Re: Why swerve is better than Holonomic... HELP
 

If they really want to use omni's, tell them to use linkage drive. Yet something tells me that we're not getting the full picture about how the mentors truly feel the swerve drive contributed to the robot in the previous years. Perhaps they don't want to repeat the stress of creating and maintaining the robot, or perhaps they want more time to work on the manipulators while still maintaining certain advantages of strafing.

As for the ramp, you want all 4 wheels contribute to climbing, even if they're pointed 45 degrees off of straight forward. Unless you have a GOOD suspension one of the four wheels WILL lift off of the ground if the robot isn't lined up straight. Any 1/3 scale model, even if built out of toothpicks, will tell you that. So omni drive trains should be ok with going up and over the ramps should they choose to 'gun it'. Yet soon the mentors will realize that what goes up quickly will also come down quickly. Now either that can be a tradeoff you live with or it's a design consideration that affects a decision.

Re: Why swerve is better than Holonomic... HELP
 

All engineering is tradeoffs ... and understanding those tradeoffs and matching the best options to the strategy you choose is where the real engineering comes in.

No drivetrain is the best. Each has it's advantages and disadvantages and these must be weighed against your strategy, your teams capabilities, and your understanding of how the game will play out.

In the end, the best drivetrain/manipulator/kicker/hanger/circular-duck will be the one that most closely assists your chosen strategy.

Re: Why swerve is better than Holonomic... HELP
 

Our team built an omni drive in 2008, and it only worked ok. We built a vex omni drive, programmed it, and it worked great. Vex can be a good tool to prototype something, but the FRC robot did not drive any where as well as the vex robot did. Could more complex programming have helped? Possibility, but in our experience, the omni drive did not work well.

Re: Why swerve is better than Holonomic... HELP
 

The traction will not likely be the challenge for a holonomic drive base getting over the bump. Unless you have some sort of suspension, it will be virtually impossible to maintain the wheel contact and proper weight distribution to the wheels in order for it to drive properly.
As you go up the bump, one or more wheels will likely be lifted completely off the ground (unless you're using 3-wheel base that's perfectly aligned with the bump), and thus that wheel can no longer contribute to any driving you're doing (which will likely change the direction you're driving, which will likely cause you to no longer climb the bump). Additionally, as your robot is angled, the weight distribution to each wheel will change, also changing the resulting normal force on each wheel (which could also cause a change in direction).

Re: Why swerve is better than Holonomic... HELP
 

There is simply no substitute for prototyping. If you want to know if a drive can climb, defend, push, turn or move sideways effectively, the only way is to make one and put it to your own test. By now many teams have done just that and have played the game, even if only with students portraying robots. Most have come to the conclusion that some pushing will take place, some climbing over the bump will be needed and accurate movement and position of the robot for kicking is a must if you want to score. If you prototype you will know if your robot will slide sideways off the bump, if it can be pushed easily or if the drive system will work at all.
I will answer again as I have so many times before. We do not decide on a drive type until we brainstorm, prototype and test. Now one should.

Re: Why swerve is better than Holonomic... HELP
 

And this is from a team that has Raul the Magnificent as their lead mechanical design guru*

If Wildstang needs to prototype to know what's what, you should too.

For what it's worth...

Joe J.

*demi-god? maybe so...

P.S. I am helping out a 2nd Year team in Columbia, MD this year, Ursa Major #2849 Look out Chesapeake Regional, the big bear is in the house...

Re: Why swerve is better than Holonomic... HELP
 

However, if you're using a holonomic drivetrain (w/ 4 45 degree angled omniwheels) that doesn't have all the wheels in contact, it will autocorrect itself, putting you straight.

Re: Why swerve is better than Holonomic... HELP
 

My initial analysis of the situation suggests otherwise. If your right wheel starts to climb the bump first, lifting the left wheel off the carpet, it looks to me like the robot will swing to left, making the misalignment worse.

Re: Why swerve is better than Holonomic... HELP
 

that also makes sense to me as well

Re: Why swerve is better than Holonomic... HELP
 

Matt, I did not see the holonomic model in action - did you get to participate in testing of 4 wheel 45 degrees holonomic drive? Was it tested if it can go up the ramp? If so, did it have to be perfectly aligned to the frame? Would it high center on a ramp (scaled down to the appropriate size)?

I know that over the past two years you have put a lot of effort into your research and concepting of different drive systems. Many times more than any other student. I understand that you feel that we are ready to go swerve, and I agree that many top teams will decide to go in that direction. Swerve, if executed correctly may give an advantage in controlling the (sections of) field. However, as you mentioned, majority of our team is new to FRC. Regardless of which drive is chosen, I believe that all of the brainstorming, testing and analyzing that was done this week will benefit all that participated. If we would have decided on day one that we are going to use a specific drive train because the student who is the head of the design "did all the research and is an expert" makes a specific recommendation, there wouldn't be much of an opportunity for learning for the rest of the team. Selection of a drive system will play a significant factor in how well the robot performs in this year’s game, but it will not be the deciding factor. I expect to see robots with variety of drive systems perform well in the competition. I wouldn't be surprised to see a robot built on a kit bot chassis to be on a winning alliance in the regional. A robot that has a great ball controlling mechanism, can self align on the target, can adjust the shots based on distance and angle, can hang, has a team with lots of driving practice and good strategy etc. can easily overcome not having most optimum drive system (I am not implying that swerve is the optimum system for this game).

While managing any design project, the team needs to understand and leverage all other aspects: experience of the team, tools and materials available, monetary and talent resources, risks, advantages and tradeoffs of different design options, time required to build, test and optimize the design, fall back plan ... etc. etc.


I will likely not be involved in the decision making (will probably not be able to make it to school this weekend) but I still believe that whatever drive train is selected, we all have learned a lot during this evaluation process. I also believe that we are very fortunate to have great pool of talent, support from teachers, parents and mentors and we have good chance of performing well this year. If we happen to choose a less difficult drive train, we will use the time we gained to optimize on other aspect of the game.

Last, please remember Dean's homework for this year. It is not all about who wins or loses during the competition, but rather how much you and everyone else learned (and inspired others to learn) in the process.