Comrades, how to chassis? We’re looking to design a standardized custom WCD for future seasons to increase build and design time for point-scoring elements of games. However, I’m quite new to versachassis and there’s a few things I’m not sure about.
The current tentative design uses 1x2 versaframe, versablocks, 1/2" hex shaft, #35 sprocket and chain, and Versa’s 3 CIM BS. Hopefully, you guys can help answer a few questions.
(1) for a rear-powered drivetrain, how are versablocks and the BS in WCD configuration attached? I’ve seen guides where the gearbox is attached to a versablock half when its the centre wheel powered. But I can’t see how a WCP cam can fit on a rear-mounted gearbox.
(2) We’re considering using the Viair 90 compressor. How should a fan be mounted to cool the onboard compressor?
(3) Related to (2), how close can a hot compressor be mounted to electricals? We’d like to minimize the space that electricals and pneumatics take up on the robot.
Thanks, friends!
P.s., this is my first new thread on Chief, so go easy on me xD
You should never need a cam the gearbox unless I am missing something. Cams should only ever be used on the wheels/blocks that have chains running to them from the gearbox. Vexpro should have a couple of very good examples on their website for you to follow.
Fans generally are unessesarry on your compressor. Unless you are running them for hours at a time during practice (don’t recommend that) a fan will generally not have that big of an impact to keep it cool. When practicing I would recommend more tanks/off board shop compressor to fill up your air every time you change your battery. This year we ran with no compressor on our robot and were very happy with how it.
Mounting your gearbox in the back adds the interesting challenge of tensioning differently than mounting it in the center. You really want to rigidly mount your gearbox and then add a tensioner to the middle and front chain runs. Tensioning the middle wheel then become weird because your back-middle chain run is pulling opposite of your middle-front chain run.
We got around this by simply running chain from the back (gearbox) to the middle, and another from the back (gearbox) all the way to the front. Then we just cams on the middle and front wheels. It is some extra added weight but was worth it in our opinion. Plus, in your setup the single chain running from the gearbox to the middle wheel is a single point of failure and has the load for both the front and middle wheel.
How would the BS gearbox be mounted then? Bolted directly to versaframe w/o versa half?
I’ve heard around chief that the viair compressors get hot fast w/o a fan. Off-board tanks isn’t really an option for our team because (a) we have no experience with them, and (b) adds a potential point of failure. fyi, we are currently using Thomas compressors, but they do take up a lot of space, so the switch is enticing.
If you are doing a WCD then the 3 Cim bs has a plate on the 3rd stage that will accept the versablock (217-3432) or the regular flange bearing block (217-3634) as long as you make provisions for it when you mill the tubing. Our team has used both types over the years and I think we prefer the regular flanged bearing block because it goes through the tube and provides support for the weight of 3 cims plus the gearbox. The gearbox does not need a cam so no worries on that because you will tension the wheel side versa block even on a rear mounted gearbox. I will attach a hole pattern and section view photo showing our robot this year with a WCD bearing block style so you can see it in the frame. Hopefully that helps answer that question.
For the compressor, you might want to create a little sheet metal housing for the fan and make it tunnel the air towards the heatsink of the compressor.
You should be mounting the gearbox the exact same way, regardless of where it’s being mounted. The cam’s go on the other bearing blocks. My team ran a 8-wheel versachasis setup this year, with the gearbox on one of the middle wheels. We used the WCP DS, so mounting was a little different.
Perhaps the issue you would be concerned about is the bearing on the gearbox blocks shifting forward without a cam in place. You could solve that with a simple bolt into the chassis to provide a stop on the bearing block.
With the versablock, you do the same thing but the middle hole is small enough for the hex shaft instead of the 1.5 inch hole you use on the bearing block style. We had a mistake on our practice bot and ended up using the versa block to realign the gearbox to the correct location (hole was drilled off center).
You will want to make sure you fasten it well enough that it does not slide. It has the same hole pattern but watch which orientation you are attaching the versa to because it can be upside down and throw you off by .125". I attached that image too if you wanted to see the clearance difference. They have the same hole pattern for most of their products.
I would run the gearbox bolts through the frame on the 2 sides where the plate standoffs mount, the two that go through the versablock and frame connect to the plate so that makes 4 bolts, and if you want to run 3 cims then I would run the other ones as well through the frame and into the gearbox plate for 6 total if you felt you needed the strength. 4 is the minimum.
Nope, just side-by-side. The BS is made to fit two sprockets regardless (if mounted in the center one chain run goes back and one goes forward) so it all fit just fine. Used hex spacers to keep the sprockets properly spaced on the shafts.
Nice! That helps. I’m curious, what is the distance between your wheels in your design? I have a 10" horizontal (excludes the 1/8" drop) distance between the wheel axles. That allows for between 66 and 65 #35 links on 12t sprockets, which I think should be fine with tensioners. I don’t know how 10" wheel pitch drives. Feedback?
Since you have pneumatics and electrical in the title of your post, I will comment on the layout of the electrical components.
You should think about how the wiring will flow from component to component. Start from the battery, then the main breaker, the PDP and fanning out to the VRM, PCM and motor controllers and motors. If you do that, you will probably notice that your current layout will make wiring difficult to execute nicely and neatly. Please note that there is generally a rule/requirement that the main breaker is easily accessible from outside your robot so the volunteers on the field can shut off your robot if it catches on fire.
You may also want to consider mounting all of your electrical system on a single panel (or as much as you can). This panel can be constructed in parallel with the rest of your chassis. It can also be pre-tested before being installed. This will make your work flow during build season much less stressful.
Ours came out to 11.5", I think it is a pretty common distance for a long bot but 10" is totally fine. An important point though, when you design that center distance you should go ahead and take the 1/8" drop into account. Make sure you set the distance between the hole centers as that number, not JUST the horizontal direction. When you calculate how many links you’ll need to make sure it is an even number. If you have an odd number of links you’ll end up with two ends of chain that can’t be joined (ie. two “outer plate” ends).
Not sure if you have use this, but a chain distance calculator can help here. Just enter in the distance you want and then adjust it until you have an even number of links.
Also, try using the search here on CD and do a search for “WCD” or something similar. I stole pretty much all of this advice from searches like that.
Nah, with it under tension from the cam it never gave us any issues. Had to make sure everything lined up well but the long run didn’t act very different from the short. Floating tensioner would have probably been the backup if we had issues.
Thanks! The 10" is really a guide for us to drill 1 1/8" holes for versablocks. The 1/8" drop is largely insignificant considering we are using cams anyways, in my opinion. 66 links gets us 10 1/8" exact Euclidian distance btwn axles, 65 links gets us 9 15/16". Our choice for not doing exact distance between axles is partially for ease of milling and partially to open up the opportunity to experiment with a drivetrain without centre drop (all versa blocks in same orientation) and rear+front omnis.
Thanks for the feedback! (I’m admittedly a newbie when it comes to electricals, preferring much more to live amongst my quarter-twenties and ten-thirty-twos :p.) My main concern right now with electronics and pneumatics is compressing it all within a space behind the centre wheel axles for space for game piece intakes.
I’m liking 319’s electrical board. The problem with adapting it to my current design is the height that the 3 CIM BS’s take up and the absence of the elevated supports from the chassis. In 319’s robot, the roborio is on the underside of the electrical panel. (Which is better, roborio on bottom or power distribution on bottom? It would be easier to practice with roborio on top, I think, but that runs the risk of aluminum dust falling into it.)
But what do you recommend with the breaker placement? I find that to be a headscratcher. 1241’s Stronghold robot had a breaker mount off to the side of the robot so that the breaker would’ve been vertical, over the side of the frame. The problem, I think, is that the wire from the battery isn’t the most flexible thing in the world.
