Drive Systems
 

I've been noticing the many different styles of drive systems, such as tank, mecanum, H-drive, and swerve. I was wondering what other people have seen and built for there robots.

Re: Drive Systems
 

Tank is the basic and, in my opinion, the best drive for most teams. It is simple and effective. I believe that even in RR tank is superior. This is most often a 6 wheel, dropped center. Sometimes you will see an 8 wheel dropped center. It provides the best traction so you get pushing power and acceleration.
The main disadvantage of tank is the inability to move sideways.

Mecanum is often used to move sideways. I am not a programmer, but from what I understand it requires rather complex programming. When done well, it is easy to use, but can be easily messed up. It provides poor tration and is easily pushed around.

H drive uses omni wheels mounted perpendicular to each other. Omni wheels hame small rollers that allow them to slide sideways, so there is a set of wheels for each direction. It has the same low traction as mecanum.

Swerve is often considered the best overall drive. It has great traction and has sideways/diagonal/any direction movement. Each wheel is mounted on a pivot so it turns beneath the bot. These are very difficult to build but are very versatile.

One of the most interesting drives I have driven is one developed by team 967. This 9 wheel drive used an 8 wheel dropped center base, with one wheel mounted perpendicular and on a piston. When the piston is activated the wheel is forced down and the back end of the bot lifts off the ground, so it is supported by the two front wheels and the 9th wheel in the center of the bot. This allows great traction in regular tank mode and the ability to move sideways. I believe in 2014 Team Titanium utilized this concept in their drive base.

What else is out there?

Re: Drive Systems
 

1114 is using kiwi drive this year. Three omnis set in a triangle.

Re: Drive Systems
 

lots of incorrect and exaggerated information in here. since the OP wasn't asking about each drive and rather what is out there, I won't turn this into thread 8,398 like this.

There were a few Killough (4 wheel omni). Here's one

At least one octocanum.

And don't forget the... kiwi swerve? not sure what overclocked is calling this.

Re: Drive Systems
 

Team 1923 built a custom drivetrain this year that incorporates some of the best qualities of different variations of tank drive. It is constructed with C-channel like a standard tank drive, but similarly to a WCD one wheel on each side is direct driven by the gearbox allowing for us to drive to some extent even if all the chains fail. Additionally to prevent damage to the chain we run all the chain within the c-channel. The drivetrain has 5 wheels on each side (3 colsons in the center and 2 omnis out at the ends). It does not use a drop center but rather relies on the omnis out at the ends to facilitate turning with minimal scrub. We chose to use 5 wheels on each side so that we could use 4" wheels and still maintain complete control while crossing over and driving on the scoring platform.

Because we lack extensive machining resources we designed this drivetrain to be built using only a drill press and a band saw through extensive usage of VexPro VersaFrame.

Re: Drive Systems
 

Here is what we call the HI Drop Drive.

The pneumatic actuated center wheels allow us enough clearance to drive over the bump and will center the robot while driving the length for ease of scoring..

Depending on how you look at it, it is either an "H" or "I", since we are from Hawaii we went with it..

This is an early picture of the system.
http://www.chiefdelphi.com/media/img...4205589a_l.jpg

More to come as the media team gets it to me..:yikes:

Good luck to everyone.

Aloha!

We did something similar on our drive this year as well.
Attachment 18572

Re: Drive Systems
 

Do those center wheels scrub a lot when you rotate?

Nope look at the pic closer... Air cylinders lift them off the floor. We weren't sure how it would work during competition, but got us to finals last weekend in Waterbury.

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We did Omni H with center suspension (Early pic while figuring suspension..which makes a huge difference took us 4 weeks to figure it out)

https://fbcdn-sphotos-a-a.akamaihd.n...a0e94dd5d6f547

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It's just a 3 wheel swerve. There've been a lot of them. (67 - 05, 148 - 08, 16 - Many years)

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I saw some hexagonal robots last year (mainly vacumn bots for some reason). Those were interesting to say the least. My favourite drive this year so far is 1114's kiwi/crab drive.

Re: Drive Systems
 

Hey! Don't forget us. Don't have a video of it on the actual bot, just the drive train for now.

Re: Drive Systems
 

We've used a 6WD and a 4WD successfully in my time. The year before I joined they made a robot with an 8WD and 8020, which still runs today.
Over the summer we may experiment with swerve drives if we get the necessary manufacturing resources to make a good one.

Re: Drive Systems
 

I put together a lesson on drive systems for our (boreal) summer 2014 "robocamp". Trying to classify drives, I came up with something like:

• Skid-steer/tank (2n+4 wheels, drop center when n>0, optional shifter)
• Linkage drives
  • Two-wheel steering (automotive style, rarely if ever seen in FRC, but I wanted to cover it in the camp if only to explain why it is rarely used.)
  • Crab drive (all wheels drive same direction and speed)
  • X drive (I made up this name, but it has 4 wheels, left-rear and right-front rotate together and mirror left-front and right-rear)
  • Fire truck steering (independent 2-wheel steering on front and rear wheels, again rarely used)
• Holonomic wheel drives (I focused here on the wheels with rollers, not whether it was truly holonomic)
  • Omni tank (a 4-wheel skid steer with omni wheels)
  • H-drive (omni tank plus a transverse-mounted strafe wheel)
  • Killough (that is 4 omni wheels in a diamond configuration, not Killough's drive)
  • Mecanum
  • Kiwi (3 omni wheels whose axle lines cross at the CoG, a lot closer to Killough's drive)
• Swerve drives (I described 3 and 4 wheel setups, and explained that other configurations were possible)
• Articulated drives
  • Holonomic wheel hybrids
    • Octanum (includes butterfly and grasshopper)
    • Nonanum
  • Crab/lobster (dual skid/steer - alternate drive is transverse to main drive)
  • Articulated shifter (different size wheels or gear ratios on different drive wheels)
  • Ladder drive (as shown above, though I did not include it this past summer, but will add this year)

I did not include a monobot, or what I've personally called a "dizzy drive" (crab with a big steerable lazy susan for the "upper robot"). I'm sure there are other possibilities.

Re: Drive Systems
 

We have a WCD with 6" (well, really 6.25") grippy wheels in the middle and 6"omnis at the front and back. The center axis is a little higher than the others so all six wheels touch the ground. It's working very well for us with no trouble getting over the scoring platform, even though the center wheels come off the ground. All three wheels are belted together on each side.

Our driver came up with a unique set of controls. We use an xbox controller. The left stick is solely for forward/backward and the right stick is solely for turns. We read both sticks and feed them into an ArcadeDrive method. Driving straight is very easy because if he lets go of the right stick and pushes the left stick forward, even if the stick is off a little to one side, we read the "y" value only from the y axis of the left stick and the x axis is 0 since there's no force on the right stick.

We developed an algorithm to "slide" the robot left or right. Basically, you use the TankDrive method to move only one side of the drive train back a bit then move only the other side the same amount. Then move forward a small amount and your are exactly one inch left or right from where you started. We attached this to two buttons (one left and one right). It interrupts the Drive command, but give control back when the slide is complete.

We worked out the trigonometry based on wheel diameter, robot width and distance you want to "slide". We had hoped to compute the required distance using vision processing but we didn't get that far. For now we just go one inch at a time.

Re: Drive Systems
 

Just FYI, this is known as a split arcade drive. Our team is also using it this year, and I can attest that it works well.

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That tank drive "slide" concept is intriguing, especially in more of a precision-driven game. What level of effectiveness have you seen with it, and how far back and forward does your robot have to move in order to achieve this slide?

Re: Drive Systems
 

My college club, Bison Robotics, at NDSU is looking to build a drive system for demonstration purposes. The idea would be to build the drivetrain, film and document our process, and put everything out on social media for others to use as a resource. We also plan on create a highly detailed Bill of Materials and assembly instructions for this drivetrain in order to make it more accessible to lower resource teams.

The idea is to build a unique/original system that can compete with swerve in terms of maneuverability and power. We are not trying to cater to low resource teams in a sense that the drive is simple: there can be a high degree complexity. Basically I'm looking for links or pictures of some of the more obscure drivetrain ideas out there.

Here is a list of drive systems which I am already familiar with:

• tank
• mecanum
• slide
• kiwi
• swerve
• butterfly
• grasshopper

Edit: I forgot octocanum and nonadrive

Are there any other systems I am missing? Thanks in advance for the help!

Re: Drive Systems
 

6WD Mecanum. (4 mecanums, 2 omnis, arranged like a 6WD). 1322 did that about 4 years ago I think (might have been more or less).

Re: Drive Systems
 

My team typically uses mecanum, and we are starting an off-season drivetrain. We understand most but can't see / make sense of some of the omni based drivetrains.

http://www.vexrobotics.com/vexpro/examples-guides

What are the pros and cons of this 2+2 drivetrain? Why only go two omnis vs 4? I could imagine some scrub reduction, but why not all 4 wheels? And if you are using 4 independent gearboxes, why couple each side with belts/chains? Are they trying to mechanically couple and equalize wheel speed per side?

Then we were looking at 1114's 2014 robot, and it looks like 4 wheel traction, but two wheels have butterfly like modules where you can drop omnis on one side (not sure if it was the front or back). Similar to the above, is temporarily reducing scrub important enough to add that weight?

Are we missing some understanding from these designs?

Re: Drive Systems
 

Let's start with "why not 4 omnis?". Answer: Sideways motion. You are trying to line up to do X, I hit you from the side. Chances are, you're nowhere near lined up now. So by retaining 2 tractions, you get less sideways motion (you're more likely to rotate than slide) and easier realignment. That being said, 4 omnis is a valid drivetrain, IFF you know what you're doing.

Next up, why couple? The Department of Redundancy Department just called, and said they give this design their approving seal of approval. In case of loss of power in one gearbox, you still get power on all 4 wheels, in addition to speed match.

And the last part, er, first part: The rotation center is different. Scrub reduction is a major item, too--4 high-traction wheels in a long configuration, all driven, will bounce 130 lbs of robot around when the robot tries to turn, in most cases. So by using omnis on one end, you get smoother turning, but you also get a very predictable center of rotation...which, as it turns out, can be quite useful in a "precision" game like Recycle Rush.

Re: Drive Systems
 

Thanks!

Has anyone seen any before/after video of 4W or WCD with and without omnis to show those differences?

Re: Drive Systems
 

There are a few pros to having two traction wheels in a setup like this. The biggest thing is that you retain some amount of tractive force for pushing matches - while omni wheels have some forward traction, most traction wheels have more, so you'll still be able to push with a 2+2 setup. The second is that your turning center is usually directly between the two traction wheels. There is, theoretically, *no* scrub in a 2+2 wheel drivetrain, because the omni wheels are the only wheels sliding laterally at all. The traction wheels become the point of rotation for the system.

The pros to belting the two gearboxes together on each side have less to do with speed and more to do with motor load. It's most obviously useful in a pushing match, but any time that your CG isn't perfectly centered it provides some benefit. Consider the extreme case where you're trying to push a robot, but your omni wheels leave the ground. This means your traction wheels can only push with 2 CIMs of mechanical power. If the wheels are belted together, you get the force of all 4 CIMs on those wheels. This same principle applies when all four wheels are touching the ground, but the force on each wheel is not even, such as when the CG of the robot is closer to one set of wheels than the other set. Essentially it lets the mechanical power of each motor go to where its most needed. It also gives the drivetrain a little redundancy, but that's not really why it's done in most cases.

It's a six wheel traction drive, with dropped center wheels. The drive behaves as a 4WD effectively, as the dropped center wheel raises one end of the robot slightly, but with a short enough wheelbase that the robot can still turn on a dime.

The reason for the drop down omni wheels (which I believe are unpowered) is not quite obvious, but it has to do with the mechanics of a high traction drive in a pushing match between two robots with compressible bumpers and rough fabric. This may sound like an extremely specific edge case, and it is very specific to FRC, but it's a real issue. You can T-bone pin a 6WD robot by pushing it hard on the center of its long side. The combination of the direction of pushing force, the two robot bumpers compressing into each other, and the friction caused by the compressed bumpers will result in the defended robot being virtually unable to escape. The drop down omni wheels change the center of rotation for the robot from the center to an extreme end, as the robot temporarily becomes 2 traction 2 omni, and the robot is able to spin free without pushing into the compressed bumper. Or, more likely, the T-bone robot continues to push as the module goes down, spinning 1114's robot out of the pin for them.

Re: Drive Systems
 

I have been using the term tumbleweed drive for this. I can't remember if I found it online or if it was use by a team member.

Re: Drive Systems
 

Replying to #18:

It's a function of the distance between the drive wheels. For this year, we have 24.5" between the drive wheels. To slide 1" we have to drive each side back a little over 7" and then drive forward a little less than 7".

Details are attached.

Re: Drive Systems
 

Of course, we've done this manually, but haven't automated it -- yet.

Thinking about some tweaks to the system:

For small amounts of slide, the amount of forward/reverse motion scales as the square root of the slide distance (and therefore time), so it should be beneficial to work out how far you're going before you start.

Also, you can slide twice as far with a 1/3 increase in time, by doing L- R- L+ R+ to go right, or R- L- R+ L+ to go left. This technique would also allow all of the distances to be equal, simplifying coding.

Re: Drive Systems
 

148, 2008, was officially known as "Tumbleweed", and was a 3-wheel swerve.

Re: Drive Systems
 

Ahh. I still like the name.

Re: Drive Systems
 

We use 8 wheel all omni arcade drive.