08-12-2008 18:12

chris31

Re: pic: New Chassis Concept

This is still being worked on but if you have comments, questions or suggestions feel free to post them.

08-12-2008 20:28

NickE

Re: pic: New Chassis Concept

Looks good!

With all that pocketing on the front and back rails, I would consider adding a crossbeam in the middle.

08-12-2008 20:29

ironbears

Re: pic: New Chassis Concept

its best to build the chasis heavy and make lighter by cutting holes out as you need that way you dont sacrafice too much strenght. Basic tankdrive?

08-12-2008 20:34

AdamHeard

Re: pic: New Chassis Concept

what is the wall thickness on the extrusion?

if it is 1/8" and pocketed, I would recommend switching to 1/16" and don't pocket it. Similar weight, less work, and depending on the pocket pattern, stronger.

08-12-2008 20:39

chris31

Re: pic: New Chassis Concept

I was waiting to see how the electronics will drop inside and chain paths before adding crossbeams of any sort into the chassis.

The walls are .15 aluminum.

Current holes are just to get an idea of how much weight can be removed while keeping structural integrity.

08-12-2008 20:44

AdamHeard

Re: pic: New Chassis Concept

.15 is not a common commercially available thickness for extrusion, are these made from sheet metal?

Either way, that's some thick stuff, for that tall of a frame member, I'd recommend thinner material with less pocketing.

08-12-2008 20:47

R.C.

Re: pic: New Chassis Concept

Great job on this and it looks nice. The thing I like about FIRST is that there are so many different designs and they each have pro's and con's to them. This design is a great design and probably a pretty light chassis. Just include someway of tensioning the chain (Andymark's New Chain Tensioner is coming out!). BTW great CAD JOB, more views would be nice.

08-12-2008 20:55

chris31

Re: pic: New Chassis Concept

Yeah. I have a few ideas starting to be drawn. Just nothing is final in CAD yet.

Its McMaster 1630T14. So you recommending something thinner with less pocketing. Thats doable. Im still playing around with best ideas for removing weight and keeping strength.

08-12-2008 21:02

AdamHeard

Re: pic: New Chassis Concept

Oh wow, that's THICK stuff. The base is .15 thick, but the legs are .26. HEAVY stuff, 2.2 lbs a foot or so.

If you do use it, find another supplier; $66 for 5' of that is ridiculous.

08-12-2008 21:12

chris31

Re: pic: New Chassis Concept

I was hoping to mill down the length of the legs of the U channel. Do you have a reccomentation on a better replacement for this U channel that would work better. Thanks.

EDIT: Not at my computer but I think it was like 1.2 a foot with pocketing and reducing leg length.

08-12-2008 21:14

Musicninja

Re: pic: New Chassis Concept

You could try dropping the middle pairs of wheels just like a half an inch, to make it easier to turn...

08-12-2008 21:17

NoahTheBoa

Re: pic: New Chassis Concept

1/8 inch or 3/16 inch drop is usually sufficient.

08-12-2008 21:19

chris31

Re: pic: New Chassis Concept

Ok. I'm still reading up on differnt distances to drop the middle wheel.

08-12-2008 21:23

Cory

Re: pic: New Chassis Concept

1/2" is too much. Your robot will be a seesaw. I would recommend 0.125-0.1875.

I would also reccomend against using C-channel. It is a major pain to machine. I think you'd be a lot happier with your results if you made this out of 1x2 extrusion.

08-12-2008 22:45

R.C.

Re: pic: New Chassis Concept

Chris I like your stuff and if you need any help with CAD, please email me. Try using 1x2 aluminum. We have using a 1/16 wall and it is fairly light. You can even pocket some out on the sides but none on the top. We created a frame that had a ton of cnc work and played battle bots with it to see if it would crumble. Plus stress testing told us it would be fine. Make sure you have a safety factor of 10 ((Just to be extremely Safe))

09-12-2008 17:56

chris31

Re: pic: New Chassis Concept

Just the 6 pieces of C channel totally 14.13 pounds whereas the same length of 1x2 with 1/6in walls is about 7.7 so I see what you are saying about weight.

Cory, whats so hard about machining C channel? Im not a machinist but the machinist didnt say anything when I drew a quick concept for him.

09-12-2008 18:00

AdamHeard

Re: pic: New Chassis Concept

Both the cutter and the vice exert lots of force on the part. Square/rectangular tubing has walls that resist forces rather well in all directions square to a face. C channell is "missing" a side which often can make it hard to clamp in certain orientations (for example, vertically you'd only be holding the ends of the bottom leg), and hard to actually cut in certain orientations (the legs will deflect from the cutter probably, leaving poor finishes). There are ways to get around that of course, but ideally you'd make machining as easy as possible.

The 2x1 will also result in a much more rigid frame, it doesn't twist along it's own long axis as easily as the C channel will.

09-12-2008 20:12

meastman

Re: pic: New Chassis Concept

Our team's robot for the last few years has had the motors directly drive the middle wheel. This could make turning easier if you drove those wheels instead

09-12-2008 20:15

gorrilla

Re: pic: New Chassis Concept

not to be negative but,

could just save yourself the trouble and use the kitbot chasssis....................

would loose the cool factor though.........

09-12-2008 22:26

chris31

Re: pic: New Chassis Concept

Adam, that makes sense. Thanks for the input.

All six wheels are powered in this design.

Well, that kind of defeats the purpose of having the chassis design the way you want it and work to your needs. It also wouldnt be much of a learning experience to just bolt some frame material together.

10-12-2008 16:50

gorrilla

Re: pic: New Chassis Concept

yeah but it saves money and valuable time.

any other teams weld theirs?

10-12-2008 17:30

chris31

Re: pic: New Chassis Concept

Sorry, Im not really looking for recommendations on why I should use the kitbot chassis.

10-12-2008 18:04

gorrilla

Re: pic: New Chassis Concept

well i was just putting it out there...............

10-12-2008 18:07

sdcantrell56

Re: pic: New Chassis Concept

Now is the time to be designing new drivetrains, and telling a team to just use the kit frame right now is not really a good way to encourage new development and growth. Yes in some instances and for some teams it would be better to just use the kit frame; however, a lot of teams can pull off a better custom chassis that fits there needs perfectly. Also we don't even know if we will be given the same kit frame this season.

10-12-2008 18:18

gorrilla

Re: pic: New Chassis Concept

i know this, and it was just a suggestion...

i also know that if my team had access to all the tools and materials needed, we probobly would...

i am all for encouragement and new growth, just commenting.......

10-12-2008 18:25

sdcantrell56

Re: pic: New Chassis Concept

You should look into having standoffs between the plates. That would add a ton of strength.

10-12-2008 19:07

chris31

Re: pic: New Chassis Concept

Thanks for the recommendation. Ill be working them into the design after I finish finals (tomorrow).

10-12-2008 19:19

sdcantrell56

Re: pic: New Chassis Concept

If you have the resources, I would recomend making your own standoffs out of delrin. This way they could be a larger diameter and distribute the load better and still be lighter than aluminum standoffs.

10-12-2008 19:26

AdamHeard

Re: pic: New Chassis Concept

If the delrin standoffs are threaded, they will be much lighter than aluminum overall, but the threads won't hold up real well.

If the they are thru holes, they bolt increases the weight a lot as it is rather long. I'd Imagine an aluminum standoff with tapped ends is lighter than a delrin standoff with a thru bolt of comparable strength,

10-12-2008 20:38

sdcantrell56

Re: pic: New Chassis Concept

That is a very good point. I have actually not thought about that before. One nice thing about a thru-bolt with a delrin spacer is that you could buy delrin round stock and make the spacers yourself saving a ton of money. We spent $150 just on standoffs for our drivetrain last year which used COTS threaded standoffs.

10-12-2008 20:52

chris31

Re: pic: New Chassis Concept

We should be able to buy raw stock and tap the standoffs ourselves, so that should be be much of a problem.

11-12-2008 09:02

rally_racin'_94

Re: pic: New Chassis Concept

6 wheel drive???

or less??

11-12-2008 09:04

rally_racin'_94

Re: pic: New Chassis Concept

how would you get it to turn with 6 wheel drive because all the wheels have a sprocket

11-12-2008 09:58

gorrilla

Re: pic: New Chassis Concept

if all the wheels are powered it shouldent have a problem turning............


its tank drive presumably not car steering.........

11-12-2008 11:43

chris31

Re: pic: New Chassis Concept

Yes, its tank drive.

Tank drive. Its been done over and over again successfully.