Tuesday, March 16, 2010

Some MARVIN Details.

So here are a few of the things I have been working on...

First, the base.  This is the original base.  I was having problems with the motors not being powerful enough, the rubber coming off the rims, and the casters were bending and not operating correctly.

This is the new base.  It is much larger, the wheels are bigger and geared down more and centered on the plate.  The casters are far more rigid and I added two more.  I have left two open axles (not shown) on the underside to add more PF motors if needed.  Each wheel can have up to three XL PF motors.  If you look at the side of the wheel housing there is a bit of axle sticking out.  I left this in case I want to add a rotation sensor later.  I also made the base more round to allow for easier turns so the corners won't get caught so much.  The wheels are the old solid supercar style so they shouldn't crush under heavy weights, plus there are two on each side.  The base is balanced so all six wheel touch the ground at the same time to distribute the weight better.

This is the light sensor communication hub I referred to a few days ago.  The clear round bricks in the middle are to diffuse the light in all directions.  The light on the sensor tends to shine directly forward and the bricks in the middle spread it.

I think I can overload this thing with PF and 9v motors.  I have two HiTechnic IRLinks and I have been doing some tests to see if I can use them at full capacity.  I learned that the IRLink is different than the IR Remote.  The remote really fills the air with signal, but the IRLink shoots forward for a limited distance.  As long as the IRLink is pointed directly at the receivers that you want to operate and all the stray and reflected signal is blocked, you can use two IRLinks in close proximity to each other.  This way I can control up to 16 more motors on top of the 18 servos directly controlled by the NXT.  I don't know if I will use that many motors, but it's nice to know that I can run up to 34 motors (WOW!)  I can stack up the rotation sensors and creatively program the bot to save on ports too.

Here is a turret I have been working on too.  It moves left, right, up and down.  It has an ultrasonic sensor  and an old RCX light sensor (behind the radar dish).  This will be used to search for light sources, obstacles, edges of tables and such.  There is one detail I'm not showing on purpose, but it is pretty cool and it's a surprise.

Anyway, you can see that I have been pretty busy.  Progress is definitely happening, not as fast as I would like, but it is moving along.


  1. Wow, this thing look cool. I like the light sensor communication doodad you made. How do you keep the robot going straight using the PF motors? How do you sync them?

    - Xander

  2. Very nice ideas, especially with the light sensors and the diffusion.

    Also, for some reason, I love that radar. You have to put it on his shoulder, then program some awesome randomish radar movements. That would be just too cool.

    Now, just add legs. XD

    Looking forward to it!

  3. Xander, I am relying on the PF motors to go approximately the same speed as each other. I have had luck with that in the past. I am not going to sync them up. I have a compass on the front of the base (along with a gyro and accel, don't know exactly how those will work yet) to do some basic directional movements, along with the three US sensors and the three touch sensors to avoid obstacles. This guy is a wanderer, so I don't plan on doing a lot of real precise movements, more general movements.

    Squiddster, thanks. I will tell you the secret, readable to only those who read the comments on this post. Right behind the US sensor there is a box. Inside that box I am going to put my Kodak camera. It fits great and is removed easily. I have a PF motor on the other side that pushes the two yellow levers inside the box to snap the picture.

    Here is my thought on how it's going to work. Marvin is a prankster. I plan to have him get into some mischief. The US sensor will locate the victim's face (as best as possible with an US) then as the prank is being pulled off, he will snap a photo at the right moment.

    I hope it works!

  4. You really have been busy! how much battery do you think you'll be hauling? (lots Of AA's or the lighter PF rechargable?)
    With the (was it 4?) XL drive motors are you running each motor from a seperate IR and battery pack to get the most power to the wheel? or are you going to be maxing out the batteries and IR's by sharing?

    Looks a lot better so far! I dont think you'll have any problems with the drive if you are using the compass for heading navigation. But you might want to use suspension on your castors if you are going for full contact to prevent the drive wheels being lifted on an uneven surface.


  5. As far as batteries, right now; 4 NXT rechargables, two nxt use standard batteries (until funds replenish) and two PF battery boxes. If I end up adding more PF motors on the drive wheel, I will add another battery box. I piled a bunch of stuff on top of the platform and drove it around with a remote and it didn't bog down at all, so I don't think I will need to add more.

    I thought about the suspension idea, but I came to the conclusion that the bot would only be used on flat, smooth surfaces. I figure that the bot will weigh about 15-20 lbs when it is complete so I don't want to add more stress than is necessary by going "cross country"