18-05-2010 21:30

sdcantrell56

Re: pic: 8 Wheel Chassis Design Idea...

Very nice for a first design although there are a lot of things that I dont see included.

How are you planning on transferring power between the wheels and transmission, and what type of shaft do the wheels ride on? I dont see any bearings or bearing blocks if you are planning a live axle system like 254 uses

18-05-2010 21:58

rahilm

Re: pic: 8 Wheel Chassis Design Idea...

We used 254's drive system in 2009 (Lunacy) and one of the best things about it was the chain tensioning system; it was really cool, and made chain tensioning a breeze. I would suggest looking into that and incorporating.

18-05-2010 23:03

548swimmer

Re: pic: 8 Wheel Chassis Design Idea...

You'll need some supports along the bottom in case you get hit from the side.

Obligatory weight question.

Any reason the flat platform is so far from the ground? The elevated CG could make your robot extremely unstable.

Great job for a first drivetrain! It's nice to see people spreading their wings and getting into CAD!

18-05-2010 23:16

Jamie Kalb

Re: pic: 8 Wheel Chassis Design Idea...

Why not direct drive one of the center wheels? This is what 254/968 do. It'd save you a run of chain, and make a lot of sense if you're planning on running live axles.

18-05-2010 23:27

apalrd

Re: pic: 8 Wheel Chassis Design Idea...

As for chain tension, I've never looked at the 254 design close up (I did watch it beat us in the finals in Archimedes this year). The simplest way is to have a screw and pull the axle further from the gearbox or other chain end, to increase the center-center distance and tighten the chain. I assume thats what 254 does.

I don't see any live axle bearings on the inside that I can see. Did you leave these out?

Is the chain inside or outside of the extrusion? It would probably be more maintainable outside.

Also - Having that shelf makes minor difference for CG. With the exception of bump cross-ability, it would be fairly low in any other game.

AND - You shouldn't need a perimeter unless you have bumpers. No real reason to prevent collisions at this level, it should be robust enough to handle it. Just from observing other teams, I can't prove this.

And another recommendation - If you got your crio model online, I suggest you open it and remove excess crap. The cRio model I have includes all of the 15pin connectors for the modules, caps on some, a circuit board inside, case screws, connectors, etc. that are not important. This is especially important if you are like me and don't have a great graphics card, this adds tremendously to lag.


I like the SuperShifters, but while you've got that live axle why not drive a wheel with the live axle?

On the live axles - You are probably going to use a hex live axle for your wheels. That is how most "West-coast" drives are driven.

19-05-2010 00:57

NickE

Re: pic: 8 Wheel Chassis Design Idea...

254 does not use this method in our drivetrains, but has used it occasionally on arms (including our 2010 arm). Our bearing blocks have points on the ends. Specially designed cams are machined out of steel or 7075-T6 aluminum to push against the end of the bearing block. As the cam is turned with a 7/16" end wrench, the axle moves outward and the center-to-center distance increases, tensioning the chain. The bearing blocks can be locked in place by tightening the two flat head screws on them. You can see the bearing block / cam interaction in the following picture.

19-05-2010 06:53

O'Sancheski

Re: pic: 8 Wheel Chassis Design Idea...

I haven't done the drivetrain yet. This was just something that I whipped up in CAD very quickly. I was going to do chain to one wheel and then off that wheel to the rest.
I do, there is one in the back and the platform on the bottom is about 1/4" thick. It is just how the screenshot was taken. The platform is about an inch off the ground.

19-05-2010 10:37

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

Your going to add a quite a bit of weight in chain if you do that. I'm doing to echo what other said and drive on of the center wheel. Now you only have four 3 stretches of chain instead of 4. Which is less failure points.

Also, you will want a support going across the middle on the front side of the chassis as well, You definitely don't want to turn the electronics board into a main support structure, if that were to snap... So yeah, just throw in an extra support across the bottom.

19-05-2010 17:35

548swimmer

Re: pic: 8 Wheel Chassis Design Idea...

Sorry for the confusion. I was referencing the entirely flat surface where a manipulator would mount.

19-05-2010 17:46

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

I would think that this is there only so that it shows you can do stuff with it. There is no point putting stuff on it because you have no idea what it you be. But an open box looks stupid. So he put some plexiglass there to make it look spiffy.

19-05-2010 18:30

548swimmer

Re: pic: 8 Wheel Chassis Design Idea...

Spiffy is good

19-05-2010 20:40

O'Sancheski

Re: pic: 8 Wheel Chassis Design Idea...

yes this was my intention... 254 put some lexan on their bot this year and on my teams but we put tons of it... polycarb is just awesome.

19-05-2010 22:50

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

OKay..... So I honestly just noticed this... Would you mind explaining why your CRio is solid gold?

19-05-2010 23:15

Jamie Kalb

Re: pic: 8 Wheel Chassis Design Idea...

Rion,

All the gangstas in FRC have solid gold CRios. It's called "blingage". If you don't have a solid gold CRio, you're not a straight-up G.

19-05-2010 23:34

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

Ah okay, I understand now. You wouldn't happen to have one I could borrow so that I so can be a straight-up G, would you? I would love to be able to feel remorse for the uninformed individual.

20-05-2010 09:30

JamesCH95

Re: pic: 8 Wheel Chassis Design Idea...

I have never seen, nor heard of, a robot chassis breaking in half. FIRST chassis are generally very overbuilt, especially with pool noddle bumpers. 95 has mounted electronics on structural members for a long, long time and never had a problem.

Extra bracing isn't a bad idea on the more open end of the frame though.

20-05-2010 11:13

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

I haven't either, that's why things are so over built. I was just stating a worst case scenario. Now... I did see the entire top of a push bot cave in at the Oklahoma Regional in 09...

20-05-2010 14:47

O'Sancheski

Re: pic: 8 Wheel Chassis Design Idea...

When I downloaded the cRIO, it came that color. I didn't feel like changing it to the correct colors. It looks cool in gold though

20-05-2010 21:43

Mike Schreiber

Re: pic: 8 Wheel Chassis Design Idea...

There is no way of saying this chassis can be used in many years to come. We don't know the game. It probably won't be very useful in the water game.

I'm also curious how you arrived at the 17 fps number if you "haven't done the drive train yet" What gearing are you using in the super shifters?

22-05-2010 09:20

O'Sancheski

Re: pic: 8 Wheel Chassis Design Idea...

I am not positive on the gear ratios yet... My team has a transmission guru and he sets up all the transmissions. I am also not sure if I am going to even use the supershifters. Our transmission guru has custom made our transmissions since 2004 so we will probably go with them.

24-05-2010 15:02

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

It's possible to know how fast something will go without "doing the drive train". If you know how fast the output shaft on the gearbox goes, and the diameter of your wheels you will be using. By then finding the circumference and then with some more math you can find the Fps.

24-05-2010 15:12

Andrew Schreiber

Re: pic: 8 Wheel Chassis Design Idea...

Which would be considered, in my opinion, "doing the drive train". If he hasn't figured out how he is driving the wheels he cannot have done the math as chain may increase/decrease the reduction from the transmission.

24-05-2010 18:36

Mike Schreiber

Re: pic: 8 Wheel Chassis Design Idea...

So then what do you define as "doing the train"?

Edit: Andrew beat me to it You cheated by posting at work! I actually have to do stuff at my job...

24-05-2010 20:10

Rion Atkinson

Re: pic: 8 Wheel Chassis Design Idea...

For a CAD person, doing the drivetrain means CADing the drive drain. Putting the axles, sprockets, ect.

24-05-2010 22:20

Mike Schreiber

Re: pic: 8 Wheel Chassis Design Idea...

Who said anything about a CAD person. The thread title is "Design Idea". Designing is more than a pretty picture, you need data to back it up...then you can be pretty.

23-08-2010 12:55

RookieWookiez

Re: pic: 8 Wheel Chassis Design Idea...

At IRI this year our team knocked an air storage tank out of a bot... also knocked their plexy glass lid off. This happened as we fell back down on top of them as they drove out from under us