How to secure wheels on a WCD chassis?

This is my team’s first year ever building a west coast chassis heading into the new build season, and we’re trying to finalize what our CAD might look like as we begin building next week.

One of the questions we can’t seem to find a simple answer to is how to secure the wheels on the outside of the frame. We’ve seen that the common solution is to mimic the shaft coming out of the gear box through tapping and using a fender washer to help support the wheel. However we also were wondering about the possibility of using shaft collars as a support instead and were wondering which of these is a better option. What is the reason is that most teams opt for the fender washer and directly screwing the bolt into the shaft?

We thought that maybe it is because a bolt directly into the shaft is way less likely to loosen and lose a wheel than a shaft collar is, but were hoping others might have a reason why so many teams go directly into the shaft.

Thanks for the help!

For Infinite Recharge we screwed directly into the shaft. I believe the thought process was it would be easier to take off wheels and replace them if they got banged up on the bumps.

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Yeah both options definitely provide ease of access to removing the wheel, and in many ways we were thinking a shaft collar might be easier as you grab an allen key and you’re done. Mostly we were curious if there’s structural disadvantages to using a shaft collar since we can’t seem to find anyone doing it that way!

You have about got it. I’ve seen shaft collars work, but I would not recommend it AT ALL. The likelyhood that your wheels will fall off is way too high. Drilling holes in the end of the shaft is probably the best method. I believe I have also seen teams use E-clips or snap-rings for this purpose.

All that being said…I would consider maybe not trying a custom chassis this upcoming season. Typically I would like to see a team build a chassis in the off-season before the commit to it in the real season. That lets you get a lot of the bugs worked out before it really matters (things like the question you just asked). If you team decided to opt out of the KOP chassis, you can still order them from Andymark (although they are slightly more than the voucher). If you are looking for something a little different, consider the upgrade kits. There are several really good teams that use the KOP chassis, and perform at a high level. Off the top of my head, 3940 does this really well in Indiana.

Good luck this season!!

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Typically we would tap the end of the hex shaft to a 1/4-20 thread and use a 1/2" long SHCS with a washer to constrain the wheel to the shaft. I turned the washer transparent in this screenshot for sake of visibility, but hopefully it helps!


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This is how we do it as well except we would us a button-head screw.
Typically we’re cutting the shaft to length on the lathe, so it is very simple to also drill and thread the end holes at the same time. In addition to our (possibly unreasonable) fear of shaft collars, a screw and washer is cheaper.

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Shaft collars are bulky, and they can be expensive if you use them everywhere

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Thanks for your help! Looks like we’ll definitely be going directly into the shaft itself.

We are taking a few risks building our first one during build season, but with the pandemic we’ve had a hard time ever getting to do it before now, particularly considering our 10 year team has almost turned completely rookie this year. We’re trying to get this all built in now so that our new team members get the knowledge and experience before we loose our experienced members! We’ve got a spare KOP chassis laying around though ready to be assembled the last day of week 1 if we can’t get our WCD to work!

Good luck to you as well!

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We used the tapped shaft / fender washer / 1/4-20 screw route as well.

If you design so your bumper “covers” the end of the shaft, use a long enough screw, and have the bumper plywood “close enough” to the end of the shaft/wheel that is another constraint that will keep the wheel from “falling off” – i.e. the screw and/or wheel is captured at least partly on the shaft by the bumper.

A shaft collar typically takes more space on the shaft – meaning more play for the wheel to shift if you lose the shaft collar.

PS: Loctite is your friend in this application!

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Yes, blue loctite on the screw is a must. We learned that the hard way when one of our wheels fell off from the screw backing out.

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And for this reason, I believe snap rings are the most reliable solution.

They are also the smallest and lightest. The only downsides are that changing a wheel becomes slightly harder, and you have to make grooves on a lathe.

To make changing wheels easier, I recommend rounding off the corners of the hex shaft on the end while you have it in the lathe.

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Not if you are using plastic wheels, if that is the case then most thread lockers are your enemy as they will attack plastics, just being near them.

The best choice is a nylock bolt. McMaster-Carr

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Wow!! I just learned about a super useful product I had no idea existed.

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If you’ve had any of the AM One For U chassis kits you’ve had some of them. They are provided in the transmission kit to attach the motors to the nylon transmission housing.

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Our team has used both methods and I can tell you from experience that they both work just fine. Despite what many believe, shaft collars are more than adequate to hold wheels on shafts in a WCD. The problem with them, and why so many teams tap the shafts and use bolts/fender washers instead is that the collars are (as CalkinsGarrett pointed out) bulky in comparison and require you to extend the shaft beyond the wheel hub, while using the other method allows you to trim the shaft to the outside end of the hub (indeed, it requires it.) But functionally, there’s no difference in their ability to retain the wheels.

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Shaft collars work fine. We never have lost a wheel using them. We generally use a shaft collar on the inside and a 1/4-20 flanged screw on the outside. The Vex Collars are a little light duty. We replace the allen socket head screw with a Torx one for a little more clamping force. You are better off using a heavy duty collar. You don’t any axial free play between the axle and the wheel. With shaft collars you sloppy with your axle length.

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What was done all my years of FRC:

  1. 1/4-20 Tapped into the Thunderhex shaft ends.
  2. Lots of blue Loctite (or other equivalent thread locker)
  3. 0.5in-0.75in long 1/4-20 button head with a washer.
  4. Tighten those suckers down real good (almost to the point where you want an impact driver to get them out)
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Ive heard horror stories about the Vex Shaft collars on drivetrain applications.

In 2014 (Before I started mentoring 4272), the drive team knew that they could still drive with 3 wheels (out of 6). They would count how many they lost each match, collect them, and then put them back on in the pit.

They ended up switching to the more heavy duty ones for their second regional, and that helped them out a lot.

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Another disadvantage of shaft collars compared to a bolt and washer: one of the advantages of WCD is that you can increase your track width by moving the wheels closer to the frame perimeter. Shaft collars will take away more track width than a screw head and washer.

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We use 1/4-20 bolts successfully.
Avoid the shaft collars with tiny screws; Thriftybot has ones with decent size hexes.
Snap rings: its vital that you turn the corners off the hex before you try to snap them on. Getting over the hex corners will permanently yield your snap rings, especially if you have an over-enthusiastic student involved. Sometimes, if you hold your tongue just right and get in just he right place, you can get one over the hex. I tried spiral retaining rings and found they have the same problem. We have pushed snap rings off the end of shafts via the 1/4"-20 on the other end :frowning: If you area using a snap ring on the inside, I suggest backing it up with a collar. Collar on the wheel side, snap ring on the outside.

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