30-08-2007 15:22

Madison

Re: pic: FRC294 Prototype base

Y'all have obviously given a lot of thought to this, so I'm just curious about what I imagine are some of the most important pieces of information for all FIRST teams -- how much does it weigh and how long will it take to manufacture and assemble?

30-08-2007 15:37

AdamHeard

Re: pic: FRC294 Prototype base

I actually don't have an exact weight because I've been so busy between work and just CADing it... I didn't have the best practices so 1/2 the stuff is missing material properties. We made almost every practical effort to lighten it though; Each rail (inner and outer) is 3 +/- .05 lbs (keeps changing slightly with adding stuff), the wheels are .4.

for comparison, Last year's with a heavier frame came it at 50 lbs or so. I'll get a precise weight soon.

As for production,
-We have a jig setup to CNC the rails. They take about 2 hours to cut each (what I've heard, I didn't see them cut); During that time, we'll have kids on manual mills and lathes cutting the small parts out (most are really easy to make) and will probably finish within the day.
-The Wheels, Gearbox plates & shafts and the Frame will be cut/welded by our sponsor (NG), with a lead time of 2-3 days.
-All efforts were made to ease manufacturing time; off the shelf spacers, the wheels match the AM sprocket hole pattern so we just bolt them on, etc...
-We could spend two solid days in the machine shop and finish it; However, We'll probably wait until week 1.5-2 to make sure there aren't any drastic changes we want to make.
-Not counting of electronics, We could have one group assemble the modules, and another do the gearboxes and mate them at the end of the day.

Also, almost forgot this... View the .dwf in 3d here.

We hope to compete with it at the SCRRF Fall Classic on 9/29.

Any more comment/critisism is appreciated.

30-08-2007 15:52

chris31

Re: pic: FRC294 Prototype base

Unfortunately the DWF viewer link you posted does not work. Could you post it again please. Thanks.

30-08-2007 16:45

Herodotus

Re: pic: FRC294 Prototype base

We've gotta get a program that automatically asks these questions whenever a piece or CAD design is posted.

I'm really liking the design. What is best is the flexibility in design you have left by allowing the wheels and gearboxes to be swapped out. That means you could theoretically use this design from game to game while only changing the parts you need to. The fact you can change it to a Mecanum drive fairly easily alone is quite awesome.

Overall a sleek design.

30-08-2007 20:31

Cory

Re: pic: FRC294 Prototype base

It takes two hours for each rail on a CNC? that seems like an awful long time.

Your design looks good though. The modularity of it is great. Reasonably simple as well.

30-08-2007 21:25

AdamHeard

Re: pic: FRC294 Prototype base

Awwe... I forgot that those were last years rails. Last year the jig cut both an inner and outer plate, the gearbox plate, the tensioner, the blocks the center wheel rode in, and two different style tensioners all at once.

Since we haven't cut the new ones yet, I'd say no more than an hour each.

31-08-2007 01:47

Gabe

Re: pic: FRC294 Prototype base

Why aren't the fronts sloped anymore? That was the eyecatcher form your frame last year that made me remember your robot from everyone else's.

31-08-2007 01:54

AdamHeard

Re: pic: FRC294 Prototype base

I have the sketches to do it, but we end up with a heavier frame. I'm hoping they won't be necessary next year, but if needed they can be added back in.

31-08-2007 13:54

Peter Matteson

Re: pic: FRC294 Prototype base

I would suggest leaving yourself a lot of leeway for increasing the ride height and attachment points for joining the 2 sides. That way when you see the layout of the field next year you can tweak you design with minimal impact to allow for the climbong of ramps, stair, logs, teammates or whatever is thrown at us in the game design.

Also the cross-members from pod to pod should have a mid span reinforcement of some kind. As soon as contact is made a few times even with bumpers you may find you no longer fit in the box.

Pete

31-08-2007 15:30

M. Mellott

Re: pic: FRC294 Prototype base

Very nice design--obviously well thought-out to cover so many design options!

31-08-2007 15:49

T3_1565

Re: pic: FRC294 Prototype base

Thats a really nice design you got there with a pretty beastly transmission system!! nice and low clearance too. I like to see that! *grins*

31-08-2007 21:16

Alan Ing

Re: pic: FRC294 Prototype base

Have you used Team 33's design before?

In 2005 we used a modified Team 33 style 4 speed transmission. Aluminum side plates instead of Delrin and oilite bearings for the sliding members. We also used 2 CIM motors per transmission through some custom gearing and added additional reduction for a top speed of around 12 - 13 FPS in high. The transmission shifted perfectly every time and it was really neat to hear it constantly shift. It served us very well that year but we did have a problem with it. The shifting gears were prone to heavy wear on our machine. All of the hard shifting caused the teeth of the gears to elongate and become pointed as well as show extra signs of wear where the gears jam into each other during each shift. At Las Vegas, I showed a set to Andy Baker, and he mentioned that everything looked like it was constructed right (proper welds and all, but that he had not seen this problem before). We ran through 5 sets of cluster gears before the season ended (2 regionals and championships).

Now I can't say that this will happen to your team since we did modify the design, but we finally resorted to case hardening all the gears with Kasenit and a small furnace before we got acceptable wear resistance.

Should you also have this problem, consider case hardening the gears. We still use the robot for demos and the gears look fine.

As a suggestion, if you automate the gearbox, consider locking out 2nd gear. With 4 CIMS, the robot stays in 2nd for only a fraction of a second and almost immediately shifts into 3rd. We played with all sorts of rpm shift points, but eventually we just locked out 2nd making it a 3 speed and the robot worked much more smoothly. Of course we could manually put it into 2nd if we wanted to.

The Team 33 design served us very well in 2005 and is about the coolest to hear operate. Were glad we made it, but frankly we don't use that design anymore since it is much easier to buy AndyMarks solution and modify them for our use.

Anyway, I thought I'd share our experiece with the 4 speed design in case you haven't tried it before.

07-09-2007 08:28

robostangs548

Re: pic: FRC294 Prototype base

Looks good, we had a design like this two years ago, we only had one problem, and let me suggest that you try to avoid this.... The wheels can't be too thick or too thin, but if they are too thin, you will have bad traction, too thick and you can't turn, so if its possible to incorporate into your design having thicker wheels in the middle of the outside two, this will give you good average steering, and there will be plenty of traction so you won't get bullied around.... Just like you, my team has been working for the last 3 years on trying to make a design that teams can't "pick a fight" with. So far, we have had some alright success, but still haven’t achieved victory, this year we have started already brainstorming ideas, comparing and contrasting positives and negatives of all the designs, and we think we have finally found what we were looking for.... are drive train is codenamed RAM and so far, it is pretty impressive from a cad standpoint. I will be posting pictures on CD soon, (when i get them) and you will be able to judge for yourself what you think of it. We all think that its pretty cool, but the competition will be the judge of that. I just want to say, that this is some amazing CAD work, and I hope that this works out for you, just make sure that you have enough traction to handle those gear boxes, or you will regret not doing it (like we did).

07-09-2007 13:55

AdamHeard

Re: pic: FRC294 Prototype base

We were fine traction wise with 5/8" tread, we're running 1" now so it doesn't wear out as fast; either way, it's the same amount of traction. There's no need to run thickner center wheels, and for turning we have a lowered center.

For the 4-speed we are well past traction liminted in 1st and 2nd gear, 3rd and 4th aren't but we won't be pushing in those. If we have the FPs to spare then even 3rd will be traction limited. Most likely for the season we will run AM Gen3 shifters, we just wanted something cool to play with.

07-09-2007 14:27

Madison

Re: pic: FRC294 Prototype base

If you're traction-limited in both 1st and 2nd gear, why not eliminate 1st altogether? What benefit does it provide?

07-09-2007 15:06

AdamHeard

Re: pic: FRC294 Prototype base

We'll probably lock out 2nd gear in code....

you got to cut us some slack on the practicality ; We know 4 speeds is overkill, but we figured since we can just bolt on AndyMarks during the season, why not try something cool now? It's the offseason, time to try cool stuff.... And in all honesty, who hasn't wanted to build a 4-speed? We all know they're impractical for most games, but that doesn't take away from how cool they are.

07-09-2007 15:17

Madison

Re: pic: FRC294 Prototype base

Now is the best time to experiment for many teams. We're also focusing a bit on some experimentation this Fall, of course.

I am not too familiar with 33's design for a transmission, so I thought it might be easier, faster and more reliable if you were to eliminate a redundant gear from its design. That said, it may also be more work and more time to make changes to it than not.

I have to be all about practicality because the Fall is the time when the mentors and I get to play around and introduce new ideas to our students, but at the same time, we're spending a lot of money doing so. I need to be able to justify the expense now with tangible benefits later. I can't spend $1000 of the team's money on something that we couldn't possibly use or build in a six-week crunch, y'know?

07-09-2007 15:22

AdamHeard

Re: pic: FRC294 Prototype base

We have a two speed variant of team 33's that was the same cost in materials to build, so once again we went for cool; both were cheaper than buying AMs though. There is no sense in making it a 3-speed, it is two 2-speeds in series now. If we gave them inverse ratios we could have [AA,AB, BA, BB] (best way to visualize it i geuss) but AB and BA would be the same ratio, so we just made it 4.

these are being built for about the cost of a single AM shifter, so that's not too bad. Also, we have a lot of excess stock/hardware that could be used during the season now.