Drop-Center Drivetrain

Hi, does anyone have any tips or thoughts on drop-center drivetrains for this year’s game? Ex: How much higher should the front/back wheel be than the other wheels, whether a drop-center drive-train would even be practical this year, etc.

  1. 1/8" is usually enough, 1/16" is usually too little. Our 2019 robot has a 3/32" drop and drives just fine. Anecdotally speaking, if you want to use pneumatic wheels this year, you should use a larger drop. We’re trying out 3/16" and if it ends up being a mistake then we’ll re-make those parts.

  2. A center drop is never really “impractical.” The only thing coming to mind is that if you’re shooting high goals, the robot will be at a different angle resting on the front set of wheels than on the back. The difference is only 1-2 degrees though, so if your shooting is delicate enough that a 1-2 degree difference makes or breaks your shot, you should probably reconsider.

We’re using the KoP chassis, which has a drop center. The amount of drop you want, depends on a lot of things…wheel type, number of wheels and wheelbase, are the most important.

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This game requires you to think a lot about drop.

This is very true. We took this into account. Due to the ball’s motion (parabola - unless a straight shot), (ex. other side of control panel), if you are off by a little bit, the accuracy can decrease exponentially based on your range. So our team (especially with inconsistent tire pressure) thought about this carefully. Unfortunately, I don’t want to give away our drivebase specs, but getting over steel crossmembers and stability when shooting should be taken into account. Good luck!

I don’t mean to be an alarmist, but if it is late week 3 and you have not yet decided on this, and don’t have the resources to manufacture a drive base quickly, do you still have your Kit chassis available?

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If you feel like your drivetrain specs could help other teams you should consider sharing.

I can’t imagine a situation where telling other teams what your drop is, wheel type, or wheel diameter will make or break your season.

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You could always add a stabilizing foot to any drop-center drive-train to make sure you’re tilted consistently when firing.

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Don’t listen to anyone that says 1/8" is enough. It’s not (for blue roughtop traction wheels at least). We usually run .150" drop and like the way our drivetrains turn better than when we use 1/8".

You can also use different type wheels in different locations on the robot, and greatly affect how the robot drives, with a specific center drop.

There is no magic number for all robots…it’s highly dependent on lots of variables.

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I know a team that doesn’t drop center but uses traction wheels in the middle and omni wheels on the corners. They’ve been using it for many years and they like that arrangement a lot.

If you don’t have a drop center, you could use slightly larger wheels in the middle for the same effect.

Etc, etc.

We are using that exact drivetrain for the first time. No drop center and it handles great! Turns 360s on itself as if it had mecanum; although no strafe

For a two years, we saved space in the robot (AM14U) and weight by omitting the front belt and pulley, only powering the rear four wheels of the bot. Front wheels omnis. Leaving out the front belts meant we could narrow the inside-outside rail by more than an inch per side. Half ‘arcade’, half ‘tank’…called it “tankade”.

Keeping a robot narrow really helps in high-traffic games.

Didn’t hurt our pushing ability at all because pushing with drop center is still usually only the four wheels that are on the floor anyway. Backs were on the floor based on weight distribution.

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Would you recommend doing this this late in the season and/or in between events? Video?

This is an unnecessarily alarmist post that quite frankly, is not accurate. If you need more than 1/8" drop for treaded wheels, you don’t have a very rigid chassis. Perhaps you would want more if you would prefer slightly easier turning / slightly less resistance to spinning, but it is by no means a need.

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This is a hot take and a bad one at that.

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It worked well for us with full CIM’s. If you have any fear that you’ll be torward the high-end weight-wise, yes, I’d recommend it.

If you’re doing a kit-bot, you could change to this in an hour with a few kids shortening churros, rebolting the outside rails, removing the front belt and pulley. You can wait to saw-off the ends of the front and back of the frame until you’ve tested and see if you like it.

Here’s our video reveal from 2018. Did it in 2017 too. https://www.youtube.com/watch?v=0xsUSSj1mrQ&feature=emb_logo

Having worked on multiple robots using blue nitrile tread and 1/8" drop, the ones where we had turning issues were definitely the robots where the CG was off-center.

In more recent years too we’ve preferenced having omnis on one or both sets of corner wheels for better point-turning around defense, and in those cases any issues there would be go away anyway.

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last year we removed our center drop by flipping our versablocks at our second regionnal, this year we’re going for 0.05" drop center

Are yall concerned about the omni’s going over the metal bar? Have you tested them?

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I explained the logic behind our decision - anymore really might not help you. Sorry - I’m sure you all heard this but I’ll repeat it - we are running a pneumatic drivebase. No need to tear down at this post . Next time I won’t say anything