2915A robots, Opportunity and Sloth V1 Release

OKAY, most people have seen our world cup robot (opportunity) and we got alot of questions, so im gonna do a full release here of opportunity, and its bigger brother Sloth, Sloth V2 has just been made so im allowed to release sloth V1 (which played at the christmas scrimmage in NZ)

Opportunity served our team well, and was a great predecessor of Henry - released here https://vexforum.com/t/lynfield-college-robotics-2915a-first-gateway-robot/19544/1&highlight=lynfield

Opportunity won us only one competition though, with it reaching the finals in all but 1 (where we versed the people who won it in semis)

Opportunity V1 had alot of issues (as do all of our V1 robots) - the main issue it had was TIPPYNESS which from watching youtube videos, alot of teams suffer from this year - Opp V1 is shown below

http://youtu.be/s2JJ9WqWZQE (sorry if its still uploading)

We fixed these problems by making the arm alot shorter and moving the main towers to the center of the robot, balancing the weigh more evenly.
resulting in V2 shown here - http://www.youtube.com/watch?v=PMTXPcej_z4&feature=g-upl&context=G2f6afb9AUAAAAAAADAA

There are a few features on this robot which no one picked up when watching videos… i think they were pretty awesome.

  1. WINGSSSSSS. These were VERY controversial, i think mainly because we put them on half way through world cup to keep them a secret… the wings were 12" chassis rails on pneumatics that flicked down as blockers, making our robot essentially 42" wide to hinder movement of opporsition, they flicked up and down so it didnt hinder us.

  2. BACKWARDS SCORING… This is a nifty little feature which we didnt quite get perfected. The purpose of this, is to score the center 30" goal from the isolation goal (Sloth is designed around this), because if you watch games closely, that center 30 is the decider half the time, and isolation robots are generally racing each other there… so why not score it from iso?


Opp motor configuration was as follows -

1 HS motor on each side of the lift

1HS and 2 269 on either side of drive

2 269 on intake


The lift was a chain linkage thingy ma boby (do we have a proper name yet?) on a 1:6 ratio


Where to begin… i dont know what to say, i really dont want to write it all out… in short we had 18 autonomous programs (9 for each color)

And thats about all there is to opportunity…

Sloth V1

Sloth V1 only entered one competition, and was plagued with problems (hence the redesign) but still managed to fight its way to finals. It was designed to score the center 30" goal from isolation

it is shown below running its autonomous routine -


It had the same motor layout as opp, yet only one autonomous as we didnt have enough time to write more. We took what we learnt developing opportunity and implemented in on sloth, hence the tower in the center. We opted for a 6 bar for strength and stability over the chain linkage. That pretty much sums Sloth up, sorry i cant say any more about sloth as we are still very protective of him… So i may have very brief answers if you ask questions :stuck_out_tongue:

Wow, my longest post ever… Hope we can be of some help with people still building and designing](http://www.youtube.com/watch?v=bmxodldQMhY&feature=g-upl&context=G2cd2bf5AUAAAAAAAAAA)

1 Like

I never actually saw the backwards scoring in action on your world cup robot. I saw the pneumatic, but never saw it actually used. What was the problem with it? Did it miss?

Also, I’m assuming Sloth V2 also is based on the ability to score in the 30 inch goal from isolation?

Good post, I learnt some stuff about those robots even though I saw both of them.

Also, Off topic: Does everyone name their robots? I’ve never really named my robots before… If I did I would probably get too attached to them and break down when I pulled them apart :frowning:

How well would you say the 2 bar with chain worked for you ?

The wings aren’t something that you can use all the time - they’re only useful in rather specific situations. Additionally, there was a bit of controversy over whether it was legal (primarily due to the entangement risk), but at the end we decided that they were legal - but since using them was a defensive maneuver, in any rule violations that involved the wings (such as tipping, entanglement, pinning, etc.), the robot with wings would be penalised (since it was playing defensively and would be judged more harshly under the gateway rules). Because we told the teams this, I think they were more hesitant to use the wings, just in case.

The main purpose for naming robots for us is so that it’s much easier for us to refer to them later. We build so many that it’s difficult to go “That robot we built in July 2011 that had tank tread intake and the slanted 4-bar” when we can just say “Java”. It may have more sentimental reasons for other teams :stuck_out_tongue:

The backwards scoring was just very inaccurate - you had to be lined up perfectly for it to work…

Your assumtion is correct about sloth V2, although we may rename it because it is very different… :wink:

We name our robots because they are like children to us :stuck_out_tongue: we talk to them as well :stuck_out_tongue:

I think the ruling on the wings were very unfair… ive had this conversation with you (and many other of the NZ Judges) so i wont repeat myself again :stuck_out_tongue:

The chain linkage worked fairly well, and was reliable - i would recommend it if you are looking for a light alternative to a 6 bar

So then why did you stop using it?

We decided that we wanted our towers as close to the intake as possible (and arms) and felt it was easier to implement a 6 bar rather than a chain linkage in such a small area

Also, something weirded out with my link, so heres a working one

1:5 :wink: my mistake, I thought it was a 36 tooth sprocket. Then I realised there wasn’t such a thing

We always try to. (With an exception of our current robot, atm its “that thing”). I think its a good thing, especially so you dont end up calling ur robots an “A bot”, “B bot” etc… which I think (from experience) can be really hurtfull for some of the subteams as they may feel graded as lower than the rest.

I was wondering how it was 1:6 when I saw just one sprocket haha.

Do you know the drivetrain speeds for each of your three revisions? (or gear ratios and I’ll calculate it myself.)

Also, did opportuntity have the ability to descore objects mostly under the plane of the goal? How about the later revisions? I also noticed you increased your intake diameter which I assume is for a greater surface speed. What would you guess the total weight of the arm is; and where is your center of gravity with the arm up? (tilt robot as if it is tipping over and where it is balenced the plane from the contact point up is your CoG, doing this on the robot’s side and back gives you a pointmass in space relative to the robot.)

Also, the only name I have ever heard of for the arm with mounted sprockets for parellel (or asmyetrical motion with different sized sprockets) is “virtual four bar.” Only recently did I hear someone call it a “chain bar” which I believe was made up on this forum.

Thank you for unveiling these great robots.
Regards, Bryan

Whoops, sorry about the lift ratio error…

Henry (the first robot) had a 3:1 drive ratio on small wheels, and the other two had a 15:6 ratio on small wheels. Heres a little except from our design notebook outlining our choice of wheels

"This year we decided to go for the smaller omni and traction wheels (double roller).

The smaller wheels were chosen over the larger wheels because it is easier to create a lower COM (center of mass) because the hole where the axle is through is lower to the ground and also a larger wheel base can be achieve even with a smaller chassis. When are large wheel is through a pillow bearing on top of the chassis, it is the equivalent of the small wheels being though the center holes in a chassis rail or c channel. The smaller wheels also allow the wheel base to be longer in a smaller amount of space, this is shown in this picture -


As you can see, where the wheels touch the ground is further apart on the smaller wheels compared to the larger wheels.

We chose a 6 wheel layout, with our first robot all 6 omni, and all of our robots after that with the middle two traction. We chose 6 wheels to spread the weight of the robot over more area, meaning there is less pressure on each. The two traction wheels in the middle are to deter people from pushing us, because we find that lots of pushing happens when you just have omni wheels.

We chose omni and traction wheels over the meccanum wheels because the maccanum wheels are very wide, and we need small widths for our wheels to fit into (so we can engulf goals etc)."

^that is relevant for the first 3 robots… and somewhat to sloth V2 (you will see in the future)

All of our robots have the ability to descore as this is a very important aspect of the game, they do so by sucking off the top object

We increased the surface area of the intake sprocket for two reasons. 1) Faster sucking/spitting (what we call intaking/outaking) speed and 2) for larger surface area to pick the 5" oriented barrels up better

I will have a talk to nimbus.ii about the CoG (she does that sort of stuff)

Hmm, virtual four bar… that name could do it

The name is “chain linkage.”
Because it uses chain to link the intake to the rest of the robot and keep them parallel to each other :slight_smile:

Yay! A proper name! Now lets see how long it takes for someone to create something really wacky like a chain 6 bar linkage… Id like to see that.

This looks like a chain 4 bar linkage: http://www.youtube.com/watch?v=fGO1Vi5NtwM

Yeah, thats a nice robot too.

But what about a 6 or 8 chain linkage though? I might have to prototype something for fun. :stuck_out_tongue:

lol, then it would be a chain scissor lift on its side :wink:

wouldn’t it need to be able to slide at the top and bottom to be a scissor? Its still a cool idea. :smiley:

Yes, an 8 chain virtual parallel linkage scissor lift seems like a very rational place to take these ideas.