Re: Show off your machining!
 

It puts a lot of load on a end mill to dive or spiral into a part, even for center cutting end mills.

For teams with ATCs, it's generally faster to just drill a quick hole and dive your cutter into the part rather than taking a while to spiral down through the part. Of course, if you have to manually change tools, its probably faster just to spiral in.

Re: Show off your machining!
 

Was going to ask this as well. It looked as if they were tumbled afterwards.

Re: Show off your machining!
 

Interesting story, glad you asked.

I got the sideplate idea from 125, I could be wrong but I believe they've been doing a sideplate style drive since 2007.

Anyway, as for why choose a sideplate style drive was because it lined up best with what machining resources we had. Last year our resources were mainly me using a sponsors shop with cnc controlled bridgeports, engine lathes, and basically everything you could want in a shop. In addition to my shop use we had some basic hand tools at the school and I talked to one of our sponsors (Mori Seiki) to cnc some parts for us. So essentially we had two machinists in two shops making our robot.

The original plan for 2013 was to make a WCD. I talked to my contact at Mori Seiki and went over some WCD part drawings with him. He felt that it would be a waste of a resource to make WCD siderails on their equipment, as they can be machined manually pretty easily. So we settled that if we were to do a WCD the only parts Mori would make would be the wheels, which left everything else for me to make which I thought was less than ideal. Thus was born the siderail design, which was designed to be easily made given our resources. We had Mori do our siderails and wheels and all I had to make was standoffs, assemble the wheels and make the bellypan.

Long story short, everything took really long to make and we didn't have a drivetrain till around week 4. This was mainly because we didn't have the time to test a siderail style drivetrain during the offseason, so we ran into a lot of issues with machining and assembly. But it all paid off and last year was the first year the drivetrain didn't fail during a match! It lasted two regionals, made it to Einstein, and won two offseasons before it finally popped a chain. The only other issue it had was when an ethernet cable got tangled in the chain, which was fixed.

Anyway, this year we've lined up a million machine shops to sponsor us and are going to make a WCD. As well as our drivetrain worked last year it took too long to make and design. I can design a WCD in my sleep and we can send off parts to be made quickly giving us more time to focus on subsystem design. Designing an original drivetrain was great, but this year we're sticking to our team motto: steal from the best and invent the rest. WCDs are proven and easy to make when you have the right sponsors, which we do now.

Sorry to threadjack.

Thanks,
-Adrian

Re: Show off your machining!
 

True. I'm used to using a cnc controlled bridgeport so predrilling isn't as fast as milling and with a helical ramp spindle load is minimal when you plunge (I use a super slow z feed). But with an ATC I can see the advantage of predrilling. Makes sense.

Re: Show off your machining!
 

Besides for being really awesome and a neat piece of machining, what is the advantage of a uni-body chassis? Is it stronger or lighter?

Re: Show off your machining!
 

I doubt they are tumbled (finish isn't dull), I'd go with a really nice face mill (2" or larger) with a very light pass for surfacing.

But Cory would know!

-RC

Re: Show off your machining!
 

Same. We've had some parts come off after using a 2in face mill with a similar finish.

Re: Show off your machining!
 

The surfacing was done with a ball end mill. I don't remember what specific toolpath I used, but essentially when looking at it from inline with the top "ridge" the endmill just follows the contour from the side, up and over the top, and back down to the side. It then steps over a very small amount (probably .010 to .015") and repeats the same motion until it machines the entire profile.

After machining they were hit real quick with a scotchbrite wheel.

I like to pre-drill when convenient (as long as the drill is in the machine) as it eliminates any chance of packing up the flutes or chipping the edge of a flute when plunging.

I think RC is talking about the yoke for the arm, which is shown as machined. It was scotchbrited later, but the finish you see on the outside of it is from a 3" aluminum specific face mill.

Re: Show off your machining!
 

Ah, that makes sense. Thanks!

Re: Show off your machining!
 

We never did any official impact testing with it or stress analysis on the CAD file but i can say it's strong enough to withstand being sandwiched between two bots (that was our unofficial test, for fun :D ) without bending at all. Weight is the biggest advantage to using a uni-body chassis though, as pictured it weighed 7lbs compared to our 2013 robot's frame at 20lbs, which was made from C-channel and extruded aluminum. We've since ditched the uni-body chassis concept as we found it to limiting, but it's still a pretty piece to display.

Here it is compared to our 2013 chassis:
http://www.chiefdelphi.com/media/photos/38612

Re: Show off your machining!
 

We had an issue with being under weight with our bot & added like 9 or 10 pounds of steel to our bumpers (and we were still under weight) ;)

Anyway, I would say our chassis last year took a lot of skill... Plus it's so holy, it could be a priest (sorry, couldn't resist the pun). Luckily, our 2 side chambers (that held our drive trains) that had the most holes, I tossed into our CAM model that we ran. Each face actually took 2 passes (one for the left & one for the right) as our CNC mounting base wasn't large enough. The other cross bars we drilled on our XY CNC Bridgeport.

Re: Show off your machining!
 

We've done alot but three of my favorites are

The 2006 robot wheel

http://www.chiefdelphi.com/media/photos/22626

and 2008 side drivetrain plates

http://www.chiefdelphi.com/media/photos/29983

2007 ball bearing shifter gearbox

http://www.chiefdelphi.com/media/photos/26986

I want to post a newer set of parts also once I get the photos together.

Re: Show off your machining!
 

This our shooter wheel this year. It weighed a little over 4lbs and had a diameter of a little over 12 inches. This started out as a 14x14 in piece of aluminum. The outer circumference was milled out, but the spokes were cut out with a wire EDM. This is very simple compared to some of the other things on this thread, but this was the first time our team had anything EDMed and it was very cool.

http://i.imgur.com/d2bTPPE.jpg