[TowerTalk] Fwd: Fwd: FW: Fwd: Worm Gears

[David Robbins]

doesn't it get even uglier than that?  at 50% if you stop the worm gear it would stay put, but if it gets bumped and starts moving the friction needed to stop it is more than the friction needed to keep it from starting under a constant load.  So while 50% might be the break point, you actually need it lower to make it self breaking, low enough to overcome the sliding friction when it is running to bring it to a stop.

Jul 16, 2015 10:04:41 AM, hanslg at aol.com wrote:

Kelly,


You can view the worm gear as the classic "block on an incline". When the incline angle is small the block doesn't move. When the angle of the incline reaches a specific angle, determined only by the friction between the block and the incline surface, the block start to slide. If I remember it right the formula for the specific angle is:


Tan(angle)=(friction coefficient)


It doesn't matter what lubrication you use, there is always friction if not so little.


Regarding efficiency; You can always determine efficiency of a gearbox. It is simply the difference between what input power is needed to get a specific output power. The efficiency is output power divided by input power. We normally don't worry about it regarding to antenna rotors but you might take in consideration when you design/build a winch for a tower, time to raise the tower, risk of overheating the gearbox etc.



It turns out that at this specific angle the energy (force multiplied by distance) required to slide the block up the incline is double the energy the block receive (mass multiplied by height), a 50% efficiency. The rest disappear as friction generated heat under the block.



The bottom line is that if you want a self-braking gearbox you should include a worm-gear with an efficiency of less than 50%.


Best 73 de,


Hans - N2JFS



-----Original Message-----
From: Kelly Taylor 
To: Hans Hammarquist 
Sent: Wed, Jul 15, 2015 4:29 pm
Subject: Re: [TowerTalk] Fwd: FW: Fwd: Worm Gears


Hi Hans,

I believe it should be impossible to turn the output shaft of a worm
drive. 

I believe it’s relatively easy to turn the output shaft of a
conventional set of gears (which is why Ham-x rotators need brakes and Spids
don’t, and why the drivetrains of hybrid vehicles work backwards to charge the
battery when coasting or braking).

73, kelly
ve4xt

> On Jul 15, 2015, at
10:24 AM, Hans Hammarquist via TowerTalk wrote:
>

> I don't remember the exact formulas and I am not sure if it is only valid
for worm gears but it turns out then you calculate efficiency for gear boxes you
have a different efficiency depending on which direction the power goes.
> 
>

> It turns out that when the efficiency is 50% when down-shifting, the
efficiency is 0 when up-shifting. I am sure you noticed that is very hard ( if
not impossible) to turn the output axle on a worm gear. (It is ~50 years ago I
had this class, 1966). I suspect the same is valid for any gear box but let
somebody else answer that.
> 
> 
> 73 de,
> 
> 
> Hans - N2JFS
> 
> 
>

> -----Original Message-----
> From: Matt 
> To:
towertalk 
> Sent: Wed, Jul 15, 2015 12:13 am
>
Subject: [TowerTalk] FW: Fwd: Worm Gears
> 
> 
> ??? Please explain.
>

> KM5VI
> 
> -----Original Message-----
> From: TowerTalk
>
[mailto:towertalk-bounces at contesting.com] On Behalf Of Hans
> Hammarquist
via
> TowerTalk
> Sent: Tuesday, July 14, 2015 4:25 PM
> To:
>
towertalk at contesting.com
> Subject: [TowerTalk] Fwd: Worm Gears
> 
> Any gear
with
> a 50% or better efficiency is NOT self breaking and will
> require a
break. Even
> a slightly lower than 50% might (most possible) need a
> break
as the efficiency
> will increase with time as the gear will "wear in".
> 
>

> Hans -
> N2JFS
> 
> 
> 
> -----Original Message-----
> From: Wilson
>

> To: John Santillo N2HMM 
>
Cc:
> towertalk 
> Sent: Tue, Jul 14, 2015 1:37
pm
> Subject:
> Re: [TowerTalk] Worm Gears
> 
> 
> Hub City touts their
helical gear units, at 90+%
> efficiency vs 60% for
> worms.
> I
> don't
know about their resistance to back
> driving, but at 50-60:1, it
> wouldn't
take much of a brake...
> WL
> 
> 
> 
> 
> 
> 
>
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