10-01-2009 20:03

Re: pic: Whats going on HERE?

I'm curious... What sort of numbers have you done on the plastic worm gears, and the amount of weight they're going to take? If I recall from my own off season tests, they aren't the strongest things out there...

Also, how are you going to deal with wire twisting? Are we allowed 4 window motors, and have you bought 2 more of the current years? We're not allowed any of the previous years, as far as my understanding goes.

10-01-2009 20:03

gorrilla

Re: pic: Whats going on HERE?

swerve drive perhaps


really dident take that long to build 4 of them, we found these wonderful boxes that were just the right size.....



we put them under our 2008 robot and the worked great,
only about 40 pounds of pressure on them i believe, there just prototypes(our first directly driven wheel) we have other more powerful motors that we could switch them out for quickly if they dont hold up, only six motors used total(4 for driving wheels and two for turning them)

as for the wires,thats something we'll have to figure out later


ps.. it may or may not be, based off your cad you posted awhile back.....

10-01-2009 20:08

Sam2197

Re: pic: Whats going on HERE?

ya have to wonder... what are the cims being used for????

10-01-2009 20:10

gorrilla

Re: pic: Whats going on HERE?

thats a suprise.......but i can tell you that thier needed(badly) in other places.... which is why we went for the window motors

10-01-2009 20:13

Re: pic: Whats going on HERE?

I'm confused as to how this could be based off my CAD. I've never done a direct drive, nor would I ever consider it. If something breaks in this module, the entire thing needs to come apart to change it.

The use of thin plate for a module will allow it to flex a hefty amount, and deflection isn't good. A tiny amount as small as .125" of deflection will take your wheel's contact patch down by somewhere around 60%, depending on the size. If it's not rigid, you lose HUGE amounts of efficiency when turning.

As far as strength of the Window motors, keep us posted on how they do.

10-01-2009 20:22

gorrilla

Re: pic: Whats going on HERE?

well the box(mostly inspiriationaly)

actually it dosent all have to come apart....the way we built it, the motor is bolted to the outside of the box, the hub is attached to the output gear, the hub is attached to the wheel, and a 1.5inch 3/8th bolt is put through a bearing which is then bolted to the other side

to remove the entire motor and wheel and replace it, takes about 3 minutes


yeah, the plate is pretty thin, we are waiting for comformation if a local machine shop can make us some thinker ones(say 1/8inch alluminum?)

pretty much, it was built to be as cheap and simple as possible(as i said its our first time Not using tank drive) we're feeling pretty ambisious this year

ps.. we have 4 window motors for driving the wheels, and we have 2 other motors that came in the kit(not sure what they are, like a bigger more metalic version of the window motor?)

10-01-2009 20:29

Akash Rastogi

Re: pic: Whats going on HERE?

Can you link to the exact one please? I don't see the point of this design btw, what exactly is the point?

10-01-2009 20:31

Re: pic: Whats going on HERE?

Hey, just keep an eye on this:

I'm not sure how you plan to drive your robot with 4 of a motor that we're only allowed to use 2 of...

10-01-2009 20:32

Mike8519

Re: pic: Whats going on HERE?

Sorry to bear some bad news...

You only get two window motors (1 of each orientation) in the KoP so this setup is not legal.

10-01-2009 20:34

eugenebrooks

Re: pic: Whats going on HERE?

You need to check that you are not violating the window motor count.
One left and one right denso motor was in the KOP, providing two
motors, not four.

Eugene

10-01-2009 20:35

gorrilla

Re: pic: Whats going on HERE?

yeah we saw that, we'll have to work something out(not to hard to get around)



oh, this one http://www.chiefdelphi.com/media/photos/28443
they were going to be v-shaped originally, but then we found those boxes...... and its the same tring setup to(with the sprocket up top)



and we know, we can only use two window motors, theres these other ones that are bigger that we are trying to make work

10-01-2009 20:39

Re: pic: Whats going on HERE?

So there aren't 4 of them. There's two separate kinds. How are you planning to keep the robot speed constant with two different wheel speeds?

10-01-2009 20:46

Vikesrock

Re: pic: Whats going on HERE?

I'm confused as to how this would work. If they are indeed crab modules you have 2 Denso Window Motors (1 left, 1 right) and 1 Keyang motor to work with with similar form factors.

What motors are you planning on using?

10-01-2009 20:46

gorrilla

Re: pic: Whats going on HERE?

on the prototype there are(sorry if i dident make that clear)

the window motors are 90pm and the other ones are like 85 so it shouldent make that much of a difference(i hope) any suggestions?

we could also use the globe motors if we have to.....

just what we had lying around is what we used...the final version will absolutely be legal...


another reason for the swerve drive is that a tank drive wont turn the robot(so we thought why turn the robot, when we could turn the wheels?)

10-01-2009 20:49

Akash Rastogi

Re: pic: Whats going on HERE?

Don't know how you tested that statement but it is quite incorrect.
Tank drive turns just fine for us....not to mention many others.

10-01-2009 20:51

gorrilla

Re: pic: Whats going on HERE?

on the FRP? with the trailer?

our 2007 robot wouldent turn at all.......maybe its just us....

10-01-2009 20:54

Akash Rastogi

Re: pic: Whats going on HERE?

Yup and yup.

Did you have your weight distributed properly across the entire base and over the four wheels? If not, then that's part of the problem. I'd suggest retrying that before you take a drastic design risk such as this. But that is just a suggestion.

10-01-2009 20:55

Dominicano0519

Re: pic: Whats going on HERE?

you know thats not bad if you use those in the front to start and then kick in two cims after you get some speed to avoid doing a burnout almost like a two speed tranny

let me just take a guess
since cims are designed to continously run and window motors are not i would guess that you are using the cims to run a ball herding mechanism and using the window motors for drivetrain

10-01-2009 20:57

Dominicano0519

Re: pic: Whats going on HERE?

you could just back up into the trailer and have the bumpers start the turn for you

10-01-2009 20:58

gorrilla

Re: pic: Whats going on HERE?

yes we did,

we had it in low gear(AM Gen2's) the wheels were just spinning(tried slowly accelerating and getting up to speed and trying to whip it around, to no avail)may be some other factor we're missing?

10-01-2009 21:00

Akash Rastogi

Re: pic: Whats going on HERE?

Hehe, or that.
Depends on the trailer orientation too.

10-01-2009 21:00

gorrilla

Re: pic: Whats going on HERE?

we cant get any pool noodles as its winter and there out of season....though when we did back up it jackknifed and made it slowly(SLOWLY) turn around halfway before it got in line with the robot

10-01-2009 21:01

thefro526

Re: pic: Whats going on HERE?

Let's put it this way, you might want to write off this design while you still have the chance. This drive train will be very inefficient with two different kinds of drive motors thats aren't linked together to equalize the power. If you really want to build a swerve with window motors as the drive motors then I'd use a coaxial swerve with centralized gearboxes to equalize the output.

Also something else to think about is that your robot is going to travel at about 2fps if you direct drive off of the window motors.

10-01-2009 21:04

gorrilla

Re: pic: Whats going on HERE?

actually more like 4-6(we actually put them on a 2x4 and clamped them underneath our 2008 robot and drove it on the FRP and clocked the speed....



anyways.....its still a prototype

10-01-2009 21:07

Akash Rastogi

Re: pic: Whats going on HERE?

Still don't see the point in this design.

This year's game does not benefit from torque...like, at all.

Just explain the purpose of this to me. Thanks.

If you decide to continue with the prototype or follow through with it, then I wish you good luck.

10-01-2009 21:07

Ian Curtis

Re: pic: Whats going on HERE?

Approximately how far apart are your wheels on the frame? With a 4 wheel drive skid steer, with the wheel centers about 30ish inches apart on the axis on the long dimension, and 22ish on the width dimension, our robot turned. We too had AM Gen2 shifters in low gear. We tried both pinning it and a gradual acceleration. In both cases it turned, although not particularly well. (Gradual acceleration turned better than pinning it)

10-01-2009 21:08

m^3

Re: pic: Whats going on HERE?

We have a 4wd long test base and it turns fine on linoleum floor (no regolith); just make sure the wheels aren't spinning before executing a tight turn. I cut throttle before turning, can easily do a 180+ spin. We don't have a trailer yet but Dave Lavery made a post on here about exploiting the trailer to turn quickly.

I think there is a definite advantage to a swerve drive, just questionable whether it's worth it this year and how well this setup would work. edit: our team decided the extra practice time with 4wd would be worth more than time spent designing/building/testing a swerve drive.

10-01-2009 21:09

thefro526

Re: pic: Whats going on HERE?

If you're using a 6" wheel and your motor spins at ~90rpm like you said then the math says that it should go about 2fps... ((18.84" cicumference) x (1.5rev. per second))/12 = 2.3.... FPS.

But even if thats wrong 4-6fps is still really slow for an FRC field. It would take you 10 seconds or more to cross the field at that speed

10-01-2009 21:11

Akash Rastogi

Re: pic: Whats going on HERE?

Plus the factor of ridiculously slick wheels.

btw, I checked Dustin's math...and its correct.

10-01-2009 21:15

gorrilla

Re: pic: Whats going on HERE?

not so much torque, with the cims(going full on, out a toughbox) the wheels just spun and spun untill the forward momentum overtook the spinning and it went forward(about 4 seconds) we wanted to test soMething that we could just drive around and not have to worry about "easing it on" with the window motors theres' almost no slipping and nearly instant acceleration(yes we've done our math)

hmm, that exactly how we had our setup...ill make sure to test it again on monday to see whats wrong(seeing as so many peoples robots could turn) i wonder what could be causing our problems?

10-01-2009 21:16

Akash Rastogi

Re: pic: Whats going on HERE?

There's your problem right there.

10-01-2009 21:19

gorrilla

Re: pic: Whats going on HERE?

i know, but in the heat of the game, i'd want to be able to have as much control as possible as quickly as possible


and about the math, I dont know, but its definately faster than 2.3 fps....(maybe we had a strong tailwind)


and if we find out this wont work, its not that hard to switch to tank drive.....

10-01-2009 21:22

thefro526

Re: pic: Whats going on HERE?

The thing is in the heat of the moment you'd just need to control your acceleration a bit. Make your acceleration progressive like go 25% then 50% then 100% throttle. Once you're moving a little bit you'll be less likely to spin wheels. And trust me, you'd rather spin wheels a bit and go 10fps than not and be limited to 4fps.

10-01-2009 21:25

gorrilla

Re: pic: Whats going on HERE?

this could also be done in programming easily, if we decide to use a tank drive....we'd only have two cims(shouldent make any difference as the kickoff showed)


basically, we could do anything, its only the second week now....just prototyping i'd thought id share

10-01-2009 21:27

Akash Rastogi

Re: pic: Whats going on HERE?

Using a tank drive (skid steering) on a drivetrain built like a swerve seems to defeat the purpose, doesn't it?



o wait nvm i think i interpreted that wrong.

And yup, sorry to sound like we're bashing your design, just giving criticism. After all, that is the point of posting prototypes on here.

10-01-2009 21:27

thefro526

Re: pic: Whats going on HERE?

Precisely, thats a good idea.... We're probably going to implement that as well. If you do a tank drive with a progressive acceleration then there's no need for a window powered swerve.

10-01-2009 21:34

gorrilla

Re: pic: Whats going on HERE?

yeah, what ever desicions we make in the next week for our shooter/harvester design, will probobly cement our drivetrain to one or the other.....


we could,just make a swere work with the 2 cims and have only 2 modules in the front? wouldent be as easy to steer though

10-01-2009 21:36

Akash Rastogi

Re: pic: Whats going on HERE?

It might be a fun thing to try in the offseason, but if I were you I wouldn't risk spending that time and energy especially in the first 2 weeks of build. Some don't realize this, but loss of time doing something a bit odd can cost you a lot more than doing something crazy in like week 3 or 4.

If I understand correctly, you'd just want the front two to be turning? Why not just make something like ackerman ("car steering") then?

10-01-2009 21:40

thefro526

Re: pic: Whats going on HERE?

Stogi Speaks the truth here.

It's better to spend an extra day thinking before you start building and make the best decision possible than to commit to a risky design like this and loose a week when it doesn't work.

That being said it's not a bad concept it just might not work for this game. The window motors would put a severe handicap on your speed and may not be robust enough for a robot's drive train.

10-01-2009 21:41

gorrilla

Re: pic: Whats going on HERE?

well that way there powered also, and we could just use two of what we have with some minor modification.....

and so far we've only spent two days on it, out of the week ....if you'all think its such a bad decision..its not that hard to just switch to something else...


as for time...its amazing what can be done in 4 hours when everybody is highly motavated and energized........

i remember last year, on the day before shipping, at 8:30 at night, we completely changed our drivebase from 4wd to 2wd with a castor and a unpowered wheel....


ps. this is what prototyping is for....