Hello All!
I was wondering if any of you were having issues where your robot almost falls over. I have seen many “dead robots” over my years in FRC, and this may be the year above all others for dead robots.
So, has your robot tipped over? How are you planning on solving this problem?
This has fortunately not happened to my team, but it is still a personal concern of mine. I hope we end up significantly underweight for ballast purposes…
Our team started off with a robot that couldn’t lift more than two totes and a bin and still drive safely. We ended up gouging out the front of our chassis to create a hole large enough for a totes to slide in, and moving everything with mass as far back as possible. Now, with most of our mass at the back of the robot, we can lift more than our robot weighs right now without it tipping.
Given, we’ve only had minimal practice driving with more than three totes, but I would say that our robot won’t tip easily this year.
Our robot has a 80 pound chassis so we have not had any problems with it. We can lift 4 totes 6’4" off the ground without tipping.
We designed ours with most of the weight at the end opposite where the game pieces go. We haven’t driven it on carpet, loaded with game pieces yet, but the little bit of driving we’ve done in the shop so far makes it look like we’ll be ok.
We calculated our center of gravity and focused everything that is above the chassis to be centered around it.
We made our base >1" under max with the wheel base in the long direction, and when we lay it on its side to do work on the bottom it takes a lot of effort. It also has a very low CG because the elevator is short and compact, and the battery and all 4 gearboxes are as low as we could mount them.
I remember getting knock out of quarter finals last year when our alliance partner tipped over, completely on their own! A problem I was careful to make sure didn’t happen to us.
It’s all about designing with the cg in mind. Probably 3/4 of our weight is within what would normally be considered the bumper zone. Most of the rest is close to that as well. The battery, two CIM’s, and the compressor are all located as far back as possible to help counterbalance the weight of a stack of totes, and we built a U shaped robots so the totes are almost halfway inside what would normally be considered the frame perimeter when we pick them up.
Our robots have never tipped over in a match, not even when those bridges in Rebound Rumble would occasionally tip too soon and put us up to 70+ degrees.
We haven’t done enough driving yet to say for sure, but once we decided on an outside lift, we made our wheelbase as long as we easily could (KOP long chassis, 4" wheels). We expect to have 30-40# of ballast (plus the battery) at the bottom and back of that length to minimize this problem. If things are still problematic, we may cantilever some of that weight outside the “frame perimeter”.
Here’s how you fix that balance problem…LOL…That tells me lots. Balance out the weight, just make the bot do a lot more!
Something tells me they will be in demand. Though once the big walls go up, they will be driving very carefully! I saw a stack of 6 capped in under 70 actual seconds w/ very lil’ wasted movement. 4 at a time from the landfill, I’d be doing a layer of 4 in 2X2, go get 4 more, and 4 more, and layer the bottom all the way across 4 high~5 high first. Allow the others to cap and stack 1~2+Bin+Litter. They hit upon a really decent design w/ little wasted moves and really sturdy w/ a low CG it appears even though at max height.
We seem to always make “tall” robots, so “center of gravity” is an issue we address yearly.
I would think you would want a long base, so that if you accelerate quickly forwards then back you won’t tip yourself easily?
Though I guess if you get swiped from the side with a long base, you may risk falling over sideways, though I haven’t seen that a whole lot.
Big footprint… Not skinny in any direction.
You have to also consider turning… If you are long and skinny, you might be okay with a quick acceleration. But if you need to turn, you could topple.
Just use your robot to right itself :rolleyes:
One of the oddest tricks I remember was in 2008. My team at the time (1747 HBR) had a problem with overshooting when hurdling the overpass which would snare the grabber on our angled forklift and tip us over to the point of being caught on the overpass with the wheels off the ground. Our fix was to (IIRC) zip tie a piece of 3/8" round stock to the lower rear frame rail, which worked as a makeshift wheelie bar and prevented the tipping issue from disabling us.
We did the sideways tipping test last night, our robot has to go to about 45 degrees leaned over before it will tip over.
Still need to do the front and rear tipping tests, unloaded and loaded. Although we kind of have a safety, since the tote stack falls over way too easily.
We did two things to prevent tipping. We designed as much wait opposite to where we hold the totes/cans as possible. That wasn’t enough, so we added weights (dumbbell plates) to the back. We also noticed that if the driver accelerated, or “decelerated” to quickly we could either tip, or lose our stack. So we implemented “ramping” code that limits the acceleration of the bot.
We’re about as tippy this year as we’ve ever been… it takes about 65 degrees before we’ll tip over this year. We’ve had that number as high as 80 degrees in the past!
We’ve designed the top deck of robot with the ability to slide back via a motorized lead screw. When we lift up 3+ totes above the top of our frame, our operator will slide the deck back, moving the C.O.G. with it. It will move forward when we’re ready to score.