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Author Topic: HAM IV Rotor  (Read 3869 times)

Posts: 17

« on: November 05, 2001, 09:23:54 AM »

I have a HAM IV rotator I bought new about 3 years ago. All of a sudden it will not go to the left unless I first go to the right. Some times it will not go either way. ANy suggestion or things to look for before I go up the tower?

73 N0WE

Posts: 21764

« Reply #1 on: November 05, 2001, 11:15:12 AM »

Sounds like something's jamming the wedge brake, or the startup resistance to rotation is higher than the rotor can handle.

What do you have mounted on that HAM-IV?  Is the load "balanced" (so the mast isn't trying to pull the rotator off center)?  Do you use a thrust bearing that takes the weight off the rotator?

If all that's okay, you might investigate wire gauge vs. cable length for the cable.  Rotator control cable resistance plays a large part in how much starting torque the rotator has.  #16 gauge _minimum_ for control wires #1 and #2 (usually black and white) is recommended, especially for any length over about 75 feet of cable.  For more than 125 feet, go to #14 gauge.  (Note: It doesn't matter much what the other six conductors [#3 through #8] are, as they carry very little current.)

Then, of course, it's possible that the starting capacitor is bad.  That would be unusual after only 3 years, they usually last 10 years or so, but anything's possible.  Thankfully, the starting cap is in the control box and very easy to replace; and Hy-Gain stocks the caps.

Based on your description, I'd think the problem is either an unbalanced load, or mechanical interference between the mast and another object such as the tower top plate, or insufficient wiring used for lines #1 and #2.  Ham-IV's are very resiliant and it's quite unusual to have problems only three years after installation.

73 de Steve WB2WIK/6

Posts: 17

« Reply #2 on: November 05, 2001, 11:28:55 AM »

Thanks for the info. I do use a thrust bearing and the antenna is just a Cushcraft A3S. My run is only about 50' so I don't believe wire guage is a problem. Even when it sticks I can hear the brake release when I hit the button. I guess I need to lay the tower down and see what I can see.

73 Jim

Posts: 21764

« Reply #3 on: November 05, 2001, 02:35:31 PM »

This does sound unusual, the HAM-IV's pretty bulletproof.

Just one last thought: Check to be sure you're either using 2" diameter pipe as a mast, or that you've shimmed the rotor to properly line up with a smaller diameter.  The HAM-IV, and the rotor plate sold by most tower manufacturers (Rohn, Tri-Ex, U.S. Tower, etc.), make everything line up perfectly (vertically) when a 2" diameter mast is used.  Using a smaller diameter mast can offset the mast from the center axis of the rotor's upper bell housing and place quite a lot of strain on the rotor, so that even when the brake releases, it just doesn't have enough starting torque to get going reliably.  Lining things up better solves the problem, if there is one.

73 & good luck!

Steve WB2WIK/6


Posts: 999

« Reply #4 on: November 20, 2001, 03:46:39 AM »

The thrust bearing could be the culprit.  I had a Rohn TB-3 bearing wear to the point that it got chatter marks in the bearing race.  This would cause the individual balls to jam against the race, or on each other and prevent the rotor from starting.  Dirt in the bearing race can cause the same problem.  These bearings are designed to run WITHOUT lube and the race MUST be clean.  The ham II doesn't have an over abundance of starting torque in any case.  If this is the condition, it will eventually kill the motor in the rotor.  Another potential problem is the driven ring gear in the rotor.  Teeth can chip or break off and jam the rotor drive train.  The ring gear can also crack, and while it still appears intact, the crack can cause a slight misalignment of the gear teeth.  I'd bite the bullet and check both the bearing and the rotor.  It doesn't hurt to disassemble the rotor every few years and clean the directional indicator pot, check the gears, and relubricate the drive train and support bearings.  These rotors are stone simple to work on.  The owner's manual gives very clear directions for disassembly.  Follow ALL the steps and don't be tempted to take short cuts.  Every step is there for a reason.  If the motor start cap is bad, just go to your local electrical supply house and get a REAL motor start cap.  Check the correct value from the schematic.  Grainger's carries them for about $3.  The start cap can be mounted on your tower right next to the rotor, which is where it should be anyway, instead of in the control box.  Wire it to terminals #4 & #8 on the rotor.  This frees up 2 wires in the control cable that can be paralleled with the left and right motor run leads for less resistance and improved starting torque.
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