Rocker-Bogie Rover , 6 wheels , picaxe 28x2, 08m2 and 08m

pippofjk

Member
Hello!

This is Rocker-Bogie Rover, a radio frequency controlled robot, that i made with the famous Rocker-bogie suspension system developed by JPL NASA for exploration rovers (like sojourner).

The main board is based on a picaxe 28x2 and a 08m2. The main program runs into picaxe 28x2, and it calculates the rpm speed of the wheels (PWM) and the orientation of the servo as a function of parameters like: rpm speed and instantaneous center of rotation. PWM values and the rotation direction are sent to the "driver board", while the servo orientation values are serially sent to the picaxe 08m2, that is used to control the servo orientation.

The driver board is used to drive the 6 motors with 3 L293D chip.

The receiver board carries a RF 315Mhz Module and a picaxe 08m serial connected to the 28x2.

Other details are:
- 2 dc-dc step down power regulator
- board with some leds and a power switch.
- 8*1.2V rechargeable battery
- a lot of wires

The links of the suspension are made of aluminum square tube and the body is made from the enclosure of a computer cd player. The body is supported from a "differential gear" with 1 dof blocked. The differential gear also connect the right suspension from the left suspension.

Pictures:


Further information about this project:
- my website: http://www.robotelettronica.altervista.org/ or http://www.robotelettronica.altervista.org/projects/rocker-bogie_rover.html(yet only Italian, English soon)
- video youtube 1: https://www.youtube.com/watch?v=nG9tA3SjhoY&feature=c4-overview&list=UUydWnLOwJ38-hxYttx-CCqw
- video youtube 2: https://www.youtube.com/watch?v=cybI-6OqhTQ&feature=c4-overview&list=UUydWnLOwJ38-hxYttx-CCqw
 
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erco

Senior Member
Fantastic robot! Great video, I really like your steering servos on the outer 4 wheels. Great mobility, very impressive!
 

Ravenous

Member
Very impressive.

Do you think it will be possible to carry much weight, using servos at the corner? I've built something like this but I only drive the center wheels - the "wheels" at the front and back are just plastic sliders. It can carry several kilos of weight but I think I will need very heavy-duty servos for steering...
 

pippofjk

Member
Thanks a lot!!!

I think that... yes could be. But i will be more worried about the way i connect the servo to the motors of the wheels. If you see these pictures: http://pippofjk.altervista.org/immagini/gm2_servo_wheel.jpg and http://pippofjk.altervista.org/immagini/gm2_servo_wheel2.jpg , you can notice that this type of connection may deflect with high weight. Further more, the servo output shaft would be more stressed.
A more solid connection could be like as: motor support + solid bearing block on the link of the suspension + servo.

Another thing that is important, in order to reduce the required torque of servos, is to align the servo axis of rotation with the point where the wheel touch the ground. Therefore, the point of instantaneous rotation of the wheel coincides with the point where the wheel touch the ground, which also is aligned with one principal axis of the wheels.

I have used hitec hs-422 servo: torque 4.1 kg*cm (57 oz*in) at 6 volt.
 

brass

New Member
Very nice build, do you have a schematic and source code for the processors you would be willing to post?
 

chipwich

Member
Amazing build! The re-use of the CD-player as a chassis is perfect.

Do you intend to program any autonomous navigation? It will be rather intimidating (but very cool) to see several of these rolling/climbing their way down the street.
 

pippofjk

Member
Amazing build! The re-use of the CD-player as a chassis is perfect.

Do you intend to program any autonomous navigation? It will be rather intimidating (but very cool) to see several of these rolling/climbing their way down the street.
Thank you!
The cd-player chassis is light and has a little thickness, but, because is made of "iron sheet", it has a great stiffness.
When i was looking and thinking for something to use as a case, primarily i was oriented to made a little frame with aluminum bars and than cover the various side with plastic sheets. But this solutions would it be more heavy and would it leave less internal space for the electronics boards.
Then, while i was making order in the garage, i found an old damage pc cd-player. So, i disassembled it, and found that the dimensions of the case were just right the ones that i need for rover!!

By the way, an autonomous navigation program is on my plan for the future.
 
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