6 wheel drop center Question

[LoneWo1f1998]

The year before I joined my team we apparently attempted a 6 wheel drop center which tore itself apart due to torque and grip. We are considering doing this base again this year, but I'm not sure how far we would want to "drop" the center wheel for maximum efficiency. Any advice is appreciated; Thanks so much.

[bmire3206]

one important question is what wheels are you planning on using? this will cause a difference based off of compression of the tires

[Kevin Leonard]

Originally Posted by LoneWo1f1998

The year before I joined my team we apparently attempted a 6 wheel drop center which tore itself apart due to torque and grip. We are considering doing this base again this year, but I'm not sure how far we would want to "drop" the center wheel for maximum efficiency. Any advice is appreciated; Thanks so much.

I have no idea how your drivetrain could have torn itself apart.

A 6 wheel drive with a drop center is a simple drivetrain that uses a slightly dropped center wheel (like less than a quarter of an inch difference between the middle wheel and the outer wheel) for the purposes of reducing the length of your wheelbase when turning.

The kitbot (AM14U3) is a six wheel drop center drivetrain.

The dropped center really isn't a big deal and shouldn't be causing any issues unless your make some ridiculous drop like an inch or something, and even then it would probably function, although not well.

If you could give examples of what happened (or even better pictures/video of the base), we could help more.

[CryptoStorm]

How exactly did it tear itself apart?

Wear on the wheels is pretty normal. Depending on your load balancing I suppose you could tear up one set of wheels which would increase the bind on the other wheels.

[RyanCahoon]

Originally Posted by LoneWo1f1998

We are considering doing [a 6 wheel drop center] again this year

Originally Posted by Kevin Leonard

The kitbot (AM14U3) is a six wheel drop center drivetrain.

Why not just use the kitbot drivetrain? If you're spending time trying to figure out how to build a drivetrain, that's time you aren't spending on the game-specific parts of the robot.

[Jon Stratis]

Originally Posted by RyanCahoon

Why not just use the kitbot drivetrain? If you're spending time trying to figure out how to build a drivetrain, that's time you aren't spending on the game-specific parts of the robot.

Given half the defenses this year, I would think that time spent on a drive train is time spent on event-specific parts. Your drive train choice is going to have a big impact on your ability to quickly and efficiently navigate those defenses.

[Ether]

Originally Posted by Kevin Leonard

I have no idea how your drivetrain could have torn itself apart.

Originally Posted by CryptoStorm

How exactly did it tear itself apart?

Do tell, please.

[LoneWo1f1998]

Again, I wasn't on the team that year so all I know is that chains were popping and the robot could barely turn even though it had been fine while testing on less grippy carpet. It apparently lurched a lot and they never quite fixed it, but were able to decrease the problem by making the wheels less grippy. As far as wheels go, we are considering 8 inch pneumatic or really anything that is 8 inch and grippy. What I really want to know is how much farther down to place the center wheel as compared to the others. This is like the fifth time I've designed a drivetrain, but we simply haven't needed the 6 wheel drop center in the past.

[Ether]

Originally Posted by LoneWo1f1998

all I know is that chains were popping and the robot could barely turn even though it had been fine while testing on less grippy carpet

Thank you. That's much more informative.

Chains popping sounds like perhaps they were not tensioned properly, or not enough teeth engaged, or chain size too small.

Not turning on more grippy carpet sounds like not enough center drop.

[LoneWo1f1998]

Thanks for helping me zero in on what went wrong that season. I'll try to look back and avoid those mistakes, but how low do you think the center wheel should be?

[Taylor]

Originally Posted by RyanCahoon

Why not just use the kitbot drivetrain? If you're spending time trying to figure out how to build a drivetrain, that's time you aren't spending on the game-specific parts of the robot.

Originally Posted by Jon Stratis

Given half the defenses this year, I would think that time spent on a drive train is time spent on event-specific parts. Your drive train choice is going to have a big impact on your ability to quickly and efficiently navigate those defenses.

What makes you think the kitbot drive train won't be able to navigate obstacles? Roboten100H has proven otherwise.

[Lil' Lavery]

Originally Posted by LoneWo1f1998

Thanks for helping me zero in on what went wrong that season. I'll try to look back and avoid those mistakes, but how low do you think the center wheel should be?

The most common "drop" in the center wheel is 1/8". With pneumatic wheels, you may want to increase that slightly, due to the deformation of the tires under weight. Hard to say exactly, given that it could change with your tire pressure and weight distribution. I find it highly unlikely you'd need to go beyond 1/4", however.

With regards to chain, also make sure the sprockets are aligned properly.

[FrankJ]

Andy Baker (Andymark) has a great power point on basic drive trains. There are many others presentations. Google is your friend, One of the big advantages of 6 wheel systems over 4 wheels tank drive is that the shorter effective wheel base makes it easier to turn. That is assuming that it is set so the robot is mostly supported by the center and one one set of the outboard wheels. Pneumatic wheels are going to make proper set up more critical. Any tank drive has to scrub the wheels to turn. High grip wheels are going to need a lot torque to turn from a stand still and the turn is likely to be a little jumpy. This is one reason many teams use omni wheels on the corners.

[Jon Stratis]

Originally Posted by Taylor

What makes you think the kitbot drive train won't be able to navigate obstacles? Roboten100H has proven otherwise.

I never said it couldn't. But a team that spends time investigating it, looking into other options, and deciding what the best drive train is for their strategy and the defenses they want to tackle is spending time on a game specific part of the robot.