If we want to have the rear wheels spinning and the front turning, how would we hook that up as far as parts. I know how to program it… I think…
So you want a drivetrain with steered wheels?
Is there a particular reason you feel this is a more ideal solution than skid steering?
I am new to this and trying to get my students prepared for the competition in Feb. We just got our kit. I don’t much. What is skid steering compared to drivetrain? Is the omni wheels the way to go? Just looking for some advice. Did’nt know how to make it turn to be honest w/o ommi wheels.
Thank you,
Eric
The inventors guide covers skid steer pretty well. You may want to read that, even though it seems cheesy it is really helpful even to experienced vex-ers. Skid steer is when you have no steered wheels. When the left wheels turn forwards and the right wheels turn backwards the robot will spin clockwise and the wheels will simply scrub against the ground. Having omni wheels either on the front or back wheels will allow the robot to turn much easier because they have the rollers, some teams even go with 4 omni wheels but i would not recommend it as this makes the robot incredibly vulnerable as it is very easily pushed sideways.
Here is a fairly new example
https://vexforum.com/gallery/showimage.php?i=4696&catid=searchresults&searchid=531343
I would also search around the gallery a bit and see what is out there.
~DK
You would have to use omni wheels, but if you really needed, you could use small wheels without tires.
There are also a bunch of other ways to make a good skid turning DT without omnis. You can use pretty much any wheel without the tire as a simple way to reduce friction, the small wheels skid pretty easily without tires. Another option is to take most of the eight off of the unpowered wheels to reduce friction on them.
You could also make the drive train short (front to back) and wide, the closer the unpowered wheels are to the powered wheels and the farther apart the driven wheels are the easier it will be to skid turn without omnis.
~DK
A west coast drive is another option - the middle wheels are slightly lower than the others so it turns easier.http://www.robotics.org.nz/images/phocagallery/Elevation/Vex_NZ_Regional/thumbs/phoca_thumb_l_DSC05587.jpg
The majority of Vex drivetrains will be able to turn in place (skid steer) even without omnis. This relies on the wheel’s ability to slide against the carpet or foam to turn by skidding in place. Don’t worry about dropping your wheels or anything. Don’t believe me? Build the Protobot and turn with it a few times.
This document has a skid-steer drive with rubberless wheel (the second project, the Flexigearbot), but it turns with great difficulty. The first project, the Basicbot, a 4-wheel drive cousin of the Protobot is far more maneuverable. In general, any design with an unpowered skids or wheels will have more drag than one where every wheel that touches the ground is driven, though omniwheels greatly reduce the drag.
If you’re just starting out, you may also find this guide helpful. Both documents are somewhat outdated, but I’m hoping to update sometime this spring or summer.
Welcome!