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chris31
12-08-2008, 05:11 PM
[cdm-description=photo]32116[/cdm-description]

chris31
12-08-2008, 05:12 PM
This is still being worked on but if you have comments, questions or suggestions feel free to post them.

NickE
12-08-2008, 07:28 PM
Looks good!

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

ironbears
12-08-2008, 07:29 PM
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?

AdamHeard
12-08-2008, 07:34 PM
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.

chris31
12-08-2008, 07:39 PM
Looks good!

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

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

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.

The walls are .15 aluminum.

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?

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

AdamHeard
12-08-2008, 07:44 PM
.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.

R.C.
12-08-2008, 07:47 PM
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.

chris31
12-08-2008, 07:55 PM
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.

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

.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.

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.

AdamHeard
12-08-2008, 08:02 PM
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.

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.

chris31
12-08-2008, 08:12 PM
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.

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.

Musicninja
12-08-2008, 08:14 PM
You could try dropping the middle pairs of wheels just like a half an inch, to make it easier to turn...

NoahTheBoa
12-08-2008, 08:17 PM
You could try dropping the middle pairs of wheels just like a half an inch, to make it easier to turn...
1/8 inch or 3/16 inch drop is usually sufficient.

chris31
12-08-2008, 08:19 PM
You could try dropping the middle pairs of wheels just like a half an inch, to make it easier to turn...

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

Cory
12-08-2008, 08:23 PM
Ok. I'm still reading up on differnt distances to drop the middle wheel.

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.

R.C.
12-08-2008, 09:45 PM
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.

Chris I like your stuff and if you need any help with CAD, please email (rcthekid1323@gmail.com)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)) ;)

chris31
12-09-2008, 04:56 PM
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.

AdamHeard
12-09-2008, 05:00 PM
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.

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.

meastman
12-09-2008, 07:12 PM
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

gorrilla
12-09-2008, 07:15 PM
not to be negative but,

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

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

chris31
12-09-2008, 09:26 PM
Adam, that makes sense. Thanks for the input.

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

All six wheels are powered in this design.

not to be negative but,

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

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

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.

gorrilla
12-10-2008, 03:50 PM
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.


yeah but it saves money and valuable time.

any other teams weld theirs?

chris31
12-10-2008, 04:30 PM
yeah but it saves money and valuable time.

any other teams weld theirs?

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

gorrilla
12-10-2008, 05:04 PM
Sorry, Im not really looking for recommendations on why I should use the kitbot chassis.


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

sdcantrell56
12-10-2008, 05:07 PM
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.

gorrilla
12-10-2008, 05:18 PM
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.


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.......

sdcantrell56
12-10-2008, 05:25 PM
You should look into having standoffs between the plates. That would add a ton of strength.

chris31
12-10-2008, 06:07 PM
You should look into having standoffs between the plates. That would add a ton of strength.

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

sdcantrell56
12-10-2008, 06:19 PM
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.

AdamHeard
12-10-2008, 06:26 PM
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.

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,

sdcantrell56
12-10-2008, 07:38 PM
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,

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.

chris31
12-10-2008, 07:52 PM
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.

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

rally_racin'_94
12-11-2008, 08:02 AM
6 wheel drive???:confused:

or less??

rally_racin'_94
12-11-2008, 08:04 AM
how would you get it to turn with 6 wheel drive because all the wheels have a sprocket

gorrilla
12-11-2008, 08:58 AM
how would you get it to turn with 6 wheel drive because all the wheels have a sprocket


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


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

chris31
12-11-2008, 10:43 AM
if all the wheels are powered it shouldent have a problem turning............


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

Yes, its tank drive.

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

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