Monday, June 20, 2011

Installing a servo in the gripper claw that will fit R2's door opening

Tonight I was finally caught up with my college term papers and could unwind with some R2-D2 work.

One thing I have been anxious to try was two servos that might be the potential to replace the gripper claw's medium size servo.  The servo is too tall, so that when I try to move the gripper claw in and out of the door opening, it hits the door hinge.

The first servo was suggested by Warren over the King's Mountain R/C.  This HS-75BB is shorter, used for R/C aircraft retractable landing great.  It has the same spindle size as the existing servo, that is where the servo horn slides onto the servo.

Before I got too carried away, I took a "before" picture in case I have refer to it...

Once the screws that secure the claw to the servo are removed, you can see the plastic horn it attaches too.  Mine came already installed and you can already tell by the rough plastic edges and holes, whoever installs these has a lot of customization to do.

With the screw removed that holds the horn onto the servo, you can see how the servo needs to sit very flush to the gripper.

With the servo removed, you can see we already have a little problem.  While the HiTec servo is shorter, its a lot wider.

I decided to line up all the servos...the HiTech, the one that came with it and a "Mighty Feather", a very strong HiTec micro-servo.

It looks like the HS-65MG (Metal Gear) is going to be the way to go.

I compared the servo horn that came with the gripper to the horn that comes with the micro servo.  Since the spline is smaller on the micro servo, I can't just use the old horn on it.  I widened the holes to match that of the old horn but careful to be a bit under, so that the screws that thread in can "bite" into the horn.

 I also had to widen the mounting holes on the ends of the servo.

The micro servo is smaller so the mounting holes will not work.  I "guess" where the holes should go, which will just wind up widening the existing ones.

One photo doesn't do the hassle this was justice!  Its close to possible to twist the nut onto the screw.  I also had to use some spacers to allow for the servo to mount securely.  

The servo horn had to be trimmed so as not to hit the supporting structures.

The micro servo sits a bit lower and as a result, the gripper arms will too.  This means they will make contact with these pan head screws.  These need to be replaced with 4-40 flat head screws and the holes countersunk for a flush fit.

Since the arms sit lower, the spacer the other one uses needs to come out.  I found that this nut plus a thin washer worked well.

And here it is, all back together.  Making sure the arms are aligned properly is a bit of an optical illusion if you use the geared teeth as a reference.  Instead, use the mounting holes.

Now you can see, after all that work, that the smaller servo will make fitting in and out of the doorway better.  With the larger one, it was bumping into the door hinge.

 And here is an example of how just changing out this servo has gained me a bit more room to work with.

It looks like, in order to have a gripper claw, I will have to accept that it will have to open straight out the middle to the door opening.  I wanted it to open at an angle, so that the arm would extend straight out in front of R2, rather than off center.

 More tomorrow!