18-06-2009 02:05

Jon Jack

Re: pic: Prototype 6WD

I can't see clearly, but why are your gearboxes offset from the center wheel? How are you running your chain?

18-06-2009 02:18

NickE

Re: pic: Prototype 6WD

Quote:

Originally Posted by Jon Jack I can't see clearly, but why are your gearboxes offset from the center wheel? How are you running your chain?

18-06-2009 10:37

JesseK

Re: pic: Prototype 6WD

I love the use of U-channel, however usually U-Channel is weaker at the bends than C-channel. This would worry me on the outside rails on a high-impact carpet game. To keep the frame stiff, I would use C-channel on the inside (usually for those dimensions you can only find 3" base with 1.5" legs or a 4" base with 2" legs and both have a ~3/16" radius on the inside corners of the bend) and 2x1" or 3x1" box extrusion on the outside. It's roughly the same weight, stiffer, and much stronger on the outside. Possibly a little more expensive depending on the supplier. For a prototype this looks good!

18-06-2009 10:43

kajeevan

Re: pic: Prototype 6WD

AM SS steel hex driven direct drive
42lbs w/no lighting
should take one day to build
can use 25/35 chain
tensioners are floaters
wheels are CNC baltic birch used in every 188 drive train
AM bearing hubs/hex hubs/sprockets/spacers

18-06-2009 20:16

Jon Jack

Re: pic: Prototype 6WD

Quote:

Originally Posted by NickE It looks like a direct driven center wheel to me. The final gear reduction is hard to see (Looks like a supershifter using standoffs instead of the stock extruded body).

19-06-2009 11:41

Andrew Remmers

Re: pic: Prototype 6WD

still looks really cool tho great jon

19-06-2009 11:43

Andrew Remmers

Re: pic: Prototype 6WD

job*

21-06-2009 12:38

Cyberphil

Re: pic: Prototype 6WD

Let me just say this. I will warn you about chains right now. There are a lot more problems that chains will have rather than gears. I will suggest you use gears before you go too headlong into chains. Ask team 79. They could have won in Florida if their chains didn't break.

21-06-2009 13:25

Andrew Schreiber

Re: pic: Prototype 6WD

Quote:

Originally Posted by Cyberphil Let me just say this. I will warn you about chains right now. There are a lot more problems that chains will have rather than gears. I will suggest you use gears before you go too headlong into chains. Ask team 79. They could have won in Florida if their chains didn't break.

21-06-2009 13:30

ATannahill

Re: pic: Prototype 6WD

The chain did not break, it came off the gear. We added some metal to our lexan to preven vibration, this was on our manipulator, not the drivetrain.

21-06-2009 14:08

Akash Rastogi

Re: pic: Prototype 6WD

Quote:

Originally Posted by Cyberphil There are a lot more problems that chains will have rather than gears. I will suggest you use gears before you go too headlong into chains.

21-06-2009 15:20

kajeevan

Re: pic: Prototype 6WD

188 has a very reliable gear drive like 25 which has never broken once during competition the 2yrs we have used it but some of us think if we had more weight like 10-15lbs we could have built a much better function. I m hoping that the mentors will allow me to build and then break it thru tests to find the breaking point of the 25 chain vs the 35 in FIRST scenarios and see if anything else breaks over an extended period. Also to figure out if floaters are good enough to tension the chain and such.

21-06-2009 15:44

sdcantrell56

Re: pic: Prototype 6WD

There is absolutely no reason that a team should be worried about using either #25 or #35 chain on a FIRST drivetrain as long as simple precautions are taken such as proper alignment and tensioning. If the chain is taut and completely aligned there will not be any problems with it breaking. Additionally, it is much more difficult to machine a drivetrain to use gears versus chain and the gears will be much heavier.

21-06-2009 19:24

Aren_Hill

Re: pic: Prototype 6WD

08 swerve, 8 runs of #25 chain, how many issues we had with them? 0
if you simply pay attention and take care when aligning and tensioning it, it will not go anywhere on you. (1 of those runs was holding back several hundred lbs of surgical tubing)


btw this is biohazard a former world champion battlebot i believe
and it uses #25 chain for the drive

http://www.botshop.150m.com/Biohazard.jpg

21-06-2009 19:56

Billfred

Re: pic: Prototype 6WD

Quote:

Originally Posted by sdcantrell56 There is absolutely no reason that a team should be worried about using either #25 or #35 chain on a FIRST drivetrain as long as simple precautions are taken such as proper alignment and tensioning.

21-06-2009 20:28

JB987

Re: pic: Prototype 6WD

Some of us out there have converted from chain to belts and have nothing but positive things to say about our experience...just different strokes for different folks.

21-06-2009 21:03

Jon Jack

Re: pic: Prototype 6WD

Even with poor alignment, 25 chain is very forgiving. On our practice robot last year there were several times when our chain was misaligned and we would run 4, 5, 6 matches without noticing and it never broke. In fact we've never broke 25 chain, ever.

Here's our history with 25 chain:

2006 (drivetrain)
2007 (drivetrain and lift on both competition and practice robots)
2008 (drivetrain and ball grabber on both competition and practice robots)
2009 (drivetrain and dumper/pickup on both competition and practice robots)

Summary: 15 applications over 7 robots.

I think the biggest secret is keeping just enough tension on the chain.

I'm not saying that you shouldn't use 35 chain or gears or belts, but 25 chain isn't a finicky as some people lead it on to be. In the end, every solution had its pros and cons, the right solution is the one that best suites your design goals still fits within your team's abilities.

23-06-2009 08:47

Jim Zondag

Re: pic: Prototype 6WD

I totally agree, #25 chain is more than adequate. We have used #25 chain in our Drivetrains for years and never had any issues (providing that everything is assembled correctly). #25 chain will not break until you put over 900 lbs of tension on it. It is pretty much impossible to apply this level of force in a FIRST robot drivetrain.

The 3 main issues I see team have with #25 chain are:
1. Alignment - If you don't line up your sprockets you will have issues
2. Frame Rigidity - If your frame is not bolted together tightly, things will come out of alignment when torque is applied.
3. Workmanship - I see lots of teams who mangle #25 chain when removing links. This can create a stiff spot in the chain where it will not bend properly. This will make it more likely to derail. It is much harder to do this to #35.

So basically, the advantage of #35 is that it allows you to be sloppier in your design and fabrication. If you pay close attention to these details, you will never have a problem with #25 chain.

23-06-2009 22:20

MrForbes

Re: pic: Prototype 6WD

Quote:

Originally Posted by Jim Zondag So basically, the advantage of #35 is that it allows you to be sloppier in your design and fabrication.

24-06-2009 00:03

Rick TYler

Re: pic: Prototype 6WD

Quote:

Originally Posted by Jim Zondag So basically, the advantage of #35 is that it allows you to be sloppier in your design and fabrication. If you pay close attention to these details, you will never have a problem with #25 chain.

24-06-2009 00:34

AdamHeard

Re: pic: Prototype 6WD

Quote:

Originally Posted by Rick TYler This is part of what I think of as fault tolerance. You can stack a lot of errors a #35 chain will still work.

24-06-2009 00:43

Cory

Re: pic: Prototype 6WD

We've never broken a chain since I've been on 254.

We've never thrown a chain either.

The one time we "lost" a chain was when we got hit so hard a sprocket broke, at which point the chain derailed.

It didn't even break. It stayed on the drive sprocket in the gearbox and somehow just kept spinning without completely destroying the gearbox.

I can't ever imagine using #35 chain in a drive again. The added size of the same tooth count #35 sprocket makes every gearbox, mechanism, etc larger, not to mention the additional weight of the chain and sprockets.

I don't believe that there's any team that's not capable of properly aligning and tensioning #25 chain if they put a little thought and planning into it, regardless of their manufacturing resources.

24-06-2009 00:46

MrForbes

Re: pic: Prototype 6WD

You're probably right Cory, but there are a lot of teams who's effort might be better spent working on the game playing parts of the robot....

#35 works, it's easy, it's cheap, it's in the kit, etc.

24-06-2009 00:46

Gary.C

Re: pic: Prototype 6WD

Quote:

Originally Posted by AdamHeard Fault tolerance is good, but there can be several pounds difference between #25 and #35 chain in a drive. As far as I've been on 973, running a west coast drive with #25 chain, we've yet to throw a chain. I know many other teams have similar successes with #25 chain. To me, it's a no brainer, if you can allign it right..... which isn't very difficult, it's an easy choice.

Quote:

Originally Posted by Cory We've never broken a chain since I've been on 254. We've never thrown a chain either. The one time we "lost" a chain was when we got hit so hard a sprocket broke, at which point the chain derailed. It didn't even break. It stayed on the drive sprocket in the gearbox and somehow just kept spinning without completely destroying the gearbox. I can't ever imagine using #35 chain in a drive again. The added size of the same tooth count #35 sprocket makes every gearbox, mechanism, etc larger, not to mention the additional weight of the chain and sprockets. I don't believe that there's any team that's not capable of properly aligning and tensioning #25 chain if they put a little thought and planning into it, regardless of their manufacturing resources.

06-07-2009 02:20

Sam N.

Re: pic: Prototype 6WD

I really like the use of your slotted bumper mounts.

06-07-2009 03:18

spazdemon548

Re: pic: Prototype 6WD

Everything looks very sound. One trick I learned from Simbotic's drivetrain back in 2008 is, if you line up the pneumatic cylinders on the shifters, you can eliminate a cylinder by linking both to an end of a new one with double the stroke.