Possible to extend output shaft on WCP Gearbox?

[Marcow]

Originally Posted by joeyxylophone

Asid: I'm a little weary of using 9mm belts to transmit power to the outer wheels, but it would give me plenty of space. Is there any risk of the belts breaking if I go down a size? I could try smaller wheels, that seems like a pretty elegant solution.

9mm belts are great, but as Chris said can easily get messed up if you're not sure what you're doing. We ran a very successful 6wd where the middle wheel used a 15mm pully that held two 9mm belts going to the outer wheels. Its just another option. If it doesn't feel safe to you, stick with the 15!

[Chris is me]

Originally Posted by Infinity2718

If you run those calculations with the kit drive train pulley sizes and wheel diameters, does a 9mm or 15mm belt meet the strength requirements? Is pulley size the only way to get a drive system from failing?

What happens if all the weight of the robot rocks on two wheels? What happens if all the weight of the robot rocks on one wheel?

The ratings are for a maximum recommended load over a long life, not ultimate tensile strength, so the belts aren't going to snap the instant your robot tips on two wheels.

Dozens of teams have run 15mm wide belts on 24T and larger pulleys and 9mm wide belts on even larger pulleys. These aren't about to snap. 9mm belts on 24T pulleys are pushing it. Smaller pulleys can lead to failure in a drivetrain. Load ratings are conservative and for use cases that aren't like FRC - using them as gospel here isn't necessary, and it isn't a poor decision to go with what's worked for many teams for several seasons, really. We push the rated limits of 25 chain all the time too.

[Deke]

Originally Posted by Chris is me

The ratings are for a maximum recommended load over a long life, not ultimate tensile strength, so the belts aren't going to snap the instant your robot tips on two wheels.

Agreed, the ratings are for 3,000 hours of use, where an frc bot would see 10-20 conservatively.

What about the 10th, 100th, or 1,000th time it rocks? The point is there is a lot of advice in this thread, it could be very helpful or not so helpful. Most of it is not fully quantified. Yes, increasing wheel diameter increases load on the belts. Yes, increasing pulley diameter decreases load on the belt. Yes, increasing belt width increases srength. Yes, increasing tooth engagement helps with power transmission. It's basic physics, but what is the design point? How much load is the difference between a belt breaking or lasting? What tooth engagement is necessary? Taking a look at the numbers can be very helpful in understand the failure modes.

Originally Posted by Chris is me

Dozens of teams have run 15mm wide belts on 24T and larger pulleys and 9mm wide belts on even larger pulleys. These aren't about to snap. 9mm belts on 24T pulleys are pushing it. Smaller pulleys can lead to failure in a drivetrain. Load ratings are conservative and for use cases that aren't like FRC - using them as gospel here isn't necessary, and it isn't a poor decision to go with what's worked for many teams for several seasons, really. We push the rated limits of 25 chain all the time too.

Define pushing it, what does that correlate to? When does it become an acceptable FRC design and the requirements it is held to?

How do you quantify a 24t pulley 15mm setup: What size wheels? What power input from the gearbox? That can be very helpful information to say we loaded our belts to X pounds and didn't see a a failure.

[Chris is me]

Originally Posted by Infinity2718

Define pushing it, what does that correlate to? When does it become an acceptable FRC design and the requirements it is held to?

9mm wide belts with 24t pulleys are the setup I've had the least experience with, but in a 6WD WCD with 4" wheels, there were issues with ratcheting, and I believe belt failure was inevitable at some point. I have heard of several other teams failing belts in this configuration.

How do you quantify a 24t pulley 15mm setup: What size wheels? What power input from the gearbox? That can be very helpful information to say we loaded our belts to X pounds and didn't see a a failure.

In 2012, my old team ran a 4WD with 6" wheels, neither wheel direct driven, using a pair of 15mm belts and 27T pulleys. All good.

In 2013, we ran 6" wheels on a 4WD with a 4 CIM drivetrain, single speed, probably a 10:1 gear ratio or so. 15mm wide / 24T pulleys. Majority of the weight was on the direct driven wheel, so maybe not a perfect case study.

In 2014, we ran 4" wheels on a 6WD with a 6 CIM drivetrain, maybe a 7.5:1 gear ratio? (around 12 FPS). This robot had the most run time of any of our robots, with at least 100 hours put in to practicing with both a competition and a practice robot, and obviously that game had plenty of pushing defense, so in a way this was the hardest test of this belt setup yet. Never ratcheted, never failed, no issues at all.