The aim of this instructable is to build a basic, little and mobil robot, simple but resistant, able to move easily through many surfaces with precision.
After many experiences, I'm in a point where I think I have achieved great results and that's why I'm posting this instructable.
The robot is a resistant and easy to build chassis made of "Actobotics" aluminium channels. Thanks to these channels we can get a great robustness and a reduced weight. I choose six wheels using six motors that give them a great traction. The movement is done by two groups of three motors. The three motors in each group move at the same time. One group in the right side and another in the left side. They give the robot a tank like movement that greatly simplifies the traction.
Great wheels give it the off-road features and the shock absorption/cushioning capability of this kind of vehicles.
The brain of everything is an Arduino board that controls all the electrical part, with a great power and able to control the extensions that may be added in the future.
The remote control is implemented using Xbee modules that are easy to use, providing a great security and a long range more than enough for a possible future experience of driving by watching its front video, FPV.
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Step 1: Aluminum Chassis
For the building of the mechanical part we will need:
- 3 pieces of 15” aluminum channel “Actobotics”
- 6 aluminum mount for the motor
- 6 gear motors of 12 V with 6 mm diameter shaft
- 6 wheels 127 x 62 milimeters
- 6 rim 2,2”
- 6 Hex Shaft Wheel Adaptors
- 36 M3x8 Screws
- 1 aluminum sheet piece of 343x190mm
- 8 M3x40mm hexagonal metalic spacer
Step 2: Mechanical Building
Preparations before the building:
- Cut one of the three 15” aluminium channels in two pieces of 7 1/2” with a small metal saw.
- Drill in the motor mounts the 3mm diameter holes that you will need to be able to screw the aluminium channel as you can see in the picture (light blue points).
- Drill the 8 holes of 3mm diameter in the aluminium plate as you can see in the picture. (magenta points).
Step 3: Chassis Assembly
- Screw three of the motor mounts in the aluminium channel as in the picture. Repeat again for the other side (light blue points)
- Join the sides using the pieces of aluminium channel you cut previously (7 1/2”) (red points)
- Screw the motors to the mounts with the shaft as low as possible as in the picture.
- Join the structure with the aluminium plate, using the separators, and using bolts or nuts depending on type of separators (magenta points)
Step 4: Electronics I, Brain and Receiver.
I am hoping that you have a basic experience in electronics, anyway it is hardly necessary to use the solder.
Materials needed for this part:
• Lithium battery 3s of 4000 mah.
• A digital electronic switch. This element is not absolutely necessary, but it is convenient for later extensions. For the current assembly, it can be replaced with a simple switch capable of handling at least 10 amps.
• An Arduino Mega 2560 board.
• A Regulated XBee Explorer board
• An XBee Pro 60mW board with antenna
• A Sabertooth board 12A dual motor driver
• A ULN 2803 and IC socket
To facilitate the mounting, begin by releasing the aluminium plate of the chassis.
• Draw on the aluminium plate three axes corresponding to the axes of the motors (red color)
• Place the 3s lithium battery in the middle of the first two red axes and three electrical contacts tab.
• Then attach the electronic switch if you decided to use it.
• Continue with the Arduino Mega board. First, solder three cables at the lower part of the plate: the red to Vin, the black to the two gnd on the side, and the white to TX1, pin 18. Refer to the picture. Be careful with the position, try to place the usb connector right in the middle of the two red axes at the right side, in order to access the usb connector from outside comfortably between the wheels and be able to program the board whenever necessary. Attach the board with six bolts and set two nuts to each bolt in order to separate the aluminium plate. Add a plastic washer to prevent short circuits. Then, fasten the board with one single plastic nut.
• Finally, place the sabertooth board at the same level with the aluminium plate using four bolts and nuts. The aluminium plate is for cooling.
• Make all the necessary connections. Refer to the drawing.
• Plug the receiver module XBee on the Explorer Regulated board and make the four required connections: 5v to 5v, gnd to gnd, Din to TX3 (pin 14) and Dout to RX3 (pin 15).
• Finally, using a piece of printed circuit islets, construct the circuit that controls the front LED lights, as in the scheme in the drawing.
Step 5: Programming Xbee
Read a configuration tutorial Xbee with the software X-CTU
• A board USB XBee explorer
• USB Cable.
Once the software X_CTU is installed and updated, simply configure each Xbee, one as transmitter and one as receiver. You just need to configure three parameters.
For the receiver: DL=321, MY=123 and BD = 3 (9600 baud).
For the transmitter: DL=123, MY=321 and BD = 3 (9600 baud).
Step 6: Electronics II, the Remote
• Lithium battery 3s of 800 mah
• An Arduino Nano of 5V and 16 Mhz or similar.
• An XBee Explorer Regulated board
• An XBee Pro 60mW board with antenna
• A joystick
• An LED
• A 220 ohm resistor
• Two miniature switches
• A plastic box
Well it's quite simple and can be done in many ways. I leave a drawing with all the necessary wiring as well as the code I used to program the Arduino Nano.
Step 7: Conclusion and Improvement Projects
Overall dimensions of the robot: 42 cm length, 32 width and 12.5 height.
Weight: 3,430 kg.
Speed depends on the motors. For my proposed 100:1 gear reduction, it reaches 0.7 m/s (2.4 km/hour). If you decrease the gear reduction, the speed will increase while decreasing traction. The opposite if you increase the reduction: slow speed but increased traction. In the videos you can see the off-road capabilities, depending greatly on the type of surface you are in, the wheels are highly suitable for steep slopes for their great traction.
The LED lights have polarity, so if they are not properly connected they will not work. You will need to reverse the connections.
A wheel may turn in the opposite direction. To fix it, just reverse the wires that feed the motor.
If the whole group of three motors rotates in the opposite direction, just reverse the connections of the group in the driver “Sabertooth”.
If the problem is that the turns work opposite as expected, the easiest fix is to exchange the pairs of power cables in the driver “Sabertooth”.
The driver Sabertooth has a voltage sensor for the lithium battery, which protects it from excessively low values that would turn it useless. Because of that, if it’s working well and at some point it stops, test the voltage of the battery and recharge it if necessary.
As next improvements I have set myself two goals:
• Add a small camera and an audio-video transmitter as used in aeromodelling.
• Design and implementation of a robotic arm.
And of course, all the contributions and suggestions will be very well received, greetings and see you soon.
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