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-   -   2015: Year of the Mecanum (http://www.chiefdelphi.com/forums/showthread.php?t=131913)

TheJoe 03-01-2015 11:16
2015: Year of the Mecanum
 
We were warned that "Change is Coming," and it certainly did.
It seems as though with the limited robot-robot interaction, we don't need the large, defensive powerhouse that FRC generally sees.

Could it be possible that mecanum drivetrains are the ideal way to go because of their maneuverability?

teafreak45 03-01-2015 11:24
Re: 2015: Year of the Mecanum
 
I would agree with you on the drive. While watching the video, I was thinking that would be the most used and best drive train for this year.

Kevin Sevcik 03-01-2015 11:42
Re: 2015: Year of the Mecanum
 
You see those bumps called the scoring platforms? Those are going to going to cause all sorts of headaches for mecanums. 5-wheel strafe drive with the strafe wheel on a pneumatic suspension should work well, I think.

smart1 03-01-2015 11:46
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1419662)
You see those bumps called the scoring platforms? Those are going to going to cause all sorts of headaches for mecanums. 5-wheel strafe drive with the strafe wheel on a pneumatic suspension should work well, I think.
I don't think there is a need to climb those, just go around them.

Jonathan Norris 03-01-2015 11:48
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1419662)
You see those bumps called the scoring platforms? Those are going to going to cause all sorts of headaches for mecanums. 5-wheel strafe drive with the strafe wheel on a pneumatic suspension should work well, I think.
This. Mecanums won't handle the bumps well, also mecanums need a very even weight distribution to work properly, I imagine there are going to be a lot of unevenly distributed robots this year...

smart1 03-01-2015 12:01
Re: 2015: Year of the Mecanum
 
I would try to set the center of gravity of the robot with the game piece, so when you lift it's balanced.

Ether 03-01-2015 12:05
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1419662)
You see those bumps called the scoring platforms? Those are going to going to cause all sorts of headaches for mecanums.
Has anyone looked at the field drawings yet? In the game video it looks like the platforms aren't that high, and there are ramps all around. How high is the platform, and what is the grade of the ramps?

ATannahill 03-01-2015 12:08
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1419684)
Has anyone looked at the field drawings yet? In the game video it looks like the platforms aren't that high, and there are ramps all around. How high is the platform, and what is the grade of the ramps?
The incline is 16 degrees, the height is two inches. This is from page 8 of the game manual. These values are nominal but the official values are in the field drawing.

alicen 03-01-2015 12:08
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1419662)
You see those bumps called the scoring platforms? Those are going to going to cause all sorts of headaches for mecanums. 5-wheel strafe drive with the strafe wheel on a pneumatic suspension should work well, I think.
Whenever we did mecanums, we always had suspension on each wheel so that all wheels were always in contact with the floor. They even went over the humps in Breakaway just fine!

Jacob Bendicksen 03-01-2015 12:09
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1419684)
Has anyone looked at the field drawings yet? In the game video it looks like the platforms aren't that high, and there are ramps all around. How high is the platform, and what is the grade of the ramps?
The angle of the ramp is 16 degrees, and the 'hypotenuse' is 7.125 inches. 7.125*sin(16) works out to 1.96 inches.

Ether 03-01-2015 12:14
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Jacob Bendicksen (Post 1419688)
The angle of the ramp is 16 degrees, and the 'hypotenuse' is 7.125 inches. 7.125*sin(16) works out to 1.96 inches.
My guess is this won't be a major issue with a properly built and driven mecanum.

Kevin Sevcik 03-01-2015 12:38
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1419696)
My guess is this won't be a major issue with a properly built and driven mecanum.
For the record, we tried mecanums in 2008 and 2009, and just the plywood under the carpet would make things go wonky if you were trying to do a precise alignment.

I'm not saying they'll be undriveable, I'm just saying they're going to make auto and certain precision tasks a wee bit more challenging and error prone than they need to be.

Ether 03-01-2015 12:46
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1419725)
I'm not saying they'll be undriveable, I'm just saying they're going to make auto and certain precision tasks a wee bit more challenging and error prone than they need to be.
My prediction: There will be mecs that struggle mightily and those that dance like olympic figure skaters.

hexane 03-01-2015 13:22
Re: 2015: Year of the Mecanum
 
From our team's experience, the only time that mecanums have ever had troubles were on the bridges in 2012. Even then, the problem was the lower coefficient of friction rather than getting up on them, and we were still able to balance 2 robots better than most teams.

chrisfl 03-01-2015 13:50
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by hexane (Post 1419778)
From our team's experience, the only time that mecanums have ever had troubles were on the bridges in 2012. Even then, the problem was the lower coefficient of friction rather than getting up on them, and we were still able to balance 2 robots better than most teams.
It was the same for us. We used mechanum in 2012 and our only problem was staying in one place on the bridge. We had no problem going up and down it while at an angle.

AutodeskGeek 03-01-2015 14:30
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1419696)
My guess is this won't be a major issue with a properly built and driven mecanum.
Amen to this. The only trouble we had with mecanum was the bridges in 2012. It wasn't impossible, we still balanced. Since it's only a 16 degree angle, it shouldn't be impossible to get over it.
Breakaway year, they had larger bumps. We went up them fine with mecanum also. Given, they were carpeted.

Some teams will struggle with the mecanum, some won't.

Bruceb 03-01-2015 14:32
Re: 2015: Year of the Mecanum
 
never used macanums before but really considering it this year. what is the prefered gearbox for these?

JosephC 03-01-2015 14:34
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Bruceb (Post 1419858)
never used macanums before but really considering it this year. what is the prefered gearbox for these?
If you have not prototyped mechanum or done it before, I would not recommend bringing it out this season. It doesn't seem difficult at first, but you will end up spending far too much time on your drive train instead of allocating proper time to your mechanisms.

Ben Wolsieffer 03-01-2015 14:41
Re: 2015: Year of the Mecanum
 
Our team has had a good amount of experience with mecanums, and we haven't any big problems with bumps. We used them in 2010 (w/o suspension) and were able to climb over the bump, and also in 2012, where we were able to easily climb the bridge.

Based on that experience I think driving over the scoring area won't be a problem at all.

Bruceb 03-01-2015 14:45
Re: 2015: Year of the Mecanum
 
the code is for the most part available if I am right so i believe if I give my programmers a macanum chassis early they will make it work. I dont see any serious mechanical issues as long as I get the best ideas from this forum.
Your thoughts on that?
again what is the prefered transmission?
Thanks

Brandon Zalinsky 03-01-2015 14:49
Re: 2015: Year of the Mecanum
 
The biggest hitch in developing a mecanum drivetrain is code. It requires lots of code testing. The hardware is much easier. The wheels are placed in standard configuration and require very minor differences in hardware required from a 4wd skid. The biggest hitch in the hardware is that you need four separate transmissions.

1058 has used 9:1 transmissions for a few years on our mecanum drives.

Peyton Yeung 03-01-2015 14:55
Re: 2015: Year of the Mecanum
 
461 used toughbox minis last year with a 12.75:1 ratio on 6" wheels. The biggest issue we had was due to a lack of suspension, one of the wheels did not contact the floor like the others.

AutodeskGeek 03-01-2015 15:08
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Brandon Zalinsky (Post 1419875)
The biggest hitch in developing a mecanum drivetrain is code. It requires lots of code testing.
For those teams that have used mecanum in the past, this is a non-issue. There's also plenty of help with algorithms online that teams trying it for the first time can use. Probably not too much testing unless you are implementing original drive styles with your mecanum wheels.

Ben Wolsieffer 03-01-2015 15:11
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by AutodeskGeek (Post 1419887)
For those teams that have used mecanum in the past, this is a non-issue. There's also plenty of help with algorithms online that teams trying it for the first time can use. Probably not too much testing unless you are implementing original drive styles with your mecanum wheels.
Yeah, the programming is not that difficult. WPILib for C++ and Java has a function for field oriented (or robot oriented) mecanum drive that works well. I don't know about Labview.

The Doctor 03-01-2015 15:22
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by TheJoe (Post 1419636)
Could it be possible that mecanum drivetrains are the ideal way to go because of their maneuverability?
MY THOUGHTS EXACTLY!!

The Doctor 03-01-2015 15:23
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by lopsided98 (Post 1419888)
WPILib for C++ and Java has a function for field oriented (or robot oriented) mecanum drive that works well. I don't know about Labview.
You do realize that the libraries will probably be very different since the introduction of the RoboRio.

Ether 03-01-2015 15:33
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by The Doctor (Post 1419903)
You do realize that the libraries will probably be very different since the introduction of the RoboRio.
Not that different. 2015 WPILib Java:

Code:
    /**
    * Drive method for Mecanum wheeled robots.
    *
    * A method for driving with Mecanum wheeled robots. There are 4 wheels
    * on the robot, arranged so that the front and back wheels are toed in 45 degrees.
    * When looking at the wheels from the top, the roller axles should form an X across the robot.
    *
    * This is designed to be directly driven by joystick axes.
    *
    * @param x The speed that the robot should drive in the X direction. [-1.0..1.0]
    * @param y The speed that the robot should drive in the Y direction.
    * This input is inverted to match the forward == -1.0 that joysticks produce. [-1.0..1.0]
    * @param rotation The rate of rotation for the robot that is completely independent of
    * the translation. [-1.0..1.0]
    * @param gyroAngle The current angle reading from the gyro.  Use this to implement field-oriented controls.
    */
    public void mecanumDrive_Cartesian(double x, double y, double rotation, double gyroAngle) {

ratdude747 03-01-2015 15:55
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1419725)
For the record, we tried mecanums in 2008 and 2009, and just the plywood under the carpet would make things go wonky if you were trying to do a precise alignment.

I'm not saying they'll be undriveable, I'm just saying they're going to make auto and certain precision tasks a wee bit more challenging and error prone than they need to be.
Unless you're talking offseason prototypes, I highly doubt that *cough *

Jalerre 03-01-2015 16:37
Re: 2015: Year of the Mecanum
 
For those talking about driving over the bumps, I do believe that is prohibited. Don't quote me on this but I think it says so somewhere in the manual. Their primary only purpose is as a scoring platform so you don't need to worry about how mecanums are going to get over the bumps.

In regards to programming mecanums, I can say from experience that it is really easy. Our team has used them for the past 3 years. Both Java and C++ (I can't speak for Labview) have methods for programming a mecanum drive (2 methods in fact, at least in the 2014 library). Just plug in your parameters and that's all there is to it.

Finally, though I didn't agree with my team in the past about a mecanum drive train, this year I can really see the advantages. Because there won't be too much robot-to-robot interaction you won't have to worry about pushing power or traction. Also strafing will be really useful when you need to line up to stack the totes and recycling bins.

nicholsjj 03-01-2015 16:56
Re: 2015: Year of the Mecanum
 
The code in labview is a canned VI. The only problem that I have had to help teams with is many younger teams make the rotation the throttle axis. Most of the time I have them switch to a button switch statement for turning and it works out fine, some still like other axis turning methods and it can be worked through with the Get axis. Our team has decided to use Mecanum since the no defense is in play and we might try to go for the stack in auto. Mecanum will work out nicely for strafing left or right and picking up as long as you use a gyro for drift. The only initial issues we are concerned with is the frame spacing for the totes and going over the scoring platforms. We think 8" HD's will be fine enough to prototype though.

Ether 03-01-2015 17:08
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Jalerre (Post 1420001)
For those talking about driving over the bumps, I do believe that is prohibited.
The game reveal video at 1:13 shows a bot driving over the platform.

jtrv 03-01-2015 18:01
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1420042)
The game reveal video at 1:13 shows a bot driving over the platform.
He might have been talking about the middle platform, but yes, the scoring platforms can be crossed.

Ether 03-01-2015 19:26
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by jtrv (Post 1420095)
He might have been talking about the middle platform
In the given context, that wouldn't make sense.

Also note that the middle is called a step, not a platform.

theCADguy 03-01-2015 19:33
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Jalerre (Post 1420001)
For those talking about driving over the bumps, I do believe that is prohibited.
I believe that you are thinking of the step in the middle. You can traverse the scoring zones, however.

Also, quick question:
Can a mechanum drive be set up where the length of the drive train is greater than the width, or does it require a square wheel configuration?

StephenNutt 03-01-2015 19:36
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by theCADguy (Post 1420219)
Also, quick question:
Can a mechanum drive be set up where the length of the drive train is greater than the width, or does it require a square configuration?
You can set it up with any aspect ratio, square, long or short (within reason)

Kevin Sevcik 03-01-2015 19:37
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by ratdude747 (Post 1419947)
Unless you're talking offseason prototypes, I highly doubt that *cough *
I've been doing this too long and I'm starting to get confused. 2010 and 2011 is what I meant to say there.

who716 03-01-2015 19:42
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by teafreak45 (Post 1419644)
I would agree with you on the drive. While watching the video, I was thinking that would be the most used and best drive train for this year.
not necessarily mecanum but a maneuverable chassis over a power chassie we would rather have a drop center then mecanum

alopex_rex 03-01-2015 19:44
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by TheJoe (Post 1419636)
Could it be possible that mecanum drivetrains are the ideal way to go because of their maneuverability?
We thought the exact same thing, after spending all of our off-season saying "well we're almost certainly doing tank drive, but if the game really wants something else..."

Our only experience with mecanum is with an off-season project, which had trouble going straight, we think because of wonky weight distribution. The programming was easy though: WPILib has a straightforward mecanum-drive function in the DriveTrain class.

lark95 03-01-2015 19:44
Re: 2015: Year of the Mecanum
 
My team is also thinking of using mecnum drive. we even have an old robot from logamotion that used mecnum we are able to drive

Kevin Sevcik 03-01-2015 19:56
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by StephenNutt (Post 1420222)
You can set it up with any aspect ratio, square, long or short (within reason)
However, the farther you get from a square configuration, the more scrub you'll get when turning in place. Also, not square configs mean the wrong mecanum layout will make your robot turn backwards. Heh.

Ether 03-01-2015 20:17
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by alopex_rex (Post 1420234)
Our only experience with mecanum is with an off-season project, which had trouble going straight, we think because of wonky weight distribution.
Weight distribution is only one of many factors which can cause unsatisfactory mecanum performance.

Here are some others:
  • too much roller axial free play

  • too much roller spinning friction

  • wheel alignment (toe-in1, camber1, and axial offset2)

  • excessive gearbox friction (improper assembly and/or lubrication)

  • chain (or belt) too tight or not properly lubricated

  • warped frame

  • frame too rigid

  • motor manufacturing tolerances

  • motor controller calibration

1Toe-in and/or camber of a wheel causes the wheel sprocket (or pulley) to be non-coplanar with the driving sprocket (or pulley), and thus contributes to friction between the chain (or belt) and the sprocket (or pulley). Toe-in also causes scrubbing friction with the floor surface.

2"wheel axial offset" in this context means that the wheel sprocket (or pulley) is axially offset from the plane of the driving sprocket (or pulley), causing the chain (or belt) to be non-coplanar, thus creating additional friction between the chain (or belt) and the sprockets (or pulleys).

Ether 03-01-2015 20:25
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Kevin Sevcik (Post 1420252)
However, the farther you get from a square configuration, the more scrub you'll get when turning in place.
For a mec, the inverse kinematics are the same1 as long as it's rectangular.

1ignoring roller friction, axial free play, and carpet compliance

Jalerre 03-01-2015 22:06
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1420042)
The game reveal video at 1:13 shows a bot driving over the platform.
I didn't see it in the manual anywhere that's just the conclusion that our team had come to. (I didn't try to confirm it I just trusted them)

craigboez 03-01-2015 22:09
Re: 2015: Year of the Mecanum
 
If you have 3 rollers on the carpet and one on the hdpe, does the coefficient of friction come into play? I assume as long as you don't break traction on any of the wheels you can effectively transmit force vectors to the ground?

alopex_rex 03-01-2015 22:13
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1420273)
Weight distribution is only one of many factors which can cause unsatisfactory mecanum performance.

Here are some others:
...
Thanks! This looks very helpful...and is also pretty intimidating, although I imagine a lot of those factors apply to any drive train one might make.

Robo Hamsters 03-01-2015 22:47
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by TheJoe (Post 1419636)
we don't need the large, defensive powerhouse that FRC generally sees.
This is actually our dilemma as our first 2 years we built extremely strong defensive drive bases first and then concentrated on offensive capabilities.

So we are now working on our strategy to switch to an all offensive bot.

Good luck everyone!

oison75 04-01-2015 17:19
Re: 2015: Year of the Mecanum
 
Our team is also considering using a mecanum drive train. We have never used mecanum before, but we firgured we have lots of resources to lean on and using mecanums will be very adventageous. Any suggestions for drive train layout, gearboxes, motors, bearings, etc? Also where're the best places to purchase mecanum wheels, I've only seen the Andy Mark ones and Vex ones... are those good? I'm extremely excited to start playing with a mecanum robot, but an also very nervous since our team is new to mecanum... Any suggestions?

mfalk 04-01-2015 21:40
Re: 2015: Year of the Mecanum
 
We used mecanum on our Rebound Rumble robot and had only slight problems getting on the bridges and that angle was much greater than 16-degrees. My thought is that robot drivers may underestimate their center of gravity when carrying loads up high and attempting to drive over scoring zones.

Mecanum Wheel 05-01-2015 02:48
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by chrisfl (Post 1419813)
It was the same for us. We used mechanum in 2012 and our only problem was staying in one place on the bridge. We had no problem going up and down it while at an angle.
Quote:
Originally Posted by lark95 (Post 1420235)
My team is also thinking of using mecnum drive. we even have an old robot from logamotion that used mecnum we are able to drive
Quote:
Originally Posted by theCADguy (Post 1420219)
Also, quick question:
Can a mechanum drive be set up where the length of the drive train is greater than the width, or does it require a square wheel configuration?
Quote:
Originally Posted by JosephC (Post 1419860)
If you have not prototyped mechanum or done it before, I would not recommend bringing it out this season. It doesn't seem difficult at first, but you will end up spending far too much time on your drive train instead of allocating proper time to your mechanisms.
*mecanum

sasha831 05-01-2015 05:10
Re: 2015: Year of the Mecanum
 
Our team used Mecanum last year with rather positive results, though its didn't feel very smooth to drive as the wheels fight each other, even when going forwards. We were not too impressed with the WPI libraries for Mecanum, we couldn't get them to work effectively, so we actually made our own libraries. If anyone wants to use/consult them, they can be found here:

http://ai-robotics.com.au/code-libraries/

For any help with them PM me, or send an email to the specified adress

yara92 05-01-2015 15:36
Re: 2015: Year of the Mecanum
 
Last Years our team use mecnum.
Can any one tell me why exactly the use of the mecnum this year is comfortable for the game

Herbblood 05-01-2015 16:28
Re: 2015: Year of the Mecanum
 
Does anyone know what happens with Mecanum on the HDPE? Our team worries about the friction or lack of friction we would have.

zachrobo1 05-01-2015 18:28
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by yara92 (Post 1422129)
Last Years our team use mecnum.
Can any one tell me why exactly the use of the mecnum this year is comfortable for the game
In the past, the reasoning behind not many teams using mecs is that they struggle mightily against defense. On open fields like Aerial Assist, a mecanum bot can be pushed around by a 6/8wd bot with ease. Now, with no contact between opposing alliances, there is virtually no defense that can be played. With mecanums being extremely maneuverable and easy to build and program, many teams feel like this is a favorable drivetrain option.

xhantari 05-01-2015 18:42
Re: 2015: Year of the Mecanum
 
An issue we found with the use of mecanum wheels on the scoring platform is the fact that when traveling diagonally over the platform, one or two wheels become elevated off the ground. Therefore, these wheels are not able to contribute to the omnidirectional movement of the robot.

oison75 06-01-2015 00:09
Re: 2015: Year of the Mecanum
 
Also, what gearboxes should you use for mecanum?

mrnoble 06-01-2015 00:18
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by oison75 (Post 1422479)
Also, what gearboxes should you use for mecanum?
We have used AndyMark's NanoTube in the past and it worked great; the gears are internal. I also like the look of Vex Pro's single reduction clamping box.

Whippet 06-01-2015 00:30
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by oison75 (Post 1422479)
Also, what gearboxes should you use for mecanum?
We used a set of AM Toughbox Nanos last year with good success.

Mecanum Wheel 06-01-2015 00:37
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by yara92 (Post 1422129)
Last Years our team use mecnum.
Can any one tell me why exactly the use of the mecnum this year is comfortable for the game
mecanum*

markmcgary 06-01-2015 00:43
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Mecanum Wheel (Post 1422499)
mecanum*
Dude. Really?

Mecanum Wheel 06-01-2015 01:04
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by markmcgary (Post 1422505)
Dude. Really?
Hello Mark. Mecanum is a commonly misspelled word. There are multiple ways to say it but only one way to spell it. If you have any questions, feel free to ask. Until then, you may refer to this handy chart:

markmcgary 06-01-2015 01:17
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Mecanum Wheel (Post 1422518)
Hello Mark. Mecanum is a commonly misspelled word. There are multiple ways to say it but only one way to spell it. If you have any questions, feel free to ask. Until then, you may refer to this handy chart:
Dude. Really?

Mecanum Wheel 06-01-2015 01:30
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by markmcgary (Post 1422523)
Dude. Really?
Hi Mark. I am trying to educate the great people of CD proper mecanum spelling. If I don't, who will? I like to think of myself as the Batman for mecanum spelling.

markmcgary 06-01-2015 01:57
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Mecanum Wheel (Post 1422530)
Hi Mark. I am trying to educate the great people of CD proper mecanum spelling. If I don't, who will? I like to think of myself as the Batman for mecanum spelling.
Holy agility, Batman!

alopex_rex 06-01-2015 10:01
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Mecanum Wheel (Post 1422530)
I am trying to educate the great people of CD proper mecanum spelling. If I don't, who will? I like to think of myself as the Batman for mecanum spelling.
I am kind of obsessive about (my own) spelling myself, so I sympathize with your quixotic quest, but you should probably be aware that people might not appreciate having their spelling corrected, especially if you're not making any other contribution to the discussion. If you're not careful it's easy to come across as mocking or derisive. When someone is trying to contribute to the discussion, and the reply they get is nothing but a correction of their spelling, that's got to be unpleasant.

What really matters is communication, and anything roughly of the form mec(h?)(a?)num is easily recognizable. The spelling is bizarre anyways. If it's important to you to get people to spell it correctly, my recommendation would be to write helpful or interesting responses to other posts, and add "FYI: 'mecanum' is the correct spelling" at the end.

Koko Ed 06-01-2015 10:15
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by alopex_rex (Post 1422636)
I am kind of obsessive about (my own) spelling myself, so I sympathize with your quixotic quest, but you should probably be aware that people might not appreciate having their spelling corrected, especially if you're not making any other contribution to the discussion. If you're not careful it's easy to come across as mocking or derisive. When someone is trying to contribute to the discussion, and the reply they get is nothing but a correction of their spelling, that's got to be unpleasant.
The dude made up an account to correct spelling. Methinks it's a troll.

Whippet 06-01-2015 10:17
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Koko Ed (Post 1422644)
The dude made up an account to correct spelling. Methinks it's a troll.
This is the first troll I've ever seen with a full rep bar.

Mecanum Wheel 06-01-2015 10:23
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by alopex_rex (Post 1422636)
I am kind of obsessive about (my own) spelling myself, so I sympathize with your quixotic quest, but you should probably be aware that people might not appreciate having their spelling corrected, especially if you're not making any other contribution to the discussion. If you're not careful it's easy to come across as mocking or derisive. When someone is trying to contribute to the discussion, and the reply they get is nothing but a correction of their spelling, that's got to be unpleasant.

What really matters is communication, and anything roughly of the form mec(h?)(a?)num is easily recognizable. The spelling is bizarre anyways. If it's important to you to get people to spell it correctly, my recommendation would be to write helpful or interesting responses to other posts, and add "FYI: 'mecanum' is the correct spelling" at the end.
I understand what you're saying. Thank you for the suggestions.

Quote:
Originally Posted by Whippet (Post 1422650)
This is the first troll I've ever seen with a full rep bar.
I can assure you I am not trolling.

Koko Ed 06-01-2015 10:33
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Whippet (Post 1422650)
This is the first troll I've ever seen with a full rep bar.
Robotic geeks appreciate good spelling.

pntbll1313 06-01-2015 10:42
Re: 2015: Year of the Mecanum
 
The spelling bugs a lot of people. here is Andy Baker's take on it

pfreivald 06-01-2015 10:43
Re: 2015: Year of the Mecanum
 
At Championships a few years ago someone cut me off mid-sentence to correct my pronunciation of mecanum....

I looked him in the eyes, dead-pan, and said, "I don't care."

He about lost his head under his little jesterly hat.

Mike Marandola 06-01-2015 10:45
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by pntbll1313 (Post 1422665)
The spelling bugs a lot of people. here is Andy Baker's take on it
I love Lunch With Andy. I watched all of them in a day over the summer. If you see this Andy, please make more.

pntbll1313 06-01-2015 10:50
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Mike Marandola (Post 1422668)
I love Lunch With Andy. I watched all of them in a day over the summer. If you see this Andy, please make more.
Looks like you're in luck. //end thread derailment

alopex_rex 06-01-2015 10:57
Re: 2015: Year of the Mecanum
 
Has anyone done anything with using a gyro to correct mecanum issues? People have mentioned it in this thread but I couldn't find any examples online (all I found were examples of how to use gyros for field-oriented control, which is cool too). It seems like it would be fairly simple to, say, store the current gyro angle whenever you start going straight (i.e. not rotating), and have a PID controller change the "rotate" value to maintain the same angle as long as you're trying not to turn. Has anyone done anything like this?

I don't think "mecanum" even has a correct pronunciation; on our team we say me-CAN-um /məˈkę.nəm/, but I think i've heard MEC-(a)-num /ˈmɛk.(ə.)nəm/, which presumably is where the "mecnum" spelling comes from.

Pollux 06-01-2015 11:48
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1419684)
Has anyone looked at the field drawings yet? In the game video it looks like the platforms aren't that high, and there are ramps all around. How high is the platform, and what is the grade of the ramps?
The platforms are two inches high and the ramps are at 16 degrees, giving robots seven inches horizontally to move two vertically.

Pollux 06-01-2015 11:56
Re: 2015: Year of the Mecanum
 
There's nothing in the manual about not driving over the scoring platforms. In fact, it makes sense that many robots would have to drive on them in order to deposit their payloads.

Tom Line 06-01-2015 12:03
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by alopex_rex (Post 1422680)
Has anyone done anything with using a gyro to correct mecanum issues? People have mentioned it in this thread but I couldn't find any examples online (all I found were examples of how to use gyros for field-oriented control, which is cool too). It seems like it would be fairly simple to, say, store the current gyro angle whenever you start going straight (i.e. not rotating), and have a PID controller change the "rotate" value to maintain the same angle as long as you're trying not to turn. Has anyone done anything like this?

I don't think "mecanum" even has a correct pronunciation; on our team we say me-CAN-um /məˈkę.nəm/, but I think i've heard MEC-(a)-num /ˈmɛk.(ə.)nəm/, which presumably is where the "mecnum" spelling comes from.
Absolutely. It's not terribly complicated either. After all your meCHanum motor set speeds are calculated, mix in a component from the gyro useing a PID. Only do this when the driver is using the strafe functions. Disable it when he is turning.

Easy Peasy.

hrench 06-01-2015 12:29
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by alicen (Post 1419686)
Whenever we did mecanums, we always had suspension on each wheel so that all wheels were always in contact with the floor. They even went over the humps in Breakaway just fine!
We did mecanums for logo motion with a flat-floor and they worked fine, but for rebound rumble, trying to climb the 'bridge' in the middle they were really problematic, even with suspension.

Remember that with mecanums, the left wheel is always pushing against the right wheel to make it go straight. So if one wheel gets off of the ground, your robot turns by itself.

Methinks that with a stack of totes on a forklift, the back-two wheels will be bumping off the ground regularly, and if you try to cross a platform at any kind of angle other than 90, you'll lift a wheel.

Last year I saw four wheel mecanums in the IAM14U frame, and maybe more often in 'butterfly' and 'octanum' drives. That that was acompletely flat floor. My recommendation is that if your heart is set on mecanums, use a butterfly or octo so you can put regular wheels on the floor when you need to. Also, note, the new frames are much more stiff than the old channel sections ones, so you'll need to do Something to keep those wheels on the ground. Something like independent suspension.

Mecanums work really well with Banebot transmissions too.

Last thing. Mecanums running over a noodle a problem? I think so . You tell me?

Ether 06-01-2015 18:49
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Tom Line (Post 1422726)
After all your meCHanum motor set speeds are calculated, mix in a component from the gyro useing a PID.
My interpretation of the above is:
1) calculate the 4 motor speeds using the X and Y translation commands

2) calculate the motor speeds for rotation using the output from a PID

3) add the the corresponding speeds from (1) and (2).
Wouldn't it be more straightforward to compute the 4 motors speeds just once directly from the X, Y, and rotation commands?


BTW, what's the significance of the CH in caps?


alopex_rex 06-01-2015 21:09
Re: 2015: Year of the Mecanum
 
What I was thinking was a way of dealing with imperfect results from mecanum, i.e., if simply using WPILib's mecanum drive function results in the robot turning when it's supposed to be straight strafing. When the driver is trying not to rotate (the "rotate" value would be zero), store the current gyro heading. Then have a PID controller that tries to maintain that gyro heading, by setting the "rotate" argument for the function. So the PID would find the value that counteracts any undesired rotation caused by mechanical issues.

Ben Wolsieffer 06-01-2015 21:11
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by alopex_rex (Post 1423237)
What I was thinking was a way of dealing with imperfect results from mecanum, i.e., if simply using WPILib's mecanum drive function results in the robot turning when it's supposed to be straight strafing. When the driver is trying not to rotate (the "rotate" value would be zero), store the current gyro heading. Then have a PID controller that tries to maintain that gyro heading, by setting the "rotate" argument for the function. So the PID would find the value that counteracts any undesired rotation caused by mechanical issues.
This is exactly what we did in the past for our mecanum drive, and it worked wonderfully. We didn't have to obsess nearly as much about perfect weight distribution.

Ether 06-01-2015 21:35
Re: 2015: Year of the Mecanum
 
1 Attachment(s)
Quote:
Originally Posted by alopex_rex (Post 1423237)
What I was thinking was a way of dealing with imperfect results from mecanum, i.e., if simply using WPILib's mecanum drive function results in the robot turning when it's supposed to be straight strafing. When the driver is trying not to rotate (the "rotate" value would be zero), store the current gyro heading. Then have a PID controller that tries to maintain that gyro heading, by setting the "rotate" argument for the function. So the PID would find the value that counteracts any undesired rotation caused by mechanical issues.
See attachment

alopex_rex 06-01-2015 21:42
Re: 2015: Year of the Mecanum
 
Nice chart--That's exactly what I was trying to describe!

Aedan Hawke 06-01-2015 21:43
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Bruceb (Post 1419858)
never used macanums before but really considering it this year. what is the prefered gearbox for these?
We've used mechanums for the last couple of years with success. Last year we made our own gearboxes and built them into our chassis. They worked exceptionally well but, obviously, were a huge drain on time. Other years we used Andymark ToughBoxes and those worked well for us. I'd recommend them unless you'd like the challenge of the custom gearboxes.

forbes 06-01-2015 21:47
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1423251)
See attachment
Thanks, that diagram is helpful.

Mecanum Wheel 06-01-2015 21:59
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Aedan Hawke (Post 1423259)
We've used mechanums for the last couple of years with success. Last year we made our own gearboxes and built them into our chassis. They worked exceptionally well but, obviously, were a huge drain on time. Other years we used Andymark ToughBoxes and those worked well for us. I'd recommend them unless you'd like the challenge of the custom gearboxes.
Hi Aedan. Just for future reference, it's spelled mecanum. It's an easy mistake to make.

Is anyone using 6 inch mecanum wheels with CIMple boxes? We will be and are going for ~11 ft./s.

dawonn 07-01-2015 00:41
Re: 2015: Year of the Mecanum
 
I think we may also going the CIMple Box route with the 6" standard Andymark mecanum wheels, with HTD belts geared for 12.5 fps.

In the past I have used a gyro just as stated above to keep the robot driving straight. It worked so well that we had a motor come disconnected and didn't notice for a few hours. :)

Saberbot 08-01-2015 13:28
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1423251)
See attachment
Wouldn't another option be to treat the feedback loop as the "rate controller" for the yaw axis? The rotation command from the joystick would be sent to the yaw controller. If it the command is zero then it will work as described in the attachment. If the command is greater than zero, then the controller will allow for more predictable rates of rotation based on the joystick command.

I believe this is how yaw control is managed on most RC Multicopters.

Ether 08-01-2015 14:16
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Saberbot (Post 1424347)
Wouldn't another option be to treat the feedback loop as the "rate controller" for the yaw axis? The rotation command from the joystick would be sent to the yaw controller. If it the command is zero then it will work as described in the attachment.
What you've described1 would work; but if you're trying to hold position, it's best to close the loop on position, not velocity.


1 ... http://www.chiefdelphi.com/media/papers/download/2796 ...... http://www.chiefdelphi.com/media/papers/2390

Saberbot 08-01-2015 14:28
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Ether (Post 1424372)
What you've described1 would work; but if you're trying to hold position, it's best to close the loop on position, not velocity.


1 ... http://www.chiefdelphi.com/media/papers/download/2796 ...... http://www.chiefdelphi.com/media/papers/2390
That makes sense. Thank you for creating these great resources.

holygrail 08-01-2015 15:24
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by hrench (Post 1422738)
Last thing. Mecanums running over a noodle a problem? I think so . You tell me?
We have 6" VexPro mecanums on our 2013 robot and we drove it over several noodles with no problem. There is a bit of bumpiness when you go over, so you might want to either stabilize the stack or just drive around the noodles when loaded, but that is true with any wheels unless you have suspension of some sort.

GeeTwo 08-01-2015 15:45
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Mecanum Wheel (Post 1423270)
Hi Aedan. Just for future reference, it's spelled mecanum. It's an easy mistake to make.

Is anyone using 6 inch mecanum wheels with CIMple boxes? We will be and are going for ~11 ft./s.
That sounds way too fast! A CIMple box has a gear ratio of 4.67:1 (14:3) which is an "80%" speed of 5310 rpm * 2 * pi radians/rev / 60 sec/min * 3 / 14 * 3 in / 12 in/ft * 0.8 = 29.8 fps! Get some 2-stage gearboxes!

If you want to calculate a gear ratio, a CIM-driven robot with an 80% efficient drive train, 1:1 gearbox and a 1" diameter wheel would go 18.5 fps (if it were on some sort of weird rail that let this happen, or it were an offset gearbox). Multiply by your diameter in inches and divide by the gearbox ratio to get your 80% speed. To calculate a gearbox ratio, multiply by your diameter in inches and divide by the desired speed. In your case, that would be 18.5 * 6 / 11 = 10.1:1. As you seem to be shopping at AndyMark (and so do we), the 10.7:1 TB Mini looks like a good option.

Mecanum Wheel 08-01-2015 15:48
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by GeeTwo (Post 1424424)
That sounds way too fast! A CIMple box has a gear ratio of 4.67:1 (14:3) which is an "80%" speed of 5310 rpm * 2 * pi radians/rev / 60 sec/min * 3 / 14 * 3 in / 12 in/ft * 0.8 = 29.8 fps! Get some 2-stage gearboxes!
We will be using sprocket reductions.

idahorobot 12-01-2015 17:33
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by Tom Line (Post 1422726)
Absolutely. It's not terribly complicated either. After all your meCHanum motor set speeds are calculated, mix in a component from the gyro useing a PID. Only do this when the driver is using the strafe functions. Disable it when he is turning.

Easy Peasy.
Can we use the gyro on the RoboRio? OR I should say how well will the gyro work on the RoboRio?

alopex_rex 12-01-2015 21:22
Re: 2015: Year of the Mecanum
 
Quote:
Originally Posted by idahorobot (Post 1426972)
Can we use the gyro on the RoboRio? OR I should say how well will the gyro work on the RoboRio?
IIRC the RoboRio doesn't have a built-in gyro, only an accelerometer.

idahorobot 12-01-2015 22:21
Re: 2015: Year of the Mecanum
 
Oops Thanks


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