# Angular Displacement

I'm working on a project in which I have to build a rover and remotely control it. Remotely controlling in the sense with basic forward and backward movement, as well as the right and left movement. This is perfectly done. But I want to turn the rover to a specific angle automatically when I give a command to it.

Like if I send a command $$\30^0 \$$ right, the rover should stop and turn to $$\30^0\$$ to its right with respect to its original position and start moving forward. I just want to know if there any sensor available to find the Angular Displacement. I know IMU sensors like Magnetometer, accelerometer, and gyroscope is used. But still, I'm so curious to know is there any other sensors available to find the angular displacement precisely and with greater accuracy.

• IMU is currently the best solution. If the Apollo mission reached the Moon, why this technology wouldn't be good for your toy robot. – Marko Buršič Apr 9 '17 at 19:01

It's called a magnetometer. Basically an electronic compass. More generally, you can get something called any inertial motion unit (IMU) which gives you way more information about your movement through space.

• But could you suggest some IMU that is more accurate for my project. I hope I've explained about my project quite clearly I suppose. – Anton Prabhakar Apr 9 '17 at 19:06
• One I've seen used in recent memory is invensense.com/products/motion-tracking/9-axis/mpu-9150 and I'm sure you'll find breakout boards for it if you look around – vicatcu Apr 9 '17 at 19:17

There exists the polarization sky compass method used by insects. Two photodiodes with wavelength filters and polarizers are used to measure the orthogonal components of the polarization of a part of the sky to find the polarization alignment. Combined with the time of day and geographical location, this tells you where the sun is in the sky. The sun is then used as the absolute reference.

You don't need to find the sun if you just need an angular reference prior to turning. Just grab the polarization alignment before you start turning and then turn until the alignment changes to indicate that you turned the desired amount.

With static photodiodes, at least a third photodiode at 45 degrees to the first two required to differentiate the actual heading since the two orthogonal components from the first photodiodes are symmetrical so you won't be able to tell if you are aligned with one by 0 degrees or 180 degrees.

You can also rotate a single photodiode+polarizer or the polarizer in front of it. It may also help to be able point and aim at a section of the sky rather than always looking straight up for reason that become apparent if you read into the polarization pattern of the sky.

There are paper online that you can read about it. "Insects UV polarization sky compass" are some of the search terms you want.