We are trying to decide between the two options for building West Coast Drivetrains. Any information either way would be greatly appreciated.
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I guess to start things off… depending on the drivetrain you have selected you might need both.
The WCP Bearing block is used normally at the drop center. This block is used to attach the transmission to the frame rail, and when tightened keeps the tube from being crushed.
The VersaBlock is best used at the ends of the drive train, where in many WCD 6 wheel system, there a chain or belt to drive the outer wheels from the centered transmission. When used in conjunction with the Versa Cams, it provides the VersaBlock a tensioning system for said chain/belt.
Hope that helps, let me know if you need more information.
We have used this combination for the last few years and are very happy with the durability and performance.
I will look through some of my pictures posted previously, more than likely an example there.
Aloha!
What are your machining resources? The side bearing blocks are only feasible if you have access to a mill or router that can machine out a slot in your tubing for them. If you can do this, then they are significantly less-bulky than VersaBlocks, but still somewhat more labor-intensive to use.
If you do have access to the machining required to use the side bearing blocks, I recommend only using them if you use chain and need the ability to tension it. If you are using belt, it is simpler and lighter to simply put the bearings directly in holes in your tube at the exact C-C distance (if you have the machining to use the side bearing blocks, you probably have the machining to do this).
This is incorrect; you’re thinking of the WCP gearbox bearing block, which is a different part entirely from the side bearing blocks. It is worth noting that WCP implies that the VersaBlock can be used for gearbox mounting in place of the gearbox bearing block, but we have found that in practice this is insufficiently robust. However, the gearbox bearing block does not require particularly precise machining.
I’ll try to get photos, but team 199 had some beautiful custom-machined WCP DS plates designed to work with the clamping bearing block. Believe what they did was essentially spliced the block to the plate, and then milled it out of aluminum plate.
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You are correct.
When I did my copy/paste quick search the GB bearing block came up.:yikes:
I saw that and I replied as we have used the combo numerous times.
I wasn’t aware of the SIDE bearing block. From the looks of it, I agree, from just looking at it, it would require better machining capability.
What frcguy is mentioning sounds like a good solution. I suppose similar to the VersaBlock concept and slimmer. Hope to see some pictures for inspiration.
Aloha!
Our team used to make our own side bearing blocks for several years inside a slotted rectangular tubing. However, the amount of machine work was too time consuming. After seeing 254 no longer use them anymore and machine/press bearings directly into the frame, in addition to modulating our frames, we stopped going that route. We use a 3/8" plate to reinforce our frame where our transmissions are mounted to our 1/8" frame. I’m not sure if 254 still uses some kind of tensioner once the chain is set, but we havent since.
Use the VersaBlock. The side bearing block requires you to machine a fairly precise square pocket in your tube for the block to ride in. The VersaBlock doesn’t require any precision manufacturing at all, just a loosely-placed clearance hole for the shaft. The main reason the side bearing block is offered is for teams that have been building drivetrains like that for a long time.
The other benefit of the side bearing block is that both bearings are held concentric via a single part, whereas the VersaBlock halves are held concentric using a screw / standoff connecting the two halves. This is an efficiency improvement, but ultimately not a huge deal for most teams.
On this topic so I don’t have to make a new thread, what is everyone’s experience with oversize 2" x 1" box tubing? The tubing I got locally was out of parallel across the 1" faces by 0.004". That’s just enough to prevent the Versablock fitting on that side. Not a huge deal to hit it with a file but its still annoying. I also tested the block on a piece of 2" x 1" x 1/16" that I got from AndyMark and it fit fine.
If you want to be certain of a good fit, the 2x1 tubing that Vex supplies and the VersaBlocks are toleranced to each other, so they will fit every time.
That said, regular 2x1 from various suppliers hasn’t caused any problems for me, even if it runs a bit oversize. I’ve only used VersaBlocks once or twice though, so maybe I got lucky.
So it sounds like our two main options are to use versablocks or press-fit bearings straight into the tube with some reinforcement.
Versablocks: sounds like they are better if tensioning will be required. They also sound easier to machine and setup. They are a bit more bulky though.
Pressfit bearings: Sounds like this option would be lighter and more compact, but requires a fixed c-c distance without tensioning. This option also would require a bit more precise machining.
Additionally, what are some recommendations for fixed c-c add for #25 chain.
Test fixed c-c adds until you find one you like, anywhere in the range of 0.007-0.025" (start on the low end) for specific run lengths & chain manufacturers & rough age [years of service].
Yes, if you want perfect fit, you should control c-c add by specific chain manufacturer and years of service on that chain. That’s why I can’t give you a number and also why belts are awesome.
Yes, this is how 254 does it, posted in their 2017 robot tech thread [too lazy to dig it up].
Side note - is perfect fit required? Nope! We’ve had anywhere between “quite a lot” and “a truly disgusting amount” of slack in our drivetrain chain-in-tube WCDs the last couple years, and it’s still worked fine (our direct gearbox drive is on the center dropped wheel).
We’ve still even been able to get some autonomous navigation working despite it.
(Didn’t work in matches. The vision navigation component tripped us up.)
http://www.wcproducts.net/217-3432 can be used with a hot dog down a hallway approach to drilling your shaft locations. Accuracy and precision be damned, just make sure you put the hole for the tensioner cam in the right spot.
http://www.wcproducts.net/217-3436 requires a machined pocket in your tube made either by a mill(manual or CNC), a CNC router, or a particularly motivated individual with a hand router and a quality jig.
Both options should be used with http://www.wcproducts.net/217-3634 which requires just a decent quality hole in the right location.
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There are standards for Aluminum Extrusions in the US. For a 2x1 Rectangular Tube the maximum allowed dimensional error is +/-0.025 inches. This error amount can include up to 1° of twist.
Individual large bulk buyers could contract for extrusions with better tolerances at added cost. Whether the Vex or AndyMark products are consistently any better than local supplier is unknown.
If you need better parallelism than standard extrusions, you would need to mill the sides (face cutter preferably).
I have never seen a 2x1 tube more than 0.005" out of dimension on the outside. Wall thickness variance I have seen more than that however.
I’ve always done 0.020" add for C-C 25 chain and 0.012" for #35 without issues. It still slackens a little over its lifetime for drivetrain, although not for things like climbers or rollers. Manufacturers generally do not recommend running timing belts on exact C-C distances, although like chain in FRC it tends to work if you do it correctly.
I might switch to #35 just to prevent the looseness from being an issue 115 had a 25 chain jump off the sprockets at our second regional in 2016 even though it did not appear very slack. #35 adds a half pound to the robot’s weight but gives some security.
Using chain-in-tube can prevent chains from jumping, period.
We used the Versablocks on our 2016.5 Test Chassis and our 2017 competition robot, and are using them on our 2017.5 Test Chassis.
For the assembly, we mounted the gearboxes on the vertical center of the 1x2 and used the WCP bearing block for the gearbox mounting.
The versa blocks are machined for a different center location, depending on which side you mount as “up”. Mounting them in the right orientation gives us the “drop” we need.
When you machine the slots for the versa blocks, make them long enough for the expected adjustment, but small enough top to bottom that the bearings are retained by the 1x2.
We used the side bearing blocks last year, and they served us well. The initial tensioning we used was so that the bearing block was only 1/4 of the way toward the parallel bar, that way we would have room to tension, as the chain stretched through the season. The only thing we would’ve done differently, which we will be doing next year, is using the WCP Cam, which you can see the hole for.
Sorry, I’m not sure how to insert an image, but here’s the imgur link. https://imgur.com/a/jDc27
The point of these bearing blocks is to be used with the cam for added tensioning. Without the cam, how did you take advantage of the sliding?
True story: back before the introduction of the VersaBlock, one of our students really wanted to make a WCD. At the time, we had no precision machining ability, and so for our preseason drive, he free-handed the slots with a dremel.
I would not recommend this approach, but it is “doable.”