Before the robot is taken apart...

[ManicMechanic]

Although our regional events are only beginning, I know that many teams are done for the year. Before disassembly, would you considering taking photos of mechanisms that you're willing to share and posting them at the end of the season? Not all photos are equally useful -- I'm especially interested in photos that have close-ups of mechanisms with straight-shot, unobstructed views. Even better are a series of a few photos showing the assembly process -- you don't have to show every screw and/or complicated CAD designs (try taking photos as you take apart and reversing the sequence). My intention is to collect these into a beginning builder's guide to share so that VEX newbies can build a few cool projects and learn some basic mechanics in the process.

Any ideas are welcome, but I'm especially interested in some things we've unsuccessfully tried to reverse engineer:

1. A spring-loaded launcher - Vexlabs's ping-pong launcher looks like it uses a rubber band, but we can't figure out how to make the hinge that activates the spring. The view is blocked by plates.

2. A conveyer belt mechanism - The video from Team 40 is shows this, but we've not been able to get sufficient friction using tank treads and plates.

3. Holonomic drive - We can visualize a static model of this, but don't understand dynamically how it moves and how to drive it.

We have a couple things that might even be worthy of sharing, but we'll to see if they're actually competition-worthy in the next 2 months.

[nonother]

I don't have any pictures to show you, but I think I can help you out on numbers 2 and 3.

2. The trick with getting enough friction is having enough force on the softballs. Remembering that friction comes from both the coefficient of friction and the force being applied. You might be able to increase the coefficient of friction by changing the surface of the treads, but that's likely not worth it. Instead you need to increase the tension of the system so that the treads exert a lot more force on the balls. As a result the friction will increase. The way to do this is to make the tread loop as tight as possible and then stretch it outwards and insert in one of the tightener pieces (the large black and grey ones) that come with the tank tread kit.

3. I think you get how to build it so I won't explain that part. The way it works is to think of each wheel as a vector force. Moving in one of the cardinal directions (straight up, down, left, or right) is trivial as you just power two of the wheels and leave the other two unpowered. To move up and to the right (say at a 45 degree angle) you need to equally power the side wheels to go forward and the front and back wheels to go to the the right. Unless you want to do vector addition on the fly in your head, you'll want to program the robot to make it much easier to drive. I know there is MPLab code already written for a simple holomonic bot floating around on the forums.

I'll see if I can dig up any pictures.

[Dylan Gramlich]

Originally Posted by ManicMechanic

3. Holonomic drive - We can visualize a static model of this, but don't understand dynamically how it moves and how to drive it.

Talk to artdutra04 about this. he built a very succesful and impressive Holomonic drive.

[artdutra04]

Originally Posted by ManicMechanic

Any ideas are welcome, but I'm especially interested in some things we've unsuccessfully tried to reverse engineer:

1. A spring-loaded launcher - Vexlabs's ping-pong launcher looks like it uses a rubber band, but we can't figure out how to make the hinge that activates the spring. The view is blocked by plates.

Today's your lucky day.





All this uses are three of the rubber links, available from VexLABS. The rubber links provide for the 'hinge', and the extra elastic band adds more 'oomph' to the launcher, as well as give the launcher a better default launch angle than the previous picture. More information and drawings from this project will be coming shortly. ;-)

Originally Posted by ManicMechanic

2. A conveyer belt mechanism - The video from Team 40 is shows this, but we've not been able to get sufficient friction using tank treads and plates.

The first thing you should do is to have the Vex tank tread moderately taught - there should not be able 'slop' in the tank tread. This will ensure that the tank tread keeps a contact force on the balls, as otherwise you'll have great friction near the wheels and bogies, but in the spans between them the tank tread will flex and the ball will stop moving.

Also try attaching a ton of the Vex zip ties onto the Vex tank treads. These work great for helping push the softballs along tank tread elevators. ;-)

If you want some great pictures of Team 40 and all the other robots that were competing at the Connecticut Vex Championship, just look on the gallery page of the ConnVex website.

http://connvex.org/?page=gallery

Originally Posted by ManicMechanic

3. Holonomic drive - We can visualize a static model of this, but don't understand dynamically how it moves and how to drive it.

Originally Posted by Dylan Gramlich

Talk to artdutra04 about this. he built a very succesful and impressive Holomonic drive.

Thanks Dylan. To learn about the basics of the holonomic drive system, I'd suggest that you read this white paper:

http://www.chiefdelphi.com/media/papers/1836

In addition to that, you can see this picture and accompanying thread for more details as well as the EasyC code to create of the Vex holonomic robot that I built last fall/winter.


http://www.chiefdelphi.com/media/photos/22353

[ManicMechanic]

Aha! Knew there was some part we were missing. Time to pull out the wallet again (sigh)!

As we checked out posts, pics, and resources, it was exciting to see the lightbulbs go off among various members. We're looking forward to post-competition season so we can get back to some of those designs.