### ELECINF344/381

Interactive web site of Télécom ParisTech's ELECINF344/ELECINF381 Robotics and Embedded Systems classes (a.k.a. ROSE, 2012 session).

# BallE kicks off

After some days of silence during which we did some hard thinking on the mechanics of BallE, we have an idea about what power of motors BallE will need for maintaining stability for a worst-case scenario. For a final load of 10-20 kg, a center of mass not higher than 50 cm (for the structure placed upon the ball) and for a recovery angle between 0 and 30° we would like BallE to stand up in less than a second. For that a total power 50 W should be plenty. We want to stick to our initial plan: 3 omni-wheels so we will need 3 motors…
There is a compromise between the motors we can aford and the power BallE needs. We think that 3 motors of 12 W should do.

After taking a look at the ballbots that where built, we liked the Japanese one the most. You can take a look at it here:

We liked the idea of using thrust bearings to support the axial load between the omniwheels and the motors. The motors that the Japanese used are stepping motors (KH56). After some hesitation and debriefing with Alexis (based on the Segway experience) we decided to use DC motors.

We took a look at Kalman and LQR and we took a deep breath…

It was decided that it will be easier and cheaper to build a metal frame for the ballbot instead of a wooden or plexiglass one (in contrast to the Japanese one).
We still have to decide upon the size of the omniwheels:) More on that, tomorrow.

For BallE,

Otilia, PHH, Scott, Matthieu

Scott Messner

### 3 comments to BallE kicks off

• I like the “follow the move” mode.

• For Kalman filters, the best book is (in my opinion) “Optimal State Estimation: Kalman, H Infinity, And Nonlinear Approaches” by Dan Simon. You may also find these two papers interesting : “A Comparison of Discrete Linear Filtering Algorithms” by G. J. Bierman (IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS) and “Numerical comarison of discrete Kalman filer algorithms : orbit determination case study” by Bierman and Thornton (IEEE)

For LQR, the best books is (in my opinion) “Digital control of dynamic systems” by Franklin and Powell.

Both available in my office and in every good bookshops / libraries.

• Otilia

Thank you for the references on Kalman & LQR.