Vex Worlds

So this Tuesday I am going to the Vex Robotics World Championships in Dallas, and wanted to share what this year's worlds bot is. It has three key features. First is the 6 wheeled tank drive, which drives the bot. The wheels are all chained together, so every wheel receives power even if one motor breaks. Also, if one or all of the chain breaks, because the chain is plastic, we don't lose power to all of the wheels. The drive changes from chained drive to direct 4-wheel drive. This makes the wheels run at different speeds, but the driver can compensate. Next, is our tower with a four bar linkage. This is where four bars are connected to two points. The bars are exactly the same length, so when they rotate around the two points, the object being held maintains the same angle no matter what. Because we can then have a vertical angle when depositing cubes, gravity assists us, and doesnt fight our progress. Finally the BHM or block handling mechanism in the front has a small gear reduction connected to tank tread. This tread along with carefully placed zip-ties picks up cubes while maintaining the same speed, even with the friction of the cubes against the tread.

Thanks for reading,
Mark.

Phone Books

Phone books are extremely thick, but one would hardly think that two phone interleaved phone books could be extremely difficult to pull apart. The idea came to me while I was doing the physics review sheet because of its massive size. Though it is extremely difficult to measure the amount of Fs-max of two interleaved phone books. For starters normal force on each page is proportional to the number of pages above it. But you wouldn't want to do that because not every page puts its full weight on the page below it, and when you pull on the books, the pages compress and there is a force of pressure created holding the pages together. Even a miniscule amount of friction force on each page, multiplied by each page and each side causes massive friction. This friction is so great, that the pages will rip appart before the pages come appart. Its a little like a Chinese finger trap, when you pull, the force of friction increases due to more pressure on each page, but when you push together the pages come appart b/c the force of pressure is outwards not inwards. I really want to try this, but I didnt have 2 phone books or 3 hours to interleave them.

Thanks for reading,
Mark.

AutoDesk Inventor

So this long weekend I spend using AutoDesk Inventor (similar to pro/Engineer) building the chassis of our six wheeled skid-steered Vex Robot. The basis behind the omni-wheels in the back is that they reduce friction on horizontal motion. This reduced friction moves the turning radius from the center more towards the front. This is extremely desirable for the competition because we pick up cubes and deliver them near the front of the robot. This allows us to turn about the grabber moving our back out of obstacles and making smaller adjustments where it matters, in the front of our robot. The VEX robot chassis uses chains to ensure that each wheel moves at the same speed, and each side moves at a constant rate. Using encoders, which count 90 times the number of revolutions, a PID can be implemented (well a P due to lack of calculus) which equates the speed side, even though the amount of voltage being passed to the motor is different. This creates straight driving (though is quite hard to test). Both the programming aspects and the physical aspects of the robot have been well tested, but unfortunately holonomic drive has been scrapped.

Thanks for reading,
Mark.

Baseball Shooter

Continuing on the idea of FRC the next component of our robot was the baseball shooter, which we used to launch the orbit balls to set distances. Normally when used on footballs and baseballs, the wheels on the shooters compress and form around the balls to transfer more linear speed, because of greater friction. This compression is necessary for a successful launch. Unfortunately, the orbit ball is made up of six plastic strips woven together, so the ball would give before the wheels. We used this to our advantage by making a path which was two inches smaller than the ball. This created massive compresssion and created a larger transfer rate of linear speed to speed of wheel. Unfortunately, unlike baseball shooters, this type of shooter would not be able to fire a ball at anything higher than 30mph because the momentum of the wheels is not great enough to sustain top speed when throwing a ball. It begins to slow down as balls enter, because of the conservation of momentum...

I dont really have much more to say, but thanks for reading.
Mark.

RT-AWD - 2 Weeks till FRC

Imagine, if you will, a tricycle. If that's not possible look to the left. This year's 'Iobotics FIRST Robotics Competition robot will feature a new type of drive train system, with interesting physics built in. It is the Reverse Tricycle - All Wheel Drive system or RT-AWD for short. This system is slightly more risky than that of a normal four wheel skid-steer all wheel drive, but is simpler than a four wheel swerve drive system. It is riskier because its center of mass must remain within the triangle formed by the three wheels at all times, or it will tip over and fail miserably. This means that everything heavy should be kept near the front, or is counter balanced on the other side. It is less complicated than a full swerve drive system because only 1 of the 3 wheels rotate, as opposed to all four or even two of the four. Accompanying the extremely fun center of mass equations is the inclusion of the drive programming equations. The equations use the fact that the back wheel that rotates forms the center of rotation. The two front wheels move in a ratio to the distence to the distance from the center of rotation. Unfortunately the drive system doesn't use any thing like ABS or traction guages that tell when wheels slip using the fact that efficent drive comes from static friction as opposed to dynamic friction. The physics and math required for these drive systems are a little out of our league because they require calculus and differential equations... But thats something to look forward to I guess.

This is just part one of three (maybe three) discribing the three main features of this year's 2009 'Iobotics FRC bot. Thanks for reading...

Mark.

Blue Planet Solution! Same day post, part 2!

Another idea, that requires energy to be transmitted wireless, or through VERY long wires are airborne wind farms. This would use the technology of hot air balloon or helium which would hold the pod at a certain height, while creating drag holding the wind farm in place. The turbines would be turned by the natural jet stream very high up in the sky. It would also leave the land open for things like solar farms, etc and it could be done in any area around the world. The only problem is that the technology for wireless transmitition of energy is not up to par. Also I have no idea what the weather would do to the farms. Rusting would be an issue as it would be inside the clouds and icing can be a problem because of cold temperatures and a moist climate.

Thanks for reading
Mark.

Blue Planet Solution!

In the grand scheme of things saving the world from global warming is about an 11 out of 10. Not just because it makes our sky look nicer, but because it would make the world a better place. My solution is solar power, but not the traditional way. Placing solar panels in space in orbit, so they always face the sun, is a solution to the weather problems such as cloudiness, vog, and fog. To transmit energy is the hitch. Currently the technique used to create wireless power is to transmit high amplitude radio waves to a transceiver, but it can only power small objects such as a PDA charger or a wifi head set. Technology would have to greatly improve in this field to transmit energy. The other problem is that some radio waves are blocked by the earth's atmosphere causing a loss of efficiency. Overall this solution is extremely clean, but costly and inefficient, science would have to improve for this solution to be feasible.
Thanks for reading Mark.