User Interface - Drivetrain Controls

[Siri]

Originally Posted by eagle33199

We've traditionally had the programming team implement several of the above options and let the drivers try each one out. They're usually able to tell us pretty quickly what they like and don't like.

I'm glad this works for you, it's our goal as well. We have somewhat limited programming resources (i.e. returning people) currently, so I'm trying to narrow down the options we ask for. We definitely want the drivers to try the promising UIs in person, though. (I was a driver throughout my student membership, I don't underestimate the importance of this.) Thanks for the on board OI switch idea. I foresee that saving a lot of time!

Too many options: I completely agree. Part of what we're trying to figure out here is how to limit our DoFs. We certainly don't need them all.

Originally Posted by Ether

...On a flat surface, your drive cannot perform any vehicle motions that the mecanum or omni cannot. All three vehicles have the same three degrees of freedom: 2 translational and one rotational. So the driver presentation is the same...

In general, our DoFs are the same. Independent-turn pivot does allow X & Y-bias snake drive, which (as far as I know), one can't do in mecanum or omni. In a sense, we also actually have more than one rotational DoF, because we can select the centerpoints of our twists. I haven't tried the math for mecanum concerning this, so I'm not sure how complicated/possible varying the CP would be on that platform. (Independently driven omni would seem to allow for this as well, but again I haven't tried.)

As far as holonomic control strategy though, that's exactly what this thread is for. We've talked to a few teams in person and received some helpful information. Many have tended to go the Halo route though, so I'm asking to see if people have other strategies. When we do figure out a successful theory, I fully intend to share it.

Maximum traction: That was one of our main reasons for trying pivot this year. It's definitely (albeit unsurprisingly) worked. We can push most standard tank drives off-axis for the same reason. Some we can push head-to-head as well, but that's more power transmission design than holonomics and transverse vs inline frictional coefficients.

Algorithms: Yes, much more complicated. It's an interesting learning curve, but we're getting there. Nonadrive definitely has its benefits, though (albeit not just in control theory).

Originally Posted by JesseK

In my general opinion, the driver him/herself should give opinions on what's best for control based upon experience. Our 2009 driver of an independent linkage drive train (like crab, but with 4 independent pods that have only 2 physical states of rotation 90 degrees apart and driven by pneumatics) wanted 8 'states' created so he could dynamically manipulate the center of rotation relative to the trailer. Some of the states were more effective than others.

Thanks for the example! This type of constraining is exactly what we're going for; I think we've just overwhelmed our driver to the point where isolating the best case is rather difficult. We're continuing to work on it, and examples are very helpful in that, thanks.

Two hands: This makes sense. We're actually doing one version of this currently: rotational+crab on one of the analog sticks and longitudinal snake on the other. It doesn't work so well for us, but perhaps a different combination.

Demos: We currently have a few different drive versions for demos/competitions, including one that disables everything except the kicker (great for young kids--highly recommend it). Never considered controlling maximum speed for the demos/pit. Smart, thanks.

Decent 2: I read the Wikipedia navigation section for the original Decent. Interesting. (Ambiguous and a little worrisome, but interesting.) Care to give me a hint, or do I need to go track down a game first released in '96?


Kamocat: 3D mice are indeed awesome. We've used them in graphical representations for higher-level calculus, and they work fantastically. Has any FRC team done this, though? The vertical axis would prove interesting in robot control, and accommodating snake is still not entirely straight-forward. Certainly a creative idea. Given our team's resources, though I'm personally not quite ready to spring for an $80 mouse that my driver's never used and my programmers have never programmed, to be used in a dynamic live action environment I've never seen it applied to. Now if I could wrangle a donation...

[Ether]

Originally Posted by Siri

Independent-turn pivot does allow X & Y-bias snake drive, which (as far as I know), one can't do in mecanum or omni.

A rigid vehicle operating on a flat surface has a maximum of only 3 degrees of freedom: 2 translational and 1 rotational. Any possible motion of the vehicle (on the flat surface) can be accomplished by the appropriate combination of these three degrees of freedom. Any motion your drive can do (on a flat surface) can also be done with a mecanum or omni vehicle.

For example, if you want the vehicle to revolve around a central point while at the same time rotating about its own axis (like the Moon around the Earth), that motion can be specified in terms of the 3 degrees of freedom mentioned above, and the mecanum, omni, and your drive can do it.

Or, if you want the vehicle to spin its back end around and pivot around a point located between the front wheels, a mecanum or omni can do that as well (again, as a combination of the 2 translational and 1 rotational degrees of freedom of the vehicle).

Or if you want the vehicle to go forward in a straight line while simultaneously spinning around its center, a mecanum or omni can do that too. (Although it would require a very talented and dextrous driver to do so!)

Any conceivable vehicle motion on the flat surface can be accomplished by the proper (time-varying) instantaneous wheel speeds (and angles). As long as the drive motors have the necessary dynamic response to create the necessary time-varying wheel speeds (and angles), the desired vehicle motion can be accomplished.

The "inverse kinematic problem" is to determine, given a desired instantaneous vehicle motion, what each of the four wheel speeds should be (in the case of mecanum or omni), or what each of the four wheel speeds plus wheel angles should be (in the case of your drive), to achieve the desired instantaneous vehicle motion.

The "forward kinematic problem" is to determine what vehicle motion will result from an arbitrary choice of wheel speeds (and angles). In general, this has no solution. Only properly coordinated sets of speeds (and angles) will result in vehicle motion without "scrubbing" the wheels on the floor.

Considering the above, the way to give your driver "complete manual control" is to allow them to independently command forward/reverse, strafe left/right, and spin CW/CCW. All possible motions of the vehicle can be accomplished by these three degrees of freedom. But, this may NOT be the best "driver presentation", depending on what types of motion the driver wants to do, because it may be too difficult for the driver to think that fast. For example, as mentioned above a mecanum or omni vehicle is mechanically capable of going in a straight line while simultaneously spinning, but I highly doubt a driver could do it without computer assistance. If a competition required this type of motion, you would want to provide a gyro and/or accelerometer or whatever on the vehicle so that the driver commands could be interpreted as field-oriented commands and then translated on-the-fly by the cRIO into the correct wheel speeds (and angles).

There's an excellent text which discusses this (cf especially Chapter 3) if you want to research it further:

Mechanics of Robotic Manipulation
Mason, Matthew T.
Cambridge, Mass. : MIT Press, c2001

~

[Jon Stratis]

Originally Posted by Siri

Decent 2: I read the Wikipedia navigation section for the original Decent. Interesting. (Ambiguous and a little worrisome, but interesting.) Care to give me a hint, or do I need to go track down a game first released in '96?

And that statement makes me feel old. Really old. I'm using Dosbox to run a ton of games from that era and older (MOO, MOOII, Descent, Descent II, Lost Vikings, to name a few...) on my laptop. Mostly I only play them when traveling (it's a nice way to kill a few hours on an airplane!)... but it's sad to know that i don't have to "track down" any classic computer game - just go pull it off the top shelf where I've archived it all...

That being said, if you're going to try tracking it down in order to experience it... be careful. There are a ton of sites out there that allow free downloads of games from that era, classifying them as "abandonware", making you think it's ok... but for a vast majority of those titles, someone still holds the copyright and downloading it from those sites is copyright infringement, just like downloading music or movies illegally. The game is only abandoned in the sense that the company doesn't support it anymore.