Moana - Wishlist

Background

Mo is ideal for a relatively flat household garden surrounded by fences. Moana is going to be a testbed for many of the features that will extend what Mo can do. So Mo will be upgraded as and when to test new sensors and features.

I found I was starting to run out of IO pins with Mo and the memory limitations of the UNO meant I was restricted with some of the things I wanted to achieve. So one of the first tasks will be to upgrade to a Arduino Mega2560. The key drivers for this are:

• Many more IO pins to accommodate more sensors.
• Much more program memory to handle greater complexity.
• 4 Hardware UARTs allowing data transfer back to the baseship.

The locomotion motors will be upgraded to cater for much steeper inclines. The H-Bridge motor driver will be upgraded to cater for the extra current drain.

Sensors

A machine that is traversing fields will have many more sensors at its disposal and Moana will be used as the platform to test them all. Navigation and (possibly) localization will be important. I've done a lot of localization experiments with Monte-Carlo but I would like to get away from having to store the map, either in the mower or in the baseship. It may be that that is what we have to do, but other options exist.

Here are some of the sensors I want to try out:

• Bump switches.
• Sonar proximity.
• Digital compass
• GSPS and waypoints
• Vision
• Active Beacons
• Passive beacons (with visual recognition)
• Gyroscope
• Accelerometer
• Odometry
• PID Control
• Return Home to Charge
• Radio/Bluetooth Link

I've used odometry and PID successfully on indoor robots with a high degree of accuracy but I believe the outdoor terrain will make it much more difficult. Bearing and accelerometer reading may be accurate enough if used in combination with other sensors.

Layering

A GPS waypoint may be enough to head towards the general area where we want to go. A compass bearing with PID controller may well keep us in a straight line until we get near. Sonar and Optical techniques may be useful for honing in on where we need to be. We need to see how accurate we can get with GPS. As far as I understand, 3 metres is about the best we can hope for with GPS, but that is pretty good in a field. A small set of GPS waypoints is far more desirable than a full blown map.

Been There Done That

When covering a large area, it may not be possible to mow everything on one battery charge. The ability to remember where we have mowed (either now, or after a charge) will add great efficiency rather than a random walk. Mowing along fixed compass bearing may achieve the straight lines we are looking for. If we keep a list of waypoints we have visited, we may have a good chance of continuing where we left off. Need some overlap to account for GPS inaccuracy.

Remote Control

It is important to have a two way wireless link to the mower. High power bluetooth gives 100 metres which may be suitable for Moana, but not her big brother. XBee may be a better option. Either way, being able to collect all the sensor information for analysis will be very useful. Also, the ability to send macro commands to the mower will be very useful. Things like 'stop', 'change heading to', 'goto waypoint', 'go recharge', 'wakeup' will probably be more useful that just using it as a remote control car.

We have the ability to send all sensor data back to the house via a radio link. We could have some complex software running on a powerful computer indoors that receives data and send instructions back to the mower. However, with the increased power of the Mega, it may not be necessary to go down that route.

March 2018