West Coast Drive Questions

Hi,
I am trying to design a West Coast drive for my team.
I have a few questions. The setup I am running is three 4 in. Colson’s on each side, and a 4 in. Omni in the front.

  1. Do I need a center drop?
  2. Do I need to use Versa Blocks for bearings, or can I use 1.125 in bearing holes?

More common configurations would be 2 colsons + 1 omni (front or back), 1 colson + 2 omnis (front and back), or 2 colsons + 2 omnis (front and back), or all Colsons. But as long as you have the center wheel or wheels dropped below the front and back ones, any of these should be fine (including the one you posted).

Yes, unless you’ve got omnis on all corners you need a center drop.

If the tubing is thick enough you can bore the 1.125" holes (NOT 1.25") directly in to it, but most teams will opt to use some form of bearing blocks. They don’t have to be versablocks specifically though.

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  1. You don’t need it if your wheel base is wider than it is long because you won’t get any scrub friction but in general it’s a good idea to have the center drop
  2. Versa Blocks are nice for tensioning your chain but you can do direct c-c with bearings in the tube( it’s 1.125 btw)
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We’ve used a WCD no drop omnis on corners works great. Highly recommend the vex bearing blocks super simple and if ya end up needing to have a drop you just flip the block.

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Careful on (1). There is always scrub friction, and sometimes you get lucky. 115 in 2016 had no center drop on a wide drivebase and suffered greatly. We had to add a drop in the end.
If you want to do no drop, put omnis in all 4 corners to be safe. Ideally, do a small 1/32" or 1/16" drop anyway.

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  1. Depends on your drive dimensions and preferred driving characteristics. The longer the drive base, the more likely it is you may need a center drop. The wider the drive base, the less likely.

  2. If you get your preferred center-to-center distance dead on, you can probably survive without versablocks. But if you haven’t previously experimented with chain/belt to know the preferred c-to-c for your chain/belt selection (accounting for wear/stretching), then Id suggest versablocks to enable dynamic tensioning.

The calculator we use also gives us belt selection and pulleys…we usually get the solidworks files from them put in a hex bore and print them.

Center to Center Belt Calculator

I would recommend a center drop (at least 1/8" overall)

Also, don’t stick bearings straight in the tube unless you can actually get a clean fit. If there’s wiggle room (like from an inaccurate hole saw) then your cantilevered wheel axles will suffer.

1/8th wall thickness is enough for bearings to be fitted into a drivetrain, however keep in mind that you’ll need additional chain / belt tensioning (unless you guess the C2C accurately) because the axles are fixed location.

Bearing blocks are nice.

I do NOT recommend the V1 bearing blocks https://www.vexrobotics.com/bearingblocks.html (the two part clamp ones) They have issues with each side bending the bolts / not aligning properly when under tension.

These ones are great: http://www.wcproducts.net/217-3436/ They can also be found on the vex website, as the V2 bearing blocks in my first link.

Oh boy. This thing is a remnant of cadathon so no guarantees on this particular drive train working other than the fact that 1619 did something similar in 2018. It’s for demonstration purposes only.

  1. You always need a little center drop unless it’s like this one with omnis in each corner or 2 colson + 1 omni.

  2. The vex v2 bearing blocks make your life so much easier. If it’s your first time and you have a mill (CNC or not), probably worth figuring out. Otherwise this playlist teaches how to make the best drivetrain bearing hole that isn’t trash.
    https://www.youtube.com/playlist?list=PLnCkiGOEMtaettWjpU6TIGMFfQsOOg8s0

Couldn’t you make do without a center drop with only 2 Omni wheels (say Omni’s only in the front)? Depending on some other aspects of your drivetrain. I’ve never tried it and a center drop might be better.

There’s a paper from 2003 titled “Drive train basics” that overviews the physics of turning. It’s a bit hard to find with the CD redesign, but I’ll try to link it later.

https://web.archive.org/web/20180701042408/https://www.chiefdelphi.com/media/papers/1443

You’re right, in theory that should work.

Here’s the thread but the link to the paper is broken.

Try looking up the VexRobotics CAD files from “drivetrain examples” to get exact measurements of the center drop but yes you will want center drop for your drivetrain on each side so that your turns can be easier and so will your performance from what I’ve been told about west coast/drop center 6 drives. Bearings will be better than drilling holes so that nothing slides inside, gets busted or bent, acts as a brace when you put the bearing in.

Me team has used WCD with precision machined 2x1 tubes and belts/pulleys utilizing WCP Belt calculator with fantastic results the last 3 years.

Would definitely recommend not using bearing blocks if you have the means to machine 1.125" pockets to a fairly tight diameter/position tolerance. Belts have been very trustworthy, low friction, and good for auto when using the spacing calculated by WCP down to +/- .0005".

In 2017, we had a particularly fun-to-drive 6wd drivetrain that used WCP SS gearboxes each powered by 2 cims and 1 minicim, geared to +18 fps with 4" omnis in the corners and 2 4"x2" colson wheels. This allowed us to do J-turns and robot drifts which was helpful for gear cycles (and super fun).

Definitely never run 6 cim/ 4 cim+2 minicim unless you have low cf wheels like colsons and considerable center drop, or omnis in the corners.

I’m actually surprised a lot more teams do not use 2x1 WCD with belts.

This was 1246’s first season with WCD.

You’ll find a CAD and full set of tech drawings here.

  • 1/8 centre drop, configurable for 4" wheels
  • Vexpro 3-mini-cim BS (we found this gearbox to be pretty reliable. Bolting a churro between the gearboxes eliminates any issues of sag. Gear ratios for 4" wheels can be found in the drawings)
  • Overall size: 30.5 x 28 (fits, I think, the last 4 or so seasons of robot rules)
  • wheel pitch of 10.25 w/ #35 chain (we found #35 to be a little too much. We do not recommend the chain setup u see in our CAD, b/c of weight. 10.25 is not C-C, but we found we could get away with quite a bit of slack with chain. Masterlinks are not recommended. Consider using vex chainbreakers.)
  • We like to use bolts and washers instead of clip-rings to hold in our axles. We really enjoyed the easy and fast maintenance and repair. (instead of using lock washers, loctite thread locker is recommended to keep bolts in their threads)

That’s just the tip of the iceberg. If u have more questions, feel free to ask.

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