I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM 4.4Nm (3.25 fl/lb) torque.
The shaft is well supported with a heavy set of ball bearings, its designed to handle a large propeller.

All the gears I can find that have the power handleing/torque capacity have a larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft and supports a prop hub.
want to add another bearing on the other end of the shaft to support both ends so I don't have
an overhanging gear on a too small shaft. This preculdes putting the stock collet assemble on the motor shaft.

The smallest gear hub I can find is 3/8" or 9.5mm.
I'm pretty sure that a set screw won't hold and drilling the 8mm shaft for a drive
pin strikes me as marginal I would fear breaking the shaft at the pin hole.

Any recomendations on how to secure the shaft to the gear?

This will be driving a pump driving an orifice so the shock loads will be almost nonexistant and the duty cycle will be
low 3 min bursts of declining horespower 4.69 peak to 1.5 at the end of the run.



Paul

On Dec 15, 9:58*am, wrote:
I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM *4.4Nm (3.25 fl/lb) torque.
The shaft is well supported with a heavy set of ball bearings, its designed to handle a large propeller.

All the gears I can find that have the power handleing/torque capacity have a larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft and supports a prop hub.
*want to add another bearing on the other end of the shaft to support both ends so I don't have
an overhanging gear on a too small shaft. This preculdes putting the stock collet assemble on the motor shaft.

The smallest gear hub I can find is 3/8" or 9.5mm.
I'm pretty sure that a set screw won't hold and drilling the 8mm shaft for a drive
pin strikes me as marginal I would fear breaking the shaft at the pin hole.

Any recomendations on how to secure the shaft to the gear?

This will be driving a pump driving an orifice so the shock loads will be almost nonexistant and the duty cycle will be
low 3 min bursts of declining horespower 4.69 peak to 1.5 at the end of the run.

Paul

Hi, Paul.
I can't give a tested answer to your question, but have you thought of
grinding a small flat on the shaft for a set screw? You surely have
access to machine tools, so turning a bushing for a gear to fit the
shaft shouldn't be a problem.

You wrote of both a propeller and a pump. Is your motor driving both
or what?

another Paul

On Mon, 15 Dec 2008 10:45:49 -0800 (PST), " wrote:

On Dec 15, 9:58*am, wrote:
I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM *4.4Nm (3.25 fl/lb) torque.
The shaft is well supported with a heavy set of ball bearings, its designed to handle a large propeller.

All the gears I can find that have the power handleing/torque capacity have a larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft and supports a prop hub.
*want to add another bearing on the other end of the shaft to support both ends so I don't have
an overhanging gear on a too small shaft. This preculdes putting the stock collet assemble on the motor shaft.

The smallest gear hub I can find is 3/8" or 9.5mm.
I'm pretty sure that a set screw won't hold and drilling the 8mm shaft for a drive
pin strikes me as marginal I would fear breaking the shaft at the pin hole.

Any recomendations on how to secure the shaft to the gear?

This will be driving a pump driving an orifice so the shock loads will be almost nonexistant and the duty cycle will be
low 3 min bursts of declining horespower 4.69 peak to 1.5 at the end of the run.

Paul

Hi, Paul.
I can't give a tested answer to your question, but have you thought of
grinding a small flat on the shaft for a set screw? You surely have
access to machine tools, so turning a bushing for a gear to fit the
shaft shouldn't be a problem.

You wrote of both a propeller and a pump. Is your motor driving both
or what?

another Paul

Putting 4+ Hp through a tiny setscrew attachment just did not feel right to me.
The motor was designed to drive a prop, I'm driving a pump.

Its for the 2009 version of this:
http://www.youtube.com/watch?v=J2vEfghqWts

We are evaluating going from presurized "Heavy" tanks to light tanks and a pump system.
It may not turn out to be that much lighter, but at least we are going to do the experiment.

Yes I can turn bushings, flats, center drill shafts etc...
I just do't have any feel for building rotating machinerery so I was asking....

The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM
4.4Nm (3.25 fl/lb) torque.

Seems like way too small a shaft to transmit that much power.

On Dec 15, 1:51*pm, Richard J Kinch wrote:
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM
4.4Nm (3.25 fl/lb) torque.

Seems like way too small a shaft to transmit that much power.

This is radio-controlled-airplane tech, margins are designed thin to
reduce mass. Since no human life is at stake the margins are often a
lot thinner than aerospace.

To the OP: most gear suppliers can supply with no bore in the center
at all, you do the machining to match the shaft. You won't know until
you call, most of the catalogs lead you to believe that only standard
bores are available.

Tim.

In article ,
wrote:

All the gears I can find that have the power handleing/torque capacity have a
larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft and
supports a prop hub.
....
Any recomendations on how to secure the shaft to the gear?


Well, if it's designed to work with a collet, build a collet. You might
find it easier/more robust to use a 1/2" shaft that you can drill/bore
for 8mm and slit for the collet function while still having some meat on
it, as opposed to a 3/8 shaft. Cut tapered threads on the exterior and
clamp the bejeezus out of it with an external nut. This is going from my
understanding that you are wanting to extend the shaft to another set of
bearings, so I'm suggesting you collet the end of a thick shaft, mount
the gear on the thick shaft however makes you happy, but not right at
the end where it takes the 8mm shaft, and the 8mm shaft is clamped into
the colleted end by an exterior nut running on tapered threads.

Or make a tiny knock-off of a QD system. Sheaves or gears with tapered
bores, and flanged tapered inserts that collet onto the shaft as they
are drawn into the bore by screws.

Or go to the irritating agony of a real shrink fit, but I hate those as
they are often impossible to get apart without breaking something -
heating the gear and freezing the shaft work better when they are
disassembled - it's hard to separate the heating from the cooling when
the assembly is assembled.

The more robust forms of loc-tite can emulate a shrink fit.

--
Cats, coffee, chocolate...vices to live by

On Mon, 15 Dec 2008 09:58:32 -0800, wrote:

I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)


Any recomendations on how to secure the shaft to the gear?

http://www.fennerdrives.com/keyless_...orque_mini.asp
or
http://www.bikon.com/english/produkte/index.html
The 8000 series goes down to 6mm shaft.

--
Ned Simmons

First, I think your shaft size is to small for the power you expect to
couple, but be that as it may. The solution to a coupling is a friction
drive. Although these can be purchased for larger diameters, you can make
your own. bore a hole in your gear with a 10 degree taper say 9/16 or 5/8ths
major diameter. Then machine a bushing with the correct ID for the shaft.
Then turn the OD to to a diameter slightly larger than the od of the bored
hole in the gear. Taper the OD of this bushing to 10 degrees. Take a
slitting saw and cut a small slit in the bushing. Then machine a clamping
plate that when screwed to the side of the gear wedges the tapered bush into
the tapered bore of the gear. The clamping force is phenominal. It is
bidirectional and never works loose. This coupling does nothing to
compromise either the integrity of the shaft or gear.
Steve

wrote in message
...
I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM 4.4Nm
(3.25 fl/lb) torque.
The shaft is well supported with a heavy set of ball bearings, its
designed to handle a large propeller.

All the gears I can find that have the power handleing/torque capacity
have a larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft
and supports a prop hub.
want to add another bearing on the other end of the shaft to support both
ends so I don't have
an overhanging gear on a too small shaft. This preculdes putting the stock
collet assemble on the motor shaft.

The smallest gear hub I can find is 3/8" or 9.5mm.
I'm pretty sure that a set screw won't hold and drilling the 8mm shaft for
a drive
pin strikes me as marginal I would fear breaking the shaft at the pin
hole.

Any recomendations on how to secure the shaft to the gear?

This will be driving a pump driving an orifice so the shock loads will be
almost nonexistant and the duty cycle will be
low 3 min bursts of declining horespower 4.69 peak to 1.5 at the end of
the run.



Paul

On Mon, 15 Dec 2008 10:51:04 -0800, the infamous
scrawled the following:

On Mon, 15 Dec 2008 10:45:49 -0800 (PST), " wrote:

On Dec 15, 9:58*am, wrote:
I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM *4.4Nm (3.25 fl/lb) torque.
The shaft is well supported with a heavy set of ball bearings, its designed to handle a large propeller.

All the gears I can find that have the power handleing/torque capacity have a larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft and supports a prop hub.
*want to add another bearing on the other end of the shaft to support both ends so I don't have
an overhanging gear on a too small shaft. This preculdes putting the stock collet assemble on the motor shaft.

The smallest gear hub I can find is 3/8" or 9.5mm.
I'm pretty sure that a set screw won't hold and drilling the 8mm shaft for a drive
pin strikes me as marginal I would fear breaking the shaft at the pin hole.

Any recomendations on how to secure the shaft to the gear?

This will be driving a pump driving an orifice so the shock loads will be almost nonexistant and the duty cycle will be
low 3 min bursts of declining horespower 4.69 peak to 1.5 at the end of the run.

Paul

Hi, Paul.
I can't give a tested answer to your question, but have you thought of
grinding a small flat on the shaft for a set screw? You surely have
access to machine tools, so turning a bushing for a gear to fit the
shaft shouldn't be a problem.

You wrote of both a propeller and a pump. Is your motor driving both
or what?

another Paul

Putting 4+ Hp through a tiny setscrew attachment just did not feel right to me.
The motor was designed to drive a prop, I'm driving a pump.

Its for the 2009 version of this:
http://www.youtube.com/watch?v=J2vEfghqWts

Man, clean your vidcam lens! g

A pump? You'll be making a truly ultimate Super Soaker, will ya?


We are evaluating going from presurized "Heavy" tanks to light tanks and a pump system.
It may not turn out to be that much lighter, but at least we are going to do the experiment.

Yes I can turn bushings, flats, center drill shafts etc...
I just do't have any feel for building rotating machinerery so I was asking....

Wouldn't a spline system work better, both in reinforcing the
mechanical connection and lightening both the shaft and gear?


--
It is pretty hard to tell what does bring happiness;
poverty and wealth have both failed.
-- Kin Hubbard

On Dec 15, 5:53*pm, "Steve Lusardi" wrote:
...Bore a hole in your gear with a 10 degree taper say 9/16 or 5/8ths
major diameter. Then machine a bushing with the correct ID for the shaft.
Then turn the OD to to a diameter slightly larger than the od of the bored
hole in the gear. Taper the OD of this bushing to 10 degrees....
Steve

Plan the job so you can turn the bushing and bore the gear hub with
the same compound setting, which means you have to be able to remove
and accurately re-center at least one of them.

Alternatively you could cut pipe threads on them and screw them
tightly together.

Jim Wilkins

On Dec 15, 10:58*am, wrote:
I'm building a small gearbox driven by a high performance RC motor.
The Motor has a shaft diameter of 8mm. (0.314)
I'll be running this system at about 3500W or 4.7Hp and 8000 RPM *4.4Nm (3.25 fl/lb) torque.
The shaft is well supported with a heavy set of ball bearings, its designed to handle a large propeller.

All the gears I can find that have the power handleing/torque capacity have a larger shaft/bore diameter.

The motor is designed to have a collet assembly that clamps on the shaft and supports a prop hub.
*want to add another bearing on the other end of the shaft to support both ends so I don't have
an overhanging gear on a too small shaft. This preculdes putting the stock collet assemble on the motor shaft.

The smallest gear hub I can find is 3/8" or 9.5mm.
I'm pretty sure that a set screw won't hold and drilling the 8mm shaft for a drive
pin strikes me as marginal I would fear breaking the shaft at the pin hole.

Any recomendations on how to secure the shaft to the gear?

This will be driving a pump driving an orifice so the shock loads will be almost nonexistant and the duty cycle will be
low 3 min bursts of declining horespower 4.69 peak to 1.5 at the end of the run.

Paul

I think you're asking for an 8mm pretzel, but that's your problem. 4+
horsepower delivered to air isn't quite the same as 4+ horsepower
delivered to gear box and pump. What I would do is to take the
(hopefully) available collet prop hub and turn it into sort of a "flex
plate" ala car automatic transmission. Your gear box would supply
support for the outboard shaft end via a nub on the hub and a matching
divot in the center of the gear box drive plate. Probably a simple
"X" form on the hub driving 4 pins on the disk on the gear box should
do the job, actual dimensions left as the student's exercise for the
day.

Stan

I posted the wrong vidoe.
I meant to post this one, the whole thread will make more sense now.

http://www.youtube.com/watch?v=dacpVhUnEXw

I have a good CNC drive on my converted chinese lathe.
So the compound does not enter into it.

Paul