Thursday, March 15, 2012

Creating a servo-saving linkage for the pie panels

I'm still working on R2's dome and getting everything situated with getting the hinges linked up to micro servos.  In the previous post, we got the hinges in!  Now, its time to figure out a reliable linkage from the micro servo to the hinge itself.

One thing I have noticed with my R2 since adding hinges and servos to the various doors and panels has been making them close snug.  Another thing I was worried about was servos being damaged by little fingers forcing doors open!  Adding a spring to the linkage would allow the doors to close better...and if pried open, the spring would give a bit before applying pressure to the servo.

I have seen how other builders have assembled similar linkages or just used a spring.  I wasn't able to bind a small enough spring that was firm enough to work.  So, I mimicked a setup I have seen others us.

Here's what it looks like when complete:

Here's the process to build it.

First I remove the plastic servo horn and drill out the first hole with a 3/32 drill bit.  The DuBro EZ connector is a 3/32 model.  To hold it in place, you need to use a hammer and tap the connector into the retaining clip.

Now we need to get our push rods ready to go.  I am using 12 inch 4-40 sized push rods that are threaded at the end.  Since we need the linkage to be small enough to fit inside the dome safely, we have to remove some material.  I remove 3/4 of the threaded section since we do not need all of it.   I trim the other end after I have the linkage made....just in case!

 Now I need to install the linkage that will go from the hinge to the push rod.  For this I am using DuBro Adjustable ball links (short, 4-40).  These will allow for some pivot and since they are shorter than the regular ones, you need less push rod.

 Next up is to slide a 3/32 collar on, the spring, slide onto the EZ connector, the spring and a collar on the other end.

 The springs need to be compressed...well, the point they have some movement but aren't sloppy.  Clear as mud, right?   The point is you want the servo to move and push the push rod, not slide around the spring.  But you need to balance it out so it has a little we are using the spring to help protect the servo and help keep the tension on the connection.  Your mileage may vary depending on the springs you use.  This is a lot of trial and error!

Once you have that trial and error sorted out THEN you can clip the end of the push rod.

Rinse and repeat a few more times!

Next time, we'll cover installing these into the dome!