4886a Robot Reveal

(Yes I know I spelled reveal wrong. It’s always something…)
Hello, as I have seen many other teams post about their robots, we have decided to the same thing in the interest of receiving helpful feedback and advice on improving our robot. This robot got us second place in the New Hampshire VRC championship where we lost in the finals by 1 point in the second match after having a battery die in the first. The match is shown here, our robot being in the red isolation: http://www.youtube.com/watch?v=nI0xzqKk-W4&feature=youtu.be. This is a slightly older version of the robot, I will include pictures of the new one, although it is still a work in progress and has changed slightly since they were taken.:cool:

Robot specs:
4 393 motors on mecanum direct drive in high torque config (we are considering switching to high speed if we can eliminate more weight)
4 269s on a 6-bar lift with a lot of rubber band assist
2 269s on two elongated side suckers capable of picking up game objects at any orientation.
Weight- Aprox 20lbs
Capacity- 7-8 if we cram it fully, but more like 5 if the orientation is not perfect. We can pick up 3-4 before the rollers start to struggle, and we have to ram a wall to get a 5th (or we can match load more).
Autonomous selector and bumpers for maximum versatility in autonomous, it can fill up the entire 30 in. goal in auto from interaction or score on the bottom of the 2 20 in. goals and then pick up objects from isolation.
Capable of scoring 30 in. interaction goal from isolation.
20 point programing skills (unofficial)

Here are some pictures of the robot
http://s1085.photobucket.com/albums/j427/zinkostar/4886a%20robot/

Nice! Now for me to go work with B team.:slight_smile:


For anyone interested, here are pics of a much older failed prototype, as well as the 4886b prototype.

Looks nice, cant wait to see you at QCC

You guys played well in the semis and I like the bot, if only we didnt break down hope to see you guys at worlds

Photobucket pics# 3,7,8 are good views, the others are mostly too close.
The tower is vastly overbuilt, so thats a good place for weight reduction.
I can’t tell how firmly your wheel rails are attached to each other, but that may be more important than usual when using holonomic drive.

The CG is really high, almost as if you intended to be able to drive over game objects.

  • If that isn’t your intent, then it seems like the batteries could be mounted lower, etc.
  • If that IS your intent, you might think about using indirect drive on the motors, so they can be moved over the wheel rails instead of inside them.
    The rubber-band assist seems likely to be poorly placed: does it help a lot to get to horizontal, and not much at all after that?

What are the gear ratios on the arm lift?
How much is aluminum?

Jgraber,
1.Sorry about the pictures. I was in a rush to take them as we had to clean up our room, as it was in a huge mess.
2. What tower are you talking about? The lift itself? Or the back of the robot?
3. We always design robots which allow us to drive over game objects. We think its a lot better then not being able to. For the indirect drive on the motors, that is so the game objects don’t catch, correct? We could try that, but it all has to go to our leader, who likes the design at the moment.
4. The rubber band assist was moved today. It helps it get horizontal and is pretty much crucial in keeping the lift itself up.
5. Gear ratios… out of memory I’m going to say 7:1. Owen is the guy who knows all the ratios.
6. As of today also, we have replaced most of the front of the table with aluminum. And all the bars in the lift are aluminum, and the bars on the side of the table are as well.
*Edit. We need as much weight as we can. Since adding the mecanum wheels, our robot has lost weight, so we are trying to find places to deliberately add weight.

Cheers,
Robert

How do you like your mechanum drive? My teams robot utilizes a simular concept and our mechanums are on the way. Do you ever have a problem with stalling? can you get pushed around easily?

We have not yet tested our mecanums in a competition. Our next one is this Saturday, so I can tell you then. As for stalling, we have not had any troubles with that. Overall, they are great in my opinion :D. The only thing that we are having a little trouble with is the drive code. The one it comes with turns the controller into an arcade style movement, we then had our coder make a simpler drive code. Just a heads up for that. I think you’ll like the mecanums.

Robert

Thanks for the feedback.

This was put on by one member of our team in order to get the weight farther back from when our arm was mostly steel and pulling it forward. We can easily eliminate most of it.

More support has been added since these pictures were taken, so this shouldn’t be a problem.

Yes, that was our intent. The game objects usually just slide off of the motors as they are much bigger, but they can get caught very rarely.

The rubber band assist helps pretty much the whole way up. It does get a little bit weaker when the arm is fully extended, and our motors engage slightly at that point to keep it up.

The gear ratio on the lift is indeed 7:1. We replaced most of the intake and lift with aluminum, but there are still a couple of steel bars because we ran out of aluminum. All of the base is steel.

Thank you for the feedback and suggestions. Keep them coming!

1x5x1 Steel C channels instead of flat plates for wheel rails will take more space, but but much stiffer and add a little low CG weight. You may need to cut or crimp in the 1x part near the wheels. Otherwise, just stacking more flat plate or 5x Channel along the outside or inside wheel rails will increase your weight and lower your CG.

Chaining the wheels together will maximize the power to the wheels and let you mount the motors over the wheel rails to keep the center more clear, as well as make it possible to change your speed vs torque if desired. Or just move the front motor, since that is typically the first to bump an object and trap it between robot and goal.

Elastic on 4-bar is typically run from back of top bar to front of low bar.
I haven’t modeled it to see how the force changes as a function of arm position.

Moving the batteries to over the wheel rails might let them be lower (for lower CG),
but will also increase your rotational inertia.
Moving drive motors to over the wheel rails has similar side-effects.

If your competition is on Saturday, I’d only play with elastic and possibly ballast.
Or possibly the speed-gearing on the 393s instead of ballasting, since your weight is less now.

Thanks again for the helpful responses.
I actually suggested using cut c-channels at the beginning, but we don’t really have many tools for metal cutting besides a dull hack saw so we will stick with what we have for now. If bending becomes a problem we could make the effort to switch.

We can’t really chain the wheels together due to the nature of Mecanum wheels. (To go sideways one goes forward and one goes back on each side).
Changing the elastic isn’t really a priority because what we have works, but we may think about it later in the season.

We are going to move our batteries to directly under where they are now, strapped over the motors in the back. There will still be space of game objects to go under, but the CoG will be lower. We are also planning to add an LCD screen where the batteries were

Now that the arm is lighter tipping is not an issue, so we shouldn’t really need ballast. We will probably also wait to experiment with speed gearing because there would be no time to stress-test and it would mess up the autonomous. Expect updates if there are any major changes.

I would like to thank whoever corrected my spelling on the title of this thread. It is always embarrassing to have a spelling error right in the title of a thread. Spelling has always been a problem for me and I am trying to get better. (I almost spelled title “tittle” but decided to look it up).:smiley:

You’re welcome. I hate reading misspelled words, so I fix quite a few of them here on the forum. I don’t change your content, though.

After our team’s most recent competition this Saturday at QCC, I have decided that the main weakness of our robot is that it is somewhat slow. I think we might try to internally gear up the 393s on the drive for speed, and test it extensively to make sure the breakers don’t trip. If it doesn’t work, we will remove as much weight as possible until it does. (There isn’t really any room left for external gearing). We will have to reprogram our autonomous sequences, but I believe it is worth it to be faster.

that double pin was funny as hell i just had to run over and get a look haha

Yeah, we each thought that the other team was pinning us. The ref told us to back off and we were both like “I CAN’T!!!”

yeah it looked like you were pinning until you looked at the gate bracket which i thought would never trip a team up because its so small, guess you proved me wrong

I switched out the internal motor gears in the high powered motors for speed, and it works!!!:smiley: Expect a much faster Aperture robot in the coming competitions.

Video and pictures from our last competition are here. I think we may make the drive base longer again to make it less tippy. (we never actually used the backwards scoring). Also with high speed gearing the mecanums have trouble moving sideways, so we took that out of the code for now. When we get more aluminum we will probably add that feature back in. Also does anyone know about the legality of high speed internal gearing for the 393s? I had thought it was legal, but <R15> prohibits modification of motors of any kind…:eek: