pic: Team 1983 Fall CAD Project



I’ve been out of this competition a little too long to really comment on the overall design (although it looks very solid). Two quick things, though:

1.) I like the built-in follower wheels. Just so you know, VEX nows sells “dualie” omni wheels in that size, too: http://www.vexrobotics.com/products/accessories/motion/276-1902.html

2.) Any particular reason the drive motors are up so high?

Keep up the good work!

It keeps the gearbox footprint out of the bellypan. Might be easier to work with things on there, but could also interfere with maintenance on the drive wheel below the gearbox.

Definitely looks solid though, what are the specs? Why the odd perimeter/flange on the edges?

Very nice design.

  1. What pneumatic solenoids are you using? They look different than any I have seen but it might just be the angle.

  2. How are the wheel shafts mounted to the frame? It looks like a 1/4-20 bolt.

Hmmm… sounds like one of those “engineering tradeoff” things! :wink: I’m just wondering about the effect on the COG.

Also, the easy-to-access main breaker is major plus.

The follower wheels are nice, but you could probably have mounted it upside-down so there’s a little less metal under the belly and give yourself a little more clearance.

I always think that if you’re going to build a robot in CAD you should at least figure out the correct center distance for a chain run, so I’m not a huge fan of tensioners. Just remember that the sliding one will probably slide, and often inopportunely.

Those are my only qualms, and it’s really just an opinion thing anyway. Otherwise, it looks pretty solid and well thought-out. Very nicely done!

Looks awesome. Great Job.

You’ll definitely want to spring load those follower wheels for accurate tracking. Other than that, looks like you’ve put quite a lot of thought into this design!

Sorry i’m asking this but what is the point of Follower wheels. What do the improve and how? I’ve never seen them before so i’m just wondering

I just finished my 7th Chassis in CAD (this year), im gonna put up the one that we are currently building for a prototype and the one I like the most in a different thread soon.

A follower wheel can have an encoder type of device connected to it to track distance traveled. Since it only rotates if the robot is actually moving, any wheel slip does not corrupt the distance measurement.

These were valuable in a game like the Rigolith game, where there was significant wheel spinning.

I imagine it is also very useful for mecanum, where it can be hard to predict exactly how the robot will move based on encoder values coming directly from the wheels, especially when strafing at odd angles.

Are those 4in AM Plaction wheels you are using or custom?

If they are the Plactions, did you make them or download them? Because I cannot find where to download. If someone can tell me where they are located I would be very appreciative.

Click the ‘Files and Documents tab’.

Thanks,

For some reason that tab wasn’t loading on my computer. (Tried on another and works.)

The CAD looks nice, the only comment I have is that you seemed to have placed a lot of mass near the outside of the frame (motors and battery). Having that inertia out there will slow down your robot’s turning speed. Maybe it’s a problem, maybe it’s not, just something to keep in mind.

Great work on the CAD; you’ve obviously put effort into realism and detail.

There are few minor details you might want to address:

  1. A few components resting on the bottom plate don’t seem to have adequate mounting tabs (the Victors do; the Spikes don’t).
  2. Add bigger radii whenever possible, to decrease stress concentration (there’s a tradeoff to be made regarding weight). A few of the lightening holes are unnecessarily sharply cornered. (Also there are a couple vestigial lightening holes, e.g. in the near corner in the photo; get rid of them.)
  3. Those bumper mounts are convenient, but very carefully scrutinize the 2012 rules
    , because your design would have been legal some years, and illegal in others. (Presuming that you recess the bumper backing into the frame rails, and depending on whether you add furring strips or rest it on the protruding bolt heads.)
  4. The tall vertical chain-tensioning slots look like they may be a weak point, depending on how well you can clamp the frame rails together with the tensioners, and how much the chassis flexes overall. They interrupt the web, weakening it. Instead, consider a small vertical slot, only where you need it.

First off, thanks to all to all for the great feedback. I’ll see what I can do to address all the questions.

@Jamie Kalb: Like Akash suggested, the drive motors and gearing have been moved up to free up space on the belly pan. While that does move the CG up a bit higher we think that it is still a good trade for easy of access and maintenance.

@Akash Rastogi: The frame is all 1/16 flat sheet that has been waterjet. We then pop rivet the sheet to 1x1 1/16 angle to create the box. Our team does not have access to a proper bend break or press break (nc or manual) so this method of construction is what we’ve come up with for using sheet. The odd flange that I think you are talking about is the backing that has been left for the angle that the sheet is pop riveted to.

The transmissions are modified super sifters with the shifting shaft moved and the last stage removed. The output shaft is coupled to the rear wheel with a short chain run to allow easy removal of the wheel for maintenance.

@Allen Gregory IV: Those are 1/4-20 bolts. We have been going back and forth between using hollow shafting with a single bolt, and tapping the ends of the shaft and using two bolts. In any case they will be dead axle.

I’ll have to get back to you on the solenoids, I can’t seem to remember the model name off the top of my head and I am out of the house.

@Ninja Bait: We considered using a specific center to center distance between the wheels to allow for a set number of links. However, we felt that the chain would still have a propensity to stretch so the tensioners were placed in the model. The tensioners coupled with the idler also move the more of the chain inside the frame and increase ground clearance, which were only more pros for this option.

@Chris Is Me: The follower wheel is spring loaded. We are using spring steel with the wheel mounted lower than its radius. It’s kinda like an upside down diving board.

@0’Sanchseski: Yes, those are indeed 4" AM Plaction Wheels.

@Tristan Lall: Sharp eye noticing that not all the electronics have mounting tabs/holes. Most of the electronic position is still up in the air between the design/CAD team and the electrical team.

Thanks for the tip on the larger radius, we’ll be going back and adding a more generous fillet to a lot of the trussing and also removing the holes you suggested.

We used the same method for mounting our bumpers last year and found it very effective. By having the bumpers inside the frame rails added a good deal of stiffness and made install and removal quick and easy.

The tensioning slot was left as is to allow more than the shown configuration for chain runs, but I do agree that as shown it takes away from the strength of the frame. We’ll take another look into it.

Thanks again to everyone. :slight_smile: Please keep the questions and critiques coming, they are more than helpful!

-Dave McLaughlin

Where’s the Like button on this thing :cool:

Those are valid reasons; I should have expected that thought went into the idea instead of laziness. But it definitely sounds like those reasons would still be served by a shortened slot put in the right spot.

We used the same method for mounting our bumpers last year and found it very effective. By having the bumpers inside the frame rails added a good deal of stiffness and made install and removal quick and easy.

That’s a sneaky use of your bumpers. Shame and kudos to you. Was that a fortunate coincidence or was it planned?

Fair enough. Just wanted to make sure it was an informed engineering decision, and not just a “Hey, these could fit like this! Wouldn’t that be cool?” Sounds like you guys got it all under control. Great work!