At the moment I have researched the Omni H drive and each drivetrain option and upgrade on Andymark. VEXPro seems to only have FTC drivetrains and I would like to know about any other drivetrains you have built, (CADs and pics would be great along with drivetrain bill of materials) I would also like to know what is an H drive, examples of and some you may have built along with the Drop Center 6? I’m trying to put together a list of goals for next years team captain so that these goals can hopefully improve next years game and build season. Thanks!
This is the general idea of a H drive. Basically a wheel is placed in the center perpendicular to the rest of the omnis and you can drive that wheel to make the robot drive sideways.
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I will add a shameless plug here for a resource that I have iterated on with a few others for a couple of years now. This was a presentation at 125’s “University Day” last year. This will go over the drivetrain archetypes from a high level and some of the factors that are involved in a drivetrain. The video of the presentation/questions is here:
And the presentation itself can be found here on The Compass Alliance (which is worth checking out in full to explore team and robot resources)
Hopefully this helps to target your search and figure out what is best for your team to pursue - your drivetrain is the MOST IMPORTANT system on your robot.
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118 has been extremely successful with time of cycles using H drive this year! Strafing has made curves barry easy for them to execute fast cycle times, because of no speed reduction ever.
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Well isn’t 118 technically using a rocker drivebase which is different from a traditional h drive?
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Side Note about Rocker Wheels: The “rocker drive” is something the Robowranglers first had on our 2014 robot which several other teams have also used with great success since then. In this style design, two wheels pivot about a central axis such that when they are “flat” neither one touches the ground. The way the wheel module is constructed, when the motor spins the wheels it naturally tilts the module such that one wheel or the other touches the ground. The wheel which touches the ground will “dig in” and actually transfer the weight of the robot onto that wheel. (If the motor spins the other way, it tilts the wheels the other direction and that wheel will “dig in”).
This sounds a heck of a lot more complicated than it really is… it works like magic in real life. I’ve never seen anything else like it and it may actually be one of the few truly “original” ideas I’ve ever been a part of. In fact, I think it may be the single coolest thing I’ve ever designed.
From here.
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Look at 148’s X019 CAD. Other recent high profile H-drive include 987 from last year (I don’t know if they release CAD) and 118 from this year (they usually release CAD at the end of the year).
I’ve been meaning to ask about the rocker-H drive, if anyone is familiar with it. It’s unclear to me from the CAD how the central module rotates around its axis so that the wheels dig in the ground. It seems like it’s just free spinning.
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My personal favorite DT is kiwi. Not always practical for FRC and the programming is a bit weird, but it’s very unique.
This is a picture of my team’s 2002 kiwi drive and how we got around the programming. If you wanna go for style points, this is the DT to use otherwise, I wouldn’t recommend it.
It’s free
Sideways bad ;((((((((
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Sideways good
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After our success with swerve this year, I have to agree.
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You’re right - it is! Isn’t that cool?
The module uses the inertia of the system to rock one way or the other the instant the motor turns on, then reaction forces against the floor do the rest.
Don’t believe me? Grab a drill, and while holding it loosely (as though it were a rocker module), slam the trigger on and off. Did you feel it jump in your hand? That inertia is what the design uses to its advantage to get the wheel to dig in.
Once it’s dug in, reaction forces from the floor take care of the rest. Try drawing the forces while one wheel is already dug in.
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Thanks. That’s what felt intuitively right (I recall feeling motors “jump” in my hand when turned on), but your explanation helped me understand the physics a little better.
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Sideways bad
If you can go sideways voluntarily, you can be forced sideways. That’s bad
Sideways good, but only a certain kind of sideways. If you maintain traction in any direction, you can fight someone as they try to push you sideways.
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Going sideways doesn’t really grant you much of an advantage over tank drive. Alignment with a tank drive isn’t hard. However, going sideways makes playing defense or resisting defense exponentially harder.
You are right tho. Butterfly drives and other jumpdrive-style dt’s are able to be “The best of both worlds” and have traction as well as sideways driving, but they’re so much heavier than normal tank drives, as well as being motor hogs, which makes them not worth it in my opinion.
From a team that did a swerve drive this year I’d be inclined to disagree. Both playing and resisting defense were much easier as we had a lot more options on how to get in people’s way or evade them. However, we still had the ability to try and push tank drives if necessary. We could usually go toe-to-toe with a KoP chassis but anyone with a shifter became much harder.
Guess it is a motor hog as you said (8 motors drivetrain).
Our team has been using WCD since 2014 and we’ve liked it quite a bit. Through 2017 we’ve had basically annual drive problems, having to fix the drive at more or less every competition, but in 2018 we switched to VexPro 3 CIM Ball Shifter gearboxes and have had no drive issues since. We’re even using the exact same gearboxes this year as we used in 2018 (after disassembling prior to kickoff, of course) and they still have had no issues. If this is still an early year for you investigating drivetrains other than the kitbot, I would recommend going for a WCD and would particularly recommend these gearboxes if you would like to experiment with two speed drives. We’ve also found that going for 2+4 instead of the standard WCD layout works well both for better controls/driving as well as allowing you to get rid of the center drop wobble, which is helpful for tall robots. Our team also wrote the Drivetrain Characterization whitepaper and would be happy to help you with any drive controls problems you may come up with.
This is where I’m going to plug my drivetrain generator (which only works with Inventor) where you can easily configure the drive CAD. We built our drive this year using this generator and it’s worked very well, though you may have to make some adjustments to the design if you want to use bearing blocks for whatever reason. I would recommend using bearing blocks if you don’t have a CNC, and some teams that do have a CNC still use them.
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