Swerve: Belts or Chain?

[Tyler2517]

One more thing about crab is that 116 inches of chain adds up to a lot of weight.
If you loss that chain your robot drops dead.
I would never chose to run a crab over a swerve the advantages of the swerve when in my opinion it would be easier to build a 4 wheel independent swerve over a crab with a turret on top. With the 4 wheel swerve you can do so much more.

Programming is harder. but mechanically building 4 identical gear boxes is easier then that plus a rotary turret that can hold weight. Add on that the system you build to turn the wheels/drive if that fails then you loss the drive.. (most of the time a loss drive means a dead robot).

[Aren_Hill]

Originally Posted by Tyler2517

One more thing about crab is that 116 inches of chain adds up to a lot of weight.
.

The 1625 robot in 2010 had 324" (27') of #25 chain on the 6wd swerve...It's not that bad....

[Bryce2471]

Originally Posted by nuclearnerd

I can see a lot of advantages of this configuration. It would be easier to build and program, it would give a robot the ability to strafe without sacrificing traction, and it would be no worse at pivoting than a standard tank drive (though not as good as a 4-wheel-independant swerve). Do you know of any team that has tried it?

One catch - as the wheels turn 90 degrees to strafe, the wheel pairing pattern would need to change to allow differential steering. You might still need 4 independent drive motors (need to think about this a bit). Even so, it would be simpler to implement the steering.

In 2012, my team did crab drive based on the wild swerve module. I was easier to implement, but the lack of steering ability made the extra weight marginally worth it. This year we did a custom independent swerve drive. I took some more development, but we are much happier with the results.

[aldaeron]

Originally Posted by Tyler2517

If you loss that chain your robot drops dead.

I agree, but how is this different than a tank drive? If you lose one side of the chain you're pretty much stuck (although you can do a funky circle). In my experience the chain typically fails at the connection point (master link) and with a long chain there will be a few more chances for failure because there are a few more master links. If inspected periodically this should not be a major issue. You can also get 50' or 100' lengths of chain at McMaster

[Electronica1]

I recall some teams linking opposite corner modules in order to turn. I can't recall which team it was but it allowed you to strafe or rotate but not do both at the same time.

[Gdeaver]

We have gone to the module form. If any of our pods fail or are suspect of not performing properly, they are immediately swapped out. Our pit crew can swap a module in < 5 minutes. Repair later. 4 bolts and 3 wire connectors and it's out. How fast can a mech, West coast drive or any other drive be repaired? I have watched teams struggle with repairs to other drives and like the repair ability of the swerve Modules. For us the goal of our team is not to win but, to mentor and teach our students to work together and accomplish hard technology tasks. 4 driven wheel, independently steered swerve is a good one to teach this. Yes the kids are pushed hard to do this each year. The pay back in their growth is great. Have to say we started to win more after the switch to swerve. To do swerve forced us to develop processes and a mindset to do it. The same processes have help with other aspects of the team. Swerve is hard but for us the pay back has been great.

[aldaeron]

Originally Posted by Gdeaver

We have gone to the module form. If any of our pods fail or are suspect of not performing properly, they are immediately swapped out. Our pit crew can swap a module in < 5 minutes. Repair later. 4 bolts and 3 wire connectors and it's out. How fast can a mech, West coast drive or any other drive be repaired? I have watched teams struggle with repairs to other drives and like the repair ability of the swerve Modules. For us the goal of our team is not to win but, to mentor and teach our students to work together and accomplish hard technology tasks. 4 driven wheel, independently steered swerve is a good one to teach this. Yes the kids are pushed hard to do this each year. The pay back in their growth is great. Have to say we started to win more after the switch to swerve. To do swerve forced us to develop processes and a mindset to do it. The same processes have help with other aspects of the team. Swerve is hard but for us the pay back has been great.

The swapping is a great point. Have you ever had a module fail in a match? How does yours drive with 1 dead module?

I agree that a swerve is a good way to teach many important skills. I have never been willing to take the risk of doing swerve during the season (if it fails then you're really in trouble if you can't drive forward!). What was it like the first year you tried swerve? Did you do a trial run during the off season?

[Qbot2640]

Love where this conversation has gone. Here's my design thus far.



Before everyone piles on...the prototype will use stuff we have laying around, like the Andymark wheels with the plastic pulleys, and mini cims for steering. It's just the start.

[Marc S.]

You could do gears instead of belt or chain.

Check out 973's iteration of the West Coast Swerve, "Emperor Swerve" & "Encore". 1717 uses a very similar and much more refined West Coast Swerve.

[Qbot2640]

Originally Posted by Marc S.

You could do gears instead of belt or chain.

Thinking about it...but afraid. Trying to keep as much of this in the "comfort zone" as possible. The real goal is to get something that works so we can start figuring out how to program it all - that is frightening!

[Gdeaver]

Teams are always focusing on the mechanical and programming aspect of swerve. You can design and create a perfect swerve and nail the programming.
Guess what, your only half way there. Teams forget the human part of this system. Control presentation and driver training are just as critical. You also have to be prepared to devote as many resources to your drivers.

[Qbot2640]

Originally Posted by Gdeaver

Teams are always focusing on the mechanical and programming aspect of swerve. You can design and create a perfect swerve and nail the programming.
Guess what, your only half way there. Teams forget the human part of this system. Control presentation and driver training are just as critical. You also have to be prepared to devote as many resources to your drivers.

In our case, it is not that we are neglecting the importance of driver training...but this project is a sequential endeavor...we can't program until we have something built mechanically, and we can't train until it is built and programmed. Right now we're trying to get something built - everything else comes afterward. Knowing my team's strengths and weaknesses, though, the programming is going to be our most difficult part by far.

[Gdeaver]

For programming start with Ether's paper on the kinematics of swerve. Several teams have published their code. You have to understand the mechanical and sensors to follow the code. Big choice is incremental with indexing or absolute encoders. Big difference in the steering algorithm. Also, your programmers must understand and embrace the principles of real time-- data flow methods. You will have a good bit of code running just for the swerve. For other mechanisms on the robot the the efficient execution of those blocks of code is critical. Your team should master a fundamental knowledge of state machines. We had problems our first year. Our swerve worked OK at home. Went to the finger lakes regional and had bad FMS lag. Our robot several times did what our team calls the happy dance. Steering goes wild. To me it looked like a grand mal seizure. We did not give up and have been driving forward ever since. Make sure your team is ready for problems and are ready to not hit a home run the first time. Are you willing and ready to make a long term commitment to perfect it? If not then basic tank drive what ever the wheel configuration can take you far.

[Oblarg]

Originally Posted by Qbot2640

Love where this conversation has gone. Here's my design thus far.



Before everyone piles on...the prototype will use stuff we have laying around, like the Andymark wheels with the plastic pulleys, and mini cims for steering. It's just the start.

I would be extremely cautious about that drive belt ratcheting given the small amount of wrap on the tiny top pulley.

[Tyler2517]

Also 9 mm pullys may not handle the thrust at that end of the gear redction. Belts like high speed over high tourqe.