A New Member of the Project 40 Family

We’re expecting!  We’re expecting this to work once we decide it’s really the “baby” we need!  This is an Anaheim Automation in-line planetary gear and if our chats with the staff at Anaheim go well, we will purchase a pair of these (twins, of course). It will give us an additional 5:1 gear ratio between the SiTech gearbox already in the azimuth and altitude drive assemblies, and the drive wheel.  Why we need this is a longer story.  But first, you can get a feel for how this is changing the designs by comparing the before and after design images:

Azimuth Drive Design - Before

Azimuth Drive Design – After


The planetary gear assembly replaces the shaft coupler that connected the SiTech gearbox on the far left to the drive wheel. Instead, the SiTech gearbox shaft is now the input to the planetary gear, and the output shaft, which is part of the planetary gearbox, is long enough for the wheel to be mounted directly on it. Since there are mounting plates on both ends of the planetary, it is secured to the base plates very solidly, and we can also eliminate the mid-shaft support flange bearing.  In the drawings, this all fits, a bit snugly, within the original confines of the mounting box.  Once the parts are in, we’ll see if we can actually assemble it that way.  I think we can now call this a drive train.  So far we aren’t planning on installing a stick shift, but stay tuned.

This change came about after the first integration tests we did with the drives and the telescope. Once we got the various components of the drives working, we were able to successfully move the telescope, but immediately found that the azimuth, especially, was slipping. After consulting the makers of the gearbox, we confirmed that the clutch was doing its job, limiting the torque that it will transmit. That’s what allows it to slip when a docent grabs the scope and drags it to the vicinity of the next target, instead of grinding the gears to dust.  In the other direction though, when the servo is engaged and slewing, the torque required to move the scope is much larger than the torque that the clutch will allow before slipping. Add a gearbox after the SiTech gearbox, they said, and that’s what we are doing.

If you are fascinated by torque calculations, I have your heart’s desire in this pdf:

Drive Design Calculations

Here you’ll find our center of mass, moment of inertia and torque calculations.  The accompanying spreadsheet:

Center of Mass3

contains both the calculations and the figure of merit spreadsheet we used to choose servos and gears.

The jury is still out on how well the existing motors will do with the mount – they are nominally within specification, according to the calculations, but we’re learning that we need to be prepared to adjust as we go. The planetary inline gearboxes are still being evaluated with the distributor’s help and will take something like 6 to 8 weeks to deliver.


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