Tips on Improving Robot Design

Just my opinion, but GET THE MECANUM WHEELS OFF!

I know the omnidirectional drive is cool, and looks promising, Any standard tank drive system will easily push you all match long. I think mecanums are cool for any purpose other than competition. Do you know how many mecanums usually make it to Einstein? As far as I know, none. Any team with mecanums are not only easily pushed, but are generally easily defended against, which, while game pending, is never a fun thing.

I think mecanums are just a waste of weight, and drivetrain, so that is my advice to you.

EDIT: Also, it looks a little back heavy. How's the weight balance working out for you?

[Taylor]

Originally Posted by SuperNerd256

Just my opinion, but GET THE MECANUM WHEELS OFF!

I know the omnidirectional drive is cool, and looks promising, Any standard tank drive system will easily push you all match long. I think mecanums are cool for any purpose other than competition.

For this game, how much pushing around was there, really? We had mecanums and didn't regret it. In fact, they came in handy when in the safe zone, positioning for the score.
In a game like Aim High or Rack N Roll, I'd totally agree with you. But here, mecanums were a viable option. Plus, it's an offseason project. What better time to explore drivetrain options to see if they're a fit for your team or not?

[Andrew Schreiber]

I'll come out and say it, I like it. Yeah, it isn't pretty and by the sounds of it has some flaws but I like that you took the time to build an entire robot in the off season. Now the $5 million question, what did you learn?

Originally Posted by SuperNerd256

Just my opinion, but GET THE MECANUM WHEELS OFF!

Like all things in engineering there are tradeoffs between this drive system and others. If not being pushed is important to you but moving sideways is not then you must take that into account. It depends on what your strategy is.

[Dad1279]

Great job, use it, abuse it, and see what breaks. If you want to give the programming team a challenge, add a gyro and have them test field-oriented driving.

Don't be so down on mecanums, especially for learning. Using that robot as a test bed, you can easily swap the four wheels and experiment with traction wheels, omni wheels, mix of the two, etc.

Mecanums are also a good choice for a demonstration robot for fundraisers and sponsor presentations. Easy on the carpeting, and maneuverable in small spaces.

The more teams experiment with mecanums, the more you will see ingenious solutions for pushing.

[EricH]

Originally Posted by SuperNerd256

Just my opinion, but GET THE MECANUM WHEELS OFF!

It's the offseason. Leave them on.

If you experiment with them in the offseason, then when the season rolls around and you build your competition robot, if (and this is a big if) the mecanum drivetrain turns out to be advantageous, you already know how to use it. If it doesn't, it's not that hard to turn a mecanum system into a 4WD system and practice with it.

[BJC]

It looks really nice. Integrating the actuation for the wrist into the 4-bar is very slick, however be wary of bending. I think when 148 did it this year they used a piston to push/pull sheet metal sliders. Basically the 4 bar was still very strong because the piston was not actually acting as a structral part of the arm. I would be concerned with the piston getting even slightly bent in a hard colision and no longer functioning properly.

Also, on your bell crank pivot down towards the bottom of your robot there is quite a lot of open shaft on either side of the arm. The further away that shaft is supported from the load the greater chance that it will bend. There is also the chance that it will begin to bend over time and continued use so it is probably worth supporting it closer in on either side so that can't happen. In any case, it is a good practice to support shafts close to the load as possible.

Overall it looks great! Looks like you are very ready for build season.
Regards, Bryan

[Madison]

Originally Posted by Cem8301

This is an off season project my team has nearly finished. It has served at a great learning tool for new students/ a first time test for pneumatics and Solidworks for the team. Any suggestions for improvements?

The picture is a bit small, so it's hard to make out many details. The first thing that I saw that I'd change is how the pneumatic cylinder on the arm is mounted -- and I don't mean the duct tape.

Right now, when the cylinder rod extends, it is 'exposed' and any side loading on the end of the arm will get transferred back against the cylinder rod. A rough impact may bend your cylinder rod and then you're in a bad place since replacing the cylinder is expensive -- both in time and money.

It'd require a rework of the upper link of the arm, but consider sliding the cylinder back toward the upper pivot so that, when its rod is fully extended, it's still supported and protected by the fixed part of that arm. I suspect your design is inspired heavily by 148. Look more closely at that robot -- its CAD model is available here -- and consider carefully why they designed their extending upper link the way the did.

Originally Posted by SuperNerd256

Do you know how many mecanums usually make it to Einstein? As far as I know, none.

Forgive the derailment, but I see this getting parroted a lot these days and I'm not convinced it's a valid argument. Folks make it seem as if the only difference between a mecanum wheeled robot and 254 et al is the wheelset. That's absurd on its face.

So, let's have it -- in your opinion, which teams were capable of winning the Championship but, by deciding to use mecanum wheels, didn't make it?

[Cem8301]

Originally Posted by PRich1477

Looks like you went with the same wrist articulation method as 148....
On the claw, you're looking pretty good. 148 has had a jaw on their claw all season, and they place tubes differently than us. We later implemented a jaw and the same placement routine as them, though we don't really use it, except when placing over an uber tube... An alternative is to do a mixed drive, like 148's nona-drive (traction-omni modules at each corner, omni in the center) or an octanum.

We were lucky enough to be stationed next to 148 at the Dallas Regional last year.... we were very inspired by their robot-- and worked on building a simplified version in offseason. I am trying to build a simplified version of their octonum drive in Solidworks right now... Though I dont think we will be able to implement it without machining the parts. I see that you guys built your own base... Is that something that you would advocate? (note: my team is fairly new at Solidworks and have never had anything machined). This was our Solidworks design for the robot I posted earlier

[Andrew Schreiber]

One of the things that is always preached at work is the concept of a minimum viable product. That is, what is the bare minimum to get done what you need to get done. Along these lines the EWCP took it upon themselves to figure out what minimum actually is. We published two blog posts, a general analysis of 2010/2011 and an in depth analysis of 2011. They are available here and here. We hope you find these interesting and helpful.

[Michael Blake]

I _really_ like your off-season persistence to build a robot from scratch taking into account the best practices of powerhouse teams... GREAT JOB!

Looking back, I wish we did the same thing from scratch, but, what we did was keep working-on/improving our rookie robot for the two off-season competitions we competed in...

As you can see below, we're kindred-spirits in our admiration of the 148 Robowranglers - Raptor model... ;-)

[IKE]

Keep up the good work guys. It is very inspiring to see young teams putting in the extra effort to learn what it takes to make a great robot. I have watched several other young teams in Michigan blossom over the last coule of years doing exactly what you guys are doing now.

They say that: "Imitation is the highest form of flattery." Personally if I was a judge, I would give team 148 an Engineering Inspiration award for posting design details and inspiring other teams to attempt such a cool mechanism. I know of a couple other teams that have completed very similar exercises.

My challenge to you guys that have built these, is to share some of the wealth you have learned. Possibly a short white-paper (1-2 pages) on some of the good, the bad, and the uglies you found while replicating the general design intent.
Doing the white-paper will help document the pros and cons for your team as well as help others attempting similar ideas in the future. It is also good practice for documenting your designs in clean concise manner to help present to judges at competition.

[Cem8301]

Originally Posted by IKE

My challenge to you guys that have built these, is to share some of the wealth you have learned. Possibly a short white-paper (1-2 pages) on some of the good, the bad, and the uglies you found while replicating the general design intent.
Doing the white-paper will help document the pros and cons for your team as well as help others attempting similar ideas in the future. It is also good practice for documenting your designs in clean concise manner to help present to judges at competition.

This is a good idea. We ran into a lot of weird design and logistics problems when making this design. For instance... I drove all around the Dallas metroplex looking for a 7/8 drill bit and brackets... And then as it turns out the drill bit I found was had the wrong shaft shape and it kept stalling in the drill press...

Thanks for the idea. I'll type it up this week.

[JamesCH95]

Originally Posted by Cem8301

This is a good idea. We ran into a lot of weird design and logistics problems when making this design. For instance... I drove all around the Dallas metroplex looking for a 7/8 drill bit and brackets... And then as it turns out the drill bit I found was had the wrong shaft shape and it kept stalling in the drill press...

Thanks for the idea. I'll type it up this week.

Unless you're doing something crazy, step drills (aka unibits) like this are awesome for large-bore holes in thin material. They are available in many variants to fit whatever you want to do. Most hardware stores have them too. They frequently have a hex shaft, so no slipping in the chuck, and cut a small amount of material at a time, so no stalling and a very low chance of catching a part and spinning it. Plus they can be used to chamfer the hole when you're done.

Just a thought...

[Cem8301]

I just finished my teams Logomotion Post-Mortum document. It includes: our process, many pictures, problems/ how we solved them, things we want to improve, and Q&A with team 148!

Official Post Portum document

[jjp]

Funny how the best innovations come after the competition. That was a very common design choice.