Does anyone know how to build a 'bot with 4-wheel swerve drive (allowing the robot to move sideways). Can anyone help me?
Jeff
Last year Chief Delphi used the 4th generation swerve.
Four wheel drive, four wheel independant steering, all using Joe Johnson’s “Pie Plate” swerve concept.
The students really put Joe and the other engineers to the test with this one.
Sometimes wild ideas of the students are great!
As far as giving you directions … we reserve that right. We will pass on that one. Trade secrets you know.
Jeff, if you get to see the 4th generation swerve, you won’t be able to take your hands off of that drive train… It is, as Mike said, “Four wheel drive, four wheel independant steering”, and therefore more than just “allowing the robot to move sideway”.
Obiviously I don’t know the direction for construction of that drive train, but I can talk about the concept. Basically they use the 4 most powerful motors out of the kit: Drill motors and Fisher price motors, mounted next to the 4 wheels (or 4 belt drive in their case). So, imagine 4 small boxes with wheel/belt sticking out at the bottom contacting the carpet. A large gear sitting flat on the top face of each wheel box, so the gear reduction connected the other 4 motors can rotate wheel box independly of each other with the correct torque/speed combination…
So if you look at it, you will see drill /FP motors sticking out horizontally from the wheel box, and and globe motors sitting vertically and window motors sitting on their side (mounted on the base) with their output shaft engaged with the gear on top of each wheel box. Of course you will have to secure the wheel boxes on the base while allowing them to free-spin (when steering motors not engaged).
The tough part is using the right sensors that tell the program exactly where the wheel box are facing. Because it is hard to program a motor to turn exactly the degree desired. After changing the wheel’s direction a couple of times, there are bound to be a few error and the wheel can never return to the preset direction (that is if you are only relying on only the program).
That drive train have great manuverability, because you can spin each wheel any direction you want and spin at whatever speed you want, therefore resulting 360 degree freedom, including spinning around the center of robot much smoother than normal tank drive. Really great at fine-tuning robot’s position for delicate tasks such as placing the big balls exactly on top of the center of the goals.
Again, I never say this is easy to understand if you’ve never seen it. To tell you the truth, my first thought when I saw that CD drive train was, “uh… I am NOT making me one of these”.
Well, if you think about it, the kit only come with 10 powerful motors (excluding the servo and torque motors), and just this design is using up 8 of them… (what’s left are the Vandoor motors and the pneumatics) That doesn’t leave too much room/weight/freedom for other device.
So, I would recommend against doing this for your robot, even if it’s just an experiment. You would rather use simpler designs and get the max out of fewer of motors, and still achieve great results.
Well, I could go into much more details of that drive train, but this message is getting a little long, and so, I am going to let them remain as CD’s trade secret. 
I will probably talk about other simpler designs later, so remember to check back… Of course others are free to talk about designs they know, as they probably know more than I do anyway…
So, basically, each wheel is driven independently by either a drill motor or Fisher Price motor? That was my biggest problem.
You said the globe motors were on top. Do they provide the rotation for the “wheel boxes” as an individual unit?
Other than that, I think I understand enough to get past the quandary I found myself in. I had developed enough of the system to rotate the wheels, but no way to drive them. The FP motors would seem to solve that, if the gear ratios and RPMs and such could be made to match the drill motors.
Thanks for your help, and if you come up with a simpler version, let me know.
Jeff
Another idea i saw where you can use just use the 2 drill motors is u mount them vertically and run chains to the wheels and send power down a shaft that the wheels can rotate around,then make a right angle gearing system at the bottom of the shaft to get the power to the wheels. sorta like if you were to drill out the middle of a caster and put a shaft through it and had another motor turning the caster.
andrew
1st and 2nd generation CD swerve did that very process. One motor swerving either 2 or 4 wheels together. It worked good, however there were several weak areas to be concerened about.
Several teams have done this. 301 Probots, 111 Wildstang, and others that slip my mind.
On our team we call that and x-drive chaise, basically because it can go on the Y-axis and the x-axis. I heard that it is very good for speed and precision, but not so much for torque. Your chaise design depends all on the game, this year you needed a lot of torque to drag those goals, and speed wasn’t really that big of an issue.
But the design is really complicated. It requires both hardware and software to be perfect. It can create a lot of complicated components, and the more complicated you can get, the less reliable your robot can be. It is a good design, saving you mostly time by not maneuvering as much.
Can anyone explain to me how drive is maintained in a front wheel drive car, when the wheels are not parallel to the frame?
im pretty sure they use an attachment (i forget the name now)that looks very much like the attachment for ratchets that you can change the angle the head is at and still apply rotation. like if you have ever seen a double bass pedal for a drum set its what they use so u can change the angle of the pedals and still kick the pedal and have it rotate to the mallet. looks like this
heres the link
but i may be wrong so if i am someone correct me
Andrew
If they in fact ARE connected by something similar to a universal ball joint, then how is power sent through the joint?
I believe it is something called the “universial joint” that allow torque from the drive shaft transfer onto the wheel. The idea of universial joint is connecting two shafts with a special joint that allow the two shafts rotate as a whole, while the angle between the two shafts remains the same angle and direction.
Here’s a simple picture of what it looks like:
http://www.tpub.com/machines/11g.htm
A universal joint is a mechanical connection between rotating shafts which are generally not in parallel, but intersecting. “U-joints” transmit torque.
Because of the two pivots on the U-join, you will be able hold onto one end of the join, then point the other end to any direction you want. So, when the steering hold the front wheel in certain angle, the universial joints are forced to adjust to a new angle when ever the drive shaft rotates.
I’ve seen a smaller version of U-joint from small part, so you might want to order one and look at it yourself…
The real name for the joint in the front end is “constant velocity Joint” of CV joint for short. It delivers motion through a range of degrees.
Warning: If your car is over 4 years old and front wheel drive you should be inspecting the “Boot” every oil change. If this rubber cover breaks, water gets in and the grease goes out. That is bad.
I suddenly get the feeling I am getting a lot more response to this question than I intended. I guess that’s a good thing…
As Mike pointed out, CV stands for Constant Velocity. What they are talking about is the rotational velocity of the output shaft relative to the input one.
Lets assume a case where you have two drive shafts spinnig at a constant speed. Connected to one is a U-Joint and connected to the other is a CV-Joint. For both joints the output shafts are at a 150 degree angle from the drive shafts (30 degrees from straight). (This is what happens when you turn a corner) For the U-Joint, the speed of the output shaft will actually speed up and slow down depending on the position of the U-joint. The output from the CV joint will spin at a… constant velocity.
I believe CV joints also allow a much larger wheel angle and thus a smaller turning radius.
It is my impression that if we didn’t have CV-Joints we wouldn’t have very many front wheel drive cars.
I hope someone else finds CV joints as interesting as I do,
Jim Meyer
p.s. I think Mike’s view of how long CV-Joints last is a little pessimistic. CV-Joints will last a long time if the rubber boots do not have any holes in them for dirt to get in. This is why some people recommend checking your CV boots for holes or cracks at every oil change. If you catch a cracked boot early, you won’t have to replace the joint, just the boot.