So the new grand challenge is out (IEEE DARPA grand challenge article).  I think it is really cool what Darpa is doing.  it looks like a very tough contest.

(Click on Picture to launch video)

After writing the PC-BOT driver I thought I should do something interesting now that it is integrated in robotFoundry. I quickly developed an IR avoidance routine and let our PC-BOT loose in the office. Eventually these routines will be part of the stock robotFoundry behaviours. 

If you look closely in the video one might notice a wire coming out of the back of the PC-BOT.  The wire is used to connect the PC-BOT’s M3 Drive system to an external computer system.  Can you guess what type of system is controlling the PC-BOT?

 We will also be adding a simulated laser scanner to the front of the simulated PC-BOT and maybe a sonar ring.  The laser scanner will be a great addition to the model and will benefit end user who don’t have a physical scanner.

Once the sim has been completed we will be announcing a limited beta release to members of the 914PCBOTS community.  If you are not a member of this community and would like to test the software out, send me an email.

Once I get the Ok, I will be able to post some nice screen shots and movies.

So it looks like my assumption was correct that manipulating the individual segments directly, somehow bypasses the physics calculations.  

I actually managed to rig my model with configurable joints and make the joints stable ( no jitter ).  The biggest gotcha that I found is to make sure that the colliders that are attached to the rigid bodies do not intersect.  If they do then there will be joint instability (jitter).

Now that I have the joints working and the slip problem solved, it is on to finish the simulation.  I have a basic walk almost finished, still needs some tweaking.

I will post some screenshots when I can

This has not been a very easy task and I seriously thought that it would take a lot less time than it did.

After getting all of the kinks out of the 3d model we started to rig the model with the different physX joints that the Unity engine had available. We first tried hinge joints and then configurable joints ( not a lot of good documentation on these joints). After the model was rigged with the joints we found that there was some very large instability in the physics calculations and the joints started to jitter, come out of their sockets and magically move the robot across the floor. We tried different parameters, bumping up the solver iteration count, reducing the projections distance / angle values and setting configure in world space true. This did help but their was still lots of jitter.

At this point we had the bright idea to just manually rotate the joints around their respective pivot points using transforms. This worked great, the robot did not jitter it could stand up and do basic stationary moves. Now, if the world was fair everything would JUST work! But it is not and we now encountered the problem of the robot not being able to move. When we start the walking algorithm the joints move like they should, but the robot starts to move on the spot! The problem looked to be that the feet were slipping with the floor.

After changing the materials of the floor / feet to rubber and doing some major testing we found that using transforms to move the joints does not actually work. What looks to be happening is that when we manually move the joints we are actually bypassing the physics calculations which causes the feet to slip because legs are not being updated by the physic engine.  

Now it is back to using joints again.  I hope this time I can get them to work properly!!!

Currently PhysX cannot report back how much torque is being applied to a joint, so there is know way of knowing when a joint has exceeded its maximum load.  This torque information is critical when simulating a robot trying to standup or pushup when it is on the ground.

I will simulate the joint torque using a method similar to the one that I have come up with to simulate a pressure sensor.  Basically I will use the Center of Mass(COM) and position of joint(fulcrum).

Once I get the formulas worked out I will post them along with some data and screenshots of one of the simulated (real) robots that I am working with.