What size propeller for a 36 V DC motor?

"John Doe" wrote in message
...
I have a Bosch 36 V lithium-ion hammer drill motor with batteries
and charger. What sort of propeller would be appropriate to stick
onto the shaft of that? Would a powered paraglider propeller be
too big? I just want to get a rough idea of how much air that
motor can push. Any experienced/educated guesses would be
appreciated.

After I looked at your question again, I see there is one answer I can give you.

A powered parachute prop is made for around 30 some HP and up,. probably. Your
drill motor is less than one HP. So no, a powered parachute propeller would be
about 36 times too big. On top of that, that drill motor is probably designed
to turn many more RPM's that a PP motor, so that would make it even more
mismatched.

You need to find some articles to read on model airplane electric motors,
something that talks about the numbers a motor is rated for. I don't remember
what those numbers are named, since I don't do electric...

You can get two motors that put out the same HP, and draw the same number of
watts, but one is designed to turn 3500 RPM's, while the other is designed to
turn 12,000 RPM's. The slow one could have a regular two bladed prop mounted
directly on the motor. The one that turns 12,000 would be designed to turn a
ducted fan. (imitation fighter turbo-jet engine) Yet, they still put out the
same power. The ducted engine would be only good at low amounts of thrust, but
allow the jet to go really fast, while the prop plane would be able to take off
in a shorter distance and climb steeply, but would cruise at much slower speeds.

There is a lot to read online to help understand these subjects, if you look a
little bit. It sounds like you would be interested. Look in places that talk
about remote control airplanes, because that is what even the man carrying
experimental airplanes are borrowing knowledge from, on the subject of electric
flight. It is just at larger scales.
--
Jim in NC

"Morgans" jsmorgan charterJUNK.net wrote:

"John Doe" jdoe usenetlove.invalid wrote in message

I have a Bosch 36 V lithium-ion hammer drill motor with
batteries and charger. What sort of propeller would be
appropriate to stick onto the shaft of that? Would a powered
paraglider propeller be too big? I just want to get a rough
idea of how much air that motor can push. Any
experienced/educated guesses would be appreciated.

....

You can get two motors that put out the same HP, and draw the
same number of watts, but one is designed to turn 3500 RPM's,
while the other is designed to turn 12,000 RPM's. The slow one
could have a regular two bladed prop mounted directly on the
motor. The one that turns 12,000 would be designed to turn a
ducted fan. (imitation fighter turbo-jet engine) Yet, they
still put out the same power. The ducted engine would be only
good at low amounts of thrust, but allow the jet to go really
fast, while the prop plane would be able to take off in a
shorter distance and climb steeply, but would cruise at much
slower speeds.

I will consider that when simulation flying.

There is a lot to read online to help understand these subjects,
if you look a little bit. It sounds like you would be
interested. Look in places that talk about remote control
airplanes, because that is what even the man carrying
experimental airplanes are borrowing knowledge from, on the
subject of electric flight. It is just at larger scales.

Flight of the Phoenix (2004)

I tried researching the printed numbers on the motor, but got
nothing.

Does the forward push on an ordinary electric motor cause abnormal
wear on the bearings? Or maybe that is countered/supported by the
magnetic part of the motor?

On 07/28/2010 10:53 AM, John Doe wrote:
"Morgans"jsmorgan charterJUNK.net wrote:

"John Doe"jdoe usenetlove.invalid wrote in message

I have a Bosch 36 V lithium-ion hammer drill motor with
batteries and charger. What sort of propeller would be
appropriate to stick onto the shaft of that? Would a powered
paraglider propeller be too big? I just want to get a rough
idea of how much air that motor can push. Any
experienced/educated guesses would be appreciated.

...

You can get two motors that put out the same HP, and draw the
same number of watts, but one is designed to turn 3500 RPM's,
while the other is designed to turn 12,000 RPM's. The slow one
could have a regular two bladed prop mounted directly on the
motor. The one that turns 12,000 would be designed to turn a
ducted fan. (imitation fighter turbo-jet engine) Yet, they
still put out the same power. The ducted engine would be only
good at low amounts of thrust, but allow the jet to go really
fast, while the prop plane would be able to take off in a
shorter distance and climb steeply, but would cruise at much
slower speeds.

I will consider that when simulation flying.

There is a lot to read online to help understand these subjects,
if you look a little bit. It sounds like you would be
interested. Look in places that talk about remote control
airplanes, because that is what even the man carrying
experimental airplanes are borrowing knowledge from, on the
subject of electric flight. It is just at larger scales.

Flight of the Phoenix (2004)

I tried researching the printed numbers on the motor, but got
nothing.

Those numbers are DeWalt part, inventory, date code, or (not very
likely) serial numbers. DeWalt would consider the motor specifications
to be proprietary information, so you'll not get your hands on it!

Even if the motor isn't made by DeWalt it'll still be custom made _for_
DeWalt, and the motor manufacturer would be contractually obliged not to
divulge details.

So you're kind of on your own there.

Does the forward push on an ordinary electric motor cause abnormal
wear on the bearings? Or maybe that is countered/supported by the
magnetic part of the motor?

It is _not_ supported by the magnetics. It may, indeed, cause
objectionable wear -- that depends on whether the motor bearings can
absorb the thrust of the prop (assuming you prop it directly).

For all but outrunner motors, you'd want a gear box anyway. Any
non-planetary gear box (or belt drive) will put a side load on the motor
shaft, but its much more likely that the motor is designed for that.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott tim seemywebsite.com wrote:

John Doe wrote:

....

Does the forward push on an ordinary electric motor cause
abnormal wear on the bearings? Or maybe that is
countered/supported by the magnetic part of the motor?

It is _not_ supported by the magnetics. It may, indeed, cause
objectionable wear -- that depends on whether the motor bearings
can absorb the thrust of the prop (assuming you prop it
directly).

For all but outrunner motors, you'd want a gear box anyway.

How about a "thrust bearing"?
"Handles thrust loads, also called an axial or side load, which is
a load parallel to a shaft. Facilitates smooth rotation between
surfaces like other rotary bearings, but their design supports
higher thrust loads. Choose from plain and ball bearing designs. "
--




















Any
non-planetary gear box (or belt drive) will put a side load on the motor
shaft, but its much more likely that the motor is designed for that.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html


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Date: Wed, 28 Jul 2010 12:09:22 -0700
From: Tim Wescott tim seemywebsite.com
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Subject: What size propeller for a 36 V DC motor?
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Does the forward push on an ordinary electric motor cause abnormal
wear on the bearings? Or maybe that is countered/supported by the
magnetic part of the motor?

Very good point. The bearings do take all of the load, called thrust, and it
depends on the type of bearing whether it can stand the end load. Most likely
that motor would not do well. It would be best to use a geared adapter to turn
the prop, and that will remove the thrust load from the motor. Check model
supply places for a suitable gearbox.

I seriously doubt that you are going to get more than 8 pounds of thrust out of
that motor, even with the ideal gearbox and prop. Probably not going to do well
to move a person on skates.
--
Jim in NC

On 07/28/2010 12:40 PM, Morgans wrote:


Does the forward push on an ordinary electric motor cause abnormal
wear on the bearings? Or maybe that is countered/supported by the
magnetic part of the motor?

Very good point. The bearings do take all of the load, called thrust,
and it depends on the type of bearing whether it can stand the end load.
Most likely that motor would not do well. It would be best to use a
geared adapter to turn the prop, and that will remove the thrust load
from the motor. Check model supply places for a suitable gearbox.

I seriously doubt that you are going to get more than 8 pounds of thrust
out of that motor, even with the ideal gearbox and prop. Probably not
going to do well to move a person on skates.

I hadn't realized this was part of the whole skater thing.

You'll do much better to drive the skate wheels with the motor --
driving a vehicle by pushing on the air is just not efficient, it makes
little sense to do so if you can drive a wheel.

(For obvious reasons you can't make an airplane go by driving the wheels
-- hence, propellers).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

"Morgans" jsmorgan charterJUNK.net wrote:

....

I seriously doubt that you are going to get more than 8 pounds
of thrust out of that motor, even with the ideal gearbox and
prop. Probably not going to do well to move a person on skates.

Right... Just depends on how easy it is to try. But maybe I can
get a feel for what sort of electric motor would do. Propeller
powered inline skating has been done with small gasoline/petrol
motors.

http://www.youtube.com/results?searc...e+jetpack&aq=f

The first clip is on topic after the cool hang gliding introduction.

But I would not want to use a noisy gasoline motor.

Thanks.

"Morgans" jsmorgancharterJUNK.net wrote:

Look in places that talk about remote control airplanes, because
that is what even the man carrying experimental airplanes are
borrowing knowledge from, on the subject of electric flight. It
is just at larger scales.

I believe that, but how come you never see a real airplane
standing on its tail? Looks like that would be a neat way to
simulate a Harrier landing, and takeoff.

On Jul 30, 5:09*am, John Doe wrote:
"Morgans" jsmorgancharterJUNK.net wrote:
Look in places that talk about remote control airplanes, because
that is what even the man carrying experimental airplanes are
borrowing knowledge from, on the subject of electric flight. *It
is just at larger scales.

I believe that, but how come you never see a real airplane
standing on its tail? Looks like that would be a neat way to
simulate a Harrier landing, and takeoff.

Actually you can do it. It is just too expensive and dangerous.

As for your project. The best is to experiment with it.
As a starter, you should calculate the power that you need.
Power is a function of battery, not motor.
The motor rated power is the sustained power that the motor and
windings can withstand for along time.

the motor power is defined by rpm x torgue.
rpm is proportional to voltage

How much rpm can your motor stand for a short time, mechanically.

torgue is proportional to current. How much current can your motor
stand for a short time. Current creates heat so the limit is heat.
If you can put cooling system to this motor you can operate it at high
torgue, at least for a short time.


Propeller theory. Propeller is just like a screw. How far does it go
per RPM.
At low speed, the air need not travel so fast, so low pitch is
desirable. In order to increase the thrust, you need high volume
running at low speed. Long propeller.

You don't need maths. Just a sense of balance.

So adjust the pitch and diameter of the propeller to match the voltage
and current rating of your electric motor.

You can exceed these ratings, but take special precautions, such as
cooling the coils.
In fact I like to experiment with overcurrent and its effects. Over
RPM is dangerous because it is mechanical. Over current is just heat
which we can control.

["Followup-To:" header set to rec.models.rc.air.]
On 2010-07-29, John Doe wrote:
| "Morgans" jsmorgancharterJUNK.net wrote:
|
| Look in places that talk about remote control airplanes, because
| that is what even the man carrying experimental airplanes are
| borrowing knowledge from, on the subject of electric flight. It
| is just at larger scales.
|
| I believe that, but how come you never see a real airplane
| standing on its tail?

Because you don't look in the right places?

http://en.wikipedia.org/wiki/Lockheed_XFV
http://en.wikipedia.org/wiki/Convair_XFY

Ultimately, yes, for electric flight, most of the innovation is
happening with models and UAVs because that's where it's more
practical. Once you get into planes large enough to carry humans, the
cost difference between electric and internal combustion becomes huge.
For example, for a powered parachute, somebody mentioned a 30 hp
engine. You could have that engine for a few hundred dollars, perhaps
a thousand, but a comparable electric setup would cost way more, and
something that will keep you up for an hour or two will weigh way more
than the equivalent gasoline powered setup and cost even more.

Full scale electric planes do exist, and I would expect more work in
that area, but it's not going to really be practical for most uses
until battery or fuel cell technology gets a lot better (or at least
cheaper.)

And also, if your model fails, you've got a pile of sticks to fix up.
If your full scale plane fails, you might be dead.

But good ideas certainly do flow in both directions.

| Looks like that would be a neat way to
| simulate a Harrier landing, and takeoff.

Yes, though the examples I gave had massive problems. The first was
never even taken off vertically!

--
Doug McLaren,
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