As the thread title says, this thread is about your ring scoring/descoring and lifting mechanism design philosophy for VEX Roundup. It’s not really suppose to be about how you built it or what you did (but feel free to tell if it’s not breaking team secrets ;)) but about why you went with the approach you did. I figure I’ll start. Team 1575B idea was to create a fast mechanism that could reliably put a single ring on the goal. We thought if we could reliably and quick get one ring on the goal, then move on to another, we could overwhelm the other team. Also, our lift was very good at descoring multiple rings at once, so it was a pretty good double whammy. So we created a 4-bar arm with a forklift with a small plate onto to keep the ring from moving and attached it to the arm so at the maximum high the forklift was tilted back to prevent the ring from slipping out. Works very well at the NOVA VRC Roundup Tournament on Dec 11, 2010, except when the other parts of the robot broke. (The gremlins were out in full force, we had everything from engines burning out to laptops crashing to VexNet controls stop talking to each other) We probably going to make some changes, especially after seeing the ACME teams wipe the floor. So what were your design philosophies?
we went with a center needle design that can hold 7 so we can go around the field scoring without having to stop and pick up again
we can also pick up more tubes while we still have tubes in our needle (unlike a claw)
we also have a fold out descorer that can descore all the tubes on a goal in less then 1 second
all we do it ram into the goal with our arm up
i’d say it was pretty successful now that we have won two competitions in a row with that design
We went for a roller intake design because we thought that it would be a more efficient intake compared to a claw or a needle. We believe that if we could do everything extremely fast, it would be worth the sacrifice of not being able to control the amount of tubes scored. Also, it really helps in putting tubes under the ladder quickly. If the opponent has no tubes to score, it really doesn’t matter how efficient they are, does it? :D. We kind of have a work around for not being able to pick up multiple tubes in a row, though it’s still not as effective as a needle. We’re also debating the creation of a separate descorer, like murdomeek was talking about, because we try to move rings directly from the posts to the ladder, something that isn’t really possible with a separate descorer.
The lift itself is a four bar (a single four bar with only two structural pieces connecting the tower to the intake mechanism) for weight purposes. We chose a four bar lift over a linear slide lift because it’s generally faster, though the motion isn’t completely linear (it’s circular), making it slightly harder to score.
I’d say it’s working out for us quite nicely, as we too have won two competitions in a row. It really depends on what your ally’s robot is and how they compliment your robot. In my opinion, a perfect compliment to a claw or a roller is a needle and vice versa.
We went with a claw because we wanted to win the skills competitions, pure and simple. We felt that a simple claw was the lightest, most efficient way to score all of the tubes on the field in a minute. It was an additional bonus that a claw can descore amazingly well, and that’s a huge aspect of the game this year. Once we had claw, four-bar was an obvious choice, and our particular variety of four-bar means that our claw never ever drops a tube and rarely sustains any damage.
To our surprise, it turned out that this design also dominated the Hawaii regionals, and so our first robot won both McKinley and East Oahu. Its success inspired our other teams to create designs in the same vein, but with extra features (e.g. insane speed, fitting under the ladder). Our last team, which is going with something similar to 1107B’s robot, was inspired in October by early center roller designs to make a center roller that was fast, efficient, and easy to drive.
[FONT=Verdana][FONT=Verdana]Very cool guys. What I’ve noticed (feel free to dispute) is that the newer the team, the less complicated the lift and ring scorer on average. At the NOVA VRC Roundup Tournament, seemed that every other team either had a forklift design, or a VEX Explorer claw for their lift. Only the more veteran teams, like ACME or Garfield, seemed to have center nose collectors and the middling teams, like 1575C, had claws. I think it probably has to do with the relative breakdown of complication of each of the scoring methods. I know that team 1575A attempted to make a center nose collector, but ran out of time and parts. Possible could the new teams not have the engineering skills or parts to create the more complicated lifts and scorers? [/FONT]
I think in general what you noticed is correct. It may also depend on the team’s background (middle vs high school) and whether they have an FRC team behind them. In retrospect at NOVA, as a coach from an experienced team, we did a very bad job of interacting with the new teams. We loaned a few tools and parts but that was about it.
I’ll dispute, as I see another easy path.
Reading these forums and watching youtube of successful designs substitutes for a lot of experience and inspiration and practice. Copy what works, and then grow your own mods from there. Thank goodness for that first drawing of a 4bar needle robot, and then the first video of claw grabbers!
- Speed is just motors/gearing/spring-assist, but I agree “generally”. The other complexity with linear slides is that they are only 12" long.
- Circular motion bug can also be used as a feature to extend reach for wall goals.
Jumping off to other theoretical methods for linear lifts:
Watt’s linkage is an opposed bar 4-bar; the center of the far bar moves nearly linearly for some range.
Chebyshev linkage is a crossed bar 4-bar; similar but probably better than Watts for this purpose.
Hoekens linkage might be the most appropriate of the near linear 4-bars.
Peaucellier–Lipkin linkage is a very historically cool 8-bar of perfect linear motion, endorsed by Lord Kelvin.
One disadvantage to all of the above, (compared to std 4-bar parallelogram) is that the linear movement is a point, not a bar, so you’d have to pendulum your manipulator, or use double the linkages to provide torque to hold out the manipulator.
The following two ideas seem the most promising as they can hold a manipulator.
- 8-bar as folded double 4-bar parallelogram, as in a student desk lamp. Gear the joints together at the elbow and the lift will be linear. A natural extension of the common 4 bar. Cody has talked about a similar folded tripled 4-bar in his thread.
- Sarrus linkage: this is a 3d space crank with 6 hinges between 6 planes. If you have 6 Vex hinges and 6 flat plates, you can model this easily.
Well, our school currently has various designs for the four teams moving on.
One is more or less just a forklift, another is a rotationally closed bucket lifted by a rack and pinion, ours is a linearly closed bucked lifted by a rotational arm, and there is also a needle design.
I’m currently working on a modification for the needle that would allow for faster scoring and rapid descoring which would likely be used by the team that already has a needle (though their is extremely topheavy, so it will need to be rebuilt).
Descoring is easily done with any sort of forklift, but the problem with needles is that wall goals are difficult to either reach or line up (you can just use a funnel-like object for moveable ones). It is this that I seek to rectify by creating a system that will not be shared on these forums, but should work well at world.
Ours will likely end up being some kind of a combo design between a bucket and a needle, though I’m still working out the details (such as weight and lift speed). one member of our team has made a suggestion (that will also not be posted) that while it would allow for the option of scoring individual rings, would not be able to sort like a needle/bucket. The problem with individual scoring though is that it is relatively hard to line up everything for it. It will likely be one of these designs.
True, but copying a design is a lot more difficult for newer teams (trust me, we’ve tried it) and NOTHING can replace practice. Even with the best bot ever, if you can’t drive it well a much simpler but better piloted bot with definitely win.
So today the team met and we started to hash out a new design. Pretty much it is a Needle/Forklift hybrid. But instead of doing what some of the ACME teams did, it will combine the best of a forklift and a Needle into one lift system. We figure it would give you the best bang for our buck as well as keep the best of both, mainly the multiple ring storage and descoring stability of the forklift, as well as the speed and accurate of the forklift.
I’m surprised less teams are copying the Cheesy Poofs this year.
Anyway, I haven’t designed a Vex Round Up robot, but my design philosophy would probably go something like this:
- Design Criteria - What must the arm do?
My design criteria:
-Dump multiple tubes under ladder
-Score single tubes
-EITHER retrieve rings from under ladder OR hopper / index rings while scoring/descoring
Figure out all the different ways to do all of the different tasks separately
-Descore: Passive fork, claw grip, roller claw grip
-Dump: Collection bin, dispose of when descoring, normal scoring method
-Score: Roller claw, Pinch Claw, Needle, Vexplorer, “Overdrive” style
-Under Ladder: Arm folds to under 4" or goes over obstacles, gripper picks up in weird orientations
-Index Rings: “Overdrive” style, “WAFFLES” style, other?
Figure out if you can do all of the tasks well with only 1 subsystem
“Well” should be defined in the first step
If not, split functions into two subsystems, giving priority to the most important one.
Which is why clonebots rarely, if ever, surpass the original. While you’re copying their design screw for screw they’re practicing.
Seems to me they’re being a little more secretive with their designs. Also, last year they came in to Pan Pacific and just wiped the floor with everyone else; this year they weren’t as obviously dominant (in my opinion).
We’ve seen that indexing rings is only situationally useful at best so far. However, retrieving rings from under the ladder, especially later in the season, would be amazingly useful. Have we seen any mechanisms yet that can do it quickly and reliably?
After watching Simcoe where there were less than 10 rings per side on the field at the end of every elimination match, I think being able to hold your own rings as long as possible has its place… just not at the expense of descoring, scoring, or picking up rings in general.
It’s early yet. The full extent of Poof cloning didn’t become evident until the World Championship last year. I’m expecting we’ll see more than a handful of them this year at Disney.
and “cloning” wouldn’t really be the word
in our early early competition at redmond, there were already robots with the SAME pickup mechanism
they did not execute the design as well as the cheesy poofs, but the mechanism was there
by the next competition, they had mastered the design (still some minor tweaks) and i’d say it works as well as 254 did in the pan pacific
the cheesy poofs just make designs “popular” because they execute and build the robot so well
Yes, and being so popular especially after last year as they were definitely one of the most talked about teams, anything they come out with is going to be looked at and admired by many.
The needle design appealed to the team, but when we looked at the CAD pictures and photos that were so generously shared, no one on the team (including the mentor) had a very clear conceptualization of exactly how all the parts went together. Last year, we made the mistake of trying to build a scissor lift that we “kinda sorta” understood – it took 3 months before the team gave up and threw together a tank tread bot 2 days before the event. Since no one was willing to beg for conceptual help on the forum, that idea got nixed before it left the starting gate.
Next attempt was a horizontal-mount 4-bar arm with staggered arms, with claw capable of holding up to 4 tubes. Staggered arms allowed over 300 degrees of movement, allowing us to traverse from straight up to straight down, minimizing the length of bars needed and reducing weight. It worked well as a concept, but the staggered arms widened the lift to the point where we couldn’t fit it into the “inside” of a U-shaped chassis and keep the width under 18 inches. Mounting it on the front of the bot caused the front-to-back distance to increase beyond 18 inches, as well as creating balance/stability issues. Another problem was the amount of “swing” – instead of lifting (nearly) straight up and down, it swung forward significantly enough to cause difficulty for the driver.
Mounting the claw on a linear slide made travel perfectly vertical, but it was so beastly SLOW – 45 seconds to lift and return to the ground again. I knew that the design would be slow, but when a student says, “I can do it, let me try” it’s hard to say, “no”, even when the math says otherwise. Doubling, even tripling the gear ratio still wouldn’t make it fast enough to be practical, and too many large gears created geometry issues.
The best hope seemed to mount the claw on a vertical-mount 4-bar lift. But while the modification was going on, one of the other builders constructed a 2-stage folding dual tank tread design in a few days that worked pretty well before the other could be completed. Given that the tournament was in less than a week, we went with that design, even though it doesn’t descore (sorry Blake).
For some reason, my team has a love affair with tank treads – they manage to make them work when all else fails. It’s not the best design for this game, but that’s how we got where we are. And I’m sure we’ll be somewhere very different in a few weeks.
Thanks for the details of your jouney.
Here are some conceptual observations regarding your linear slide.
- There are more ways to power linear slides than just a gear and rack.
You can use an arm that slides/rolls against lift, which uses the slides to constrain the movement to vertical, for example.
- Speed is ‘just’ gearing. It seems like there should be a way to combine a nested slide such that the center gear operations on two racks at once, extending them both equally. This gives double the speed, because it is double the extension for the same gear revolution.
- Potential Energy is Potential Energy; Linear slides have some additional friction and mass, but otherwise, similar motor power should be able to move payload with them at similar speeds of a tread or arm. Springs/Rubberbands/Latex-stretch-tubing is your friend, as it can easily exchange spring-potential-energy for Gravitational-potential-energy with zero cost in motors. Find the delta GPE with lift at high-low positions. Find a number of springs x stretch length with the same PE. Find a way to link them together. An offcenter gear sprocket works well for an arm, it probably works well for a gear train to a rack as well.
All that being said, it is yet to be proven that tracks are not the best solution. Since treads move only the cargo mass, there is no need to worry about springs to exchange GPE and SPE (other than to move the arms that hold the treads).
One of my teams has a half track with an undriven omni on the front. With the advanced treads every 5 tracks it has a super grip on the floor, but not enough that it won’t turn. With some gearing, it’s wicked fast, but has the ability to push other robots out of the way. Nice turn ratio with a fwd/back tread spin.
As one of the mentors says “half tracks are always a crowd pleaser”
As far as lifts go we have a number with some pretty cool designs. The slide / rack is popular but they have figured out that the big gears can drive as well as the 12 tooth. One is a 4 bar linkage with slides, so the front “fork lift” can be tilted at will. It’s a handful to drive, but if they get together on it they will be very impressive. In any case the rack gear support bracket is the best $10 you will ever spend.
Thanks for your thoughtful comments. After a much needed rest, my brain is ready to “get back in gear” to struggle with these ideas a bit.
How could an arm be used to produce linear motion? All the arms I’m envisioning produce arc-like motion, though with a large enough radius it could look nearly linear. If constrained by a slide, there would be significant binding/friction where the motion deviated from the line.
We considered this but ran into problems with the geometry, i.e., fitting the right supports in place without parts running into each other. To have a center gear configuration with racks on the sides, the gears would lay side-to-side, which means the axles run front-to-back. The weight of rings and a claw or holding device means a cantilevered axle is not strong enough to support the axle, and putting supports on front and back introduced complications we couldn’t overcome, including not being able to use the double length of linear slide (nearing 24 inches) rather than single length. As it is, the design as shown only uses a single length (nearing 12 inches), which makes it impractical as shown, even if it were faster. I would love to see a design that makes use of this idea and gets the full extension in both directions, but so far, no one on the team has been able to “see” it.
The team keeps gravitating back to the idea of a linear lift with dual tank treads (again)! What we bump our heads against is how to affix metal to wobbly plastic treads (or HS chain, which we don’t have) in a stable configuration. Zip ties don’t cut it.
I’m not sure if our roadblocks are due to a lack of insight, lack of parts or other reasons. Perhaps if we bit the bullet and bought gear boxes, support brackets, and a few other nifty gizmos, we’d see how they could solve our problems and the light would come on. However, without seeing an immediate need for the parts, we can’t justify the expenditure, as there are plenty of items on the immediate wish list that we are still waiting to buy.