With two competitions under our belt, I think it’s probably about time to reveal how well our massive mythical cube-hoarder bot has been doing
It doesn’t work.
6-12 cubes is a whole lot of weight; we didn’t have issues with power (our RD4B was geared at 25:1 and had a rubber band assist). The problems came from the material strength of the parts we were using. I guess that part of it was that our design wan’t the greatest (it could probably have been reinforced and refined a lot more) but the fact stands that a dozen cubes weighs a LOT. If anyone else plans on building a super heavy-lifter bot, make sure to reinforce EVERYTHING. The axles in our compound gear train bent and popped out of their mounts under repeated stress, our new shiny aluminum C-channels bent and warped, and the whole thing rapidly turned into a huge mess. We did a hasty rebuild and tried to repair or replace what we could before our first competition, but our quick-built robot didn’t do all that well, and neither did the second iteration at the next competition. We have another event coming up Saturday, and we are scrambling to build an effective robot in time (We are going for build quality this time, not some grandiose master robot :o )
Moral of the story: Build quality is just as important, if not more so, than a good design.
I will put up updates here for the new robot, and hopefully it works out well on Saturday. We’ve failed a bunch, but in the process we have learned a lot about how to go about building a Skyrise bot.
3 main questions
-Did you use a centralized gear tower or two gear towers (one tower on the left and one on the right)?
-Assuming you used two gear towers like the common design, did you use gears on both sides of the channel or just one side?
-And finally, were your axle lengths between the tower(s) shorter than 1.5 inches?
The shorter the axles, the less chance of gears skipping and therefore less twisted/broke axles. This video has more information on the topic: http://youtu.be/YrEfxDRlTLo
Basically what ifticar mentioned. I used an rd4b with 1.5 inch axles in sack attack and it survived the rigor of competition. A bit longer and it yielded. I know teams in the past have made axles even shorter, so if they yielded at approximately 1.25" it may be impossible to lift 6-12 cubes with axles.
Because of this, this may indicate that screws must replace axles, or the load needs to be distributed among other shafts in a more complicated, yet doable way.
We had two gear towers; all of the bars were geared together to distribute power and load as much as possible. The innermost gears (the lower ones on the upper stage and the upper ones on the lower stage) were the ones that bent the most. Our axles were just over 2 inches long between the bearings, and the bars were only attached to a gear on one side. Those were, I believe, the main issues; the longer axles gave too much space for a bend to occur and doubled-up gears would have certainly helped. Our redesigned lift we are working on now does both of those things, however; we are keeping the width between bearings down to just over an inch and we have doubled up the gears to help spread the load more.
However, oddly, the bending on the C-channels was about halfway along the length of the channel, as you might expect from the stress of a heavy load. There was little damage to the gear-mounted end of the channel, so I don’t think that the single-sided mounting was too much of an issue.
Darn, I wanted to see it Yea, you want your #RD4B to be extremely thin. Ours is 1.875", but could easily be 1.5". These lifts are also REALLY unstable, and, well, “floppy”. Even built well, there is still lots of give in the lift (especially side-to-side).
Any pic’s of your “hoarder”
I’m looking forward to seeing you there man. 4417B is a force to be reckoned with this year!
We had a competition on Saturday with the new rebuilt robot, and so far the redesign looks promising. We had a rough start since I finished the robot at about 11:30 the previous night and thus has absolutely no experience driving the thing; we lost our first three matches. However, we improved greatly as both of our drivers got better at using the new robot, and by the end of the competition we could reliably score about 20 points each round by ourselves. This robot definitely has a lot of potential; the problem is that I’m not that great at driving it yet, so I’ll have to spend a lot of time practicing. :o
Here’s some specs; I’ll get some pictures up Wednesday when the team meets up again.
KETOS IV (soon to be renamed “Twin Dragons”)
***** 4-motor holonomic drive with 2.25" wheels and IMEs on the front wheels, geared internally for torque
***** 2-motor main arm, a RD4B geared at 25:1 with independent top and bottom sections, with a 1-motor clawbot claw that swings out from one side and locks into place
***** 2-motor secondary arm, a 6-bar geared at 5:1 mounted on a turntable powered by one motor, with a passive cube intake
***** 1-point autonomous that simply drops the preload and deploys both arms
WIP Upgrades:
***** Main arm will be widened slightly to increase stability and will have additional reinforcement on the gear train to prevent skipping
***** Secondary arm will have a pneumatic claw instead of a passive one to reduce mistakes while handling cubes
***** Autonomous will build at least one Skyrise and score the preload on it (will not interfere with autons that push a cube onto the Base)
***** Main arm claw will be replaced with a wider-opening specially designed claw rather than the small pre-built one
***** Turntable will be mounted more securely to minimize wobbling under heavy loads
Basically, the robot is a Frankenbot created by combining a dedicated Skyrise builder with a simple cube scorer. The secondary arm is mounted on the back left corner of the robot, with the larger main arm taking up most of the right side. The mini-arm faces forwards to begin with in order to fit in the size constraints, but swivels around to the left or the back to grab cubes. The main arm’s claw is folded 180 degrees to the left and is pinned by the mini-arm before deploying at the start of the match; a bent strip of metal holds it quite securely in place once the rubber bands pull it into position. We have never had the claw come loose once it is clipped into position. Only once did it ever fail to hook, and that was only because someone had bent the hook on accident while fixing the robot. Once everything pops out, the side driver can grab cubes from the central stack quite well while the main driver builds the Skyrise. After building each section and turning to the Autoloader to grab the next one, the side arm can score a cube on the Skyrise (though only if it is two sections or less tall). The main arm can build up to 6 Skyrise sections, and the mini-arm can score on the low posts.
We ran into a rather interesting and unusual problem at this Saturday’s competition; due to the asymmetrical design of the robot, the mini-arm (which is mounted on the left) is almost completely ineffective while playing on blue, while on red it is incredibly useful. We were stuck playing on blue for most of our rounds, unfortunately, which meant that we effectively had just one arm instead of two for those rounds. In addition, our driving is still pretty shaky, and we had some other issues for our first two rounds (out of only five) so we placed very, very low in our qualifiers. In addition, our arm is just barely too short to get a sixth Skyrise in; if it were an inch higher it could do it. We also didn’t get around to doing most of the improvements I listed in the last post, except for the claw replacement (which works beautifully).
We’re getting better, but our bot is definitely still a work in progress. I hope to get a video up soon so we can get some feedback on our design.
