Chassis - Team 772 2011 off-season (update)
 

I finished updating the chassis.

Old thread is : http://www.chiefdelphi.com/forums/sh...ad.php?t=97193d

Gen2 Andymark transmissions
6WD (IFI 6" diameter 1.5" wide)
1/8" sheet metal
0.75" flanges for structural support
Direct drive to middle wheel

Changes:
Sheet metal to 1/8" from 0/09"
Put supports across transmissions
Moved Back/Front plates to outside
Put Belt pulleys onto wheels
inserted Hub onto middle wheel for direct drive
Made a few more flanges for structural support (note: could not put too many on bottom because the belts would rub against them)

Frame weighs 9.27 pounds without motors or transmission.
Chassis total weight is 27.35 pounds

Any more questions or Tips for improvement are appreciated.

Re: Chassis - Team 772 2011 off-season (update)
 

I don't understand the point of the material below each wheel.

Re: Chassis - Team 772 2011 off-season (update)
 

Style points

Re: Chassis - Team 772 2011 off-season (update)
 

Bumper support? Your not the first person to ask me this, but yes it mainly is just for looks. They dont add alot of weight, but i may remove them.

Edit: I just remembered the real reason. They are supporting the transmissions on the inside

Re: Chassis - Team 772 2011 off-season (update)
 

The transmissions are too low to the ground to allow you easily and legally mount bumpers to the side plates. I'd still recommend raising everything up to reduce your ground clearance.

Additionally, by removing the trapezoids from the side plates, you can add another flange along the length of their lower edge and make everything stiffer. Right now, the trapezoids do nothing but hurt you.

Re: Chassis - Team 772 2011 off-season (update)
 

The picture shows how the transmission is mounted to the side plate. If i remove the trapezoids, the bottom two supports will not be held on by anything. However, by moving the transmissions further up and removing the trapezoids, the two Top supports now would have nothing to hold onto, unless i change the sheet metal design (also changing wheel height). I could change how close the trapezoids extend to the floor (shorten them by 0.5"), make some flanges on the bottoms of the trapezoids and then the floor clearance would be about 1" (currently .5"). Would this be a better alternative?

Re: Chassis - Team 772 2011 off-season (update)
 

You want to change the sheet metal design -- by moving the gearbox up and changing the wheel, you'll lower the entire frame neared to the ground. Since a typically legal bumper height is between 1-7" or so from the ground, that puts the frame in the sweet spot.

Flanges on the bottom of the trapezoid won't really do anything useful to make the frame stiffer. A flange that runs, uninterrupted, along the entire bottom length -- just like you have on top -- is the most rigid solution.

Re: Chassis - Team 772 2011 off-season (update)
 

I'll have the design changes up by tomorrow hopefully.

How much ground clearance should I make it? Im thnking 1 inch so the bumbers are even with bottom or robot. Should it be loweror higher?

Re: Chassis - Team 772 2011 off-season (update)
 

1" is probably fine. The bumper rules will usually reflect the sort of field the game is played on -- so if the field is largely flat or if it has only gentle inclines, the typical 1"-7" bumper zone will work fine. If robots are expected to navigate steeper ramps, additional ground clearance is required and the bumper zone will reflect that.

Re: Chassis - Team 772 2011 off-season (update)
 

I finished faster than i thought. The new chassis is actually heavier than the old one. The new weight is about 0.5lbs more.

Re: Chassis - Team 772 2011 off-season (update)
 

Looking good! Now you'll need to add some material to that center wheel's mounting hole and add a bearing so it can be direct driven.

Re: Chassis - Team 772 2011 off-season (update)
 

Here is how i did the direct drive to the middle wheel.

Basically, the output shaft is connected to the hub (keyway) which is inside the wheel and bolted on. I put a support axle on the other side which is inside the bearing on the wheel.

Will it work? Or is this a bad idea?

Re: Chassis - Team 772 2011 off-season (update)
 

No, this is probably a bad idea. You want support through all the material of the wheel to the end of the gearbox output shaft on a bearing. It is definitely much easier to use a wheel or attach a hub that allows the output to go through the wheel and rest of a bearing.

Re: Chassis - Team 772 2011 off-season (update)
 

I cant find a bigger shaft than this one. I already have the biggest from andymark. How can i find a bigger one? I can try to make it smaller inbetween the wheel and frame too, but i dont think it will be long enough.

EDIT: It will fit but it will be extremely close. About 0.03" clearance

Re: Chassis - Team 772 2011 off-season (update)
 

Someone with more knowledge can probably let you know if its a good idea or not, I'm far from an expert. I'm just basing that off what I know about driveshaft support in direct drive systems.

If anything, just machine your own output shaft. Its a pretty simple lathe op.

Re: Chassis - Team 772 2011 off-season (update)
 

Getting closer, but you still have a ways to go.

Shorten the frame. There is no need to make it that tall. Height adds weight. You can take out at least a pound out of the frame by making it shorter.

The flanges on the front of the base aren't long enough. Make them 1.5" - 2" long. That frame will bend otherwise on impact.

Connect the two side plates. I like to do it by making the outer plate have really long flanges and pop-rivet to the inside plate. This will make the sheet metal tubes holding the wheels very strong. Right now, the plates will easily bend upon impact, potentially dropping your wheel out of the frame. Not pretty. We have used standoffs before, but I really liked making the flanges longer.

On a frame like this, it helps to draw in some sort of electronics base plate, and to use that as a structural member. Bolt your frame to it. This will help keep everything square, and augment the flanges on the front and back. Some teams use a large piece of aluminum plate with holes to keep the weight down. We've used 1/2" baltic birch before to good effect. Your call. We are looking at making that plate out of punched aluminum next year.

Which brings me to my next question. If you are going to try to make this (either during the season or now), what machines do you have access to? The triangles look like they won't punch out, though this all depends on which punches your sponsor has. Design for manufacture is huge. Will it be CNC bent, or hand bent?

While you are at it, how are you going to do bumpers? I like how 971 did it last year, but there are other ways. Now is the time to think it through. We could swap bumpers in O(1min) with ease, and have thoughts on how to make that even faster for next year.

Do you have a plan for tensioning the chain?

Re: Chassis - Team 772 2011 off-season (update)
 

Will be done tonight.
Im guessing you just mean the front and back plates. I can do this :)

By stand-offs you mean braces, kind of like an axle with no wheel on it? I think i would prefer extending the flanges on the tops and bottoms of the frame. However this makes it hard to get into the frame to do work on the robot of needed. Or am i thinking something different form you?

I thought you couldn't put electronics on any metal. I will do this but it will be lexan instead of aluminum.

We already have a bumpers skirt to use for next year. But placement will be done soon.

I have been thinking about this alot. And i think i know what i should do now, so i will put it on my list to do.

Re: Chassis - Team 772 2011 off-season (update)
 

Standoffs can take many forms. One of the easiest is to put a spacer on a bolt between the two plates, and then clamp down. You can also thread both ends of a piece of stock that is the right length, and screw bolts into it. AndyMark's transmission is held together with standoffs. When designing standoffs, the larger in diameter the standoff, the stiffer the joint.

Leave pleanty of room around the wheels for getting in. The flanges will make it harder to access, but will make it a lot stiffer. In 2010, when 971 did a box frame out of sheet metal, the two parts were flexible when separate. Once they were bolted together, the entire frame stiffened up remarkably, and we didn't have a problem. This is how 971 did our frame last year, and it worked quite well. We are going to make some minor modifications, and do it again this year if the game fits it.

You can put electronics on metal. They must be electrically isolated from it though. This just takes a little bit of care. You can buy nylon screws to bolt the motor controllers down, put a rubber gasket underneath the cRIO, and you should be fine. 254 has done metal bases for 3 years now with no issue. The nylon screws make it so that if the contacts on the motor controllers touch the screws, they won't conduct electricity.

If you are going to go through all the work to get this machined and designed, I would seriously consider making 2 sets and swapping them. It will look a lot more professional and the skirt will not catch on anything.

I didn't see a response to the question about machining capabilities. That will help us evaluate your design for ease of manufacture.

Re: Chassis - Team 772 2011 off-season (update)
 

Oh yea. My dads company has a water-jet machine, he also told me that he could get it laser cut for us. I dont now If they have a CNC machine to bend the pieces, but i know they have hand ones, we also have one in our shop. We do have access to every machine to make this chassis. And we are going to be build this one before kick-off, to train the new kids, and to test the new BETA if we get chosen.

Re: Chassis - Team 772 2011 off-season (update)
 

New and improved :)
Electronics Base is there, its just hard too see, thats why theres a huge reflection in the center of the robot
except now the frame weighs 12.16 pounds without wheels/transmissions.



Any more questions, or improvements??