.
https://www.intlwaters.com/gallery/displayimage...10032&pos=-2691

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That's a nice looking gearbox. The gears look to be a little weak though, wider gears would be a good idea. Gearbox bearings need to be fairly tough with a minimum of 16mm od if you use 5mm or similar shaft. Stainless bearings are a good idea too because corrosion seems to affect gearbox bearings even when regularly lubricated with oil.

Dave