SimpleBot Chassis Assembly

= SimpleBot Chassis Assembly =

The main chassis of the SimpleBot is made from a corrugated plastic called CorFlute, which is cheap and fast to laser cut. The SimpleBot creator, Andrew Fisher, came up with this design.

Chassis Parts
There are two pieces - a large base plate, and a smaller front bumper plate.

You may have to press out some of the cutouts from the plates, if the laser cutter didn't cut them all the way through. A screwdriver or a craft knife will help with any particularly stubborn pieces.

After all the cutouts are removed, the front bumper clips onto the base plate like this:



The pieces are both symmetrical so there is no "wrong" way to attach them.

Mount Raspberry Pi
After clipping on the bumper, we screw the Raspberry Pi onto the base plate on top of 10mm high standoffs.

'''Take care when mounting the Raspberry Pi as it is sensitive to static discharge. Ground yourself before handling it.'''

The standoffs you'll have are slightly different to the ones shown in this picture. The actual standoffs have a female threaded hole in the bottom and a male threaded extension at the top.

Mount the standoffs onto the four small holes in the base plate:



Use the four short nylon bolts to screw the standoffs into place through the bottom of the plate.

Once the standoffs are firmly mounted, place the Raspberry Pi on top and screw it down using the nylon nuts. The USB ports on the Raspberry Pi should point forward, towards the front bumper.



Continuous Rotation Servo "Motors"
The motors for the SimpleBot are continuous rotation hobby servo motors.

Flip the chassis assembly over so the Raspberry Pi is facing down, as the motors and battery pack are mounted on the bottom.

The servos are aligned with square mounting holes, like this:





The shaft on each servo should be closest to the front of the SimpleBot, near the bumper.

Each servo is held on via two cable ties. Each cable tie runs through the mounting holes, around the servo.



Here's a close up of one side of the SimpleBot:



And the other side:



In these photos the cable ties may be a little too tight, as the CorFlute base has bent a little at the side. This doesn't really matter, but they don't have to be this tight!

Battery Pack
The 6 cell battery pack is also mounted using two cable ties to form a "cradle" under the robot base. Unlike the servos, you want the battery "cradle" to be a bit loose so you can pull the pack out to change batteries.

Start by screwing the two leads from the battery pack into the DC jack. Note that the red lead goes to the "+" terminal, and the black lead goes to the "-" terminal:



Then insert the Alkaline AA cells in the pack.



'''IMPORTANT: Once the batteries are installed the DC jack terminals carry 9V, and can potentially damage electronics if they brush across them. Take care not to rest the DC jack against any of the electronics! It should sit out to the side away from the rest of the robot.'''

With the SimpleBot base upside down, place the battery pack between the two servos. The lead should come out towards the rear of the robot, pointing away from the front bumper.





The cable ties to form the "cradle" are inserted into square mounting holes on each side of the battery pack, underneath the Raspberry Pi. This can be a little bit fiddly, it may be helpful to place the battery pack off to the side after sizing it up, and then slide it back in once the cable ties are loosely inserted.





From the top side of the SimpleBot, the battery cradle cable ties will look like this:





Wheels
The SimpleBot has two wheel assemblies, and each assembly is made up of a sandwich of two pieces of Corflute, a cross-shaped servo horn, and short pieces of wire. We're using thin "wire wrap" wire.



Place two of the Corflute wheel pieces together, aligned so that the ribs on the wheels are at right angles to each other for maximum strength. Sit the servo horn on top, with the thick mounting lug facing up:



Cut 4 short pieces of wire (about 7 or 8cm each is plenty), bend them in half, and insert them through the servo horn and the holes in the Corflute:



The central mounting hole on the horn should line up with the hole in the centre of the wheel, with the wires poking through:



Once everything is lined up, twist the wire ends together tightly to hold the horn in place:



Cut off the extra wire, and bend over the twisted section flat against the wheel to keep it neat.

Repeat for the second wheel.

After you think both wheels are securely tied onto the servo horns, mount the servo horns on the servos and screw them down in the centre:





"Sled"
Unless you want to update your SimpleBot to become a "BalanceBot", it will need something for the chassis to balance against on top of only two wheels.

To keep costs low, the SimpleBot uses a simple cable tie to form this "sled" to balance against. Forming the "sled" is a little tricky to explain, you may want to go and look at a completed SimpleBot in order to understand.

Start by flipping the robot upside down, and push a cable tie through the end two sled mounting holes as shown, with the "tab" on the inside of the two holes:



Take the outer end of the cable tie and wrap it all the way over the top, through the innermost mounting hole, then back through the adjacent hole. You have to feed the tie through as you go:



Once you're sure it's looped OK, push the end of the cable tie into the tab. Don't tighten it right up yet! You need to check the height is OK.



Flip the robot over, and adjust the cable tie until the robot seems to sit flat on the "sled". Then cut off the end of the tie:





PiLeven
Mounting the PiLeven is fairly straightforward, it just presses down onto the Raspberry Pi header as shown:



SimpleBot Shield
Mounting the SimpleBot Shield is also straightforward, it drops onto the PiLeven as shown:



Connections
Mount the Ultrasonic Rangefinder sensor by dropping it into the 4 pin header at the front of the SimpleBot.

Connect the servo motors by feeding the connectors through the small holes in the base plate, then plug them into the two "motor" headers. Orientation of the servo connections matter - the yellow signal wire faces towards the front of the bot, as shown.

Connect the Wifi adapter by plugging it into a USB port on the front. In the position shown, the antenna doesn't interfere with the Ultrasonic rangefinder (although the rangefinder does appear to detract from the wireless reception a little bit).





Power Connection
The battery pack plugs directly into the DC jack on the back of the PiLeven. Don't plug it in until you've prepared the SD card to boot up the Pi.



Removing the DC jack connection will power down the Pi immediately, always try to shut down Linux before doing this.

All Done
Congratulations, you built a SimpleBot!



Next step is to prepare the SD card and perform the SimpleBot Initial Software Configuration.

Back to SimpleBot Assembly Overview