Metalbot – Work-in-Process

Metalbot – Work-in-Process

We’ve been working on a fun new robot we call Metalbot. Our goal was to build an autonomous rover with a unibody design that was machined out of a single block of metal. We started with this 13” x 9” x 1.75” block of 6061 aluminum:

Metalbot_Stock

When the machining was done, the robot’s body looked like this. It’s a hollowed-out shell that is about 1/8” thick with holes, slots, and pockets for the motors, LEDs, sensors, and other  electronics.

Metalbot_Unibody

Once Metalbot was assembled with the internal components, it looked like this:
What do you think? We think it’s pretty cool looking. Do you like it?

Metalbot_Side

Metalbot_Corner_View

Work-in-Process Pics

In this first picture (which was taken through the polycarbonate enclosure), we clamped the part vertically in the vise and we’re using an 1/8″ end mill to machine the detail on the front of the nose. In a previous operation we clamped the stock flat and machined the top of the robot, so that work is already done. Because this part has features on every side, machining it required us to clamp the stock in the vise in 8 different orientations: top, left side, right side, back, front, 45-degree left nose, 45-degree right nose, and bottom.

Metalbot_Machining_Front

In this next picture, we’re on the last setup, machining out the large pocket on the underside of the robot. This turned the aluminum block into a 1/8” thick shell. The large pocket appears to be glowing because the ring of LEDs we installed around the mill’s spindle are shining into the coolant that has filled the pocket. We’re using a 25mm (.98”) modular end mill here, which is designed to remove material fast. Of course, there were a lot of metal chips, but it’s important to remember that aluminum is easy and efficient to recycle.

Metalbot_Pocketing

In this picture we’re half way done digging the pocket and we have the machine take a break from the hard work to chamfer the outside contour:

Metalbot_Chamfering

Once the body is machined, we screwed in the wheels, motors, and electronics, which are screwed upside down on the underside, where they are easy to access when the robot is turned over. We will install a bottom plate later.

Metalbot_Assembly

Then we did the wiring and soldering:

Metalbot_Soldering

Here is the underside of the robot with most of the electronics installed. We’re using an Arduino Mega and a 4-channel Motor Controller, along with 4 Pololu gear motors to drive the mecanum wheels, which will allow the robot to strafe. The robot is also equipped with 6 Ping ultrasonic sensors for autonomous object detection, a LIPO battery, a main power switch, 6 NeoPixel RGB LEDs to indicate the state of each sensor, an Xbee Radio, and a panning servo (black thing in the middle). The robot will also be equipped with an MP3 module and speaker for sound, but those haven’t been installed yet.

Metalbot_Underside

The robot’s finished body is 8” wide and 12” long. The rover can be fitted with either the mecanum wheels shown or CNC-machined conventional wheels (not shown). Our original goal was just to machine a cool looking rover out of a single piece of metal, but as we went along, we decided to add some flexibility into the design for future enhancements in case we wanted to do more with it. The robot has been designed with a central spine of holes and ridges for attaching future add-ons, including a servo mounted in the center, which will support a pan-tilt turret for a camera, gun, or arm. We have designed the pan-tilt turret to utilize the Actobotics ecosystem, but other pan-tilt mechanisms could also be used. There are also holes on the front and rear of the top deck that are compatible with the full range of Actobotics components such as brackets, hubs, and channels, which really adds a lot of flexibility.

The next step is to work on the sensors and software programming. With its mecanum wheels, it should be able strafe like a champ very soon.

Here are a few more pictures of Metalbot so far. Let us know what you think. Do you like the overall design?

Metalbot_Top

Metalbot_Front

A Counter-rotating Differential

A Counter-rotating Differential

Back in November of 2011 we posted an article about our first Spirit II Mars Rover. Among other things, that rover included a counter-rotating differential (or universal joint) integrated into its rocker-bogie suspension system. If the front wheel on the left side of the rover went upward over a large obstacle, then the differential would push the three wheels on the right side downward, and vice versa. Its purpose was to stabilize the rover when traversing rough terrain. We made that first counter-rotating differential from bevel gears, aluminum rods, aluminum plates, and screws. Its shafts were connected to each side of the rocker-bogie suspension system. The function was simple: If either of the shafts rotated, then it caused the other shaft to rotate in the opposite direction. Our original version worked quite well, but it was also large, bulky, and a bit difficult to keep running smoothly.

Recently, our friends at Actobotics / ServoCity sent us a couple of their new bevel gears to try out. It’s cool how a few new parts can fire up your imagination and get you thinking. We decided to see if we could create a new counter-rotating differential for a future Mars Rover project. We were very pleased with the results. The new differential is much smaller than the old version, so it will fit nicely inside the box of a Mars Rover, and its operation is smooth and robust. Camille took all the photos of the new differential.