I am pretty new to all of this robotics stuff, I am more of a car person. So when my school’s robotics team was showing me their previous robots and some other team’s creations I noticed that all of them had a 6 or 4 wheel skid steer set-up. Now using my previous experiences I wondered why no other team uses rack and pinion steering like a car I mean its durable, also using four wheel steering like the Gmc Quadrasteer you can turn on a dime just like skid steering.
It’s also called Ackerman(n) steering and you should be able to find some threads using the search function found above. Ackerman limits your maneuverability and adds unnecessary complexity to a robot that would be more maneuverable with a much simpler tank drive.
I’m also going to beat SuperNerd in welcoming you aboard!
Teams have done it, but it’s not as favorable. You don’t get as much pushing power with 2 motors powering the bot, and you can’t maneuver as fluidly as other drives. We used this in 2008, if memory serves correct, and it didn’t work out so well.
Since you’re a car guy, I’ll put it like this. In a pushing match between 2 cars. both with the same weight, traction, and motors, who would win: A standard car, or a car with power to every wheel? Or a car with more wheels and power to them, for that matter.
Also, which is more maneuverable: A standard car, or a wheelchair?
You could power all of the wheels with Ackerman, which would minimize or eliminate the loss of traction by less normal force on drive wheels.
Or a car with more wheels and power to them, for that matter.
More wheels does not mean significantly more traction, though some people have found small benefits to having more tread on the ground, this effect is secondary to the type of tread and the weight of the robot.
Depends what you mean by maneuverability. It improves your ability to turn while driving at high speeds and move in arcs, but it makes turning on a dime difficult or impossible.
Other than 2008 (which had several Ackerman robots), most games have not required the kind of smooth arcing motion Ackerman is capable of. Most motions tends to be like go-stop-turn-go-stop-turn-go, which is what skidsteer is good at.
This is the main reason why most teams stick with skid steer. The kitbot is skidsteer, and can be built in one day. Even a custom chassis skid steer does not take very long to fabricate, compared to an Ackerman drive. Additionally, it usually uses steering motors that could be used elsewhere (and if you want to keep those motors down to just one or two, instead of four, you must design a linkage to keep them at the proper angles). Skid-steer’s simplicity makes it much easier to have a moving chassis early in the season, and to have more time and resources to use on a manipulator.
Y’all forgot the biggest reason not to go with Ackerman drive. It’s called Swerve Drive. For making two more wheels able to turn (and the two that turn in Ackerman turn more fully), you get to move in any horizontal direction without turning at all!
Besides the limited turning ability–an Ackerman has to do a Y-turn to accomplish what a skid can do with a simple spin–it’s a somewhat complex drive. While swerve (or mecanum or omni) is also complex, it’s somewhat of a simpler type of complex.
Ackerman was a good drive choice for that game. The aft end of the robot would follow the forward steering wheels. There were penalty points for going the wrong way around the track. So if you were going to build a speeder to rack up running / lap points it would have been the way to go. A number of teams had auto mode that could score 3-4 laps in the first 20 seconds.
In game play, this is one of my favorite games. The combo of kickers, placers and speeders made for some pretty amazing game play moves.
Well to be fair, I think the consensus in this thread (and in FRC in general) is that the main benefit of Tank/Skid/Differential vs. Ackermann is that it is much better for maneuverability over short distances and/or slow speeds. The common story I give to my students is this:
How many turns/maneuvers does it take to move a car into a parallel parking space? How long does this take?
If you have a robot that needs to pick up a ball that is 3 feet to your right, and you have Ackermann steering, how long would it take to get there? If you had tank/skid/differential steering, how long then?
Ackermann is much better when you have high speeds and/or turns that do not require any form of strafing translation, i.e. like a race track. The OverDrive Game was designed to mimick a race track, hence several teams going after the Ackermann design and some were very successful. However (in my personal opinion) in most games in the past most teams with Ackerman steering would be at a huge disadvantage compared to a simple skid steering robot, with just looking at maneuverability by itself and not considering complexity/cost/use of motors/resources, etc.
Just a little side information, Ackermann steering refers to a specific type of car steering geometry. With Ackermann steering, the wheels will actually be at different angles during steering travel to more accurately approximate the path in which they are traveling. Cars have Ackermann steering for a variety of reasons: decreased scrub, better front end traction, etc.
Here’s a picture to explain further:
Not all ‘Car Style steering’ in FRC is necessarily Ackermann Steering, some teams in 2008 used parallel steering to some success, among other methods.
my team’s pretty still pretty young but we’ve been trying to test different drive trains. we’ve used tank and mecanum so far. we always do a lot of research and last year we were thinking of using swirve which is based of cars. we were worried about a few things. that swirve is still relativity new and that we did not think that we had enough time to work on it. there are some teams that use swirve but it takes dedication for months to make it work correctly. Getting it to work the way you want it to is not easy. So if your team has the time and resources, I would recommend that they start researching and prototyping this idea during the off-season. my team plans to do the same. this reduces the risks of having your robot not fully function during competitions.
This is not only for your idea but for everything you do in robotics! wouldn’t you rather know that your team has build something that actually works, and works well? this is why veteran teams often do well: they have experience.
Another very important reason skid steer “trumps” any car-like driving method is that skid steer keeps the middle of the machine open for game functions. For example, in 2010 it would have been difficult to make a kicker work around this or in 2009 or 2006 it would have been more difficult to pick up balls from the ground. The front-middle of the robot is prime robot real estate.
Plus that whole thing with it being more complex and less manuverable.:]
it would be probably at least twice as heavy, because you need a rack and pivoting wheel mounts, like the ball joints in cars.
look at skidsteer equipment, and the kind of small spaces they operate in, and compare that to driving a car.