Letās Talk aboutā¦ Mirrors.
First, Iāll give a bit of background on the last 2 weeks. 2 Saturdays ago, we lost our 9-5 meeting because of the snow we were getting (also canceled our two FTC teamsā events). Usually, when we get snow around here, itās somewhere from 25-32 Fahrenheit (~-4-0 Celsius), and it is wet snow. Well this time, it was cold cold (for here) meaning that the temperature through day and night never got much higher than 25. The snow was hard and icy which meant that it didnāt melt, and it was extremely slippery. This meant we ended up losing meetings and school throughout the week until Friday. Almost every day though, school was initially scheduled to be held on a delay and then adjusted to a full shutdown. This meant that we didnāt schedule full team meetings online as it seemed unnecessary. Anyway, TLDR: We lost 22 hours of build time (our normal weeks are 16 hours).
Okay, Iāll get to the mirror part
Every day, I wake up, and go look at the mirror. I say āMirror mirror on the wall, I can surely change this part of you today, rightā and it replies āsketch can not be solved.ā
Even though I graduated last year, Iām still helping with the CAD. Iāve made a point to not take leadership of a design, they get to choose how and where, but Iām still helping them with some of the more complex stuff (specifically geometry sketches). Now, Iām no expert, hence the initial topic of todayās post. This year, we were initially thinking that it would make sense to intake from the shoot part of the source. This meant that there were three different (heights/angles that would have to be displayed neatly in a sketch. (because the amp and the source were at similar heights, understanding the sketch might be confusing to some of the kids) So, I decided that Iād set up 3 master sketches, one for each field element that the robot would interface with. I didnāt want to take the time to set up a new dt and bumper shape-set each time, so I decided that Iād mirror them.
As we got further and changed robot concept, what had started as a small time saver became more. It consumed me. A bit of an exaggeration, but after making the ground intake geometry and deciding on a setup, I decided to work on the sketch of the plate. Of course, I resorted to what Iād been doing and mirrored the intake geometry, dt/bumpers, and shooter. This was fine at first, but eventually, I started to run into problems. I would attempt to change the distance of a line or even delete a hole and I would make the sketch over-defined. Well, thatās basically where my story ends, but I mostly wanted to tell it for the moral. Be careful with the mirror feature (at least in onshape). I thought I had circumvented having errors but when adding holes to the intake mounting plates, I experienced an error that after attempting to troubleshoot for close to an hour, Iāve decided to give up on. So, what should you do if you want to do what I did? Honestly, Iām not entirely sure, but maybe one good general rule is to not mirror a mirrored part of a sketch. If thereās a feature that acts like a one-time mirror/a featurescript, that would be pretty cool, but with my limited knowledge, Iām unaware of one.
Anyways, Letās talk about geometry
As outlined at the end of our last post, we decided to go with a design that was heavily inspired by the cranberry alarm ri3d. However, as amp scoring was one of our absolute top priorities, we deemed it necessary to edit their design. So, after prototyping and testing the intake wheel spacing shown in the video linked in Loganās post, we decided that we could intake at pretty much any angle from vertical to where CA did. This meant that our primary issue was finding geometry that lined up both to shoot consistently into the amp (as close to almost vertical as possible), and still be able to line up with the shooter. After fiddling with stuff for a few days, I came up with a design that had the shooter mounted ~10" higher (to provide a better handoff angle) as well as at a 55-degree angle below the horizontal for the shooter (CAās was 60 degrees). Hereās the 3 angles as well as the intake dimentions:
How else our intake is different from Cranberry Alarmās
Unfortunately, we donāt currently have a CNC router or mill, and although the schoolās shop has manual mills the use of them is dictated by the machining teacher being there and helping. Heās one of the founders of PHRED (retired from mentorship), and we greatly appreciate him, but sometimes we wish that he would let even another mentor be trained by him so that weād have more flexibility. Anywho, the point being that we donāt drill holes very precisely. We therefore decided that it wasnāt a great idea for us to use any gears. So, that left us with belts and chains as the options for rotation and power for our intake. Though we have enough belts, we do lack variation in pully sizes when it comes to hex shaft, so we decided that chain was the simplest and fastest bet for us. We also decided that we needed to be able to adjust the C-to-C distance between the two sprockets to make removing the chain as seamless as possible. To accomplish this, weāve decided to use 80/20 as an adjustment tool. Additionally, weāll use 2 NEO 550s to drive the separate intake wheelsets.
Item not visible in the CAD
One of the ideas that CA used that we found particularly simple and effective was the centering polycarb. We intend to incorporate this element into our design. We will also cut a slot into the PC so that our beam break sensor can stop the intake rollers.
New Parts (mostly REV ion)
Today we got in a ton of our new parts and mechanisms that we ordered just prior and post-kickoff. Among the notable parts were the andymark 2-stage climber in a box system, plenty of MAXspline adjacent parts, and MAXplanetary. We also ordered additional spark maxes so we could fill the required 15. Here is an image of our first REV order as well as what arrived today:
Wrap up
Iāll leave info on the shooter design, climber, and other pieces to our mech lead (also because I didnāt help with them). We should have a post about that in the next couple of days. Additionally, it sounds like software is getting close to being ready to release an update. Loved being able to see so many teamsā progress while we were snowed in, and just weāre overall so thankful for the FRC sharing community as a whole.
Oh, and hereās the whole robot in CAD (very not polished):
Rufus ~ 847 Design Mentor
