[TowerTalk] Prop pitch question

[Grant Saviers]

Hi Stan,

My small PP moves a bit more back and forth in heavy wind, but does not 
drift.  I think that is the backlash in the large gear reduction. 
Talking to K7NV about this he mentioned the advantage of the smaller PP, 
which is what I have.

Here are some "off the top" ideas, I've not seen an off-the-shelf 
product but one might exist

Maybe try to modify a motorcycle drum (or maybe disk) brake.   Use 
standard brake shoes with a HD solenoid to actuate the brake.  (would 
need power all the time) Although it would be better to have push and 
pull motion.  One downside is the positive feedback in drum brakes so 
"reverse" may  be needed to get a release after high "forward" torque.

An easier idea is a band brake, a car drum inside out. Assuming there is 
enough shaft to hold a disk (cast iron preferable).  It has no positive 
feedback so takes more actuating force.  Short stroke linear actuators 
are available with lots of force, run on 12v or 24v. (a lot on ebay, 
check if it has power off load capability).

Here is a possibility,
https://www.coxreels.com/band-brake-heavy-duty_8_28_1423.html

Some googling turned up https://knottbrake.com/categories/band-brakes/

A fair amount of work, but so is climbing the tower a dozen times....

Grant KZ1W



On 5/22/2020 09:29, Stan Stockton wrote:
> I have an extra large prop pitch that has been turning a large 40m Yagi for 13.5 years.  Unfortunately the gear reduction on the extra large prop pitch is only 5830-1 instead of 9576-1 for the small one.  I am guessing the small prop pitch would hold it.  At any rate, although it does a fine job of turning the antenna, and would hold most any antenna you could imagine,  the prop pitch has never been able to hold this antenna in place.  I've probably replaced the coax jumper between the hardline at the top of the tower and the hardline on the boom a dozen times after big winds.
> 
> I know that mounting the prop pitch outside the tower with the proper gears and chain I could make it hold the antenna.  What I would prefer is to install a brake of some kind that would stop the shaft coming out of the bottom of the motor to keep it from turning.  I would think the torque would be small.  I haven't tried it but want to think I might hold that antenna in place with my fingers on the shaft coming out the bottom of the motor??
> 
> Anyway, the question is this.  Does anyone have an idea for an off the shelf product that could be adapted to stop that shaft when I wanted to "park" the antenna or after it is rotated with a delay?
> 
> Thanks... Stan, K5GO
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