Modular Building Systems

Thanks to our trip to CMP this year, we’ve stepped up our fund-raising capability and anticipate a larger budget for next year’s build. As a team with no in-house machining capability beyond a chop saw and a drill press, and not enough mentor knowledge to justify increasing by more than about one new tool a year (unless we find a machinist mentor), we’re looking for alternatives.

For the rookie Rebound Rumble year, we chopped up a KOP chassis to make a ball intake, then overloaded it with a tall frame of 80-20, resulting in a wonky top-heavy 'bot. I think we’re still sweeping up shavings from that swiss-cheesing. The next two years, we swore off kits and prototype systems and used aluminum angle and channel, but due to time constraints, we had to use our withholding allowance to finish up our manipulators. This year, we forgot to opt out of the KOP chassis. Once we had our requirements, strategy, and basic architecture, we realized that the KoP Chassis could be modified to meet our needs - and could have done so every year so far. We actually had both our practice and competition robots operational before stop build day and changed our decision as to which was which about lunchtime on Washington’s Birthday. However, we still struggled to fabricate a simple manipulator design, and though we continued to try things between Bayou and CMP, our robot at CMP was essentially the same one we competed with at the regional because we couldn’t get those great ideas built stiff enough, or light enough, reliable enough, or within the transport configuration.

After seeing some of the great robots at CMP built on VersaFrame, we’re thinking that this or a similar system might help take our fabrication abilities up a notch. We also have an incoming student who’s learning CAD (he cadded up some of our parts for external machining this year), and we’re looking at a 3-d printer to make sensor mounts and oddball adapters.
I did find a nice thread singing the praises of the Vex Versaframe system . I also have a catalog of the Tetrix Systems; Tetrix Max looks useful.

So here are the questions:

  • Are there any other modular building systems we should consider, or perhaps just an source of pre-drilled extrusion and gussets that could provide a similar advantage?
  • What are the relative strengths and weaknesses of the different systems (including strength, cost, quality, flexibility, and ease of use)?
  • How well/poorly do each of these systems interface with each other, the KoP chassis, FRC-legal motors, and off-the-shelf and custom-made sensors and manipulators?
  • Do you have any other info that would help with deciding which (zero or more) of these systems we should adopt?

Another option you may consider is outsourcing your machining. I know several high performance teams with limited in-house machining capabilities who essentially CAD the entire robot and outsource the individual part fabrication (usually sheet metal) to a sponsor. This is a direction that 5188 is trying to move in as well. You do need a strong design/CAD subteam to make this successful.

And a sponsor that will machine enough parts to build a robot. So far, NASA is our only sponsor who has extended us any machine time. What they have done for us as been great - we’ve been able to get custom weights for our Rebound Rumble shooter, wonderful hooks for our Ultimate Ascent climber, a shaft keyed for Aerial Assist, and some tote-grabbers for Recycle Rush, but we can’t get anything on a chassis or large arm scale.

As you noted, we’d also have to get a lot faster at CADding - so far, we haven’t been able to CAD fast enough to keep up with our build, so we’d have to take it up several notches for it to *accelerate *the build.

I would highly recommend VexPro VersaTubing. 5254 is a young team with extremely limited machining resources in Upstate New York.
This past season, their robot was almost entirely made from cut-to-length sections of VersaFrame, and it made finals at two events, seeded first at one of them, and was a first round pick in their division at championships.
They did so by building simply and within their resources.

I feel it is more important that your team learn to design a robot than it is to draw a robot in CAD. Designing the robot requires thinking about what it has to do, what materials it can be built from and how it can be manufactured… This thinking is what determines the quality of a design, not how the design was implemented. Once one has worked out a good design, it can be implemented in CAD or on the back of an envelope. If your team is not sufficiently fast at CAD, then the designers will spend all their time “putting parts on the screen” instead of thinking about the design. Your team may get the most value by using CAD as a tool to work out things like geometries (how long does the Canburglar need to be and where does the pivot point need to be).

Last year, we had one student who is a very proficient CAD operator who drew up all kinds of mechanisms that ultimately did not work, could not be built or did not have adequate strength (catapult). He also was of the opinion that “CAD is perfect”. We have professional designers at work who make the same sort of mistakes.

This year, we threw out the custom sheet metal trays for holding our electronics and control system because the CAD of the robot was missing the parts needed to retain the sprockets on the shafts for the drive wheels. Adding those parts meant the shafts protruded too much into the electronics tray and would hit the electronics components. The design was extremely tight and the close proximity of the parts on the electronics tray and the drive wheel assembly meant that neither were serviceable and assembly could only happen in a particular sequence.

If you are using a sponsor to make parts for you, make sure they will deliver the parts in the timeframe you need. I recall watching one Houston area team un-bag their robot and frantically finish the assembly process because their sponsor was late and delivered the parts the day before bag and tag.

I’d go as much versaframe as possible and use the 1:1 drawing on paper-glue-drill press method of making any gussets that need to be different and accurate.

I’d also highly recommend getting either a scroll saw or a bandsaw to help make anything more custom/ irregular.

Try to CAD the robot before you build it to make sure that everything lines up before you build it (IMO, CAD is pointless unless you use it to design your robot. If you build before you CAD, there’s no reason to CAD because it’s not influencing anything).

I’d avoid tetrix because of the cost if possible. Same reason I’d use wood (it really does work well for most things).

The best robots in FIRST are rarely the ones that are crazy complex, try to make a simple robot within your means.

Even if you think you can’t handle it, get a mill and learn how to use it. They are invaluable for making things in precise locations; you could make your own versatubing if you get anything with more than 12" of table movement. There are plenty of videos online about operating one.

We used Tetrix Max in 2011 when it was just called Tetrix, since that was what everyone got to help build their minibots (before everyone wised up to the One True Way To Build A Minibot that called for just the motors and bronze bushings and battery). I imagine there are a few valid uses for it on an FRC machine, but they are few and far between.

4901 used VEXpro Versaframe gussets last year on their robot, paired with our Worseaframe self-drilled tubing. Worked out pretty nicely for us. In years prior with 2815, we’d often build with nothing but 1x1 square tubing, angle aluminum chopped for gussets, and a ton of pop rivets. 80% of what was above those bumpers could be found at Lowe’s, and it netted three banners in two seasons.

There are certain extruded shapes that lend themselves to robots, such as Bosch FMS, 80/20, or the new-for-2015 Rev line. We used FMS this year since we’re supported by Bosch, but if I had to go and put cash into a system I’d probably give Rev a good look since it accepts more standard hardware and has a very simple process to get linear motion working. In all my experiences though, this gets heavy after you start adding on connectors–great for prototyping and mockups, limiting in production. (Rev uses flat gussets that are less of a weight issue, since it was designed with our applications in mind where FMS and 80/20 get used in industry a whole bunch.) Generally speaking, I’d recommend tube over these lines unless linear motion was a must-have. (Vex now has a linear motion kit for Versaframe, but I haven’t had a chance to get up close with it yet.)

Not as much of a kit, but since you have CAD expertise coming in I might also suggest sheetmetal construction. The ability to place holes and bends precisely where you want them is nice, and odds are pretty darn good that there’s a company within an hour’s drive capable of doing it. Even if you have to pay a few hundred bucks for their services, it may save you the frustration of trying to figure out how to string something together out of COTS items. (Would’ve saved me a lot of frustration in 2012 with our shooter.)

Hope this helps!

Thanks all! We’ll keep all of this in mind as we move forward in our fabrication processes. I got approval this evening to go forward with a budget proposal to make this work, so please continue if you have more!

And OBTW, I’m presuming that you didn’t realize you were breaking R15 and/or T12:

For a team with the amount of tools you say you have I would highly recommend using the VEXPro VersaFrame. We use it a lot after build season, and we love using it. It is light and simple to create a mechanism with. I have also seen a fare bit of posts from teams who have built a complete robot using it, and found that their robot’s competitiveness increased immensely due to it’s reliability (you still need a good strategy though!).

Here is a quick link to the website for VersaFrame.

Yes, we’re working on improvements there, too. We got about half the team to Karthik’s presentation at CMP, and we’re going to create a Game Analysis, Strategy, and Scouting group (though I’m not sold on the GASS acronym) which will be a cross section of departments. After game reveal, this group will break down the rules (especially scoring) to help formulate the requirements/goals for design. They will also prowl CD looking for ideas and doing “advance scouting” throughout the season. This group will incorporate the drive team, and will design the controls - to date, our controls usually reflect what is easiest for the programmers to code rather than what lets the drivers work most effectively.
Finally, at competition, having the scouts and drive team work together from the get-go should help both with qualification strategy sessions and with alliance selection; poor communication and lack of trust between what little scouting we had and the drive team was an issue in previous years; it worked a bit better this year because of personalities, and we want to make it work by design.


Thanks, everyone, you’ve helped me convince the team to try this out. I’m trying to put together a budget and parts list for a versaframe build project, but I can’t seem to find any documents that are complete enough to make a parts list, or even a complete tools list (e.g. hole saw size). Would someone please direct me to where I can find answers to the following (and follow-on) questions?

  • Are there any documents which show how the versaframe blocks come together?
  • It appears that you must drill large holes in the tubing for axles to pass through. How large they should be? Where they should be centered? What are the tolerances?
  • Are the clamping gearbox, clamping bearing and WCD bearings alternatives for or must they be used in conjunction with a face bearing mount? I can find pictures of the pieces either completely isolated or completely integrated, but nowhere in between.
  • How do the various gears, sprockets, and wheels say on the shafts - is it strictly shaft collar based, or do I need some more hardware?

For the clearance holes we’ve used a one inch hole saw in the drill press (by hand would probably work too as long as you’re careful that it’s straight). We usually just put them vertically centered on the tube. It doesn’t need to be super accurate, off the top of my head +/- 1/8" feels like it’d be plenty, but I’d have to run some math to verify that; I don’t recall vexpro publishing a number for it anywhere. If you end up drilling the hole a bit off it’s pretty easy to feel if the shaft is rubbing against it and a little bit of filing will fix it.

The clamping gearbox and clamping bearing blocks do everything needed to hold the bearing, just stick them on a piece of 2x1 with a hole for the shaft to go through and you’re good to go. Do be aware if you’re using the plastic ones that it’s easy to over-tighten the bolts on them and strip out the part that stops the nut from spinning, at which point removing it is basically impossible without destroying it in the process. Additionally, you’ll need to make sure that you have something in place to stop them from sliding along the 2x1, the friction from just clamping them on isn’t enough to keep it from sliding during heavy use; they have four holes to go through the tube for doing this, I’d highly recommend marking out these holes with calipers or some other nice measuring tool and doing them on a drill press. Be aware that while they do come with bolts to go through the clamping holes, there are not enough for all of the other holes, so you’ll want to either buy some to the right length, or be ready to cut down a bunch of bolts.

Versablocks go on about the same as the plastic clamping bearing blocks, but don’t have holes for bolts going through the tube (although I suppose you could put a few through the pattern that is on them). The WCP Cam works quite well for them if you need to tension chains—the hole for it doesn’t need to be particularity high precision either.

I don’t have any experience with the WCP bearing blocks, but it looks like you might need something to hold the bearing in it; I guess that could be done by just having spacers on the shaft hold it in, but there might be a better way to do it.

For holding everything on the shafts together all you need is collars. Vexpro’s delrin spacers are nice to have around in a variety of sizes. If it won’t be under significant load 3D printed spacers can work too. We will sometimes drill and tap the end of a shaft and hold everything on with a bolt and a washer; this can be a bit of a pain to do, but it holds everything on the shaft more securely than collars (we’ve occasionally had collars slide off of shafts if there’s significant load along the length of the shaft.

Thanks, Nyle! I’ll digest it this evening, but it looks to be enough to puzzle out the rest.

You also might want to take a look at this webpage:

Be sure to check out the drawings at the bottom of each project page, also the application and guides page has some instructions for some drivetrains to get a feel for the system.


This guide can answer a lot of your questions.

Thanks all, these certainly cover all the ground I can think of. I thought I had been all over the Vex site, but completely missed the examples-guides portal page.