Wanted a higher torque, more “pushy” mode for fighting off defense and low speed z turning for aligning shots. Not to forget that 6 inch wheels were a bit too heavy as we are at 119.3 with 4 inch wheels
Great looking robot! Can’t wait to see you guys up at Fayetville should be a lot of fun!
I understand going to smaller wheels for weight, and lower speed for alignment, but lower gearing =/= more pushing power/torque in general. The amount of pushing power you have is directly related the the traction of your wheels. Once your wheels break free and start spinning on the carpet, it doesn’t matter how low your gearing is, you can’t increase your pushing power. For most FRC robots running 4 CIM drive at 150lbs (with battery and bumpers) and high grip wheels like the Andymark tread or blue nitrile roughtop from McMaster, this gearing limit is around 11-12 ft/s. At that speed, you will still spin your wheels on the carpet when you run up against a wall/another robot/etc., so gearing lower does not help your ability to push. Gearing faster than that, in general, will cause you to stall your motors before your wheels break loose. This is bad, and will blow breakers and overheat motors.
The exact gearing that this occurs at is dependent on the actual coefficient of friction of your wheels, the motors you’re using in the gearboxes, and the total weight of your robot. This is why most teams that do 2 speed gearboxes run around 5-7 ft/s in low gear and 15-19 ft/s in high gear, giving them one traction-limited gear that will accelerate well and won’t stall the motors in a pushing match, and one high-speed gear for getting around the field quickly.
The good news is that at 2.3 and 12 ft/s, both of your gears will probably be traction limited, so you’re probably not at risk for stalling motors. They’re fine speeds for driving around the field and for precise alignment. Just don’t be fooled into thinking you get more pushing power out of the low gear. Unless your high gear stalls the motors before the wheels spin, they will both have the same amount of pushing power.
I think what shocks me the most about your machine this year is the lack of 8020! What caused you guys to move away from that material this year?
Team Driven robots haven’t had a lot of 8020 for the last few years (2010 was the last robot with a lot) It’s heavy and unnecessary most of the time.
[strike] We haven’t used 80/20 for the chassis since 2010. 2010 (rev 2) through 2013 have all been welded tube [/strike]
Clint beat me to it.
Our coefficient of friction on the VEXpro wheels is 1.2 which is higher than most others and our weight full loaded will be around [strike]175[/strike] meant around 150. I can’t think right yet. I haven’t recovered from build season. (putting weight in bumpers to use as a counterweight)
You should look at the Q&A, specifically Q480:*
Can weight be added to the bumpers as long as you stay under the 20 lbs limit?
No, BUMPERS must be constructed as outlined in [R24].
*
I haven’t seen the actual bumper construction but using Figure 4-4 (Bumper Cross Section) and the “1 in. limit for hard parts”, you can add right at 14.5LBS to a otherwise “normal” set of bumpers simply be using 1"x1"x.125" steel angle iron (.8lbs per linear ft) on both the top and bottom of a full-perimeter set of bumpers.
While this might be considered playing in the grey area of the Question 480 response, it wouldn’t seem to be in violation of R24 in any way I can see.
Further, by using .1875" or .25" angle iron you could increase your bumper weight even more!
120 lbs robot + 13 lbs battery + 20 lbs bumper = 153 lbs.
Mike is right about the metal trim. There doesn’t seem to be be any specs on what that trim must be, so using it to add or manage your weight should be perfectly legal, as long as your bumper assembly remains under 20 lbs. We considered doing it ourselves, but found a place to put the weight within the robot. I think the Q&A response refers to adding “weight” in the form of some ballast piece that is not part of the legal bumper construction.
The “pegs” that attach the bumper to the frame are solid blocks of steel with absurdly large hardware to hold it all together. Nothing illegal that we know of. Like jspatz1 said we aren’t putting a ballast in the bumpers, just over constructing them within bounds
So I understand why you guys did it. But how are you liking having your shooter facing perpendicular to your robot’s driving direction? Are your drivers handling it okay? 1405’s 2012 robot had the same set-up, and I was not a fan. I felt it made driving a little counter-intuitive.
I personally like a lot. It seems easier to realigned to a target if the first shot is off. It does get a little tougher lining up with the feeder station but after a batteries worth of driving and trying different possible ways to pull up to the feeder station I finally got it figured out. I haven’t found any big issue besides the feeder station one yet. So no big complaints.
Like Luke said, it’s a lot of personal preference, but I tend to find it easier to evade being defended since you can strafe instead of having to realign a shot every time