Castors?

[jeffmorris]

The Vex Robotics Kit doesn't have castors for making wheelchair-based robots (two large driving wheels and two castors). Any suggestions for castors that fit the metal parts? The holes on castor mounting plates should be the same size and spacing as the holes on the metal parts.

[JVN]

The Vex Robotics Kit doesn't have castors for making wheelchair-based robots (two large driving wheels and two castors). Any suggestions for castors that fit the metal parts? The holes on castor mounting plates should be the same size and spacing as the holes on the metal parts.

I don't have an answer to your question about buying casters... however:

A free spinning omni-wheel provides the same properties of the caster. This is one option you could use.

If you don't want to purchase omni-wheels, you can take the rubber off the standard small Vex wheel, it will slide along the floor with very little friction, and also behave like a caster.

Another option is to build skid-plates. Many of the plastic parts in the Vex kit are great for this purpose (the Vex pillow-block comes to mind).

[KenWittlief]

Ironically a skid plate is more easy to control than a castor - it has the same frictional characteristics in all directions at all times, where a castor has different resistance to motion depending on which direction its pointing.

[petek]

How about ball casters (http://www.pololu.com/products/tamiya/0066/)? These would be great if you don't have any obstacles to roll over. One big advantage of ball casters is that they don't tend to steer the robot like conventional pivoting wheel casters (like on a wheel chair), making it more responsive and easier to program autonomous motion.

[Billfred]

How about ball casters (http://www.pololu.com/products/tamiya/0066/)? These would be great if you don't have any obstacles to roll over. One big advantage of ball casters is that they don't tend to steer the robot like conventional pivoting wheel casters (like on a wheel chair), making it more responsive and easier to program autonomous motion.
Seconded. Both of 1293's robots thus far have used casters on one side or another. In 2005, it didn't matter much (mainly because our autonomous was drop the arm, drive forward about 12.93 inches, and knock the hanging tetra off).

In 2004, however, making sure our casters were perfectly straight became essential to the proper performance of Bob's autonomous mode. (Whether it actually knocked off the ball, however, is another story. :rolleyes: )

[Arefin Bari]

How about ball casters (http://www.pololu.com/products/tamiya/0066/)? These would be great if you don't have any obstacles to roll over. One big advantage of ball casters is that they don't tend to steer the robot like conventional pivoting wheel casters (like on a wheel chair), making it more responsive and easier to program autonomous motion.

Very good idea I must say. Those ball castors work really well. Team 108's 2005 robot had 4 of them on there. It was easy to use and it worked.

For Jeff's purpose I would suggest what John has posted above. Omni wheels, or take the treads off of the wheels, or even use the plastic pieces... they work great.

[ManicMechanic]

Another option is to build skid-plates. Many of the plastic parts in the Vex kit are great for this purpose (the Vex pillow-block comes to mind).

Sorry to resurrect this dead thread -- we've just started working on castors. What do you mean by the Vex pillow-block? What does it look like? Does it come in the basic starter kit?

[JVN]

Sorry to resurrect this dead thread -- we've just started working on castors. What do you mean by the Vex pillow-block? What does it look like? Does it come in the basic starter kit?

Sorry... the piece that looks like a real-life pillow block.

The official Vex terminology is "Bearing Block"

You can see them on this page if you search "bearing block":
http://www.vexlabs.com/vex-robotics-starter-kit-parts.shtml

JV

[Lil' Lavery]

To elaborate on John's post, this (http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1872859&PMT4NO=8471809) would be an example of an actual "Pillow Block" bearing.

I'd say use a skid plate, ball bearing, or omni-wheel vs. a "traditional" caster wheel for easier control (although I prefer to have full control and no "dead" wheels).

[leehyungjin4u]

:confused: :ahh: :confused: where do we buy ball castors/casters??? approved by FRC????:ahh:

[Arefin Bari]

:confused: :ahh: :confused: where do we buy ball castors/casters??? approved by FRC????:ahh:

Go to www.mcmaster.com and type in "casters;" it will pop up with bunch of results. As long as you are not using something that tears up the carpet, FRC will approve it. They are also COTS item so make sure to include that in your BOM.