4476 W.A.F.F.L.E.S. Reveal

Here is a reveal video we made of our robot this year: http://www.youtube.com/watch?v=q8ALmAyPo6c&feature=youtu.be
Unfortunately, we will not be attending championships. There is information about the robot in the video. I you have any questions, feel free to ask.

Main features include:

-8 motor transmission
-Elastic powered bucket to score in troughs
-Standard “spatula” intake

Could you please explain how your transmission works? I’ve never seen one like it.

That’s incredibly clever. Love the use of drive motors to reset the elastic bucket, and maximize your drivetrain power.

The shifter is hard to explain so I will do my best. Our team has been working on this design since December of 2011 and we have never come across anything similiar to it either. The concept has not actually changed that much since we started designing it. Firstly, there is a motor module as we call it. It is 4 motors attached to a plate. This plate is standoffed to another plate and they sandwich the motor gears in between them. On the side opposite the motors, there are linear slides. The motor module slides back and forth on the drivetrain by a piston pushing it. If the piston is extended, the motor gears will mesh with drive gears that will in turn send power to the wheels. If the piston is retracted, it will mesh the motor gears with a different set of gears creating a different ratio. This set of gears will also send power to the wheels. I’ve created some illustrations to help with understanding. One is of the side of the motor module. The other of is the overall system. We CADed almost every iteration of the drive so I might be able to get some CAD screenshots of it aswell if needed.
motor module.jpg

Interesting… I will have to look into this.

After our final competition, we made some more improvements to the transmission. It now shifts much quicker, is more compact, and has less overall system resistance.

Still a few more tweaks we are making for this coming season to make the drive even more reliable

Last questions… How many pistons do you use to lock your basket? and how does it relock automatically? Where are these pistons placed?

At around 2:26 in the release video there is a good clip of it. If you pause the video at 2:26, directly to the left of the rope, there is a small c-channel pointing to the top right of the screen. It has one of those 45 degree plates bolted to it at the top. You can also see the bearing that it pivots on bolted to the angle. The c-channel extends all the way to the bottom of the robot, almost hitting the ground. At the bottom of it, there is a piston attached to it and the drive frame. When it activates, the c-channel pivots back and forth. The 45 degree plate hooks onto a standoff at the bottom of the bucket to hold it down. When the bucket is at the bottom, it presses a limit switch which can also be seen to the left of the c-channel at 2:26. With code, we tell the piston to activate the lock to hold down the bucket when the switch is pressed. I attached a picture of this. We use one single acting piston on the bucket lock. At 4:01, there is a brighter view and you can see the piston extended at the bottom of the robot. During the clip at 1:28, you can see the 45 degree plate lock over the bucket standoff.
bucket lock.jpg

thanks… you’ve been a big help with designing the last bit of my bot for next year.

How exactly are you attaching sprockets to the gears? The way your drawing looks it looks as if it eats axles for breakfast.

Do you have any issues with gears skipping if you run low on air?
You think you could show some of the CAD?

For converting gears to chain, we simply have a gear on the axle being driven by a motor gear. Then, we have a sprocket that turns a wheel on the same axle.

I’m not quite sure what you mean by ‘eating axles’. If you mean that we brake axles, we haven’t had too many problems. We have only twisted 1 axle in about the 1.3 years that we have had this drive. But, we have bent a couple of axles by the piston slamming the motor gears into them. If you mean eating as in uses a lot, yes, it uses more axles than that the standard 4 wheel direct drive layout. But we didn’t run out of axles. We did run out of bearings though.

We do have skipping problems when the air is low. But, two air tanks is way more than enough to keep the drive working perfectly through a match. When the air is at a high level, we will never skip gears. We will brake HS chain before we skip gears. But we’ve broken a lot of chain.

I have dug up an older version of our shifting drive! This version’s official name is Transmission 2.4. In relation to the current drive, it would be the grandfather to what is now version ~3.2. This older version has 10 wheels and only 6 motors on drive. It has gear ratios of 1:3 and 3:1.

The first picture is the overall system with metal.

The second picture is from the outside of the robot with the outside C-channel, linear slides, and motor module plate removed. The motors shift to high gear on the right and low gear on the left. If you look close enough, you may start to wonder why there is an extra 12-tooth gear in the low gear as it does not contribute to the ratio. If that gear was not there, the drive would switch direction every time we shift. This is something that our team decided we did not want to put in the robot’s code. Instead, we simply add the gear and everything works out fine.

The third picture is of the actual driven axles. The high gear axle has two sprockets on it that are chained to sprockets on wheel axles. The low gear only needed one.

The fourth picture is of just the sprocket axles. The highlighted sprockets get chained to their respective highlighted sprockets in the fifth picture. The rest of the sprockets get chained to the same size sprocket that is beside them to create a system that every wheel is powered by a 1:1 ratio.

I hope that this information and these pictures are helpful. If you have any further questions feel free to ask.
Transmission 1.0.jpg
Transmission 5.jpg
Transmission 6.jpg
Transmission 2.1.jpg
Transmission 3.0.jpg

This is worth noting. Over time the axles did bend. With more support this is unlikely to occur as much.

To put some numbers to that, at about 55-50 PSI, very harsh maneuvering (eg. full power forwards, then full power backwards) it will slip. At 50-40 PSI the transmission really starts to get in the danger zone. In speed mode only very gentle maneuvering will cause the gears not to slip, but in torque mode it’s completely fine. Normally when we are practicing we re-pressurize here. Below 40 PSI driving in high gear is virtually impossible, though it still functions is torque mode, though that would probably fail at like 20-15 PSI.

Hmm have you looked at using spacers on the piston to reduce the throw? This may help with the slamming because right now it seems as if you are letting the piston only extend halfway and the gear is what forcefully stops the piston. and you have no control over where it ends. If you added spacers and reduced the retraction distance you should be able to calibrate it so it just meshes the gears enough but doesn’t slam into the gear. Unless of course the teeth are not lined up. Which it seems like they should stay lined up…

This could be useful. Our team will definitely look at this.

Right now our main focus is developing torque distribution on all the chain and axles to minimize stress found in our bearings, and especially chain when pushing an immovable object. Transmission version 4.0 is well underway.

love it ! … especially the elastic bucket lift :wink:

Thanks! :slight_smile: That was one of our favorites too.

How do the gears on your motor plate not slip when they are simply being forced into another gear using a piston? I would assume that the power of the motors would simply overpower the piston, forcing it back in enough to allow the driven gear to slip.

We haven’t really done any of the math on it but it doesn’t slip at all (even when driving against a non-movable object) when the pressure is good. When the pressure is lower, the gears do start to slip. The pistons are fairly strong.