Robotics Activity

The 4Bot All Wheel Drive IP Based Robotic Vehicle

Resources

bulletG&S chassis & deck kit
bullet2 side rails (3/4" Aluminum angle 1/8" - 14" long)
bullet1 headlight / bumper bracket (3/4" Aluminum Angle 3/64" - 7.5" long)
bullet1 Battery Holder bar (Aluminum Flat bar 1/8" - 7.5" long)
bullet1 Rear lower deck (6mm Sintra PVC board - all decks)
bullet1 Front lower deck
bullet1 Upper deck
bullet1 Power panel
bullet4 - 2" Threaded standoffs (Aluminum FF #4-40)
bullet2 - 2" Threaded standoffs (Aluminum FF #4-40 with 5/8" studs)
bullet12 - 3/8" Threaded standoffs (Nylon FF #4-40)
bullet4 - 3/8" Threaded standoffs (Nylon FM #4-40)
bullet2 - 5/8" #4-40 hex head screws
bullet10 - 1/2" #4-40 hex head screws
bullet21 -3/8" #4-40 Hex head screws
bullet12 - 1/4" #4-40 Hex head screws
bullet3 - #4-40 lock nuts
bullet12 - #4-40 machine nuts
bullet 2 Lynxmotion MMT-02 Motor Mount kits
bullet2 - Motor mounts
bullet8 - Motor Screws
bullet4 - 3/8" #4-40 Hex head screws
bullet4 - #4-40 Lock nuts
bullet 4 - 200RPM 12V (M12V200) geared motor
bullet 2 - Lynxmotion Hex mounting hub kits
bullet2 - Aluminum hubs for a 6mm shaft
bullet2 - Set screws
bullet2 - Wheel mounting screws
bullet 2 Lynxmotion Off Road Robot Tire kits
bullet2 Proline Masher 2000 tires
bullet2 Nylon Wheel hubs
bullet Instructions for Tire assembly (on-line)
bullet1 Fuse holder (chassis mount)
bullet1 6a fuse
bullet2 Banana jacks (red and black)
bullet1 Minature SPST toggle switch
bullet1/4" and 1/8" spade connectors
bullet2 LED holders (headlights)
bullet18 ga stranded wire with crimp on connectors for drive motors
bullet18ga stranded hookup wire - Main power
bullet24ga stranded hookup wire - Voltage sensor, servo controller, sbc
bullet26ga stranded hookup wire - Headlights
bulletHigh intensity LED system (from electronics activity)
bulletPhidgets
bulletSBC, SBC2 or SBC3 - upper deck is configured for all
bullet8 Motor servo controller
bulletHC Motor controller
bulletPrecision voltage sensor
bulletTemperature sensor
bulletDistance sensor
bulletSolid state relay (Single or Dual)

Background

The 4bot is a 4 wheel, robotic platform which uses low pressure, oversized tires and a Phidgets single board computer (SBC) for control and sensing. It can be configured for a variety of uses. In its basic form, the 4bot will be configured with a pan and tilt camera, battery voltage sensor, head lights, and a high intensity LED mounted coaxially with the camera. In subsequent challanges, additional components and capabilities will be added to the 4bot. The 4Bot communicates using a wireless adapter connected to an access point. Because it uses TCP/IP protocols it can be controlled locally or over the Internet 

Chassis Fabrication

Step 1

Connect the 4 motor mounts to the Aluminum chassis rails. Use the 3/8" hex screws and locking nuts. Line up the motor mounts with the rails. Idealy, the mounts should be "flush" with the outside, vertical side of the rail (for wheel clearance).

Step 2

Connect the back lower deck to the chassis rails as in the next illustration. Use 2 1/2" hex screws and nuts for the 2 forward holes. Use 2 1/2" screws and 2 of the 2" aluminum standoffs for the 2 rear holes. The standoffs will hold the upper deck. The back, lower deck should be oriented with the 2 large holes to the left of centre.

 

Step 3

Connect the lower front deck and the headlight bracket to the chassis rails. Make sure the 4 large holes are positioned over the motor mount screws. Use 1/2" screws and nuts.

Step 4

The 4bot is designed to use a rechargeable gel cell which is fairly heavy (but is cheap and gives a good endurance). It will be carried on an aluminum strap 2" below the lower deck.

Start by locating the 2 standoffs with studs. These are the lower standoffs. Insert up through the rails and secure tightly with a nut. The chassis is shown upside down in the next illustration.

Next add a locking nut to each stud. This is used for spacing so that the upper deck remains level.

Finally, screw on the last 2 standoffs.

Step 5

Next attach the battery support. Use 2 3/8" hex screws.

Step 6

Install the small nylon standoffs on the back lower deck. Use 3/8" hex screws (one exception - the standoff in the lower right corner will require a 1/2" hex head screw as it has to go through the aluminum chassis rail). Hand tighten!

Note: Many of the images that follow have been made from mock ups and may not show all the installed parts such as the 2" standoffs for the upper deck, etc.

Next install standoffs on the upper deck. The 4 forward standoffs will hold the camera servo motor. They are threaded on the top(FM). Only install the back 2 first or you will not be able to install the servo. Install the front 2 after the servo is in place.

Step 7

Next install the motors. Use the included screws (4). Don't use longer screws as they will damage the motor core.

Electronics Assembly

Step 1

The Power Panel contains a switch to turn the 4Bot on/off, a fuse holder to protect the electronics from a short circuit, and banana jacks to attach a charger for the main battery. Locate the power panel and the main components.

 

Install the fuse holder (don't install the fuse at this time) and SPDT on/off switch. Use the included positioning washer with the switch with the small "tang" inserted in the small hole below the switch hole. When you tighten the switch nut the tang will keep the switch aligned. The banana jacks are installed with the red jack on top.

  

Step 2

Locate a 1/4" and 1/8" spade connector (see photo below). Cut 2 pieces of #18 red stranded wire about 7 cm long. Strip 1 cm from the end of each wire.

Twist one end of each wire tightly together and crimp the 1/8" spade connector to the joined wires. Crimp the 1/4" spade connector to one of the other ends (test the crimp by pulling the wires).

Push the 1/4" spade connector on to the fuse terminal as shown below. CAREFUL. You may want to support the fuse terminal with needle nose pliers. Don't crack the terminal off! Connect the 1/8" spade connector to the red banana jack. If it is loose, nip the connector with pliers to make it tighter.

Twist the remaining bare wire tightly and solder to one of the terminals on the SPST switch. If you twist the wire tightly enough you can insert it in the terminal. If not, tin the terminal and wire, hold the wire on the terminal and solder.


Step 3 

Locate a 1/4" and a 1/8" spade connector. Cut 2 pieces of #18 black wire, each about 20 cm long. Stip 1 cm from all the wire ends.

 

Twist one end of each wire tightly together and crimp the 1/8" spade connector to the joined wires. Crimp the 1/4" spade connector to one of the other ends (again, test the crimp by pulling the wires).

Connect the 1/8" spade connector (2 wires) to the black banana jack. Again if the connector is loose, nip with pliers.

Step 4

Locate 2 1/4" spade connectors. Cut 2 pieces of #18 red wire, each about 20 cm long. Stip 1 cm from all the wire ends. Crimp the 1/4" spade connectors to the ends of one of the wires. Leave the other wire with 2 stripped ends.


Connect one of the spade connectors to the remianing fuse terminal. Careful, don't crack the terminal off.

Solder one end of the other red wire to the remaining switch terminal. See above for advice on soldering to the terminal.

You will mount the power panel to the 4bot later. If fabricated correctly, the power panel should have a red and black wire with spade connectors. These will connect to the battery.  The black and red wires with bare ends will connect to the motor controller terminal which will act as a power distribution point.

      

Step 5

Time to wire up the bot motors. Locate the pre-assembled wiring harness for the motors (see below).  (If not available, you will have to make your own. Do not solder the wires on the motors as you may melt the brush holders inside and ruin the motor!)


The single wire crimp attaches to the front motor and the double wire crimp to the back motor. Careful when you install the wires  as the terminals are fragile. The black lead is installed on the negative (-) motor terminal and the red on the positive (+). The bare wire end is routed through the chassis and will be attached to the HC motor controller output terminals.

 

Step 6

Mount the following Phidget devices to the rear lower deck on the installed nylon standoffs: Note: newer phidgets have mini usb ports. You may have either in your kit so be sure you have the correct USB cables.

bulletHC Motor Controller
bullet8 motor servo controller
bulletPrecision voltage sensor
bulletTemperature sensor
bulletIR Distance sensor (front)

Mount the voltage sensor first. Instead of screws, use 2 3/8" FM nylon standoffs. Screw the threaded end through the mounting holes on the sensor. The IR distance sensor is mounted on on top with 1/4" hex head screws. You will need to remove it later to wire the voltage sensor!

Repeat for the other side with the temperature sensor.

Mount the HC motor controller and the Advanced servo motor controller as shown in the next image. (The servo controller may be a new version with a mini USB)  Use 1/4" hex screws to secure.

Step 7

Mount the SBC2 or SBC3 to the upper deck. Mount the solid state relay (SSR) as shown. The SSR will control the high intensity light. Note: You may have a dual SSR which you can mount in the same place.

Insert  a servo motor (HiTech 322 or 422) as shown in the next illustration. You need to angle it down. Once inserted, install the last 2 standoffs on the front and secure with 4 machine nuts. Don't install the top deck yet as you need to wire the phidgets on the lower deck.

Step 8

Mounting the distance sensor under the front, lower deck.

You will need to fabricate a right angle bracket from aluminum or from plastic on the 3D printer (or you may already have one in your kit). The sensor is mounted on the centre line so that the sensing element is exactly 10 cm from the front bumper. This is because the sensor will not work when the object the sensor is reflecting Infrared light off comes closer that 10 cm. The software is set to show the 10cm as 0 cm. The sensor has a range of 10 to 80 cm, so with this setup it will be 0 to 70 cm. See the image below. (Try to line up the holes better than the ones in this image :)

 

Step 9

The lower back deck has to be wired before the top deck can be attached.

Attach the power panel to the chassis side rail using a 1/2" hex screw and locking nut. Make sure the fuse holder does not come in contact with the large capacitors on the HC motor controller. Turn the fuse holder and tighten if needed. Make sure there is no fuse in the holder at this time.  NOTE: The power panel shown below may be different than the one you previously fabricated. However their function will be exactly the same and the placement of the various wires will be the same.

Cut a 15cm piece of red and black #24 wire. Strip one end about 0.5cm and the other end 1 cm (you might "tin" the 0.5 cm end). Insert the wires (0.5cm end) in the power terminal block of the servo motor controller and tighten. Make sure you follow the color convention!

Cut a 10cm piece of red and black #24 wire. Strip one end about 0.5cm and the other end 1 cm. Insert the wires (0.5cm end) in the power terminal block of the voltage sensor and tighten.

Strip 1.5 cm from the ends of the black and red #18 wire coming from the power panel (red is from the switch and black from the common banana jack terminal). Cut a 20 cm piece of #24 red and black wire and strip 1 cm from one end of each. This will power the SBC on the upper deck.

Twist all the red wires together to form a tight bundle. Do the same for the black wires. There should be 4 wires in each bundle. Apply solder (tin) to the bundle to keep the wires together.

Insert the prepared wire bundle ends into the large power terminal on the HC motor controller. Observe the correct polarity.

Locate and attach the red, black, and white sensor cables (4") to the sensors. In the next image 4 sensors are shown.

 

Attach short USB cables to the two motor controllers.

Attach the IR sensor cable(s) to the IR sensor boards.

The drive motor power wires should be neatly routed under the deck using cable ties and stick on anchors. Do not cut any excess wire until that is done. Strip the ends and tin. Secure in the motor terminals following the color pattern as shown below (red on the outside - why is the right terminal connection reversed??)

You can attach the battery leads from the power panel to the battery at this time. CAUTION: THE FUSE MUST BE OUT OF THE FUSE HOLDER BEFORE YOU DO THIS.

Ask the instructor to inspect the back deck wiring before proceeding!

The photo above shows a Lithium Polyimer battery, You will probably have a lead-acid gel cell which uses spade connectors.)

Step 10

Attach the 3 rubber "bumpers" to the headlight bracket using #6-32 screws and nuts. Press into place the black holders for the LED headlights.

 The LED headlights should be prepared using the included #26 twisted wire and heat shrink. When they are ready, snap them into the holders and push the retaining ring over the holder. Route the wires neatly along the bracket and back along the chassis. Use tape to secure.

Step 11

The top deck has a number of openings for routing cables from the lower deck. Before you attach the top deck you will need to bring up the following cables:

bulletThe four sensor cables
bulletThe #24 power wires for the SBC
bulletTwo USB cables
bulletTwo headlight cables

The sensor cables can be plugged in as follows (the code won't have to be changed if you follow this pattern)

bulletAnalog Port 0 - Voltage sensor
bulletAnalog Port 1 - Temperature sensor
bulletAnalog Port 2 - Rear distance sensor
bulletAnalog Port 3 - Front Distance Sensor

The SBC has a digital output terminal strip on the left (left in the image below). The terminal on the right is the one and only ground on this strip. You need to strip the ground wires for both headlights, the solid state relay, and if you have a "horn" that as well.

All the grounds are twisted together and secured in the single ground terminal.

The positive wires are secured in the following sequence (for no changes in the code)

bulletDigital Output Port 0 - headlight (does that matter which one)
bulletDigital Output Port 1 - headlight
bulletDigital Output Port 2 - Solid state relay
bulletDigital Output Port 3 - Horn (if equipped)

The 2 power wires from the lower deck connect to the green power terminal on the SBC. Make sure the black wire is on the left*. When you have the high intensity light ready to mount, it will get its 12volt power from this terminal. The USB cables are plugged into a convenient slot. The 3rd cable in the image below belongs to the camera.

* Note: for the SBC2 the silk screen markings on the bottom of the board, + and G(round) are reversed, which is clearly an error. The Ground is nearest the power jack!

Step 12

When you have the high intensity light ready, mount the current regulator (circuit board with heat sink) ahead of the solid state relay. Use a plastic standoff and a couple of screws to secure to the upper deck. The high intensity light mounts on the camera bracket.

The wiring diagram for the high intensity light. Use #24 red, yellow, and black wire.

The camera setup is the same as the Pan and Tilt activity you have completed. The difference is that the pan servo motor is mounted directly on the deck and the rotator base is not used. The pan motor is connected to the servo controller output port 0 and the tilt motor to port 1. Note: do not put the plug in backwards as it will damage the motors. You will probably need an extender wire for the tilt camera. there are a couple included in your kit.

Getting Ready to Roll

If you havn't attached the wheels yet, do so now. Make sure they are on the rims and have air! It's easiest to mount the aluminum hubs on the motor shaft first. Screw in the set screw so that the hub just slides on the shaft. Make sure the set screw is facing the flat spot on the shaft and push the hub on until it stops. Tighten the set screw very securely with the hex key used to construct the robot.

Now the tires can be installed using a larger hex key. Your instructor will have the proper allan key to fit.

The SBC may need to be configured. If it does, connect it to the ethernet switch of a router. Your instructor will guide you through this activity.

Software for the 4Bot (unzip and place folder on desktop)

When all is ready, start a ping to your bot's IP address and if you get a reply, start the VB6 application which should be configured for your 4bot. If you are using a physical joystick/game controller make sure it is plugged in and detected before you run Visual Basic.

 Good Luck!!