So I have gotten lots of Kudos in this thread. However, sooner or later, we all take our 'turn in the barrel' and I thought I should reveal one of mine on this project. If I make a change to incorporate a good suggestion, I don't count that as a fail, but here is a clear SNAFU.
There are a lot . . . a LOT . . . of reads of this thread and not much participation, so I conclude there are a lot of newbees lurking around who don't speak up or ask questions. To those folks this post is dedicated. Even a well seasoned engineer does not always hit a home run each time up. Don't be discouraged if your project does not work at first. Just keep on truckin' and make it happen.
OK, moving on to the fail. Below are photos of the claw that grabs the BT30 adapters and swings them around between the carousel and the spindle nose. The challenge in this part is to get it to snap over the adapter without excessive force (which may not be available from a small servo motor), and yet have a sufficient hold on the tool to function properly and safely (#1 priority). The current prototype meets those goals, but only up to a certain arm speed. For a typical DIY project, it would be completely adequate at a nice slow pace, but this ATC is slated for 'kick ass' performance and I do not want any impediments to that goal. Well at least not designed in.
The design shown works perfectly as expected, but the hold on the tool failed testing at the speeds I intend to run the arm. Sudden extreme decel at the end of the swing (the spindle nose) can dislodge the adapter (and whatever expensive and razor sharp tool it is holding). Finding a powerful spring that could be somehow mounted on the unusually shaped claw without interfering with other operations was a very big challenge. Ultimately as you see, I cut a channel to house the heaviest spring I could find. The swinging finger on the claw snaps smartly, but is unable to retain the tool during a sudden stop. There is no real estate on the part to allow for a larger spring and the back of the claw is off limits because it 'parks' against the mill column to clear the rotating carousel.
Result: back to the drawing board. Ashes to ashes, dust to dust and scrap to scrap. The claw started as chunks of 7075 scrap and it is now very expensive scrap.
The replacement design is completed, but not fabricated. The solution was to add a rocker in place of the swing finger. The rocker stays in either open or closed position via a high powered 'over center' spring plunger arrangement. Most important, the new claw has a positive mechanical lock. It can grip the adapter simply by moving over the groves in the same manner as the failed claw, but it is not able to release the tool until a mechanical interference is withdrawn. Similar in function to the interlock on the drawbar actuator.
Photos will be in the next post . . if I can figure out how to do the thumbnails.