pic: Prototype 6WD

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

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).

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!

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

Okay, I see now. I couldn’t tell if that was a SS or not.

still looks really cool tho great jon


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.

Properly aligned and tensioned chain should NOT break under FRC loads. I know many teams have been using #25 chain for years without problems. If you feel uncomfortable using #25 chain feel free to use the heavier #35 because it will allow you to be lazy when you are tensioning and aligning.

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.

Actually most teams who switch to just gears: you guys, 25, 1403, some more, tried chain first just like the rest of us.

Yes chain has its problems and gears sometimes have their benefits in a DT, but when the design is based on good tensioning and weight is considered their priority you can’t go wrong with chain.

We were happy not to have any chain in our drive train this year too though :smiley: But I wouldn’t necessarily bypass chain, especially when its a veteran team like Blizzard.:wink:

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.

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.

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 :wink:


That’s asking a lot from some teams (though I doubt that 188 isn’t up to the task). Across the three teams I’ve worked with, it’s always been #35 chain for various reasons (paranoia, the free ten feet in the kit, doubt over our abilities to reach the necessary precision for #25, lack of need to try). I’d want to try it on a test robot before relying on it for competition, just to make sure our old tricks are adequate.

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.:slight_smile:

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.

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.

This is a big benefit for many teams…maybe not yours…but still…