03-10-2006 13:55

Madison

Re: pic: VEX Wheel Prototype

What type of machine was it printed on and from what material? Also, what's the overall diameter and width of the wheel? What do you plan for the wheels moving forward?

Rapid prototyping by FIRST teams is fascinating. It offers some advantages in saved time and money, but it can also make the manufacture of some complex parts seem a bit too easy. I'm curious to learn more about your experiences.

03-10-2006 15:46

AdamHeard

Re: pic: VEX Wheel Prototype

Right now my team is using a RTP to protoype some wheels.

don't worry about it being too easy, it can only make prootypes as the material is not near strong to be functional in nearly all cases.

03-10-2006 15:58

Madison

Re: pic: VEX Wheel Prototype

Well, that's exactly the point, I think. It's possible to create on these machines shapes and objects that are physically impossible to create with traditional machining technology. It's possible to, if you're not careful, get yourself caught up in a plan that relies on some parts that are too difficult or time consuming to manufacture because the rapid prototyping process offers no visibility into what it takes to translate that idea into a usable form.

03-10-2006 16:04

AdamHeard

Re: pic: VEX Wheel Prototype

Well the wheels, and any other parts we plan to do, are to check fit. Also, it's nice to be able to take it and show the team what the wheels will be, rather than a CAD drawing. It's hard to convince my team to do anything new doing the off season, so it helps.

Well, i'll have the wheels done saturday and post them.


I like the vex wheels too... too bad their illegal : / (even though i know you have no intention of using them in competition).

03-10-2006 17:30

Chuck Glick

Re: pic: VEX Wheel Prototype

We have a Dimension BST 768 printer. It uses abs plastic. The outside diameter of the wheel is 3.125". And i'm using the 1" wide roughtop material used on the IFI traction wheels, secured with gorilla glue (hope that answers the going forward question).

The ABS plastic is quite strong, definately strong enough for a vex bot, but not strong enough if used in a high stress envronment. The machine is a great way to make simple parts quickly, and to help proto the larger ones. Even though the printer makes things easier, it definately takes a lot of time. This wheel took 5 hours to print. If it was just a solid wheel with no spokes, it would probably take around 12. Also our printer seems to be tempremental at times, and will just not work, which leads to a phone call to our local technician, and is usually back up and running within a week of that phone call.

04-10-2006 19:20

ChrisH

Re: pic: VEX Wheel Prototype

The technical name for the process used in this case is Fused Deposition Modeling (FDM). Sir Charles is right in that the plastic used is quite strong for a plastic. But all materials have their limits. Even the strongest plastics are at best as strong as weak metals. The trick is to keep the stresses within the safe operating range of the material.

There are other processes available like Selective Laser Sintering (SLS), which is a little faster in terms of build time and bigger in volume than FDM, but it uses nylon which isn't quite as strong as ABS. That said, nylon is still plenty strong when used properly.

A couple of seasons ago we built some Mecanum wheels on an SLS machine. We ran them for hours on a practice robot under less than gentle conditions and they are still just fine. Dirty, but otherwise sound. We didn't use them, but the reasons had more to do with performace in the game than any fear of breakage. They are still kicking around the shop, if we find a need for them we can always get another set built. I have the models so we could have them within 72 hours of somebody pressing the GO button.

Based on that experience, I'd go ahead and run a set of FDM wheels on an FRC robot if I thought they were thick enough in the right places and built solid instead of sparse. I might even do something tricky like build in a sprocket.

It should also be pointed out that all of the rapid prototyping processes can be used to make patterns for metal castings or if you really need the strength, forging blanks. An RP machine of any sort is a valuable addition to any team's tool box.