Any Hirschman Gurus Out There?
 

The power antenna on the old ball & chain's 1993 300E went out a while ago. Finally got around to looking at it one evening this week. After digging into the antenna mechanism and reading a bit on the web, I cannot figure out why Hirschman designed it the way they did.

Here's how it works. There are two large gears inside the case. They are the same diameter, spin on the same axle, and are adjacent to one another. The topmost gear (looking down at the mechanism) is driven via a worm gear that is powered by the electric motor. The bottom gear engages the teeth on the flexbile antenna lead to raise and lower the mast. The top gear drives the bottom gear via a torsion spring. So the two gears can move a little bit relative to one another, but for the most part they are locked together.

There is no clutch mechanism. When the antenna reaches the top (or bottom) of its travel, everything just stops. The motor appears to be on a simple timer circuit - power is applied for a few seconds, about half of which is spent moving the antenna, the other half is spent locked up at the extreme upper or lower limit.

So my question is this - why the heck did they use this complex/expensive/failure prone torsion spring to couple the two gears together? Ultimately the two gears are locked together, so why not just glue, screw, or bolt them together?

BTW, the failure on mine is the cast in little plastic pin on the lower gear - it' driven by the torsion spring to transfer the rotation from the upper gear - broke off. All the force to rotate the gear was applied through this one point. I guess it only lasts 12 or 13 years. :D It appears to be a somewhat common failure.

Since I cannot figure out the value added by the whole torsion-spring-gear-coupling-assembly, I can't decide if it's OK to just screw the two gears together. Any thoughts from an ME (or ME wannabe)?

- JimY

As a guess, I would say that since it's on a timer circuit, the antenna motor is going to keep turning for a finite period of time no matter what. So that means if something is stuck or preventing the mast from moving either up or down, you could potentially burn out the motor or strip the motor worm gear. Sounds like a safety measure to me.

i can get you a gear if you need it,

http://www.geocities.com/odemer@sbcglobal.net/


Try this link out. Not personally used, but have heard great things. Good luck.