06-02-2010 18:35

,4lex S.

Re: pic: How 125 is rolling this year...

How are they holding up from an elasticity standpoint (meaning, do they deform under the weight of a robot by much?). They look awesome; however, if you could embed LEDs... (not so sure on how the rules would like that, but it would look cool)

06-02-2010 18:54

coldfusion1279

Re: pic: How 125 is rolling this year...

Urethane is very stiff, and since those wheels look relatively solid, I wouldn't think there would be any deformation at all.

That is a really cool project, something that most, if not all, teams could do feasibly in a short period of time. Thanks for the post.

06-02-2010 19:04

Akash Rastogi

Re: pic: How 125 is rolling this year...

How many of these can we expect at our doorstep on Monday?

You'd think 125 would go with red wheels though.

06-02-2010 19:12

Brandon Holley

Re: pic: How 125 is rolling this year...

You got it right. This stuff is something like an 85 or a 90 on the Shore D scale, which is very rigid. The fiberglass adds some extra rigidity.

EVERY SINGLE TEAM IN FIRST can do this. For teams that like to use the same type of wheel from year to year this may be something to consider. If you invested in a multi cavity mold, a team could feasibly have all of their wheels for the season in a couple of hours.

Haha, these are 4 inchers, so I don't think they'd fit what you guys are using. Someone accidentally threw out the red dye :-/. We plan on using some withholding allowance to make some red ones. Oh by the way each one weighs less than 3 ounces.

-Brando

06-02-2010 19:24

Akash Rastogi

Re: pic: How 125 is rolling this year...

Hahaha man I knew I had seen a similar wheel before.

http://lh5.ggpht.com/_yaSezzGIV6Y/Si...ke%204inch.jpg

Really look forward to seeing these in person in a few weeks.

06-02-2010 19:32

V_Chip

Re: pic: How 125 is rolling this year...

Less than 3 ounces?

Great idea. Kudos

08-02-2010 10:52

Brandon Holley

Re: pic: How 125 is rolling this year...

A few hours worth of work this weekend.

-Brando

08-02-2010 11:40

sdcantrell56

Re: pic: How 125 is rolling this year...

How durable is the urethane specifically in impact? Also was the bolt pattern molded in or was that machined separately?

08-02-2010 16:46

Bruceb

Re: pic: How 125 is rolling this year...

Where do you get the materials? The silicone and the urethane? What do they cost? Do you cast the wheels with the bearings in the mold or do you machine the wheels later and install them?
Thanks
Bruce

08-02-2010 16:59

Brandon Holley

Re: pic: How 125 is rolling this year...

During some pseudo-tests the wheels have performed well. One wheel was able to support 165 pounds of weight bouncing on it (me bouncing up and down). This was in the vertical (weaker) orientation. We'll be doing more testing this week. The thing the wheels have going for them is the tread will buffer some of the blunt impact force.

The hole pattern on the old wheel we used had clay partially filled in the bolt holes. This allowed for us to essentially have pilot holes that were drilled through on the drill press.



There is a store in Boston that sells www.smoothon.com products. However, you can purchase these online and have them delivered to your shop. To make the wheels you see here it cost us 45 dollars. Silicone is capable of holding a remarkably tight tolerance when using it to create molds. We were able to use the hole in the old wheel which was designed for a press fit (~.874") as is. The bearings were then pressed into the new wheels...simple as that.

-Brando

08-02-2010 17:11

hillale

Re: pic: How 125 is rolling this year...

I've had an inkling for the longest time about crossing the bump. After watching the 118 vid, even thought they're crossing quite quickly, I'm a little worried about the different loads of landing on the wheels directly and at an angle. It's going to be rough on the chassis and drive train of everybody out there. How many spare wheels are you guys making, just in case?

08-02-2010 17:20

Brandon Holley

Re: pic: How 125 is rolling this year...

Who said anything about us crossing the bump???


-Brando

23-04-2010 17:23

Andy Bradley

Re: pic: How 125 is rolling this year...

Those wheels look sweet, and would be a great off-season project. I looked at the smooth-on site that you mentioned, and found a wide variety of products. Can you tell me exactly which silicone (for the mold) and which urethane (for the wheel) you used? Is it the smooth-cast 305 plastic in the 00M00 30 silicone rubber as shown in their video? Also, what type of fiberglass did you add? Thanks in advance.

23-04-2010 22:53

Jamie Kalb

Re: pic: How 125 is rolling this year...

Hey Brandon,

How were these wheels in retrospect? Are there any changes you wish you had made, or did they perform pretty much the way you wanted? This is such a neat concept!

24-04-2010 01:11

Brandon Holley

Re: pic: How 125 is rolling this year...

The mold was made from Mold Max 30. That is the "multipurpose" silicone, that can be used for pretty much anything. I've used other varieties, but the Mold Max 30 is just awesome stuff and super simple to use. The wheel was made from task 9 urethane. I've had less experience using the rigid urethanes, like the task series, but from my experiences with it in these wheels, it is also very good stuff.

The fiberglass we used was just simple fiberglass cloth you would buy from home depot/lowe's and then chopped via scissors into ~1/2" long strands and added to the urethane.




These wheels show a lot of promise in regards to FIRST robots. There are some definite changes I would make to the wheels in regards to geometry, but thats about it. What we are going to do over the summer is machine a block of wax into a wheel with more ideal geometry. We are then going to use that wax wheel to create a new mold. We want to produce some of those wheels from the mold and put them through some tests. If they perform like we expect they will, we want to make a multi-cavity mold. This will allow us to pop out 2-4 wheels at a time and essentially make wheels a standard item for us to design around.

Let me know if you have any more questions.


-Brando

14-10-2010 10:41

Bruceb

Re: pic: How 125 is rolling this year...

Has anyone else tried this? Any success? Brando, what mods did you come up with for this wheel? Can I get a picture of the actual mold? I don't quite get how you get the entire wheel molded on all sides without any machining.
Thanks
Bruce

14-10-2010 11:39

r2davis2

Re: pic: How 125 is rolling this year...

Those look very nice, I'd love to see how well they work out on an actual drivetrain.

14-10-2010 13:42

Brandon Holley

Re: pic: How 125 is rolling this year...

Here is a picture of just the mold



If you don't mind small imperfections on the face of the wheel then you don't need to worry about machining. Because you are using silicone as your actual mold cavity, the regular rules of molding can be stretched. Things like undercuts and 0 degree draft can be done because the silicone is compliant and moves out of the way of the way of the part when removing it from the mold.


These wheels are from our 2010 robot, so they were in this past years competition. Changes are in the works to make them even more reliable, cheaper, faster to turnover and easier to make.

-Brando

14-10-2010 14:34

Bruceb

Re: pic: How 125 is rolling this year...

So, to make the mold you just laid the master on the bottom of the mold box and poured the silicone over it? The top side of the wheel is as smoothe as the urethane was poured, correct? Or did you pour it high and machine off the excess?
Bruce

14-10-2010 16:03

Brandon Holley

Re: pic: How 125 is rolling this year...

The mold "box" base was an aluminum plate with the bolt hole pattern drilled into it. This was then used to hold the master (aluminum) wheel down to the plate. I then hot glued a bucket with the bottom cut off around the wheel.

Yes, the top side is as smooth as the urethane is poured. Some of our wheels have just the poured urethane surface on top. As we tweaked the process though, we added more glass to the urethane, which resulted in a "bumpier" surface on the top. To enhance the look of the wheels we did start pouring high and machining the excess away. One of the enhancements to the process we are trying to make is to eliminate that step, although it only takes a minute or 2 for that operation per wheel.

-Brando

14-10-2010 16:14

Bruceb

Re: pic: How 125 is rolling this year...

What is your final chopped glass to resin ratio? Are you still using 1/2 inch pieces of glass or have you gone shorter?
Bruce

15-10-2010 08:46

Brandon Holley

Re: pic: How 125 is rolling this year...

Our pieces of glass are between 3/8" and 1/2". Right now to measure the amount of fiber we place in the mold, we place the chopped fibers in a cup and gently tap the cup on a table to flatten the fibers out a little bit. We use the same style cup to measure out the urethane needed for the wheel. We then use a 1:1 ratio of urethane to "tapped down" fiber by volume. Our wheels typically needed about 80 mL to fill the wheel safely, so obviously for the 80 mL of urethane, we needed around 80 mL of tapped down chopped fiber.

The amount of fiber we use is something we still want to play around with. I feel with the geometry tweaks we plan on making that we can reduce the amount of fiber necessary.

-Brando

15-10-2010 10:55

Bruceb

Re: pic: How 125 is rolling this year...

Have you looked into buying precut fiberglass? You can get in in pretty short lengths that might mold better.
Bruce

15-10-2010 13:49

Brandon Holley

Re: pic: How 125 is rolling this year...

We used chopped fiber at the time because we had cloth laying around that we could use right away. Certainly playing with the size of the fiber would be another variable to explore, and is something we'll certainly be looking into.

-Brando

19-01-2011 15:04

KRUNCH DUDE

Re: pic: How 125 is rolling this year...

Where did you purchase the urethane? It's amazing how well this could work for other applications.

19-01-2011 15:20

Brandon Holley

Re: pic: How 125 is rolling this year...

www.smooth-on.com

They have a huge selection of materials to choose from. You can use their data sheets to pretty effectively choose a resin yourself, however their customer service is also super helpful, so if you are not sure, feel free to ask them.

The different resin sizes come in pretty handy as well, where trial sizes are cheap and get you a couple parts, and larger sizes can help get you through a large run.


-Brando

19-01-2011 15:42

KRUNCH DUDE

Re: pic: How 125 is rolling this year...

Do you remember what kind you used?

19-01-2011 15:48

Brandon Holley

Re: pic: How 125 is rolling this year...

We used Task 9 for the wheels, however that may not be the best choice for whatever application you are considering. I highly recommend doing a little research for yourself and coming to your own conclusions so you know for sure that you are using the best resin for your needs (and you'll get to learn a bit too about mechanics of materials and material science!!)

-Brando