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Unread 20-11-2013, 00:23
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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.

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Originally Posted by yash101 View Post
I'm not trying to grief here, but 28 pounds for the drivetrain sounds horrendous! I do not know how much our mecanum drivetrain weighed, but I know that it is well under 28 pounds!
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.
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Unread 20-11-2013, 00:28
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Re: Team 2471 swerve drives

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Also, doesn't swerve have a high latency? As of what I know, holonomic drive can have very little latency
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.

Quote:
There are a few teams that have the resources and ability to pursue swerve or other complex drives. The poster appears to have the capability and commitment to do swerve. The rewards can be big. Putting aside the competition aspect of swerve and think how much knowledge and skill a swerve project can give students.
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.

Last edited by Bryce2471 : 20-11-2013 at 01:46. Reason: spelling
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Unread 20-11-2013, 00:42
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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).
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Unread 20-11-2013, 01:05
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Re: Team 2471 swerve drives

Where is the 28 pound number coming from. OP says it weighs 37 pounds in his first post.
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Unread 20-11-2013, 01:39
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Re: Team 2471 swerve drives

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Originally Posted by tickspe15 View Post
Where is the 28 pound number coming from. OP says it weighs 37 pounds in his first post.
thank you, I don't understand where that came from either.

Quote:
I'm not trying to grief here, but 28 pounds for the drivetrain sounds horrendous! I do not know how much our mecanum drivetrain weighed, but I know that it is well under 28 pounds!
Although this is the first time it's brought up. I guess some people didn't read my first post.
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Unread 20-11-2013, 14:33
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Re: Team 2471 swerve drives

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Originally Posted by Bryce2471 View Post
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.
At 120 rpm, a 90 degree rotation only takes 1/8 second. That's probably why it feels like less than 1/2 second.
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Unread 20-11-2013, 17:39
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Re: Team 2471 swerve drives

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Originally Posted by yash101 View Post
If done correctly, mecanum will also get the same things done. Our robot was able to push the other robots around at competition. With locking mecanum, we will be able to stun the other teams when we enable it and sideload ourselves, making it impossible for us to be moved! I will inquire about how much our drivetrain weighs tomorrow, when we have robotics.
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.
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Unread 20-11-2013, 17:50
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Re: Team 2471 swerve drives

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Originally Posted by bobcroucher View Post
At 120 rpm, a 90 degree rotation only takes 1/8 second. That's probably why it feels like less than 1/2 second.
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.
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Unread 20-11-2013, 18:13
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Re: Team 2471 swerve drives

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Originally Posted by AdamHeard View Post
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.
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.

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Unread 20-11-2013, 18:22
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Re: Team 2471 swerve drives

Quote:
Originally Posted by Bryce2471 View Post
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.

Ah, I assumed you were quoting free speed. Yes, you are geared faster then.
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Unread 20-11-2013, 20:07
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Talking Re: Team 2471 swerve drives

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Originally Posted by Bryce2471 View Post
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.
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!

Last edited by yash101 : 20-11-2013 at 20:16.
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Unread 08-12-2013, 21:20
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Re: Team 2471 swerve drives

Quote:
Originally Posted by Ether View Post

Gdeaver alluded to the importance of swerve/omni Driver Interface (DI), and that segues into a question I've been wondering about lately.

Does anyone know of a team who has implemented a DI mode I will call1 a HaloAR (AR=Auto Rotate), as described in this thread posts 5, 6, and 9?


1until someone informs me that such DI has already been named
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.
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Unread 08-12-2013, 23:25
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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!
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Unread 09-12-2013, 07:19
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Re: Team 2471 swerve drives

Quote:
Originally Posted by gpetilli View Post
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.
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?
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Unread 09-12-2013, 07:24
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Re: Team 2471 swerve drives

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Originally Posted by yash101 View Post
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!
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.
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