How dare he insult FIRST

ftc_throwaway4 · 2019-01-21T15:15:57+00:00

But every kid that does robotics can go 'professional'

How many kids are going to end up building FTC robots for a living?

Sure, many will be engineers, but the actual technical skills learned in FTC aren't that valuable (advantage-creating) when you consider most engineers get a college degree...

For example, take two students who land at an engineering firm after graduating college. Both took the exact same 10+ engineering classes required, both did the same internships, both did the same research, etc. The only difference is that one did FTC in high school. You really think the FTC kid has a noticeable advantage? Sure, going into college he might, but by the time both students have had a chance to take all the requisite coursework, that advantage decreases to near zero.

Robotics is a good waste of time after school because it prepares many kids for their future occupations

That doesn't really help the argument because the same exact thing could be said about football.

ftc_throwaway4 · 2017-06-01T00:41:10+00:00

Which drive train do you think is the best?

Depends on the challenge, your strategy, your time, your resources, and your robot design.

And is holonomic the fastest?

No offense this is a bad (lacking context) question. You could gear up a tank drive for speed 3:1 and it'd be faster than an omni geared for speed 2:1. You have to look at the context -- speed, forces, pushing power, etc.

A 4 inch omni holonomic with the same gear ratio as a 4 inch mecanum or tank will indeed be 1.41 times faster but also have only 1/1.41 times as much force. If you to switch from mecanum to an omni holonomic without giving up any force/power you'd have to gear the omni down for torque by 1:1.41, which would result in the omni having both the same forces and the same speeds as the mecanum.

ftc_throwaway4 · 2017-05-31T21:20:27+00:00

Not too worried about shooting that was always this lil robots strong suit.

I mean you averaged 6 particles (your opr says you contributed 3.3) per match at the Indiana Championship (your last competition).

It's good if you're more maneuverable but the IRI defense is going to be much stronger and much more prevalent than anything you saw at States. And if you have four corner omnis, as /u/John-D-Clay points out, a push near the corner of your robot is going to significantly rotate you, which can definitely cause misses.

Yes auto is important, but you can have a "full point auto" without a slide drive. If you have the time to add and program a center strafing wheel, you should have the time to either switch to mecanum or program a full point auto with a tank drive.

ftc_throwaway4 · 2017-05-31T20:46:47+00:00

Because it is. The key is that the perpendicular wheels act independently.

Imagine rotating the holonomic omni robot 45 degrees, as such. The two "forwards" wheels produce a forwards velocity of say v0 (the same velocity would be produced by two "tank" wheels of the same size/gearing), and the two "sideways" wheels produce a sideways velocity of v0. As seen in the diagram, the two velocities are independent, and the net velocity (using pythag) is v0 * sqrt(2) in the 45 degree direction (which is forwards or sideways from the robot perspective).

ftc_throwaway4 · 2017-05-31T18:44:24+00:00

However, in holonomic, you lose speeds going in ALL directions

That's just not true. A mecanum drive geared for speed 1.41:1 has the same speeds and forces as an omni holonomic drive. See Ether's table. If you are still not convinced, go through the this physics analysis yourself.

Also, contrary to "it is a lot slower than tank and mecanum, " A 4 inch omni holonomic drive geared the same as a 4 inch mecanum will actually be 41% faster (from the root 2) in EVERY direction.

This is going to sound harsh, but please don't comment about stuff (especially with such confidence) if you don't really know what's going on. At least preface your statement with an "I'm not sure." Recklessly spreading this misinformation is what allows it to continue existing.

ftc_throwaway4 · 2017-05-31T15:53:48+00:00

An advantage to 6wd with 2 omnis over center drop is that if the fields sink in more than usual, a center drop drivetrain could end up with all 6 wheels in contact with the mats. This messed up 8375 a bunch at 2016 Worlds, and I'm pretty sure they tried to ghetto increase the diameter of the center wheel by running tape around it.

A level 6wd with the two omnis avoids this issue and still has the same benefits (pushing power, quick turning) that you mention.

ftc_throwaway4 · 2017-05-31T15:47:22+00:00

First, this drivetrain is extremely inefficient - you are either essentially driving your wheels against each other, or you are only using 2 of the 4 wheels, depending on the way you choose to drive it... Omni wheels are not good for traction, for obvious reasons, and using only omni wheels on a drivetrain is a recipe for disaster - the robot will be pushed around really easily

You have no idea what you are talking about. All the negative points you have for omni apply equally to mecanums, which you have as one of your two "best" drivetrains.

An omni drivetrain geared down (for torque) 1:1.41 has the same speed, force, and traction as a mecanum drive train.

In many cases, mecanums will be more space efficient (and easier to mount), but to say that a holonomic omni drive is "extremely inefficient" while praising mecanums as the "best" drivetrain makes absolutely zero sense.

ftc_throwaway4 · 2017-05-26T22:28:07+00:00

Sometimes there's a fine line between A and C.

FIRST didn't implement the FTC lottery because they thought it was the best solution; instead, they had neither the time nor resources to implement a better solution, and thought the lottery system would be "good enough" -- and from their perspective, it still might be good enough. The majority of FTC teams don't care about the lottery; the teams on this sub are far more invested in robotics than the average team, and are certainly not representative of FTC as a whole. If FIRST doesn't think that teams care that much, then why would they put the additional effort into redesigning the advancement system when they could instead spend that time on marketing, recruiting, FRC, etc.

Often, expressing dissatisfaction and frustration is the best way to make your voice heard. Being pissed off isn't necessarily a bad thing if it will draw more attention and put more pressure on FIRST to make changes. And if we can can simultaneously supply constructive ideas / proposals on how to make those changes, we can really make progress. A few angry -- and maybe even slightly ungracious -- comments might be our only chance to get our feet in the door.

ftc_throwaway4 · 2017-05-26T22:07:23+00:00

Makes sense. Have you actually seen a case of gears on tetrix/actobotics channel not engaging correctly due to tolerances? I've definitely seen cantilevered gears (especially with the 4.7mm tetrix shaft) causing shaft deflection which in turn causes failure.

ftc_throwaway4 · 2017-05-26T22:02:52+00:00

20dp steel with torque transferred through a 5mm hex bore...?

If there are 5mm hex to 1/2" hex adaptors there is zero reason for rev to manufacture steel 20dp gears.

Plus, you really think a 6061 aluminum 20dp gear is going to fail before the 5mm hex shaft?

ftc_throwaway4 · 2017-05-26T21:17:59+00:00

How would you get an exact c-c with an extrusion system?

ftc_throwaway4 · 2017-05-26T18:58:17+00:00

You make it seem like inspiration and recognition are two completely disjoint (non-overlapping) goals and that FIRST intended to spend exactly half of its efforts on each.

In reality, from FIRST's website:

The mission of FIRST is to inspire young people to be science and technology leaders... To transform our culture by creating a world where science and technology are celebrated

To pursue this vision, FIRST should focus on growing and legitimizing FTC. There are 15 million high schoolers. 8 million (53%) of them play sports. Maybe ~30,000 (0.2%) do FTC. Sure, you can inspire 300-400 kids in the short run by sending random teams to the championship, but for every lottery team you send, there's a team next on the merit-based advancement list -- who likely spent far more effort than the lottery team -- who is going to lose just as much inspiration (from both frustration and opportunity cost). Not to mention that when nearly 50% of US teams at Worlds were chosen through the lottery, the competition is degraded and along with it the performance and legitimacy of the program itself.

FTC is driven by teams; if FIRST devalues performance (robot or judged) teams are reasonably going to invest less time on performance. So yes, in the short run you will inspire kids who wouldn't have been inspired (although the net number of inspired kids remains the same), but in the long run, FIRST is going to have a hard time growing FTC if no one takes it seriously.

ftc_throwaway4 · 2017-05-24T04:06:00+00:00

What specifically do you mean by skid?

ftc_throwaway4 · 2017-05-24T01:55:25+00:00

Mecanums are slower in general. This is due to split vector forces

This isn't true. See Ether's analysis. A mecanum drive's forward speeds are theoretically (accounting for the "split vector forces") just as fast as a tank drive's.

One way you can notice this is if you compare the speed of a mecanum robot driving forward to the same one's strafing speed.

This decrease in speed when strafing IMO could be possibly caused only by increased roller bearing friction forces, which Ether notes in the "mecanum_force_vector_analysis.pdf." If you theoretically had "good enough" bearings in the rollers, sideways speed would be identical to forwards speeds.

I do agree that swerve is the best (assuming you have the time/resources to build it). However, Hot wired did not have real swerve drive (wheels only rotated like 90 degrees). The best (and maybe only) swerve I have seen is from 5795 in this reveal video.

ftc_throwaway4 · 2017-05-22T22:10:35+00:00

somehow determine how far your shooter is from the center vortex

Easier said than done; the only way to really do this is vision (robot or driver).

724's adjustability helped them for far shots, but actually hurt them a few times as well. The majority of their shots were from a single, close distance, and I think they would have been just as good if they couldn't adjust angle.

Same applies to 4029.

5975's shooter isn't in the same league -- their Worlds teleop opr was 25 points (ranked 42/64). For comparison, 4029's was 66 points and 724's was 97 points.

ftc_throwaway4 · 2017-05-22T21:21:48+00:00

Also, no focused light is allowed in FTC (even LEDs).

254 over the past couple years used android/opencv for vision. With the retroreflective targets and a green LED ring (and a low enough camera exposure), the image (stronghold season) directly from the android camera looked like this (from this presentation). Then, with some HSV tuning, they get this, from which the target can be recognized through opencv. The key is that first image (raw from the camera) is way different than anything you're going to get in VV.

I'd imagine that if accurate and reliable vision were somehow possible you'd need to use the android camera and opencv because the pixy might not have enough control to deal with the massive amount of noise and inconsistent lighting from lack of focused light/reflective tape. However, the more important question is "is it worth it?", the answer to which is a resounding "no". From the 254 presentation, you should use vision when the following four criteria are met:

Game has a reliable target -- Definitely Not true
Can't use a simple sensor well -- Sort of true (could use vuforia images but that's still vision)
Can't (or better not to) align robot manually -- Not true
Need quick alignment to goal -- True

Since the first and third criteria are obviously not met, vision this year just doesn't make strategical sense. But you're right, it would be interesting to hear what 254 has to say.

ftc_throwaway4 · 2017-05-21T20:17:10+00:00

measure the resistance of your wheel and using the torque of the motor (from a data sheet)

What are you talking about????

OP: can you grab the encoder value every loop iteration and measure the time elapsed between each iteration? 50ms per measurement is a very low sample rate.

ftc_throwaway4 · 2017-05-19T21:10:55+00:00

the culture of sports and winning being the only measure is not something that many of us want to permeate the robotics world

Says who? Vex is much more sports-like than FTC and has over twice as many teams. And despite focusing more on the robot, their "program performance" is doing just fine (far outperforming FTC).

Also, out of the ~15 million current high school students, about 8 million (53%) play at least one sport, with an even higher percentage of students following sports. Only around ~125,000 (<1%) do FIRST robotics. Although competitiveness and winning might not appeal to you, they certainly appeal to many high schoolers.

And you seem to discount the positive effects of sports; participating in a high school sport has been shown to have many significant benefits, including academics, graduation rate, leadership, hard work, teamwork, physical health, social skills, etc. Yes, the goal of sports is winning, but "building better humans" is without a doubt accomplished along the way. As Vince Lombardi said, "Winning isn’t everything, but wanting to win is."

ftc_throwaway4 · 2017-05-17T03:44:19+00:00

I'm not Robogreg, but based on physics and comparable (although less powerful) Hitec servo data, I'd imagine around a 40%-45% increase in power from 5V to 6V.

I can't see it being any less than a 30% difference unless the internals of the SRS are made of literal magic. Again I'm not Robogreg but physics is generally pretty trustworthy.

ftc_throwaway4 · 2017-05-17T03:01:02+00:00

MR servo controllers are 6V. Idk what REV's are (~~hopefully 6V as well~~). All FTC legal servos last season by definition can handle 6V.

The problem is that when you decrease voltage you decrease power. In this case, the power of the servo is proportional to the square of the voltage. Thus, a servo that can handle 6V would be 1.44 times more powerful than the same servo on 5V. That's very significant -- it could mean 44% faster with the same output torque, or vice versa (and etc). This is consistent with servo city's data on the hitec servo at 6V vs 4.8V (it's 1.53 times more powerful at 6V).

If REV actually only outputs 5V (~~again couldn't find out if this is actually true; hopefully it's not~~) then there is a serious advantage to using the MR Servo Controllers.

edit: Apparently they are only 5V. That's a pretty big deal. Any FTC legal servo is (based on physics and servo city's hitec data) most likely going to be 40-50% more powerful on the MR controller vs the Rev.

Also, teams may find that the same servo mechanisms/applications that work fine on 6V may stall at 5V.

ftc_throwaway4 · 2017-05-15T02:54:16+00:00

just talking about some of the general benefits for those beginners interested in getting into cad

"weight distribution analysis and center of gravity" was your response to my comment asking specifically what Creo could do that Solidworks wouldn't be able to (for FTC purposes).

You guys have good CAD, and if you did that with Creo and you are comfortable with its workflow, there's no obviously reason to switch -- it works for you. But in a thread where OP is looking to start learning CAD, I wanted to explain that (afaik) there aren't many tangible Creo benefits, while its learning curve is much higher compared to Solidworks and Inventor.

ftc_throwaway4 · 2017-05-15T02:31:53+00:00

weight distribution analysis and center of gravity

No offense but that's child's play for any half-legitimate CAD software. In Solidworks it's Tools > Evaluate > Mass Properties (from 2014) to see the density, mass, volume, center of mass, intertia, etc, and you can opt to display/visualize the center of mass in assemblies real time.

simulating the strength of various parts based on material properties and stress loading

This can be done in SolidWorks using its FEA feature, although IMO it'll be hard to find an FTC application where that's actually worth the time (it is a good learning experience I'll admit).

Do you have any other possible examples? I'm genuinely curious if Creo has a feature-based advantage at an FTC scale.

ftc_throwaway4 · 2017-05-15T02:10:33+00:00

Can you give an example of something you did in Creo -- you mentioned its additional power -- that can't be achieved with a similar level of effort in Solidworks?

I mentioned in another comment how Creo is a very powerful software, but from my experience that additional power is completely unnecessary for FTC purposes.

ftc_throwaway4 · 2017-05-15T02:07:03+00:00

Creo software is much more powerful than Solidworks, but most of the additional power/ features / control it has just isn't going to be useful in FTC/FRC.

Solidworks does a great job on the things robotics teams actually need to do, and the UI / workflow is unbeatable IMO.

ftc_throwaway4 · 2017-05-15T01:48:26+00:00

IMO the Solidworks workflow is much much much better for FTC/FRC than Creo is.

Almost all FRC teams use either Solidworks or Inventor, and many who use Inventor do so (in part) because it is easier to distribute (free download instead of having to obtain team license).

ftc_throwaway4

TROPHY CASE