I’m trying to understand the handoff of the cone in this design. Hopefully you can help clarify it for me.
Is the pinch roller design set up to only acquire a cone by pinching the flange such that the cone tip is pointing away from the robot? When that is complete then the arm swings down to grab the cone by the body and the pinch rollers then have to do a short reverse to release the flange and let the arm take the cone to the scoring position?
the intake retracts after the cone flange is pinched, flipping it upright using the bumper so it can be grabbed
Have you considered launching/shooting game pieces at all? I notice that it would meet a lot of your over-arching design goals! Except perhaps maybe do a bunch of things we haven’t done before.
Not yet, but something along those lines would be an interesting addition!
Hi @joemost,
This year we are using ROS + a Jetson on our robot for a couple things. The primary use is for
LiDAR but we may also plug in other cameras, who knows. But the purpose of the web interface is to display all the data coming from our ROS nodes on a fancy web page instead of having to SSH into the Jetson and view via RVIZ.
The interface itself is just a React app using roslib to connect to web socket setup by rosbridge.
What you see in that picture James sent before was some AprilTag detection running on ROS and then sent via the websocket to the webpage.
The idea was to have a nice interface to see all of the LiDAR data coming through and maybe have a top down view of where the robot is on the field.
You can see all of our ROS stuff here: GitHub - first95/95_ros: ROS Code for team 95.
Not much right now but hopefully there is more to come.
Mk1 production released! By a wide margin this is the earliest we have had a robot design hashed out.
We are going to be using carbon fiber tubes for the first time on a competition robot in our effort to keep CG and arm inertia low.
For now we have chain-drive for the shoulder and virtual 4-bar but may be looking to make those capstan drives in the future for additional weight savings and learning. @JWC_95 will make a post going into some of the shoulder design details once he has a chance to sleep.
A few random updates:
@Justin_Foss the geko-type tape did a few degrees better for the cone (didn’t test cube) than the drawer liner.
Pasta Pincher/Pasta Roller confirmatory prototype looks good. It’s 1:1 on a CIM with 1.5in c2c axle spacing with one roller wrapped in drawer liner. Seems capable of collecting cone flanges at reasonable angles even with just a 1/4-assed effort.
Special shout-out to 9016, Syosset’s rookie FRC team. We had a nice Zoom call with them this evening. They are an ambitious team moving from FTC to FRC and have a running swerve chassis already!
As James mentioned, I did most of the work on the arm assembly in Onshape. Some design requirements that I considered heavily were Lightness, ease of replacement of parts, and rigidity. James and I went through several iterations of the linkage between the moving arm and the support structure. We considered using Max spline as what the arm rotates on but it was heavy, and we were concerned it couldn’t handle the torque forces on the arm (~40 ft-lbs stationary with a very crude calculation). We settled with thunderhex shaft because we have worked a lot with it, and we could use 10-32 bolts to translate the torque directly from the sprocket to the arm(in purple). All of the carbon fiber spars are 1.125*1.125" and use scab plates (green) and nylon spacers to ensure the carbon fiber can be easily replaced and to ensure that the carbon fiber is under uniform stress(more in previous posts). This does add some weight, but the benefits of efficient replacement outweigh the harms of a slightly higher center of gravity. We are using #25 chain to interface with the sprockets, but the chain will be connected to wire rope for most of the long wire runs between the main sprocket(purple) and on the virtual four-bar linkage (VFB RED). I had to revise my support structure carbon fiber (also red) to ensure the VFB chain could clear the carbon fiber tube when the arm is fully retracted. We are mounting two motors as close to the floor as possible to lower CG and to have a redundant mechanism driving both arms (through the thunderhex shaft) if one motor decides not to work. Feel free to ask questions, as I’m sure this post is unclear, and there is plenty more that went into the design. the arm assembly (not including the gripper) is ~12 lbs, which is pretty light if you ask me.
I knew 95 would find a way to make this game look simple! I love the blue bent sheet metal hard stops - creative way to fit those in there.
I’m curious about your dead axle setup on the pivot joint - if the thunderhex isn’t spinning couldn’t it be bolted to the uprights rather than in a bearing hole? Also is there concern about the thunderhex bending on an impact?
MAX Spline setups also have the ability to transfer torque through the bolt pattern in their sprockets or MAXhubs. Tons of info as to how you can transfer torque with them in their build guide: REV ION Build System - ION BUILD SYSTEM
The hex shaft is only carrying the synchronizing torque (e.g. whatever the lag is between the left and right sides) between the two sides of the arm, not the full lifting torque.
We did model out (most of) a MAXSpline shoulder joint. It solved some packaging issues (the wild v4b bracket being a big one) but our hex shaft design wound up lighter overall. Since this shoulder joint is ~4ft in the air it seemed worth shaving a couple pounds off of it.
@Justin_Foss had an excellent request - what are the different mechanism configurations for doing the stuff?
Starting configuration
Tipped cone acquisition (looks like I may need to fuss with roller height a little more), rollers counter-spinning
Cone handoff, run rollers counter-out to spit out cone
Cube scoring
Cube ground intake, both rollers spinning in same direction
Cube handoff ish, both rollers running to scoot squishy cube out (may have some as-yet-not-designed static pincher kind of springs to hold the cube in case the intake roller is over-driven)
Cube scoring
Thanks for coming to my TED talk.
Welp…
Our primary sheet sponsor is absolutely slammed and likely won’t be able to make sheet parts for us for ~3 weeks. A lifetime in build season. So we are going to rework our existing model to work with flat sheet metal than another sponsor can plasma cut, 3D printed parts, potentially weldments, and other parts we can cut on available cnc routers.
This has me seriously stressed, but I think we can pull it off.
Sending good vibes. Been there.
Currently going through this struggle but with our milling machinist. Keep your head up!
A tip we picked up from 3538 and are still playing with lightly. Robojackets used a vice sheet metal break like this for their entire robot. not sure what thicknesses/length it maxes out at, but we have done 1/8". @Allison_K could tell you more.
Thanks! We have a 4in version of something like that for quick parts in the pit.
Our home school has a variety of sheet forming tools that we will likely be dusting off, including a decent press brake and 4’ pan and box brake (as well as dusting off our bending skills). Sadly, nothing we have can beat the ±.0015in laser and CNC press brake from our sponsor!
@Rufus_t_Doofus, let’s talk about linear mechanism binding!
I derived this equation for estimating the likelihood of binding a linear mechanism.
A way to reconfigure this free body diagram to be more applicable to this year’s likely mechanism is as a laterally-extending telescope mechanism. It may be the case that a and b change as a mechanism is deployed, so you should use the smallest b and largest a values to be conservative.
The conclusions are intuitive:
How does this inform mechanism choices in FRC? In bearing selection of course!
A plain bearing, like Igus Drylin from the KoP makes a great example: best-case we’re looking at a coefficient of friction of 0.05-0.12.
Ball bearings/roller contact bearings also have an ‘effective coefficient of friction’ that is well understood. There are numerous sources for these numbers, the first one I found through google is here.
While 0.05 is impressive for a plain material contact pair, it is more than an order of magnitude higher than the effective coefficient of a ball bearing. To move the earlier equation around:
µf<b/(2a)
As the bearing friction decreases we can support a larger eccentric load and/or reduce the base of support without binding.
If you have a linear mechanism it is worth running your configuration through this quick calculation to see if it is likely to bind. For our intake we have a bearing spacing (center-to-center) of 4.5in=b and a total intake reach past the bearing center of ~16.5in=a. So we get:
4.5/(2*16.5) = 0.13 = µf likely to cause binding
So we would be REALLY close to binding if we used plain bearings with a µf of 0.05-0.12, but super comfortable with a roller contact bearing with an effective µf of 0.002. Looking at the factor of safety:
0.13/0.12 = 1.08
0.13/0.05 = 2.6
0.13/0.002 = 65 for the win
Our minor disaster recovery plan:
Scatter-brained update time!
We added slot features to our made-at-home sheet parts. This helps the bends to form where we want them and we chose this because we do not have CNC press brakes to work with, just a ratty pan and box brake. But it got the job done.
The intake redesign to avoid sheet parts (oof) relies on the MAXPlanetary gearbox structurally. I think it’ll be fine, they are stout.
I’m printing more parts because, of course, our print farm order is delayed.
Chassis assembly just kinda winked into existence. Packaging looks good, just like CAD said it would. We mounted the compressor a little differently than CAD and it does boop the slide a little, but nothing we can’t fix.
We still have some redesign work to do on the superstructure to build it a little differently, but I think we’re in good shape right now to release those parts for fab on Monday.
Gotta plead mea culpa on one thing though: I futzed one of the fitup sketches and we all missed it at review time. The rails interfered with the swerve modules just a smidge. A few minutes with a bandsaw and jigsaw had us back in operation, luckily.
What kind of metal do you use for your bending?
5052 H32 aluminum. I find it machines pretty well and is highly resistant to cracking during bending. It is a pretty common sheet/bending alloy in industry.
