Thursday, August 7, 2014

ArrBot: Class 3 Notes

Today's class will be a bit more entertaining than the last two classes.  Now that we have the components, we're going to assemble the robots!

(pictures forthcoming!!)

You should have prepared for class:
  • Robot body and wheels
  • Two CR servos
Bring to class:
  • Robotics kit, including the above
  • Soldering stuff
  • Small (but not tiny) phillips screwdriver.  Look at the screws in the servo kit.
  • Sandpaper, medium and fine grit.
  • Hot glue gun, if you have it.  I'll bring some extra hot glue sticks if you don't mind sharing your hot glue gun.
Building the Robot

tl;dr: put all the 3D printed parts together and put the battery and breadboard on top.

Front Wheels

Fit the front wheels onto the axles.  Most likely they won't fit, and will need to be sanded down.  Even if they do fit, you will want to sand them to make the axle and the interior bearing surface of the wheel as smooth as possible.

When each front wheel turns smoothly on its axle, use one of the "large" servo screws to attach the wheel to the axle.  You might have to open up the hole in the wheel a bit so that the wheel will turn freely.  Heating the screw a bit will allow it to screw smoothly into the axle.  Tighten the screws so that the wheels don't wobble, but not so tightly that they bind against the wheel.

Put some dry silicone/teflon lubricant between the axle and the wheel.  Not too much, it gets a bit messy if you use too much.

Drive Wheels

The drive wheels come in two pieces.  Take the long servo arm and fit it into the slot.  Press the outside part of the wheel tight so that the servo arm is held firmly in place.  Trim any excess plastic off the servo arm.  Add a bit of hot glue to hold everything together.  The teeth should be centered on the wheel.  Attach the servo arm to the servo with the small screw in the servo package.

Note that there's a wrong way to put the drive wheels together.  The gears should end up in the middle.  If the gears are touching the side, you've done it wrong.

Mounting Servos

You can do this in either of two ways.  If you have some extra screws, you can screw the servo onto the body.  There's a flat surface that will accept the screws.

You can also just hot glue the servo to the body.  This seems to work fine as well.  Use a thin layer of hot glue, and press it tight with your fingers to ensure a square, tight fit.

Battery Pack

Solder or crimp a servo lead onto the battery pack.  Put "+" in the center and "-" on one side.  This will allow you to attach the battery to the breadboard on pins inserted into RAW and GND.

Make sure your battery pack fits within the ArrBot treads.  If not, hot glue a bit of cardboard or other material the bottom of the breadboard (remove the paper backing covering the adhesive first) so that it clears the treads.

The Stack

Pull the paper off of the adhesive on the breadboard.  Put some Dual Lock on the top of robot body, top and bottom of the battery holder, and bottom of the breadboard.  Stack all this up and lock it tight.

If you don't have Dual Lock, use some Velcro or any other stuff that looks like it might hold everything together.

The Treads

Finally, put the treads on the wheels.  Note that there's an indentation on one side of the tread, that should be on the inside and line up with the gear teeth.

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