Instructables

[Video] Large Scale Mold Making - Part I

This is another multi part series. This is a long project for the 2007 ASME Human Powered Vehicle team from the University of Central Florida. I will be breaking up major tasks into smaller instructables as the entire process is gargantuan.

Here's a Botched together video. The fast paced part is 1 hour of work ;)



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Step 1: Background

We're making an HPV! That's human powered vehicle ;) We are required to have at least 1/3 of our frontal area covered by a fairing (a fairing is just an aerodynamic shell -- like your car's outer skin). We're going for a fully enclosed (aka "sealed") fairing.

To tackle this manufacturing problem, we will be making a "female" negative mold. Similar to how casts of fish are made. To make this mold, we first need to make a positive "male" plug.

This instructable is a guide! I'm not going to instruct you on how to make the shape - there's plenty of resources on that. Instead, I'm providing rough instructions on how to start this task.

Our mentor currently works for Lockheed Martin as a model maker. When it comes to composites, this man knows his stuff. This is my third year working on this type of project, and he has provided a wealth of information and advice. If you'll be tackling a similar scale project - find yourself someone that has the experience to guide you in the right direction.
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TimmyMiller2 years ago
aye, she be seaworthy alright. : D :P
tinker2343 years ago
wow
freakmonkey6 years ago
hey, i'm hoping to do something similar to this for my senior design project at UCF in a couple years. I was just wondering where you get your materials(foam, fiberglass, etc.).
trebuchet03 (author)  freakmonkey6 years ago
hit me up on eMail --- same instructables username @ gmail.com

I've got a digital copy of my logbook, contact information, vendors etc. etc. If you're serious about doing this, I get involved before it's your senior design project... The project is a lot of work (for the class, the competition and the actual project) ;)

I'm going to be around next year - and I'm sure as hell going to be involved again (It's just so much fun) :D Check this:
http://primitiveengineering.com/ucfhpv/
stasterisk6 years ago
I like the high-speed fume fanning
thisisno7 years ago
Too bad you weren't there to document the sanding/ post sanding procedure. After sanding, was the foam plug coated with some sort of body filler substance (like Bondo) to smooth out the surface? You may have mentioned this in a subsequent post, but I didn't catch it.
trebuchet03 (author)  thisisno7 years ago
Yes, I will make a post about that process... Not really any pictures (I might be able to dig up some), but I can give details. The plug is sanded to shape... Then coated with fiberglass and resin (no hardener). It's allowed to fully cure (a few days). Then, bondo filler -- sand - bondo - sand - repeat until you've got your shape....
GeoffCj7 years ago
Some friends have built surf kayaks by carving blocks of foam, glassing the outside, then hollowing out the center. Essentially there is no female mold, just a male plug.

http://www.ptone.com/boatbuilding2002/page1.html
Sounds like the process used to create the Frank-n-liner: http://www.recumbents.com/wisil/wianecki/frank-n-liner/default.htm
trebuchet03 (author)  GeoffCj7 years ago
My little avatar picture was made with a male mold and vacuum bagged to reduce weight :) It worked pretty well, except the vacuum kinda crushed the plug in the process :P
sharkilepsy7 years ago
very cool...I use this blue foam to make models for metal castings...just out of curiosoty what are you using to make the negative? Of course I haven't seen your sanding process yet, but look into getting a sureform(or similar) wood rasp if you don't have one already. They work beautifully for rapid material removal in the early stages. I've also found that drywall screen gives an excellent final finish much faster than 400+grit sandpaper. WEAR A RESPIRATOR (not a dust mask)! Blueboard foam is extremely abrasive, like breathing in glass, and probably carcinogenic.
Just wondering, why copy Cheetah when the Varna has proven faster? Also I must say I really like the paint job on your Gold Rush clone.
trebuchet03 (author)  PurplePeople7 years ago
Just wondering -- you haven't seen our frame design.... You've probably seen the three wheels - you could probably guess tadpole design from the foil shape. You don't know what steering method and mechanism we're using, you don't know how any of our parts are put together etc. etc. All you have to go on is a wood mock up that was used for rider kinematics and seat angle.

1. WindCheetah uses a U-joint steering mechanism. We're not
2. WindCheetah doesn't have an adjustable boom
3. WindCheetah has a pretty cool off axis rear axle - we're doing more traditional chain stays
4. The only company I've seen mass produce a 700c tadpole is Big Cat HPV
5. WindCheetah is glued together
6. We have never seen a cheetah in person (at least I have never) :P
7. Hell, for a short while, there was a Kevlar drive belt in the boom (someone else did this, but there is a better way to do it :P)

I don't know what you're referring to about the Gold Rush... We've never made a LWB :P Could you elaborate?


Trikes have decades of experience and technology behind them. An engineer is obligated to learn from past experiences of others and him/herself and apply these lessons to his/her design. At no point during the design process did any team member take out any measuring equipment and place it near a manufactured design. This is why the general low riding 'bent tadpole shape is in fact general. This is why a SteinTrike looks like a Cheetah looks like a Catrike looks like Sun (well, maybe not a sun :P) looks sorta like a tripendo (minus the leaning :P).

We sat down with successful vehicle designers and got lessons in vehicle dynamics, stability, angle tolerances, bump vs. brake vs. 0scrub, etc. Took in information about our rider sizes and built a vehicle around the riders. Applied all the "stuff" we've been learning as engineering students and out popped a design we couldn't manufacture. Add more research, some design tweaking and hey, the model actually works! and our shows won't hit the fairing!

As for the fairing.... That starts off as a basic foil and then is fit to the vehicle ;) To be honest, I think it somewhat resembles a super high mileage car I saw awhile back (except we need peddle space) :P



As for why tadpole? Well, lets just say some members had some rather nasty bruising because least year's SWB has twitchy steering and a steep learning curve (I finally figured out the problem -- the trail is terrible). So smack on a third wheel - stability problem solved (at leas that was the original thinking, they didn't know better at the time).

What you must understand is.... If you can reliably put down power - you're now somewhat competitive - you've taken a huge step. I've been there with a terrible design put together in a quarter of the normal time it takes. I was there milling new parts on a hotel floor making "precision" holes with a power drill and then putting it together with JB weld and pipe clamps :P

While speed is cool and all.... It won't win the whole competition ;) How many people do you know that are willing to commute to work every day in the Diablo II? I'd love it, but it's not practical.


Lastly... Don't take any of this the wrong way ;) I'm not being nasty (but re-reading this, I can see how it could be taken the wrong way). Besides, if the senior design professors even thought we were copying someone else.... Heads, genitals and fingers would be rolling - and not on an HPV :P
Whoa. I didn't mean to seem critical. Just comparing the various fairing shapes.

Your avatar looks a bit like a late model Gold Rush smoothed out into a plump Virtual Edge. And the blue plug looks a lot like Cheetah (not Windcheetah).

As for advice or critique, there's none to give. Experience seems to be the only teacher in this game and mine does not really extend to streamlined machines, except for the one time I got a test ride in something called the Baby Varna.

From your anecdotes, it's certain that the obstacles are common to HPV builders all over. For instance, I've had to pack sand into a joint repaired with epoxy to give it enought structure. My favourite quick set adhesive is a Vise Grip plier. And nothing speeds up your wheel-building skills more readily than a 2 hour deadline to finish a trio of 20-inch racing slicks.

Good luck at the races. They're hard. And that's what makes them fun.
trebuchet03 (author)  PurplePeople7 years ago
No worries :)

As for the fairing in my avatar :P If I remember how it was done - it started (the model that is) as a foil and then bits were cut off and some bits were added on :)


This year, my school is hosting the event. Se we got to pick the course :) It's going to have slower speeds, but the layout is more technical. We'll need an extra helping of straw bales :P
hay_jumper7 years ago
Ohhh... This is exciting. I'm writing an instructable on RTV rubber molds. Can't wait to see your technique.
trebuchet03 (author)  hay_jumper7 years ago
What a great idea :) Sounds like a cheap source for small molds :P And it cures at room temp :P I've been away from this project (due to spring break and family), so I hope I don't miss all the fun parts :P And I hope my teammates are taking lots of pictures :P
trebuchet03 (author) 7 years ago
Holy crap... 2200+ views today o.0
CameronSS7 years ago
I want an Instructable on making HPVs now. Then again, my shoes are HPVs.
trebuchet03 (author)  CameronSS7 years ago
Ahh, but can your shoes go 60mph? Or the world record of over 80? Ours wont, but we should get some decent numbers - barring massive technical failure :P
with a big enough rocket, a low-friction wheel system......hmmm....possibilities... I want pictures/video when this is done! I've always wanted to do one of these, but my budget of broke is a bit small.
trebuchet03 (author)  CameronSS7 years ago
hehe -- well that would be a rocket powered vehicle :P As for budget.... you could buy a semi decent {used} car.... I mean, that stack of foam is a bloody fortune (for broke people like us :P).
Fake_Name7 years ago
So it was: Spray glue, stack next level, add weights, wait, repeat? Woldn't it be more efficent to simply assemble the whole thing and then compress it? That way you wouldn't have to wait for the glue to dry each time you add a foam piece.
trebuchet03 (author)  Fake_Name7 years ago
We need the plug to stay together on it's own AND have a good bond at the edges to get good transitions after sanding.

We had two options available.

1: Spay on adhesive - dries fast, requires a few minutes (with weights) between layers to ensure a good bond
2: Resin without hardener (the hardener attacked our foam in a bad way) - dries very slow (An estimated 3-4 day cure time), all layers could be layed up at the same time

So this really saved us a lot of time. We're looking at a total of of less than 2 hours of gluing for the whole thing - including wait time between layers.


Remember, there's always a different way to go about thing ;) This was just the most convenient/time effective/cost effective for us :)

Spray glue, stack next level, add weights, wait, repeat?

In a gross anatomy sort of way - yes.
rashfreedom7 years ago
Is there any reason you didn't use a hot wire cutter? I cant wait until the next installment.
Hot wire cutters would release serious fumes, so would smoothing out the form with an electric grinder. I speak from experience. If you don't want to spring for having your pieces cut via water jet, try using and electric turkey knife. Just be sure to add some oil between the knife blades.
trebuchet03 (author)  Original Replica7 years ago
Oil! Brilliant! Why didn't I think of that :P We have to carve certain parts and our poor carver was getting bogged down. Why type of foam is okay for hot wire cutting? Just curious :P
bpwagner7 years ago
Could I make a Kayak this way?...hmmm...let me think....
trebuchet03 (author)  bpwagner7 years ago
Absolutely! Our Lockheed friend built human powered hydrofoils :D


The trick is how you lay up your glass and core. I don't know the major details, but I doubt you'll need anything stronger than what we had last year - which was either E or S glass with a K-mat (a fiberglass backed scored foam) core. It was very structural. But you're best bet is to talk with someone experienced in small craft construction ;)
freehand7 years ago
you competing in the shell-eco marathon? if you are, for what team? if not, where and for what team? good luck
trebuchet03 (author)  freehand7 years ago
Nope, ASME HPV Challenge : http://www.asme.org/Events/Contests/HPV/Human_Powered_Vehicle.cfm

ASME: American Society of Mechanical Engineers


Our Team is from the University of Central Florida
lemonie7 years ago
Did you have problems with 'fumes'? I think I see wafting & fresh air breaks, but it was the dust-masks that got me thinking in that direction. L
trebuchet03 (author)  lemonie7 years ago
Personally, it didn't bother me (sad to say actually). Previous work (even when protected) made that happen. But most of everyone else was bothered by the solvents. And to be honest, those "comfort masks" won't do anything. Eventually we realized the wind was blowing in the right direction and we opened up the door which helped a lot. Extended exposure to those solvents will make you stupid - I'll add some warning when I get back home :P
Do tell us what they were when you do. Touluene, xylene? They almost certainly carry the warning "use in a well ventilated area", but who does...? L
ewilhelm7 years ago
I assume you cut the foam without using the waterjet's garnet?
trebuchet03 (author)  ewilhelm7 years ago
oh yeah, that would have been overkill :)
Is this what eventually turned out to be your avatar? I always thought that thing looked like a HPV, but I was never sure.
trebuchet03 (author)  Tetranitrate7 years ago
Yes :) Last year's HPV which was a 2 wheeled recumbent. And in the competition, that fairing was used as a road rash preventative (a few times) o.0 This year, we got in touch with Big Cat HPV (the people that make Catrike) and got some of the finer points of 3-wheeled recumbent design, steering geometry and stability. So this year's HPV is a little bigger, a lot lower and has three (fully enclosed) wheels.
Ferrite7 years ago
I have been thinking about making a sailboat out of fiberglass using a foam mold and this looks like a good start. Looks like a fun competion!
wombat77 years ago
cool, i'm looking forward to the layup instructable.
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