Interview with Ketan Rasal

Featured Engineer

Ketan Rasal

Ketan Rasal - Research Assistant , Robotics System Lab; Santa Clara University

Image: The ASV (Automous Surface Vehicle) used for underwater mapping

How did you get into electronics/ engineering and when did you start?

Engineering always fascinated me, specifically the field of Robotics. Mechatronics is the heart of Robotics. I did my undergraduate studies in mechanical engineering which was a start to understanding the basic structures. I realized that in order to move and control the Robot, I needed to learn more about Electronics. That was the main reason that brought me into this field.

What are your favorite hardware tools that you use?

I like to use the Roboteq Motor controller hardware. I consider it a very robust controller for handling the spikes, back EMF, etc, and it can handle high current without damaging the control circuitry. It has a sensor feedback option (encoder & potentiometer) which helps for closed loop control. The inbuilt PID loop optimizes the system performance. The control inputs we can use are RS232, Analog inputs, RC. All these features are compressed in one small circuit which makes it easy to use in many of our Robotic applications.

What are your favorite software tools that you use?

I like Matlab the most. Not being exactly a software guy I feel the programming language is easy and convenient. It is pretty straight forward. The use of variables is excellent. Data management is really convenient and easy to use. Simulink, part of Matlab, allows us to see how the signal is being routed. Instrument handling is also easy in Matlab, as Robotics is all about connecting sensors and sending data to actuators.

What is the hardest/trickiest bug you have ever fixed?

I was working on one sensor pod which is used to take temperature, oxygen and light data from an algae pond. We had been facing a noise issue in the sensor data. We tried to do lots of corrections in the circuit, modifying the sensor offsets, changing resistors, but nothing seemed to work. The trick was just to add a battery with more capacity. There I came to know how important it is to consider voltage and capacity of the battery for any mechatronic system.

What is on your bookshelf?

We have many books in our lab. The favorite ones are “Introduction to Robotics – J. Craig”,
“Applied Mechatronics – Mard & Smaili”, “Guidance and Control of Ocean Vehicles – Fossen”.

These are all main books from which we use the theory and apply it on real robots. “Understanding Space – Sellers” is also one of my favorites. This book talks about broader perspective of the systems, mechanical and electrical, that all together builds spacecrafts and satellites. Also the magazines like Ocean News and Technology, IEEE journal – Ocean Engineering are good references to see what is going on in the field.

Do you have any tricks up your sleeve?

Check for the right Baud rates, parity, stop bit, etc when you are trying to collect the data from the instrument. Also before pulling the data directly into the code, it is easier to check it in HyperTerminal.

What has been your favorite project?

My favorite project is an ASV (Automous surface vehicle) used for underwater mapping, with feed forward control, on which I am currently working. For mapping there are many constraints like keeping it level, slow speed, strict line following, etc. With the conditions we face in the field, the wind, water current, waves, all cause unwanted vessel movement. By measuring the wind speed and direction and giving the input accordingly, we can overcome these disturbance forces using feed forward controller. We have added canards to balance SWATH (the name of the ASV) by sensing the roll and pitch. This project is the favorite for me because it has so many small systems integrated together that work synchronously.

What type of sensors do you use?

On the Science payload side, there are multiple sensors on the boat that we use to create the bathymetric maps. The primary sensor is the multibeam sonar made by Imagenex, Delta “T”. The GPS path and attitude sensors are from Trimble, Sonardyne respectively. We are using the open source MBSystem software for generating plots.

What do you use for the controller? What do you use to communicate with the SWATH?

We have an off board computer which sends wireless commands to SWATH. The communication devices are called a Richochet modem (128 kbit/s). A Matlab algorithm sends commands to Richochet which are then received by another Richochet on board the vessle. This passes motor commands to the BasicX microcontroller which relays the information to an AX3500 Roboteq motor controller for position control. At the same time GPS and Compass data is collected by microcontroller which is transmitted to the off board computer for the further processing.

Where do you do your testing?

We test in Stevens Creek Reservoir, CA most of the time. That is mainly for tuning our controller and sensors. We had recently been to Lake Tahoe and mapped some parts of Emerald bay for Geologist. We also work with USGS scientist. In the past, we had previously worked on north side of the lake looking for geological features.

Do you have any note-worthy engineering experiences?

The autonomous kayaks we use have trolley motors mounted on a wooden plank. The mount is not a hard mount but worked well. But one day while testing we forgot to check the mounting properly and one motor came loose. We were not able to move kayak as the motor could have fallen in water. Learning I took it from it is, however you confident about the stuff you should check all the connections, mounting before deploying.

What direction do you see your business heading in the next few years?

Robotics is definitely a booming field. As we develop the field, new applications for robotics will keep coming.

What challenges do you foresee in our industry?

The main challenges we face are to fulfill customer requirements using the available budgets and equipment resources.

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