Spirit II Mars Rover

Friday, November 4th, 2011

Mars Rover – Side View

We have always loved the Mars Rover robots Spirit and Opportunity, so we decided we would build one of our own. Today we would like to introduce our Spirit II Mars Rover, which we designed and built in honor of the great Spirit I that explored Mars for more than five years and gathered evidence that there was once liquid water on the Red Planet. The true challenge and fun of building Spirit II was to study and reverse engineer how NASA built theirs. The NASA rovers have several unique and very specific characteristics that we wanted to incorporate into our robot, especially the “rocker-bogie suspension system,” which allows the rover to roll over rocks that are 50% the height of the front

Mars Rover – Corner View

wheel (try that in an automobile!). We watched videos, read the NASA white papers, and even studied their patents. The key to the suspension system was the configuration of the wheels, the multi-jointed swiveling chassis, and a special counter-rotating differential that we built. Mars Rovers also have a very unique way of turning: they use servos to rotate the wheels at each corner 45 degrees, then spin to the desired heading. And, of course, Spirit II is solar powered like the original. Although it was difficult, in the end, we are very pleased with how Spirit II turned out. Enjoy the pictures and video below.

Here are a few construction photos (click the picture to see larger image):

Here we are working on one side of the rocker-bogie suspension system.

Here we’re working on the counter-rotating differential and how it connects to the rocker-bogie suspension system. When the robot rolls a front wheel over a large rock, the suspension system tilts upward. The differential turns the rotation in the opposite direction, thereby tilting the opposite side of the robot downward to make sure the robot’s center box stays steady and level. Here we have assembled the back half of the rocker-bogie suspension system. The Counter Rotating Differential we designed and built for our Mars Rover.

Here we are assembling the wheels, each of which has dozens of pieces. We cut the aluminum shafts, screw the wheel plates together, assemble the universal hubs, attach the treads, and on and on…


Solar Power System

Chassis for Mars Rover

Differential for Mars Rover

Technical Specifics

  • Design and Construction: Beatty Robotics
  • Software: Beatty Robotics
  • Microcontroller: Arduino Mega
  • Aluminum sheet & tubing, gears, fasteners, hardware, and much else: McMaster-Carr
  • Motor Controller: Dimension Engineering Sabertooth 2×12
  • Motors: Lynxmotion
  • Servos: (4) Hitec Digital + (1) Hitec for pancam
  • Servo brackets, hubs & other hardware: Servocity & Lynxmotion
  • Aluminum tubing & hardware: ServoCity
  • Solar Panels, wires, cameras, and much else: Sparkfun
  • Battery: 12V Lithium-Polymer
  • Radio: Xbee
  • Remote Control Hardware & Software: Beatty Robotics
  • Wheels: (6) Vex Robotics
  • Wheel Hubs and other hardware: AndyMark
  • Voltage Regulators: Pololu & Dimension Engineering
  • Relays: DFRobot
  • Differential: Beatty Robotics

Comments (36)

  1. Jan, Norway
    September 9th, 2011

    AAAAAAWEEEESOOOOMEEEE!!!!!!! Really love it!!!! Like to see even more photos of its inner workings, though! Keep it up! 🙂

  2. Camille Beatty
    November 2nd, 2011

    We’ve posted a new image that shows the electronics. Click on the photo to see the full-sized photo.

  3. Julius
    March 1st, 2012

    Dear colleagues,

    We are writing you on behalf of Student Science Association of Kaunas University of Technology (Lithuania). We would like to invite you to participate in the international contest of robots “Robots’ Intellect 2012”. The event is being organized the second time in the Baltic States. This year contest will be held on May 3rd, 2012 in Kaunas University of Technology campus. The goal… of this competition is to motivate young people to take interest in high technology, artificial intelligence, robotics and other current topical areas of science and technology, as well as to try their personal skills and knowledge in creating their own robots.
    In 2011 no one won the jackpot “The Golden Sack” filled with 9000 Euros, so it was left to grow and wait for the competitors of 2012. MINI gold back is 500 Euros. The main task remains the same as the last year: a robot must find the golden sack on the special track with obstacles and fetch it to the start line. What is more, robots will have a chance to compete in other tasks, such as line tracking, labyrinth and others.
    Also, during this event, there will be robots’ exhibition, in which anyone, who has a robot, even the simplest one, can participate.
    If you are interested, don’t hesitate and register for this competition.
    For more information please visit our website
    Contact us if you have any questions, it will be our pleasure to answer.
    We are looking forward to seeing you in the competition “Robots’ Intelligence 2012”, May 3rd, 2012.

  4. Lars
    September 13th, 2011


  5. Alex
    September 24th, 2011

    Amazing!!!! Me and my 5 year old love it.
    He told me the other day that he wanted to build a robot, i think i have just found something we can build. How did you make the wheel plates?

  6. Camille
    September 24th, 2011

    Thanks, Alex. When you say you just found something you can build, do you mean the Spirit II or something else (if something else, let me know what it is). The round wheel plates come from the Pro section of Vex robotics.

  7. Pete
    October 12th, 2011

    This is the most awesome hobby robot ever!
    I love the way you have done the differential in the middle.
    I had read the descriptions on NASA and Wikipedia sites, but couldn’t figure out how it worked! Your design is so simple and elegant.

  8. Camille
    October 12th, 2011

    Thank you, Pete. We appreciate it. We had a lot of fun designing and building the Mars Rover. We are glad that someone appreciates our differential, which we thought was pretty cool. 🙂

  9. Kamil
    October 13th, 2011

    your spirit II is just fantastic…

    Actually, I built one a little less precise approximation of Spirit rover myself. . It’s called Spirit Junior, and it is a tribute to the now deceased original Spirit…

    For the next year competition I’m building the rocker-bogie drive for it, but I’l make a little different approach. But your differential mechanism is very inspiring. I’m gonna have to make some modelling of it if it is usable in my robot too ( robot has to carry a 10kg off load and I’m not sure how robust I can create this mechanism ), otherwise I make some simple balancing mechanism on the front.

    Great thanks for inspiration

  10. Camille
    October 13th, 2011

    Kamil, Very impressive. I like your Mars Rover a lot. Nicely done. What do the sensors on the tower do? (By the way, I like your use of the crawler chassis. We are currently working on a new robot that also uses a crawler chassis)

  11. Kamil
    October 13th, 2011

    Thanks, it took lot of hours from my past year…

    On the tower there are 2 webcams to detect edge of road, then there is Kinect as obstacle detector. In the box up on the top there is gyro/ accelerometer/ compas.

    The crawler, as it turned out was a good choice for this app. It has great torque at low powerdraw ( it works for 2.5 hours on 7.2V 4.5Ah ). Only thing i was concerned about was the plastic parts of gearboxes, thats one of the reason why I want to change it to rocker-bogie. The other reason is that I always wanted to build a rocker bogie :).

    Btw, what torque (kg/cm) has those servos you used for steering?

  12. Camille Beatty
    October 13th, 2011

    Your sensors sound excellent. Is working with the Kinect difficult? Do you have to use a programming environment like .Net or something?

    Regarding servos: I started with these (which is what you see in the video, although they are painted gold):

    They work OK, but they weren’t quite strong enough for rugged outdoor use, so I’ve upgraded to these servos, which are very impressive and stout:

    Servos of this quality and torque are extremely expensive, but required for the Rover’s unusual steering mechanism. Due to NASA’s original design, there is a big “Moment of Force”(, which the servo has to be able to withstand. When you design your rover, do everything you can to minimize the “Moment Arm” (the horizontal distance from the downward force of the leg and the center of the wheel.)

  13. Kamil
    October 13th, 2011

    I started a new comment as it was getting too thin :).

    The plan is to make the center of the wheel in the axis of ration. And Simmechanics spitted out that for the size and weight of all components ( gear, motor, construnctio itself ) in the maximum acceleration of robot ( 2 m/s/s ), the minimum torque of the servo needs to be at least 0.3Nm. Servos I intend to use are 2.2Nm so it should work…

    And Kinect SDK is .NET, especially for C#, and very easy to use. As I’m a java dev, it is quite enriching experience ;). In general Kinect works great – very stable. If I will be not able to find another thousand euros for Lidar, I’l buy another one of these to cover wider area ( kinect cover 62 degrees ).

    And data from the Simmechanics on the center differential mechanism is out – torque on robot of my size and weight will be 207Nm, there will be needed a gear with diameter 2″… So I’l rather do some simple balancer on the front…

  14. Spirit II – Mars Rover: INSIDE VIEW | Beatty Robotics
    November 2nd, 2011

    […] Posted by Camille Beatty on Nov 2, 20110 comments […]

  15. Machina
    December 13th, 2011

    Compliments to you on a beautifully designed rover! Favor me one question. The rover internals show one dual amp motor controller driving 6 motors and servos, correct? Kindly explain please…

  16. Camille Beatty
    December 13th, 2011

    Thank you. We appreciate it. Yes, there is one Dimension Engineering Sabertooth 2 x 12 AMP motor controller. The three motors on the left side are wired together to the controller’s first channel. The three motors on the right side are wired to the second channel. Even though there are 6 motors, it’s not necessary to have three dual motor controllers. You only need one dual motor controller. The motors on a side operate in unison. In addition, there are four high-torque servos, one directly above each corner wheel, that will rotate the orientation of that particular wheel in order to set the wheels at forty five degree angles so that the robot will rotate in place around its center (this is how the NASA rover makes its turns. It actually rotates in place, then goes forward. You can see it doing this in the video). We programmed the Arduino to direct those servos through a tiny servo controller (a Pololu Maestro 6).
    Let us know if you need any more details than that.

  17. Matheus
    January 22nd, 2012

    we found what I was looking, I am a Brazilian who was eager to build a rover that neither NASA and I think your site. Looks really like
    I wonder how you managed to create and how many days or months it took. Cause I want to create a display in my school project

    very good

  18. Camille
    January 22nd, 2012

    Matheus, Thank you for your positive comments. The Mars Rover took several months to build. The best place to start is to look at the detailed pictures on this site including links to the other pages (like the interior shots). Then check out all the companies/websites where we purchased the component parts (list at the bottom of the page). The part we’re most proud of is the rocker-bogie suspension system, which we made out of aluminum tubing.

  19. Matheus
    January 22nd, 2012

    The more or less you spend?

  20. matheus
    January 22nd, 2012

    hi remember me, I wonder if you have e-mail, for I want more information about what you used on the robot

  21. Matheus
    January 23rd, 2012

    What you put down (in box) is counter-rotating differential rocker-bogie suspension system?

    Since already obliged

  22. Camille Beatty
    January 23rd, 2012

    I’m not sure I understand your latest question. The counter-rotating differential is the three bevel gears inside the box. Each set of three wheels (on each of the two sides) is attached to it via an aluminum shaft. The counter-rotating differential is part of the rocker-bogie suspension system (which is visible on the outside of the box as the legs, wheels, connecting tubes, etc.).

  23. Shireen
    March 4th, 2012

    CustomColor has always done me well no scrtached slides or negs, good prints, etc. I need some med format enlargements done, so I’ll have to pay them a visit in the new spot. Little known fact if you return the boxes that slides come in, they’ll give you $0.15 per box in cash.

  24. Matheus
    January 23rd, 2012

    But where and how you connected all the wires?

  25. VERON
    February 15th, 2012

    please give me the wheel assembly details

    thank you

  26. VERON
    February 15th, 2012

    please give me the wheel assembly details of spirit mars rover


  27. Camille Beatty
    February 15th, 2012

    Vernon: The wheel components are from the pro section of Vex Robotics.

  28. VERON
    February 29th, 2012

    sir i am very curious to know about the remote control system schematic diagram and as well as on board schematic diagram of mars rover spirit.

  29. JKamil
    March 1st, 2012

    Hello again,

    I wrote here about half a year ago, I was looking for inspiration then. Now the robot is almost finished… in the end I reimplemented your differential idea – I call it Beatty’s differential drive 😉 and it became an inner joke… See here , on the bottom of the page there are some images of it…

    Here is also image of whole rocker bogie – great thanx for inspiration.

  30. Camille Beatty
    March 1st, 2012

    Hello Kamil. Good to hear from you again. I’ve looked at the work you’re doing. It’s fantastic! Well done. I’ve put a comment on your site. I’m honored to have a differential named after me. That’s cool. 🙂

  31. Arnab
    July 31st, 2012

    I would like to know about the steering mechanism of ther Rocker Bogie. The steering Servo Motors are usually not directly connected to the driving motors, they use some kind of “[” shaped frame. If I am using that design, how do I use the servo to turn the wheel. Directly connecting the servos to the frame is not an option. Please Help. Thanks

  32. Camille Beatty
    July 31st, 2012

    Arnab: You are correct. The servo motor shaft is screwed to a hub, which is screwed to an L-shaped motor mount, which screws to the motor. Here is an example of the motor mount:

  33. Mars Rover – Motion Test Video | Beatty Robotics
    April 12th, 2013

    […] system worked very well, but as expected, it behaved a little bit differently compared to the first Mars Rover we built. On the first Mars Rover we installed a counter-rotating differential gear box in the central shaft […]

  34. Brian and Jordan
    June 25th, 2013

    Hello again and thanks for your quick and detailed response to my earlier note. I’ve been reading the web sites you recommended (ServoCity et. al.) Great resources! Perhaps I can put off the mini mill purchase for another couple projects.
    A few more questions if you have the time:

    1. I’m curious about the Spirit II motor mount design process. Did you consider using a larger bracket that would allow positioning the vertical leg tube directly above the wheel axle? Just curious if this element was driven by aesthetics (similarity to NASA’s Spirit), function, or stock part availability.

    2. The horizontal transmission shaft seems to be connected to the leg tubes by ServoCity 90 degree tube clamps secured on either side by a collar. The 90 degree tube clamps have a 1/2” bore and I understand the shaft is 3/8”. Can you describe how you connected the tube clamps to the shaft and prevented any rotational slippage?

    3. Is the bracket that connects the middle and rear wheel assembly to the chassis down tube an off-the-shelf part or did you fabricate it?

    4. Can you describe the components and design of the joint that allows the middle and rear wheel to pivot within the bracket? I can’t quite tell from the photos but it looks like it involves two 90 degree tube clamps pivoting on an axle. I’m curious about the spacers and bearings etc. used to make a pivoting joint.

    Thanks for taking the time to share your work with the rest of us. Much appreciated.

  35. Camille Beatty
    June 25th, 2013

    1. Putting the vertical leg directly above the wheel axle is a good idea and would eliminate the considerable moment-arm (right angle force) that is applied to that area with the current design. The reason we went with the current design is because we wanted it to look and function similar to real mars rover, and also, we were trying to use parts we could find.
    2. Set screw
    3. Fabricated it. Tricky area. Take a look at the new Mars Rover. On that one, we used a ServoCity swivel hub (which didn’t exist when we built Spirt II).
    4. See #3.

  36. Luke
    November 7th, 2015

    Very Cool ! Which type of antenna did you use for the Rover ?

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