Re: Team 2471 swerve drives
 

Very impressive drive system. Now that you have one iteration done and currently testing, you can continue to develop and make improvements to put yourselves further ahead than a large majority of teams for the 2014 season (assuming that a swerve drivetrain is beneficial next year...) Abuse it until you find what breaks!

I am curious about the Black and Decker gearboxes you used. Do you have more details on what model you purchased and what modifications you needed to make? I'm a fan of cheap off the shelf components like this.

I don't believe that I've ever helped construct a FIRST robot with a drivetrain that weighed less than 35 pounds. I would argue that reducing the weight of the upper structure of the robot is much more important. If you have a 28 pound drivetrain and 92 pounds worth of other mechanisms/components, then the drivetrain is not the part that needs to be redesigned.

Re: Team 2471 swerve drives
 

I'm confident that this swerve will not have latency problems. The modules can turn at around 120 rpm and still have enough torque to spin the wheel under load. the wheels will never have to turn more than a quarter turn, so the most you could wait to drive is .5 seconds. In practice it turns out to be much less than that. When driving it, the latency is not even noticeable.

Thank you, It's cool to here someone that has done this several times has confidence in us. I agree, even if this project never gets used on a final FRC season robot, there will have been a lot of benefit to the team from what we have already done.

Re: Team 2471 swerve drives
 

While being pushed from the side it does increase traction, however from what I understand it does not increase traction while pushing head on. Regardless, swerve can run super grippy wheels that mecanum cannot(2" wide rough top).

Re: Team 2471 swerve drives
 

Where is the 28 pound number coming from. OP says it weighs 37 pounds in his first post.

Re: Team 2471 swerve drives
 

thank you, I don't understand where that came from either.

Although this is the first time it's brought up. I guess some people didn't read my first post.

Re: Team 2471 swerve drives
 

At 120 rpm, a 90 degree rotation only takes 1/8 second. That's probably why it feels like less than 1/2 second.

Re: Team 2471 swerve drives
 

Congrats, go start a thread on it so I can go grief about how my 8wd will weigh less than it… Seriously, are you contributing anything to this thread other than your infatuation with your drivetrain? There's a million threads about people talking swerve vs mecanum, go necro one of those.

Re: Team 2471 swerve drives
 

Based on our swerve and 1717's, I'd say you can gear your turning faster. Easily in the 180-200 rpm range and get a responsiveness gain.

Re: Team 2471 swerve drives
 

I believe the current gear ratio is faster than 1717's. Our current ratio is about 87:1. The number 120 was just a number I chose because it's in the middle of the motor's range. Thanks for the suggestion though.


On a side note, here is a render of a future frame I CAD'd. It is built with a 110" perimeter. The swerves are 3" wide and 9.375" long. Sorry for the low quality render, but it was my first time trying to making a render.

Re: Team 2471 swerve drives
 

Ah, I assumed you were quoting free speed. Yes, you are geared faster then.

Re: Team 2471 swerve drives
 

Sorry, I was talking about the 7 pounds per transmission


That's pretty cool. It seems much easier to build because the parts are more spread apart!

Re: Team 2471 swerve drives
 

Yes, FRC1559 is planning this for 2014. We are implementing a fusion sensor of a compass and gyro in a velocity PI loop. The gyro is the P velocity feedback and the compass is the I feedback (conceptually it directly reads the integrated error).

When turning, the current heading is updated to the current compass. When not turning, the PI loop is closed loop to hold the heading (which helps reduce affect of gyro drift).

At initialization, the robot snaps a zero heading. At any time the driver can press a "hat" button to command the heading to be one of the primary orientation (plus maybe feed station). The PI loop will drive the orientation while the driver continues to command XY translations.

We have this working with our asymmetric Killough drive, but only have about 30min of testing under our belt. Focus has moved to a similar fusion PD loop for X and Y with a follower wheel for velocity error P and an accelerometer for the differential error D.

Re: Team 2471 swerve drives
 

This is partially off topic, but if you were trying to lock direction/orientation using a gyro or accelerometer, would you use a coprocessor or would you use the cRIO? Don't you need to continuously monitor it to make sure that the results are accurate? Also, what about some mechanism that works like an array of optical mice? I guess that the FPS would be a tad high for the mice sensors, but it should be able to gather movement!

Re: Team 2471 swerve drives
 

That's really neat. I've ever thought of using two different sensors, an angular rate and an absolute rate sensor as two different sources of feedback for a PID loop. Out of curiosity, which compass sensor are you using and have you had interference issues in the past?

Re: Team 2471 swerve drives
 

You would use the cRIO. The cRIO is perfectly capable of doing all the math fast enough for any FRC task excluding vision. We've played with the loop time to see how the responsiveness changes, and you can't tell the difference between 20 Hz (50 ms loop time) and 100 Hz (10 ms loop time), both of which the cRIO can do easily. Once you start going faster, you don't gain anything. The mechanisms themselves don't respond fast enough, the motor doesn't have enough torque to make a noticeable change in 1/100th of a second.