Monthly Archives: September 2008

Navigation

While we’re furiously working away to complete the rover construction in time for the challenge, the majority of our other systems are complete.  The next one we’ll talk about is the navigation system.

While this is clearly crucial to completing the mission the on-board vision system is relatively basic.  We are using a stereo-camera to provide a live video stream back to our ground-station/control centre.  This will be our primary vision system and used to navigate the rover, search for the samples and aid the robot arm when collecting them.  In order to make full use of the capabilities this provides we have mounted the camera to a pan and tilt unit.  Coupled with a pair of bright headlights we will be able to use this unit to pan around the crater floor once inside to search for the samples, without wasting additional power driving around the site.

The video below shows the PTU with the camera and headlights attached, in both lit and and unlit conditions.

And here’s our dev-bot with the arm attached on the back and the camera on the front.  These will be next to each other on the final rover however this allowed us to check the camera was capable of giving a clear view of the arm workspace.  It looked great!

 

The devbot rover with arm and PTU/camera/headlights attached.  The combined unit did a great job of illuminating and videoing our lab!

The devbot rover with arm and PTU/camera/headlights attached. The combined unit did a great job of illuminating and videoing our lab!

Also visible in the photo above is the prototype part for the secondary area of our navigation system, the long bar with coloured LEDs at each end.  These lights will be attached at the very front and back of Selene, and will allow us to use our relaybot camera to orientate ourselves back toward our entry point once we have collected the sample.

 

 

The relaybot, with the camera visible mounted on the front

The relaybot, with the camera visible mounted on the front

The principle is fairly simple, while the primary purpose of the relaybot is to allow for wireless communications between the lander site and Selene once inside the crater, the fact that it will have some element of mobility will allow us to position the relaybot on the edge of the crater rim, where we estimate that it’s field of view should cover the entire site we have to explore.  Once we have located and collect the soil sample the relaybot camera will detect the alignment of the red and green LEDs mounted on Selene.  Once directly pointing at the relaybot we will have a clear indicator that we are pointing at our entry point, and therefore the optimal location to exit (in order to achieve maximum points!).  We anticipate becoming easily disorientated and lost after searching the crater floor, this system will allow us to quickly regain our bearings and direct the rover back home to the lander!

Advertisements

Power System

The Pioneer 3 is powered by 1 to 3 lead-acid wet cell batteries.  These provide a nominal 21AHr of energy, and under normal use should provide power for Selene well over the 2 hour time limit for the challenge.

However, they are particularly large and heavy.  So thanks to the guys at Lincad, we now have a Li-Ion battery pack roughly half the volume (casing aside) and less than half the weight while retaining the same 21AHr capacity of the originals!

 

The new, smaller Li-Ion battery underneath the original Lead-Acid cells.

The new, smaller Li-Ion battery underneath the original Lead-Acid cells.

The new battery provides a number of benefits, the most significant of which is the more convenient shape.  The new battery sits in the belly of our chassis, lowering the center of gravity and providing easy access through the bottom of the rover.  The smaller size leaves room for the additional flipper control mechanisms inside the chassis.

Sample collection

As promised here is some more info on one of our subsystems, used to collect the sand sample we’re going to be looking for once inside the crater.

The robot arm is a 5 degree of freedom manipulator provided by Mobile Robots as a Pioneer 3 accessory.  As standard it is equiped with a two-finger gripper, however we have modified this to carry a scoop/storage container tool.

Robot arm holding a sand sample

Robot arm, here attached to our development Pioneer, holding a sand sample

This over-sized scoop is placed in position by the arm.  Once collected the sample will remain safely in the container as we return the rover to the lander, where it can be detatched and deposited.

Updates are a’coming…

It’s been quiet on the blog recently as we’ve been hard at work getting our rover up and running ready for the challenge on the 20th October!

We’ll be posting some photos later but here’s a quick run down of our progress to date…

The track lifting mechanism is now completed and working, using our microcontrollers we can stow and deploy the tracks as required depending on the terrain.  Due to the total size of our tracks we just now have to wait for the (patient, brilliant) workshop guys to drill and tap the hundreds of holes needed to attach our grousers to the belts!

The navigation system has been completed, and works in two parts.  We have a stereo camera mounted on a pan-tilt unit for our primary navigation once on-site.  We’re ironing out a few bugs but its nearly there.  The second part is a “home-beacon” system, incorporating our secondary rover/relay station, positioned on the rim of the crater.  As well as acting as a communications relay the rovers on-board camera will detect coloured LEDs on the primary rover in the crater, and the ground-station software will use this to help orientate the rover toward our entry/exit point on the rim.  With the dark environment this is likely to be a crucial aid in the task of returning the sample back to the lander site.

Our communications system is also now completed.  Based on 802.11b/g wireless ethernet, we have successfully completed remote teleoperation and range testing of our development rover, with a total record distance of over 300m, non-line of sight connectivity from the control site!  We also incorporated endurance tests of our new, smaller and light-weight Li-Ion battery pack, and were thoroughly impressed by the results.

More info and pictures will be coming up, and we’ll be posting more regular updates as we approach the challenge date.