12-07-2015 22:31

Lil' Lavery

Re: pic: Four Speed Three CIM Gearbox

What advantage(s) do you expect from having a four-speed, 3CIM gearbox over a two-speed 3CIM gearbox? A four-speed 2CIM gearbox? Heck, even a single-speed 3CIM gearbox?

Basically, why? This seems like overkill.

12-07-2015 22:33

AlexanderTheOK

Re: pic: Four Speed Three CIM Gearbox

And for the 2016 FRC game, OVERDRIVE 2: OVERKILL. This game is played on a 10 meter by quarter mile field in the streets of Miami. Any robot to get to the finish line in 10 seconds wins by default and gets a free ride to champs!

12-07-2015 22:35

Kevin Leonard

Re: pic: Four Speed Three CIM Gearbox

It's a cool piece of machinery, and looks pretty sick to boot. I believe you said you weren't seriously considering this, as it has no real advantages over a two-speed in most games.

Ever considered taking that third and fourth position and turning it into a PTO? That wouldn't be very important in a game like 2015 whatsoever, nor a game like 2014. But, for example, in 2013, 254 used a PTO to power their awesome climber.

12-07-2015 22:35

asid61

Re: pic: Four Speed Three CIM Gearbox

It looks quite well done for the project. It's not useful for competition, but it looks good anyway.
Nice render too.
For the top shaft of the gearbox, instead of using a hex bearing, I would round down the end of the shaft and use a round bearing.
If you only have 2 standoffs going to the mounting plate, I would change it to 3-4.

EDIT: +1 on the PTO idea.

12-07-2015 22:50

Gregor

Re: pic: Four Speed Three CIM Gearbox

Did you read the description?

12-07-2015 23:07

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

To me, the big "why" is why have four speeds over about a total 3:1 high-to-low ratio? If you're going to bother with four speeds, spread them out a bit wider!

At a minimum, I would put the shifts a factor of 2:1 apart, resulting in an 8:1 overall ratio from high to low. At a "standard" 2.56:1 ratio between shifts, the total range would be 16.77:1. At 3:1 per shift, it would be a massive 27:1, which could be a real game changer in some highly defensive games or games with steep ramps. Especially if you want to reserve some CIMs for manipulators!

12-07-2015 23:09

ratdude747

Re: pic: Four Speed Three CIM Gearbox

Another good PTO example: 1114's hanger in 2010 (which was sickly fast )

12-07-2015 23:11

hectorcastillo

Re: pic: Four Speed Three CIM Gearbox

Thanks, yeah I know it's really overkill. So basically to answer the question of why I decided four speed, my team is working on the summer design project thing that was put out a couple weeks ago. The end game involves chasing down a mini bot on the field, so the end game team wanted to be able to travel at the mini bot's speed (~13fps) to line up with it and a faster speed to catch up to it. We also wanted to be able to move around a little slower with more control for adjusting shots and in case anyone wants to push us. I know we could've gone with a two speed and controlled the speed with code, but that's what the team decided to go with. Also, it gave me a nice challenge which is always fun.

Our 2013 drive train gearbox used a PTO to power our climbing mechanism as well. There was something wrong with the throw of the shifter that made it not work, but it was still pretty cool. I don't think there's an opportunity in the game that we're designing for to use a PTO, but I did think about it while designing this.

12-07-2015 23:15

Lil' Lavery

Re: pic: Four Speed Three CIM Gearbox

Description wasn't posted when I posted my comment.

12-07-2015 23:19

hectorcastillo

Re: pic: Four Speed Three CIM Gearbox

When I was playing around with the JVN calculator I was trying to get them as wide as possible. The limiting factor, though, was that the two speeds that we wanted for the end game were 17fps and 12.72fps, which put limit on how much i could work the speeds while still keeping it realistic. I guess I was just focusing on the speeds needed for this game and not the wide array that there could have been.

12-07-2015 23:24

mrmummert

Re: pic: Four Speed Three CIM Gearbox

Hehehe..been done already sort of...


https://youtu.be/efvCDYTj0Wk

12-07-2015 23:46

waialua359

Re: pic: Four Speed Three CIM Gearbox

Impressive Design!
Team 368 made a 4-speed transmission in their 2005 robot, IIRC also.
Cool stuff!

13-07-2015 01:25

zinthorne

Re: pic: Four Speed Three CIM Gearbox

Sorry for me asking, but what is a PTO gearbox?

13-07-2015 01:35

z_beeblebrox

Re: pic: Four Speed Three CIM Gearbox

https://en.wikipedia.org/wiki/Power_take-off

13-07-2015 01:57

asid61

Re: pic: Four Speed Three CIM Gearbox

They're used to transfer power from the drivetrain, which usually has a lot of power to spare, to other mechanisms, usually for an endgame.
Lifting oneself in 2013 could be accomplished using all 6 cims in a drivetrain, for example.

13-07-2015 11:06

Ryan Dognaux

Re: pic: Four Speed Three CIM Gearbox

This is really cool. If you can find the machining resources to make one I would totally do it as an off-season project. Sure it may not be the most practical thing for the competition season but you'll learn a lot while doing it. You could also design up a 2 speed variant and make that too and do a comparison - maybe even post a white paper so we can all learn about it. Good stuff!

13-07-2015 18:15

Cory

Re: pic: Four Speed Three CIM Gearbox

Under what scenario would that be useful? Once you can break traction you see no benefit to moving slower, unless somehow you needed to very precisely position your robot with fine movements.

13-07-2015 22:17

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

Who says that your robot always has the same weight? I seem to recall that there was a game in which robots extended a ramp to lift their alliance partners. I also "blue skied" a robot for Ultimate Ascent which would have literally grappled its alliance partners and made a 90 point outside climb (code name Fezzik, for fans of The Princess Bride). If you wanted that same robot to also fly around the field scoring frisbees for the first hundred seconds of the match, having a multi-speed PTO transmission with a total span of 20+:1 would have been epic.

13-07-2015 23:19

magnets

Re: pic: Four Speed Three CIM Gearbox

I always love these hypothetical crazy gearboxes and ratios people come up with. Practical, maybe not, but definitely awesome.

Assuming your robot was geared for 18 feet per second in high gear, and 0.67 feet in low gear (a 27:1 spread), you'd need to have a 1800 lb robot (or group of robots) to take advantage of the gear ratio and never trip the breaker in a pushing match. If the robot weighed any less, you could get away with a smaller spread and never worry about tripping a breaker.

That sounds like my kind of game!!

14-07-2015 01:27

thatprogrammer

Re: pic: Four Speed Three CIM Gearbox

2002 meant your robot could be several hundred pounds due to how heavy the movable goals were. 71 could drag over 900 pounds that year!

14-07-2015 11:25

TJP123

Re: pic: Four Speed Three CIM Gearbox

503 found them quite useful, so much so that we had two separate PTOs. 4 CIMs to power our can grabbers and 2 for the elevator. The drivetrain could use 2, 4, or all 6 CIMS.

14-07-2015 11:27

Kevin Leonard

Re: pic: Four Speed Three CIM Gearbox

I mean to be fair, there was no reason to have 6 CIMs in the drivetrain this year either. I know of a team on Einstein that was running two motors. I heard it was two Mini's at one point, but I don't recall.

14-07-2015 13:15

TJP123

Re: pic: Four Speed Three CIM Gearbox

Not one reason? Hint: I just gave you one.

Don't think of it as a 6-CIM drivetrain, think of it as a 6-CIM powertrain, powering three very different motorized mechanisms in an extremely effective and efficient manner. Many ways to skin a cat.

14-07-2015 22:22

hectorcastillo

Re: pic: Four Speed Three CIM Gearbox

That's very interesting. I've only thought of PTOs as using all of the motors at once for one function or another. It hadn't yet crossed my mind that you could be running multiple functions simultaneously by splitting up the motors like that and being able to control these functions independently.

Although what advantages would it serve to have power coming from the same place if you could just use more motors for a different mechanism? The only reason I can think of is because there is a limit on the amount of CIMs you can use and it's hard to get that kind of power from other motors, so for climbing or stacking you'd want to be able to tap into those motors. But for example there wouldn't be much of an advantage from using a PTO to also power an intake system that could easily be powered by a smaller motor. It would actually be kind of wasteful.

14-07-2015 23:44

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

The ultimate FRC PTO would have six CIMs each running at a bit under 20A, each generating about 150W. A slice of this massive 900W (that's about 1.2 HP) would then be available to whatever functions the robot needed to perform, whether it was drive, lift, pickup, place, throw, can grabber, or whatever screwy function the GDC required that year. If tapping the "correct" amount of energy off of a rotating shaft and applying it to a task was easy, this would definitely be the way to go. And OBTW, if you weren't using all 900W, perhaps you could spin up a flywheel, which would allow you to draw a few hundred extra watts later when you need to "go to eleven" for a bit. Theoretically, this sort of PTO sounds like heaven for a game like Aerial Assist which involved defense, driving, shooting, and (at endgame) climbing. The devil's in the details, as always!

And, for the record, my prediction: The first FIRST team to execute this sort of PTO will join 71, 118, 254, and 1114 as one of the top five teams of all time (unless, of course, it's one of those four who do so).

15-07-2015 08:01

Kevin Leonard

Re: pic: Four Speed Three CIM Gearbox

First of all, you obviously can't make a list of the top FRC teams of all time without including 67.

Second of all, the ultimate PTO would use every motor available and just shift however many motors necessary to any function.
(However you'd have to have some crazy programming scheme or something to keep from browning out like crazy)

I also think the first team to do this won't be one of the greats; I think the first team to try it won't get picked at their event. That's insanely complicated, even for a team like 254 or 118. I would love to see someone do it successfully though. it would just be a mechanically sick robot to check out.

15-07-2015 08:36

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

The reason for stopping at 6 CIMS is that they are capable of efficiently turning every amp you can get through the main breaker into mechanical energy. Once you do that, any additional motors are meaningless.

And I did mean the first team to successfully execute it, not the first to attempt it.

15-07-2015 09:37

Knufire

Re: pic: Four Speed Three CIM Gearbox

https://www.youtube.com/watch?v=h3l6Xqts4to

15-07-2015 15:16

The other Gabe

Re: pic: Four Speed Three CIM Gearbox

in 2014, a 3 CIM gearbox helped my team be the most dominant team in the PNW for the first 3 weeks (ish). no one could catch up to us, and our rams on defense rekt teams with loose ball carry. we didnt have a 4 speed though... it was just all fast, all the time

15-07-2015 18:32

Chris is me

Re: pic: Four Speed Three CIM Gearbox

I think you went quite overboard on the weight reduction on the outer plate. A pocketed 1/8" plate with no flanges, especially with the reduction being supported off of the end of the plate past the standoffs like that, will have some issues with flex and rigidity. With gearbox designs posted to CD in general there's often an overemphasis on lightening the plates as much as one possibly can, when it's really not that substantial of a weight savings over a more conservative lightening pattern or even unlightened plate.

15-07-2015 19:18

AdamHeard

Re: pic: Four Speed Three CIM Gearbox

The CIMs aren't very efficient actually, there are more efficient motors in the kit by a good margin (lower power though).

It'd be nice to get a high power, high efficiency motor on FRC legal list.


Also, it's simpler for teams just to add more motors and gearing independently than it is to centralize PTO it all. It just doesn't make sense for FRC.

15-07-2015 20:47

waialua359

Re: pic: Four Speed Three CIM Gearbox

We are one of those teams.
Due to weight constraints, we went from a robot that had 6 motors similar to that of 2014 to a robot with only 1 CIM on each side. We started with a 2 CIM 1 Banebot 775-18 on each side, then got rid of the Banebot for several regionals, then finally 1 CIM on each side at CMPS. We did this in order to make weight as we added 1, then 2 ramps and also to add our upper claw to hold the trash can in place while stacking.
This game was perfect for having just 1 motor on each drive, considering all we did eventually was make stacks from the feeder station.

15-07-2015 20:49

hectorcastillo

Re: pic: Four Speed Three CIM Gearbox

Thanks for the feedback. Would you suggest that I cut back on the lightening holes, add some flanges, and/or thicken the plate?

15-07-2015 20:56

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

All of the motors that are significantly more efficient than the CIM have their peak efficiency at a much higher speed (11-17k rpm vs 4500 rpm). This means that another level of gearing will be required to reduce these high-speed inputs down to a mechanically useful speed, offsetting most of the increase in motor efficiency. And you'd need more motor controllers, too. At least you could use a single encoder to know the speed of your power train.

No argument. Everything that is currently an independent motor would have to be replaced with a clutch, CVT, or similar mechanism, which brings us back to Kevin's original suggestion to use the shifters on a PTO rather than to make a 4 speed single function transmission.

I often find that at least thinking about (and sometimes even building) the extreme cases leads to ideas that prove useful later. IIRC, the OP tossed this up as a bit of a "blue sky" thread, and I've been treating it as such. Checking back, OP included "probably weighs a thousand pounds" and "I do not actually intend to build this thing." As a result of this thread, I now know to keep an eye out for high power jobs that don't require simultaneous wheel drive. 2013 and 2015 both provided this sort of challenge (pyramid climb and can burglar respectively), so it can't be that rare. It wasn't in my mental toolbox six months ago.

Another thing that makes me really like the PTO concept is the addition of a flywheel. It is possible to tap more power from a PTO with a flywheel for a short period than from motors, especially given the new motor brownout situation. I like having a defined brownout over an undefined one, but it will probably be several years before the FRC community learns to take the best advantage of the new opportunity/challenge. At which time we'll switch to yet another control system ;-P>

Thinking a bit more, 2014 (Aerial Assault) also provided a PTO possibility with the ball thrower. We had six CIMs on our 2014 robot, two for a "kicker" and four for drive. (We used pneumatics and an AM gearmotor for the ball pickup.) We nearly always threw the ball while stationary, so sharing all six CIMs between drive and a more elegant and powerful launcher might have been an improvement on both fronts, especially as most of our "accelerator" designs would have thrown the ball from higher off the carpet than the kicker did.

15-07-2015 23:08

The other Gabe

Re: pic: Four Speed Three CIM Gearbox

Why did they do that? was it just like, one of the kids said in a meeting, as a joke, "you know what would be cool?" and everyone just kinda went along with it.

also on the subject of small motors on drivetrains, I know that 2471 was running their Swerve on a mini-CIM for each wheel by DCMP in order to have more weight for a better can claw & some can burglars, with no discernible difference in performance from when the had a CIM per wheel.

15-07-2015 23:33

EricH

Re: pic: Four Speed Three CIM Gearbox

Nope. 2007 was PHYSICAL. Not only was there ramp climbing (up all random sizes and slopes of ramp), but there were 5 other robots on the field, all trying to score or block scoring in the same general area. This "area", the Rack, was a structure that could be slid and spun around, took up a fairly large chunk of real estate in the center of an otherwise flat field...

... and needed some degree of precision to place scoring objects (inner tubes) onto its scoring pegs.

All I'll say as far as it being physical is: Aerial Assist was rough. Now extend and beef up the appendages another couple of feet or so. And "meet in the middle" autonomously...at speed...or under driver control...while trying to score...or block scoring...


118 had a pretty decent swerve the previous year, but for this one they added a pair of F-P motors to a 4-CIM, ran all the wheels off the same gearbox and the same turning motor, and had a turret on top to allow for scoring in any orientation they felt like being in.

Basically, lots of push and lots of maneuverability were judged "pretty important" that year. (Though... IIRC, Einstein was a bunch of 6WD skid-steers that year, with maybe a couple of non-tank drives around.)

23-07-2015 00:18

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

I'm still wondering what was up with that central gearbox that was later distributed. It appeared to be an essentially 1:1 gearbox which brought four CIMs together onto a single shaft, which was then redistributed around on four separate swerve shafts. It seems to me that it would have been easier and more efficient to put a CIM on each swerve shaft, but to include a sprocket which tied the four shafts to the same speed to allow redistribution of energy as needed (e.g. as loading increased on two wheels due to acceleration away from them).

23-07-2015 00:32

AdamHeard

Re: pic: Four Speed Three CIM Gearbox

They combined it all into a single shifting gearbox (reusing a Dewalt drill planetary). They also added 2 FP motors, so distributing it would've been harder.

23-07-2015 08:38

ratdude747

Re: pic: Four Speed Three CIM Gearbox

Traction. By combining the motors onto one shaft, in addition to allowing for a single dewalt shifter, it also allowed any one wheel to have all the motors power available. Thus, even if a wheel lost traction, the full pushing power would still make it to the ground through the others.

Another good example is 148 in 2008... they did 2 FP plus 4 Cim, going to three swerve pods, which were steered with a van door motor. Since they had no "front" (it was an equilateral nonagon lap runner), they had no need to "steer". As a result, they could both run laps well AND provide very good defense (and this was one of many reasons why their CMP alliance were champions).

23-07-2015 09:09

GeeTwo

Re: pic: Four Speed Three CIM Gearbox

I didn't notice the shifter. With that bit of info, the central gear box makes perfect sense. While separate CIMs which are chained to keep the same speed would have also allowed the power generated at one wheel to be used at another, four (or six) shifters would be more complex (and costly and heavy) than the "gear manifold" and a single shifter.