pic: Final 2011 Drivetrain

[Bill_B]

Probably planning on milling the bumpers out of solid pool noodle stock, too. Ever wonder how they drill that hole down the middle of pool noodles?

[Andrew Y.]

Originally Posted by poohbear

Hey comrads!

Here's our team's final design for our first drivetrain ever and its pretty innovative if i say so myself

-the body is milled from a solid block of 7071 aluminum (with our sponsor's five axis mill) to retain the maximum structural strength.
-the wheels are decagons instead of circles. NOW can we squeeze in more than tangential contact every tenth of a rotation, therefore we get more traction.
-the wheel formation allows for no "getting pushed around" and great defense. We might be the rookies, but thanks to our ingenuity, we're not going to get bullied on the field
-these four wheels are directly driven by CIMs so we can zip across the field at 154 fps according to JVN Design Calculator (great tool by the way guys).
-the bot fits in a 26x26 square. its octagonal shape allows for surface area for electronics.

I know its pretty good, but what are some design tips you veteran teams might want to bestow upon us?

P.S. The manipulator is coming soon with just as much innovation as you see here. Watch out for team 3815!!!

P.S.S. We would like to thank our professional mentors for their wisdom and guidance in designing this beastly beauty.

JUST INCASE THIS IS N OT A TROLL JOKE

Hey Poonbear, my name is Andrew and I am a mentor for the Westminster School's Robotics team, team 2415, the WiredCats. I looked up your team number and I see that your team is from North Forsyth County. My team is located in Atlanta and are not too far from you guys and that you guys are rookies.

I see that there are a few design flaws (and boy do I wish that we had a 5 axis CNC mill) and we are always looking to help other teams whenever we can. If you would to set up a meeting, some students as well as myself can make the trip up there and help out some if you would like.

But remember, time is of the essence in this situation, we dont have much time left in the season but I know that if this is not a joke, we can really get something workable together.

Thanks and good luck in the season,
Andrew

[poohbear]

Thank you bunches Andrew Y.

Its nice to have a helper after such criticism and mockery

I have made a few major changes to the drivetrain since posting this though...

- With the help of our mentors, we have designed a magnificent two-speed (8fps & 16fps) crab-drive instead of the previous traction drive. We think this will handle this precision-based game a little better. Sacrificing power and speed for maneuverability.
- The bot is now decagon shaped. Soon 100% of decagon robots will have won championships too watch out JVN
- The wheels are still decagons. no one worry

Parts are about to be sent out for metal bending this next Monday. (yes, we told our sponsor that it would be too excessive to use their mill)

In addition, our prototype mini-bot is driving up the pole on average in 2.2 seconds and our prototype roller-gripper quickly grabs all three types of tubes. The lift is still being designed, but I'm happy with where we are. We also are prototyping a "secret weapon" to supplement these necessary mechanisms for the game. It might give us the leading edge It seems like a good rookie season so far. I'll friend you, andrew y, on facebook and we can get together to discuss designs sometime.

[ProgramLuke]

I would be extremely hesitant to attempt a crab/swerve drive as a rookie team (or even a veteran team!!!) if you haven't done some sort of offseason project to learn how to build one. I would suggest sticking with the 6wd that comes in the KOP so that you can devote more time to your manipulator.

[BJC]

Who exactly is your sponsor?

[SudoSammich]

I'd have to agree with luke on this one, swerve drive seems a bit ambitious for a rookie team, especially a rookie team with only four weeks of the build left. 5 axis CNC aside, you still need to be able to accurately assemble, program and learn to drive one of, if not the most, complicated drive system usually attempted in FRC.

It's possible, I suppose, but at that point I'd imagine the professional mentors you have would be doing more of the work than the students, as a rookie team's students generally wouldn't be able to accomplish such a feat. While I've seen rookie teams compete at the top levels of our regional in the past, it was due to the simpler, more solid mechanisms that worked well together and a good driver. Additionally, by the sound of it you haven't really started to BUILD your robot if you're still working on CAD sketches at this point, and that's no small undertaking. Best of luck if you try to pull it off, but I'd be very cautious to first look at a crab system two weeks into the season.

P.S. 2.2 seconds on the minibot? I remember seeing that a 5 lb minibot utilizing ALL the power from a tetrix motor (i.e. no loss in the system, which is just a wee bit impossible) would climb in 6.5 or so. Conservative estimates from that landed a competitive minibot at 7 seconds. It's entirely possible I'm not remembering the thread correctly, but 2.2 still seems a bit extreme.

[Chris is me]

On the off chance that you guys still aren't trolling, you guys still have quite massive delusions of grandeur - a two speed decagonal swerve drive is ridiculous, especially if you haven't started building or control yet, and especially if you're a rookie team.

Also, trolling CD is a terrible way to get your team attention - mostly because it's the bad kind of attention.

[kenavt]

For reference on team 3815:

https://my.usfirst.org/myarea/index....ils&tpid=52979.

Their (only) sponsor is "Automation Direct": http://nfrobotics.byethost2.com/?page_id=75

Website: http://raiderrobotics.co.cc/.

Frankly, from their sponsor, I doubt if they have the resources to pull something on this scale off. If anyone could.

[Creator Mat]

Where would one get a block of aluminum that big? We are sponsored by caterpillar and are able to order material through their tool room, and off hand I'm pretty sure we couldn't get our hands on a block that big (regardless of price).

On another note even if this isn't a troll post (i'm pretty convinced it is however), it is a fun thought experiment on way out their ideas. Plus I wouldn't be surprised if a veteran team or two experiments this off season with a non circular wheel just to see what happens.

[quinxorin]

Responding to the previous few posts, here's the actual calculations:

CIM starting stall torque (the maximum amount of torque it can exert before stalling and not moving):

343.4 ounce-inches.

Converting to foot-lbs:
(343.4/16)/12 = 1.778 ft-lbs.

Force exerted by each wheel (assuming the wheel is 8in), therefore, is:
1.778 x 3 (4in, the radius, is 1/3 of 12in) = 5.366 lbs-force.

Apparently, each wheel exerts 5.366 lbs of force pushing forward.

Now, let's look at the friction properties of the wheels. Because the wheels are perpendicular, they will have to overcome each other's friction in order to move. At least 2 of the wheels will have to slide at all times.

We can assume that high-traction treads have a coefficient of friction (μ) of at least 1 on carpet, though it is probably much greater (think 1.7-2). I will use 1 as the estimate. An object (i.e. the wheel) is capable of sliding if the following inequality is true: F(force) x μ > weight. The robot, including batteries, bumpers, and the minibot, will weigh 169.2 lbs. Therefore:

5.366 x 2 (there's two wheels) x 1 > 169.2
10.731 >169.2

That inequality is definitely false. Therefore, your robot will not move. Sorry, but it's the sad truth. And that doesn't even include the actual force it would take to move the robot, just to beat the friction of your other wheels.

A lot of people have been posting like me, that the drive train simply won't work. But none have posted a recommendation. If you want traction and not speed, here's mine:

build a six-wheel drive train, wide type. Use traction wheels on one pair of opposing corners and omnis on the other (otherwise your robot won't turn well). Use a gearbox with a ratio of at least 12.75:1 (standard AndyMark Toughbox). If you REALLY, REALLY want traction, put belts on it. I don't recommend that, though.

Here's the lesson to learn from this: You can have traction or you can have speed. You can't have both.

[LLogan]

I would just like to mention that I believe this team branched off from team 1746.

Team 1746 is the "Forsyth Alliance." It unifies a handful of high schools from a district. It looks like North Forsyth split into their own team, probably consisting of many members that used to be on 1746.

While they may be a new team, they probably aren't "rookies."

I thought the troll was hilarious, anyway.

[Grim Tuesday]

Originally Posted by Bill_B

Probably planning on milling the bumpers out of solid pool noodle stock, too. Ever wonder how they drill that hole down the middle of pool noodles?

Ive always assumed that they were extruded that way...

[Hawiian Cadder]

Originally Posted by Grim Tuesday

Ive always assumed that they were extruded that way...

i always thought they were a strip and had a well hidden seam somewhere.

[ratdude747]

Originally Posted by poohbear

Thank you bunches Andrew Y.

Its nice to have a helper after such criticism and mockery

I have made a few major changes to the drivetrain since posting this though...

- With the help of our mentors, we have designed a magnificent two-speed (8fps & 16fps) crab-drive instead of the previous traction drive. We think this will handle this precision-based game a little better. Sacrificing power and speed for maneuverability.
- The bot is now decagon shaped. Soon 100% of decagon robots will have won championships too watch out JVN
- The wheels are still decagons. no one worry

Parts are about to be sent out for metal bending this next Monday. (yes, we told our sponsor that it would be too excessive to use their mill)

In addition, our prototype mini-bot is driving up the pole on average in 2.2 seconds and our prototype roller-gripper quickly grabs all three types of tubes. The lift is still being designed, but I'm happy with where we are. We also are prototyping a "secret weapon" to supplement these necessary mechanisms for the game. It might give us the leading edge It seems like a good rookie season so far. I'll friend you, andrew y, on facebook and we can get together to discuss designs sometime.

you have no idea what you are getting into. my current team tried crab thier rookie year. that was all they were able to do. NO manipulator. NO driver practice. NOTHING but a drivetrain. and they started on day two. you are starting two weeks into build season. you have little to no chance of getting it right.

design and build a manipulator and mount it to the kit drivetrain. you need to get it in your head that polygon wheels are hard to make and even harder to use. cavemen invented the wheel. not the decagon. there is a reason.

not to mention oddball frame shapes are only for those who have a lot of human resources and experience.

if you are a troll, leave. go. get a life.

if you are an idiot, quit this nonsense while you are ahead.

if you are unaware, get your head into the game and rethink your work.

sorry to be uber-critical, but i do not tolerate stupidity well.

[sdcantrell56]

Wow! Way to put down any chance of inspiration for this rookie team. I don't think this is the right way to approach there ideas as out there as they may be. Perhaps you should use all of your asuperior knowledge to help instead of criticize.

Originally Posted by ratdude747

you have no idea what you are getting into. my current team tried crab thier rookie year. that was all they were able to do. NO manipulator. NO driver practice. NOTHING but a drivetrain. and they started on day two. you are starting two weeks into build season. you have little to no chance of getting it right.

design and build a manipulator and mount it to the kit drivetrain. you need to get it in your head that polygon wheels are hard to make and even harder to use. cavemen invented the wheel. not the decagon. there is a reason.

not to mention oddball frame shapes are only for those who have a lot of human resources and experience.

if you are a troll, leave. go. get a life.

if you are an idiot, quit this nonsense while you are ahead.

if you are unaware, get your head into the game and rethink your work.

sorry to be uber-critical, but i do not tolerate stupidity well.