Two of our grade 11 students took it upon themselves to design and build a drivetrain during the pre-season. Matt and Jonathan did a spectacular job, putting in a lot of time working out all the details in CAD, and then machining all of the parts themselves.
I encouraged them to try some new things, since that’s what the pre-season is for. Here are the specs:
-Fully geared
-8wd, front wheel raised 3/16"
-6" aluminum performance wheels
-Single speed: 10fps (it’s all about acceleration)
-Riveted frame construction
-Fiberglass belly pan
-Beefy, heavy construction (didn’t care about weight on this one)
Very nice!
One speed 3 cim definitely has it’s advantages, less parts weight and complexity. easier to predict when driving(less thinking about shifting/waiting for auto shift). At 10fps I can’t see you guys popping a breaker unless you were REALLY trying, maybe a push fight against a 2cim shifter going at 6fps. I remember you guys browning out a few times last year at 9fps, is there any way you are looking to avoid these brownouts in the future?
This project probably started before vex did their unveiling. Now that the 3 cim ball shifter is available would you consider it as a replacement for your beloved single speed?
We typically run only 12 Gauge wire to our motors. We try and standardize on two gauges: 12 and 18. Very generally (there are always special cases) motors will get 12 gauge, and everything else that requires a circuit run from the PDB will get 18 gauge. It’s pretty simple for our students to follow, and for them to explain during inspections.
This is the first time we’ve used Talons, and are very curious about their linearity, and how they’ll behave with our software PID control.
Once it’s driving we’ll likely post a video, but I doubt it’ll be much more interesting than any other FRC drivetrain doing laps.
The brownouts from our 2013 robot were traced back to a faulty 12v->5v DC-DC converter for the radios. We didn’t catch this until we were on Einstein when the field support crew informed us that our radio (not cRIO as we originally thought) was losing power. We replaced it at some point on Einstein as we were placing the robot on the field for a match - I don’t remember during which match. After that, the brownouts ceased.
Our drivetrain choices are driven by game strategy requirements. I wouldn’t rule out a multi-speed gearbox in the future, but there would need to be **very **good reasons. We optimized last year for multiple 36ft start-stop sprint between the feeder station and pyramid, and for getting around defenders. Optimizing for, say, Overdrive in 2008 was a different matter completely. I don’t think our team has ruled out anything, but we always try and find the simplest and most reliable solution to achieve the objectives that our Strategy team sets. Being able to build something that’s maintenance free is also a big deal.
If the drivetrain strategic objectives were the same as last year, I think it’s safe to say we’d stick with the single speed. In fact, we might’ve gone down to 4 CIMs, as the 6 CIM decision was somewhat a product of our power-takeoff climbing time requirements.
The weight distribution is definitely biased for just a drivetrain, however I don’t lose any sleep over it. We developed this drivetrain with the intent that we hope to actually use a similar design on a full FRC robot someday. There’s room if we need an open front for an intake, and the top-half of a robot is usually weight biased as well. We actually didn’t know which end of our drivetrain would be the front of our robot until close to week 3 last year - and this gave our programmers fits! We intend on testing this drivetrain at full competition weight at some point, so ballast will be going on, and the weight distribution will be adjusted at that point.
What are you expecting that is different with Talons regarding PID control? I believe that you guys mentioned that you were using CAN last year. I’m not too familiar with it, but if I recall correctly it does some of the framing for you regarding PID control. I guess that part will be different.
However, we used PID control last year for our drivetrain running 4 Talons. Proved to be accurate within 3 inches over a 100 inch drive if the count-to-inch conversion was accurate, and that was with little tuning on the drivetrain (“Test mode” only works for one motor at a time, and we relied upon it for rapid tuning). For FRC purposes, I can’t imagine that non-linearity is that significant between, for example, a Talon or a Jaguar running CAN.
I doubt it. In my opinion, two speed transmissions are silly and largely unnecessary. In most robot games, the vast majority of your movements will be short sprints from game piece to goal, and avoiding other robots in between. This calls for acceleration, not a high top speed. Slower is faster.
This is really cool. I’ve been CADing some very similar designs (putting gears inside the rectangle tubing), so I have a few questions. What type of gears are you using, aluminum, steel, what manufacturer? Also gears do not absorb force like belts and chains do, how are you planning on mounting the bumpers so the forces from collisions are dispersed correctly? The drivebase looks awesome, I can’t wait to see what 610 comes out with this season.
Over the years based on our experiences, I find this very true.
However, when we had our software controlled auto transmission in a previous year, we found that to be highly effective…except we scrapped it when our roll pin from the dog gear went sour in matches. We didnt last an entire tournament without having issues with it.
The first time I saw shifting was 2001 (I think) at the SVR regional when 254 used low gear shifting to balance on the bridge much easier. It was very quick that year. EJ drove…maybe he can comment if it was worth it.
I’m kinda lolling at the thought of EJ driving a robot in a FRC competition.
I used to share this thought, but have found through experience that the idea that slower top speed=faster isn’t necessarily true. My current belief is that you should optimize your acceleration by reducing the mass of the robot as much as possible, and as a last resort, adding more power. Limiting your top speed to improve your acceleration is a risky proposition at best. We geared our robot too low in 2012 (where conventional wisdom would say that you needed acceleration a lot more than speed), and we really found it limited our performance. Sure, we accelerated quick, but it took forever to go anywhere.
This offseason, we played with an approximately 90lb bot (not including bat and bumpers), and geared to go around 18fps with a WCP DS. Simply put, the acceleration and speed were fantastic, even compared to a bot only 30lbs heavier. 18fps adjusted was a good speed for short runs around defense too. We got heavy d played on us all through quals, and we only really started shifting in elims. That robot flew, and it was because it was light and we geared really fast.
My opinion tends to be that for robots with a decent center of gravity, speeds of 16+fps are reasonable for most games (with a shifter). Of course, others have different well supported ideas about the “best” top speed.
I agree with this thought. 6 motors is just so easy now, especially if they keep even half of the motors available. If you have the motors I see little reason in not going 6 motor drive.