01-08-2011 15:42

Chuck Glick

Re: pic: Uber 3.0

As a former driver and build team leader, I would highly recommend you re-evaluate your choice of gearing. While 16ft/s may sound nice, it is often hard to control for an inexperienced driver. It is a nice speed for a high gear in a shifting drivetrain, however for a 1 speed like you have designed, aim for the 8ft/s - 12 ft/s range. It is a good range to be in and your driver will thank you.

Other than that, nice cad. Looks great.

Did you use JVN's design calculator? and if so what current pull are you getting off of that setup?

01-08-2011 16:20

Re: pic: Uber 3.0

Looks nice! The only thing is like what Chuck said, 16 fps is cool, but for us drivers, it takes some getting used to, especially if that's the only speed available to us. Personally, I prefer around 12 fps for rough driving, such as competition driving, since most of the time you must be able to swiftly maneuver around the 5 other robots on the field.

01-08-2011 16:29

dodar

Re: pic: Uber 3.0

You guys have to remember though, that is 16ft/s as is. This is only the base, you have to remember that there will be close to 100-110lbs more on this after a competition gets announced which would probably slow it down to around 13ft/s.

01-08-2011 16:31

AdamHeard

Re: pic: Uber 3.0

The weight won't slow it down one bit, the friction in the drive will however.

He could be quoting 16 fps as the number after frictional losses as well, that's what we usually do.

Either way, 16fps is too fast for single speed in most modern games. Maybe it would have been okay in 05, and depending on your role this year as well. You could get pretty roughed up by a solid defender though.

01-08-2011 16:50

Brandon Holley

Re: pic: Uber 3.0

Reiterating what others have said, for a single speed, 16fps is probably a bit too quick (whether its theoretical or actual). If you do eventually go for multiple speeds, 16fps (actual) is actually quite beneficial.

This past year we geared for an actual speed of 18fps (~22fps theoretical). It was just a tick too high for our liking. In the future we'll probably shoot for 16fps actual.

Looks good though. Keep improving.

-Brando

01-08-2011 16:59

Hawiian Cadder

Re: pic: Uber 3.0

We geared our robot for 14.4 feet per second this year, and it was way, way fast. it was pretty controllable while it was moving in a straight line, but turning took a long time to get used to. The only reason to gear so high, would be if you had more motors in the drive-train (6 or even 8). That way the torque at the wheels stays roughly the same as a slower robot, and you can control the speed with software (our robots from the last 3 years used the thumb button on the joystick to half all motor output values.)

01-08-2011 17:14

AdamHeard

Re: pic: Uber 3.0

When doing your drive calcs at such high speeds, you should also check the time it takes to go a certain distance over the range of gear ratios.

If you had done this, it really would have emphasized that you guys just went a bit over the point where acceleration tanks on 4 CIMs.

We started doing this a few years ago, and it's totally changed how we gear our robots.

01-08-2011 17:23

Akash Rastogi

Re: pic: Uber 3.0

Looks good! Very similar to something I recently drew up, however I had shorter flanges and the outside driverails had the flanges facing in. It also looks like your inside rails and outside rails are different parts, if you can keep the entire chassis to two unique parts, it'll cut down a little prep time for your fabricators, it will also provide another bearing mount for that output shaft of yours. (which I would extend out and support at the end, unless your gearbox is designed with this in mind and you mount your drive wheels closer to the inside rail).

edit: I really like the electronics mount you've got.

01-08-2011 17:37

Chris is me

Re: pic: Uber 3.0

I would lower the speed down to 12 FPS after friction or lower. This isn't traction limited and you won't be pushing anybody but it is a competitive single speed for a driver with practice and good code.

01-08-2011 18:03

Mr. Lim

Re: pic: Uber 3.0

If Kajeevan asks me for 16 fps, I give it to him... .

After 5 years piloting an FRC robot, I guess 12 fps just doesn't cut it anymore, eh?

I have to ask, why did you go single-speed? Did you just find that you didn't use low gear enough to justify it? Spinning on axis, even with the 3/16" rocker, seems like it would be an issue...

Speaking of the 3/16" drop-centre, is this based on what you saw from your drivetrain last year? I know we upped our rocker a bit, but I don't think we ever got it as high as 3/16". Do you know of any other teams running this amount of rocker?

Would you be willing to share CAD files? I have a few students who would, no doubt, be interested in gaining inspiration from your work.

Who is your sheetmetal sponsor?

Are you building this in the off-season?

My favourite part: 1" of GROUND CLEARANCE

Looks great Kaj! I think Riddhesh will have a good time piloting this thing around in the future...

P.S. I don't see any encoder mounts... your former electronics mentor is disappoint... smh

01-08-2011 18:14

Billfred

Re: pic: Uber 3.0

This year, 2815 was geared around 14 on the CIMple Boxes. I think it's the fastest robot we've built in practice*, but we only went for it because we had a veteran driver who's been with us since our rookie year. If we had rookie drivers, I'd probably have adjusted the sprockets to make it closer to 12.

I'll ask another question: How are you planning to mount a manipulator onto this design? There are plenty of valid choices here (not a trick question, promise!).

*Granted, Lunacy and Breakaway weren't really known for their high-speed driving...

01-08-2011 18:25

Chris is me

Re: pic: Uber 3.0

It really shouldn't be. Our single speed drivetrains have turned very easily above 10 FPS. It takes a lot to make turning an issue with a proper 6WD.

01-08-2011 18:53

kajeevan

Re: pic: Uber 3.0

Mr.Lim you are correct I just never used low gear often enough to justify 2 speeds. I would always go around rather than threw a bot it just seemed faster and when we did play defense it would be positional and in the rare case T-boning which was only needed for last second events and not long periods of pushing. Also I'm sure Riddhesh of all people can mesh speed with finesse after 09's performance.

The 3/16'' drop will be a test if it doesn't yield favorably then we'll go back to 1/8''.

Encoders are on the gearbox under the electronics board

Sheet metal sponsor is Sable Metals.

Yes this is going to be the summer project hopefully to start next week and of course I'm willing to share my CADs I'll email them over.

For manipulators depends on the function I'm sure it won't be difficult.

01-08-2011 19:43

Colin P

Re: pic: Uber 3.0

I'm going to go out on a limb and say that a team with a CADer this good should have the resources to pull together an experienced drive team. If they do this over the summer, they'll have all the time in the world to practice.
Plus they could always just run their drive at 75% and have a turbo button.

01-08-2011 20:05

Conor Ryan

Re: pic: Uber 3.0

Really great design, looks solid, well put together mechanically and probably will translate well to almost any potential competition from that perspective.

The speed issue will really be determined when the game happens and should be a factor of where the game pieces are set up and the driving lines that will happen (consider 2010's layout vs 2011). It just so happened this past years game called for really high speeds but others (2010) called for slower speeds/higher acceleration.

The inspectors, FTA's, programmers and anybody else on the field would really love it if you repositioned some of the core electronics like the Main Switch, cRio and Router (yeap include that too) into one highly visible and easy to access location. You also might want to get some input from some Electrical guys on how to set up the "non-core" electronics better from a wiring perspective to maximize accessibility when stuff doesn't go as planned.

Those who pay attention to that type of detail on all perspectives don't go unnoticed and it makes everyone else's life easier.

(Like consider the possibility of having somebody else's arm crash into the hardest to get to Victor while severing the wire and you need to replace all of it in 2 minutes because your alliance partner already burned your only time out on Einstein, thats the type of detail I'm talking about)

But don't get me wrong, you are seriously on the right track right now.

01-08-2011 22:17

Rob Stehlik

Re: pic: Uber 3.0

Nice design!

I have to agree with Mr Lim that my favourite feature is the 1" ground clearance. Last year I think you were driving a hovercraft
I wouldn't worry about all of the comments about your choice of speed. It may well be that 16 ft/s is too fast for a single speed, but the way you have set up the gearbox makes it very easy to change the ratio. Just swap out the sprockets in the gearbox, shorten the chain, and away you go. Actually, this is a very good reason not to design with the gearbox directly driving the middle wheel.

Unless we get ourselves a sheet metal sponsor, feel free not to share the CAD with our guys. As pretty as your design is, 610 can't build that way.

02-08-2011 00:37

MattC9

Re: pic: Uber 3.0

YES 16fps is WAY to fast, im sure you already know that by now, but i will show you how to fix it by just getting 1 part. The AM 12t double sided sprocket http://www.andymark.com/product-p/am-0736.htm. This will bring your gearing total down to ~8:1, as a driver i would enjoy a 8:1 reduction.

Hope this helped.

02-08-2011 03:04

Chris is me

Re: pic: Uber 3.0

What do you mean by 8:1? A reduction means nothing without wheel size and a reference point.

02-08-2011 09:28

JesseK

Re: pic: Uber 3.0

Here's my logic on the gearing:

If you gear for high speed, and can play the game very well:
- Defenders will come block you
- If you only have 16ft/s as an option, the defenders will succeed in blocking you most of the time
- If you can push through the defense via a low gear, you will be a power house.

If you gear for high speed, and can play the game decently enough for a 2nd pick:
- Defenders may not block you
- You can do cross-field 'under the radar' things, such as carrying a specific shape for an alliance this year. Game dependent though (wouldn't work in 09/10)

Thus, IMO, single-speed gearing for high speed is a risk and a tradeoff. The decision is inconclusive until the game is announced, yet the great thing about single speed gearboxes is that they're easily adjustable.

02-08-2011 09:39

Borobo

Re: pic: Uber 3.0

If you are going to spend the money for a sheet frame, go for 2 speeds. 16 is too fast to be the only gear, but assuming the game next year involves complicated and minute maneuvering, an 8/16 or nearby ratio could be a good gearbox

02-08-2011 10:58

Chris is me

Re: pic: Uber 3.0

You would be surprised how few teams actually have high traction drives that can play effective and smart defense. Teams like 233 and 1503 had single speed drivetrains and I don't think anyone would argue that they were "successfully blocked most of the time".

02-08-2011 12:24

Mr. Lim

Re: pic: Uber 3.0

Kaj,

Here are some links to similar 6wd drivetrains:

http://www.chiefdelphi.com/forums/sh...ad.php?t=68613
http://www.chiefdelphi.com/forums/sh...ad.php?t=68825
http://www.chiefdelphi.com/forums/sh...ad.php?t=68847
http://www.chiefdelphi.com/forums/sh...ad.php?t=77678
http://www.chiefdelphi.com/forums/sh...ad.php?t=78065
http://www.chiefdelphi.com/forums/sh...ad.php?t=78101
http://www.chiefdelphi.com/forums/sh...ad.php?t=86155
http://www.chiefdelphi.com/forums/sh...ad.php?t=86732

The guy seems to know what he's doing, except for the fact that he seems to having something against ground clearance. There's some epic story about how his 2009 Curie division finalist drivetrain got high-centered on a flat field...and how he fixed it by building a drivetrain with even less ground clearance in 2011. Then again, in 2011 he made the Galileo finals at Champs.

I think the key is less ground clearance = more success.

There is no doubt in my mind, that if you can finally figure out a way to have negative ground clearance, a trip to Einstein is in the books.

P.S. Honestly Kaj, you're now more in a position to give advice on these matters as opposed to receive it. I don't know too many students OR mentors who have actually designed, sourced, machined, assembled, and driven IN COMPETITION as many quality drivetrains as you. Ian Mackenzie, Tristan Lall or Hinkel Yeung can't even boast resumes as extensive - certainly not as students.

P.P.S. Ground Clearance

02-08-2011 13:17

Brandon Holley

Re: pic: Uber 3.0

Yes we did all of this analysis as part of our standard approach to drive design. The original intention was to come in significantly underweight which we were able to do to some degree. This helped to counteract the drop in acceleration you would expect from gearing for such a high speed.

On full field runs, our gear ratio worked as we wanted it to. To go along with all of this, we had a control scheme (known as Cheesy Drive) that allowed us to control the robot remarkably well at high speed. Our problem was misreading the game slightly, where full field runs weren't as necessary as we thought they may be. Knowing what we know now, we wouldn't have shot for such a high speed.



-Brando

02-08-2011 13:31

JesseK

Re: pic: Uber 3.0

Actually, I'd estimate that I understand the world of FRC robots as much as you. Rather than "surprised", I am fully aware of this probability year to year, including my own team's inclusion in it. Regardless, you ignored part of my logic: were PINK and Spartronics geared for 'high speed' such that they (even unknowingly) traded off the pushing torque for more speed?

PINK, iirc from DC, was geared for 12 ft/s after friction. They traded the extra speed for more torque so they could go to a single-speed drive without the worry of being pushed around most of the time. This tradeoff was obvious from just a short conversation with them, so I'm not deducing it deduced so much as I'm re-stating it. Only they can say how much they felt they were pushed around this year since video seems to be rare for 2011. For the first 0:45-ish of the 3rd Finals DC match, we totally shut them down*.

*Then our chain broke, and all of the coulda-shoulda-woulda's set in ... lessons learned for the future, heh.

02-08-2011 13:39

M. Mellott

Re: pic: Uber 3.0

Nice modeling, and I LOVE the V8 look!

02-08-2011 22:13

R1ffSurf3r

Re: pic: Uber 3.0

at champs we went down to about 7-8fps, but the ratios weren't our only problem earlier on. our arm was still geared waayyyyy to high. it was about 1 second to rotate from collecting on one side to collecting on the other with a single banebot. as a result power and acceleration seemed to tank when the arm was moving about (which is ideally quite a lot).

in the end we just weighted up to 120 and geared to be traction limited because we don't like getting pushed around

02-08-2011 22:33

MattC9

Re: pic: Uber 3.0

What is this cheesy drive you speak of?

02-08-2011 23:21

NickE

Re: pic: Uber 3.0

Check out the drive code in this: http://www.chiefdelphi.com/media/papers/2397. For more information, talk to Austin, Tom or Kiet would be your best bet.

Nick

02-08-2011 23:25

MattC9

Re: pic: Uber 3.0

Sorry, I'm not a programmer so I don't have the software to view it (CAD actually takes up most of my computer) but i will have one of my guys look at it and explain it to me, but thanks for sharing!!

02-08-2011 23:36

AdamHeard

Re: pic: Uber 3.0

You have the software to view it, the type of code they (and most of industry) uses is just text.

03-08-2011 22:11

Wildcat

Re: pic: Uber 3.0

is that thing rockin a V8?

04-08-2011 03:10

AustinSchuh

Re: pic: Uber 3.0

The code definitely makes a huge difference. The drive code in that paper ran on 2 of the robots on the winning alliance last year. It helps make a 16 fps robot controllable and fluid.

06-08-2011 07:17

ratdude747

Re: pic: Uber 3.0

I am going to differ from the crowd and say that the high gearing is OK.

here's what you do:

in the code, use a button/toggle to scale back the joystick inputs to create a "virtual gear". you can also route this to a throttle if you are using joysticks instead of a gamepad. my team has a demo bot made from an IFI kit chassis and the 2011 kit cimlple gearboxes... we had to make the output cog larger to fix chain tenison issues and as a result, we had to map a scalar to the left joystick throttle (in arcade mode, the only stick) since by default it was too fast.

this year's competition mecanum used a "turbo trigger" to give the motors full power, otherwise, the joysticks were scaled back.

the only other note is you will have a lot less torque but depending on what you want to do with it, this may be more or less of an issue.

06-08-2011 09:43

apalrd

Re: pic: Uber 3.0

Two comments:

While this does work, you are now limiting your motors to a max of a certain power output (since you can never feed them full voltage)

We implemented something like this to create an automatic "1.5" intermediate gear, of around 9 ft/sec (low is usually ~5.5, high 12) which was automatically used when the elevator was above the score-mid height (and another "1.7" intermediate gear of about 10-10.5 when the elevator was in the score mid range). However, we implemented this as a speed request instead of a power request, so the closed-loop speed control could give the motor full power to accelerate or push. Why? Because just blindly limiting motor power gives little benefit (why not just change the gear ratio to make it correct? For a chain drive it takes a few sprockets from Andymark to correct an error that should've been found when you did the initial drivetrain math). However, limiting speed but not power allows the speed control to give full power to accelerate, and we found it useful when scoring.



Also, while I like the cheesy poofs code (and 33 re-implemented it for an off-season project), I still don't get why the code Nick pointed to (cheesy poofs 2010) has a switch for QuickTurn vs SpeedTurn. Why not just do quicktunrs when the throttle is at 0 and speedturns the rest of the time?

That said, the cheesy drive algorithm is very solid.

07-08-2011 01:19

AustinSchuh

Re: pic: Uber 3.0

That switch is partially that way because it has always been that way. We have found that particular choice to work well, and have no desire to change it.

Say you want to turn 5 degrees. If the robot is still in "SpeedTurn" mode, you can slam the wheel to one side, and it won't move. Then, you can tap the quick turn button. This will cause it to send +- 1 to the wheels for a very short amount of time. The net result is a turn by a small amount without having to steer carefully. We find this rather useful. This move is a lot harder to do if you try to turn the wheel with quickturn already engaged.

I also like being able to send any set of powers to the left and right wheels. So, the "SpeedTurn" algorithm won't let you send +1, -0.1. But, if you hit quickturn, you now can send that set of values out. This can't be done if the robot does it automatically for you.

Also, I am a big fan of devices having a psychologically linear response*. Having a device switch modes without a command from the user doesn't fall into that category for me. If you are driving slower and slower, and have the wheel in a full turn, once you stop applying throttle, the robot will stop. If it switched into QuickTurn automatically, it would instead suddenly start to spin. That rubs me the wrong way.

If you have any more questions about why the code does what it does, fire away. I like to believe that every line of code in the drive algorithm is there because it is necessary and helps handling.

(I have heard that the algorithm for QuickTurn isn't quite right in that code. It should be that quickturn does left = throttle - turn; right = throttle + turn; rather than setting throttle = 0.)

*It doesn't have to actually be linear by the technical definition. The driver should feel like turning the wheel twice as far turns twice as much, or the elevator moves twice as fast, or etc. It may not actually be that 2x the wheel moves 2x as fast, but if the driver feels that way, he/she will be able to control it better.

22-08-2011 19:03

lemiant

Re: pic: Uber 3.0

What did you do to get such a good render?

22-08-2011 19:08

kajeevan

Re: pic: Uber 3.0

I just used inventor studio, very quick.