Thread: Wheel Envy?
View Single Post
  #26   Spotlight this post!  
Unread 11-02-2010, 04:34
techedguy's Avatar
techedguy techedguy is offline
Technology Education, PFHS
AKA: Sal
FRC #4520 (Roboteknix)
Team Role: Coach
 
Join Date: Nov 2008
Rookie Year: 2008
Location: Spokane, Washington
Posts: 64
techedguy is just really nicetechedguy is just really nicetechedguy is just really nicetechedguy is just really nicetechedguy is just really nice
Re: Wheel Envy?

I didn't mean to stifle my team members into silence...far from it. I was suggesting that not EVERY detail be revealed before the regionals play out. Being that we're in a week 1 regional...that's not too far away.

Rubber: We cast in a Mold Max 20 silicone and not knowing the nature of this material to inhibit the cure on the PMC 780 urethane rubber when the mold is new we have had to add some Post Cure processing. Essentially we've since baked our silicone molds at 150 deg F for 4.5 hours and we've post-cure processed (baked) our early rubber rollers for 4 hours at about the same. This has resolved the tackiness issues of the surface of the rollers. The Mold Max does an awesome job...captures every detail (or defect) and so some of our rollers are absolutely perfect (aluminum mold master) and others were cast from wax copies of the aluminum master (therefore some surface bubbles in the rubber...but tiny ones). Now that the silicone molds have had the alcohols or other chemical agents baked out of them the rollers come out nearly perfect with little to no post cure processing needed (but it is still done to improve the properties of the rubber). We're almost to 56...and a few spares... Each batch of silicone and rubber was vacuumed after mixing and after pouring to remove as many air bubbles as possible...so far only one detectable defect in a roller after 40+ have been poured.

It'd be much more scientific if we had programmable ovens and the like but a $8.25 toaster oven from the thrift store does the job in a high school shop. We disconnected the top elements to avoid direct melting or scorching issues.

Word the the wise...we have a great ventilation system and have been running it continuously. The cure accelerant "Kick It" is good at curing rubber fast and clearing sinuses faster if you don't have ventilation. Don't play with this stuff in your household or basement if you know what I mean. PMC-780 even has warnings about "not intended for household use".

As far as the very tips of the rollers go the geometry is such that I don't believe they will have any issues...we're dying to have these cured up so we can run them around. The chassis is bare until the rollers all cure!

Why 7 spokes? because it worked in SolidWorks. They were machined from solid T6 6061 by a sponsoring company for us. We want to cast them to make molds for duplication purposes when we have the time and materials...they do not need to be this strong (but they are, so that's nice). SolidWorks also revealed the weight of the assembled wheels before we had even cut or cast a part...and now we know it was right.

I'll make sure Brandon posts pics of the process and we'll reveal all once the documentation is completed and posted to the site. More pics of everything will be revealed as soon has he has them in his possession I am sure.

www.roboteknix.com
__________________
Salvatore Lorenzen, M.Ed, Ed.S.
Mentor/Coach/Teacher

I am not who I hope to be, but I am trying. I am giving it my all to improve me; and I’m thankful at the end of each day that I’m not the guy I used to be.

FRC #4520 - Misfit Toys

2012 Spokane Regional WFA
2009 Idaho GIANTS Award