pic: 303 Prototype Sheet Metal Drivebase

[Brandon_L]

Originally Posted by Sam_Mills

If you are willing as a team to put this much effort into improving drivetrain performance, IMHO the effort would be better placed learning how to correctly implement timing belts (hint; dead space center to center, no tensioners). They are efficient, light, and far more durable than they are often given credit for.

I second this. As scary as belt drives sound, they're actually easy to plan out and put together. In our case this season, they were nearly maintenance and worry free. Plus your wallet will thank you.

[otherguy]

I'm a programming/electrical type, so take what I say with a grain of salt. From the images, this chassis seems like its going to make maintenance difficult.

Some things to consider:

1. Make it easy to replace any part. In the event something breaks in your DT (gears, wheels, bearings), you don't want to have to sit out a match because it takes a long time to do maintenance/repairs. Consider making openings in the top of the covers above your parallel plates, and some in the bottom of the belly pan. openings in your belly pan directly below your gear boxes can allow you to drop the entire assembly without having to have access from the top of the robot (that's how we've done it at least). This requires some attention when designing the superstructure though to provide the rigidity you'll be losing by cutting up the belly pan.
2. Maybe it's just that I can't see it in the images but, it doesn't look like there's a way to access the screws that mount the motors to the gear box from the outside of the chassis. At a minimum this is going to make replacing a bad motor very difficult. The same goes for holes to access the screws that attach the gear box to the chassis (those ones are pretty critical if you want to build this).

[Chris is me]

Make all of your idler gears dead axles that double as standoffs. It makes your frame much, much more rigid, saves a little weight, and is generally a "free" way to add rigidity.

Be sure to consult with your sponsor to see what kinds of tolerances can be held around two bends. Axle holes may not line up if they can't bend vary precisely.

[Lil' Lavery]

Why do you want to have a gear powertrain? Saying that 341 and 25 have them is not a sufficient answer. What advantages does it you? What issues with other powertrain solutions you've used does it solve?

Originally Posted by Chris is me

Make all of your idler gears dead axles that double as standoffs. It makes your frame much, much more rigid, saves a little weight, and is generally a "free" way to add rigidity.

Not to mention it will save on hex bearings, which are notoriously hard to procure for FRC teams. Based on the picture, it cuts a minimum of 18 hex bearings out of the design, and presumably 36 if you were to use round bearings in their place on the idler gears. Using Vex prices, that would also result in over $120 in savings, as well.

[TylerS]

Originally Posted by Lil' Lavery

Why do you want to have a gear powertrain? Saying that 341 and 25 have them is not a sufficient answer. What advantages does it you? What issues with other powertrain solutions you've used does it solve?



Not to mention it will save on hex bearings, which are notoriously hard to procure for FRC teams. Based on the picture, it cuts a minimum of 9 hex bearings out of the design, and presumably 18 if you were to use round bearings in their place on the idler gears. Using Vex prices, that would also result in over $60 in savings, as well.

There are only two hex bearings outside of the one's in the gearboxes. The rest at circular

This is simply an off-season project to look at the efficiency and feasibility of such a design. Whether or not we use it in the official season is to be seen. The center to center for all the wheels are compatible with .25 chain with no idlers so we will be testing it with chain as well as gears.

[cbale2000]

Honestly, the gear setup of this drive reminds me a bit of the one my team built this year. This is a slight variation on that design, which I've been working on in the off season...



This is our second time we've built a gear-drive system and we've been quite happy with it, even more-so since VexPro has made building them so easy. Here's a few things we've liked about gear-drives from our experience:

• Durability - Unlike chain drives we've built, this years robot had zero failures in the drive system. After 3 competitions and a little cleaning the gears on our robot this year still look brand new. Maybe we're just bad with chains, but we've yet to build a chain-drive robot that can claim such durability.
  
• Size - Gear-drives can be made to be much more compact then chain or belt drives since all the force can be transferred on one line of gears (unlike with sprockets or belts which require 2 sets of sprockets in most configurations on >4 WD robots)
  
• Pushing Power - I can't speak for all gear-drives of course, but in our experience we have yet to find a robot that could not be pushed by our gear-drive robots (Though part of this we believe stems from the wheel positioning, not just the gears).
  
• Ease of Maintenance - Unlike a chain or belt drive which requires taking apart the drive module or de-tensioning the drive. Wheels on our gear-drive can be removed by simply pulling out the clevis pin axle and dropping the wheel out the bottom of the drive. Assuming there's a replacement ready, a wheel swap can be done in less than 30 seconds (not counting the direct-drive wheels of course which require a bit more work). That said, the only time we've needed to change wheels was due to tread wear.
  
• Efficiency - I'm not qualified to speak to the science of this, but based on our experience we've found that our gear-drive robots seem to have far less friction in the drive system. I suspect this may be due to the lack of tension in a gear-drive system (or, again, we could just be bad at making efficient chain-drive systems).

Now, of course, the big downside to gear-drives is cost, it's certainly much cheaper to build a 6 wheel chain drive than a 8+ wheel gear drive. Recently VexPro has made it substantially cheaper and reduced build times compared to when we had to either build or buy all of our components custom made.

All that said, unless the next game challenge prohibits it (or makes it undesirable) we plan on using a gear-drive again next season.