Author: Sci

Some experimental pretty things

I recently took a £20 commission from a dear friend to make a basic modification to a set of driving goggles. She wanted them “steampunked” and I had a lovely bit of filigree from a 1920/30s wall clock. I’m sad to see it go, but it did seem to be the perfect use for it. So on with making some Winged Messenger goggles.
The first thing I had to do was cut out the middle of the “sun flare”, as it had an odd number of points.

I then filed and put it on the sanding disk to get the burrs off and round the edges. The natural tarnish looks good and authentic, so there didn’t seem need to polish it.
The brass is also thicker than I remembered, so it didn’t seem like it would need extra reinforcement, and I just drilled out the existing holes to put in some rivets.
Standard rivets? Yes. But the frame on the goggles is silver, so the aluminium rivets fade in very well. Okay they’re not real metal (aluminised plastic frames), but the mix is pretty good and it drilled nicely. Too nicely. It was hard to stop the drill pulling through and through the padding.

Still, basically turned out nice. :)

Will be dropping it to them at Expo at the weekend rather than posting it as the timing’s not right for postage (will be refunding the postage, of course).

I’ve also just tried styrene water-clear resin for the first time, and have learnt a few things.

  1. It’s cheap.
  2. It STINKS. The whole workshop. Even after airing it for several days.
  3. 6% shrinkage is a problem when casting eyes, unless you’re costuming as something from a Rob Zombie music video.

The latter is actually an interesting effect, though likely to be hard to reproduce exactly. The pulling away from the mould due to shrinkage during gelling has left river-delta style patterns down the sides, with a clear centre underneath.
It may be avoidable by using a double-fill to take up the slack (but that may increase optical distortion), or a very thin mould that will pull in with the shrinkage due to surface tension (but may distort the shape).
The urethanes are more expensive, but looking more reliable. Will be making a comparison set tomorrow. The cure time is much shorter on PU’s compared to styrenes (3-5min vs 15-20). Gives much less time for proper degassing. May be doable degassing in-mould in a small fast chamber.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

New MkIII benchtop degasser

So I’ve finally managed to get some bits together and assemble the new smaller degasser.

I used the fire extinguisher from the MkI degasser, which I cut shorter. Sadly it’d been out in the rain, as well as having been used for degassing previously.
Even sanding it heavily obviously didn’t remove all the traces. I used a nice zinc primer on the inside which seemed to take, but once I went over it with white enamel it refused to bond where the resins had previously splashed.
Next time I’ll fork out for some Hammerite. I’m not even sure this enamel will survive cleaning any spatter off the inside later.

Found that Poundland is doing rather large tubes of two-part epoxy! Handy stuff to have around. Especially for £6 cheaper than Araldite. It does reek of fish before it sets though.
The 99p Shop nearby provided a cheap frying pan which got cut up into the lid surround. Fitted so tightly there was no need for a retaining pipe-clip strap.

I brazed a load spreader to the UTA manifold, and glued it on. The nossle holder of the extinguishers base perfectly holds the up-to-air filter so it’s a ready-made support. Without it I’d be worried about the lever-handled ball-valve dislodged the manifold after only a few uses.

Made a proper handle from some curved extruded aluminium and some bolts. Again, glued onto 10mm polycarbonate cut to size. I’m unsure if it’ll need internal lighting yet. The white inside reflects a lot of ambient light and it’s not as deep. Will see.

So I now have a nice small degasser for using on the workbench! Both controls are nice easy to use lever-handled ball valves. I should be able to leave the pump running to the catchpot and simply switch the two valves for fast control.
It should make the degassing of the resins prior to pouring them far simpler. And if one is sealed under a static vacuum, the other chamber can be used under pumped vacuum.

One thing to note is that it looks messy because the Poundland 131 epoxy is thinner and slower-setting than Araldite. But if it works, it works, and it seems just as strong when set.

As another improvement to the system I also mounted up the MkII chamber, pump and catchpot to a plank of wood. It reduces the footprint a bit but mostly stops them from moving around in use and flexing the pipes which can result in leaks or manifolds breaking.

Will try to get a short demo video up on youtube.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Buster: Car and batteries examination

So here’s the lil fella I picked up for £3..

This little mock quad-bike is pretty lightweight. There’s some metal framework for the axles, but the rest is all a moulded plastic body. I’d be worried about it taking the weight of extra parts if it wasn’t designed to cart around reasonably large children.
The rear drive wheels are pretty worn, and all are the cheap hollow plastic variety.
They’re a lot wider and with less grip than the ones on the original Buster’s frame as best I can judge from the few photos. I’ll keep it in mind as it may have issues with drive and steering.

The rear wheels have separate drive motors, driven together on a static axle. Cheapest design, but running the motors together should be fine.

Controls are pretty simple. Two sealed 6v lead-acid batteries, a two-button toggle for forward and reverse, another for fast and slow (seems to switch the batteries from serial to parallel connection, so 6v to 12v) and a foot pedal switch to make it go.
The controls on the handlebars are purely for show. There’s nothing in them beside a horn powered by a separate set of AA batteries.

I should be able to strip off a few odds and ends, but as it’s a monocoque they’ll be a limit. And since I’m running out of space here, my Buster will need to be able to be stored outside.
I suspect the control electronics may be a bit smaller, even using as close to 1970s parts as I can. Maybe if I upturn a plastic bin on them that’ll be sufficient rainproof housing.

I was quite excited to find it used two 6v batteries, as that’s what Buster was designed to run on. However when I measured them they only read 2.27v each.
Lead-acid batteries are also not meant to be concave.

My charger wouldn’t read it as needing the charge. Rather wish the charger gave out more information on battery status. Charging complete has the same indication as being unable to charge.

As a last-ditch effort I pried the sealed cover off one of the batteries and found three rubber caps. On pulling one off there was a characteristic sucking noise. All the cells were under vacuum. So I suspect the car may have been left out in hot sun for a long time, and literally boiled the batteries dry. So when they cooled the covers were sucked on.
With nothing to loose I grabbed a bottle of demin water and proceeded to refill the cells with a syringe through the tiny vent holes.

Sadly, that didn’t work. Even after a few days for the plates to re-wet, the readings didn’t change at all. Due to construction there’s no way of getting electrolyte back out again to check the gravity. At this point though it’ll just be simpler to spend the £20 buying a new set of more powerful batts.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Buster: A lucky find

Currently got a bunch of things on order, and a nicely full order book. Hurrah.

Yesterday though I spotted something outside a local charity shop. A Fisher Price ride-on electric car.

When I was a child, I used to get a book out from the library over and over again. “Build your own working robot” by David L. Heiserman, published 1976 (ISBN 0-8306-6841-1). The hardback, it was bright orange and missing it’s dust cover. I read and re-read it, fascinated by the diagrams that were inexplicable yet tangibly logical. I must have been 8 at the time.
I wanted my parents to get me a pair of those electric kids cars just so I could make the robot in it; Buster.
At £100 each though, that never happened. And one day some git took the book out and never returned it. I was gutted for a long time.

Last year though, I found a paperback copy on Amazon. And now, for £3 I have the perfect electric car to do it.

After 21 years, I can finally build my own Buster. I have the chance to fulfil a childhood ambition.

I, of course, will blog it. :)

The tech involved is pretty crude by modern standards, being started in the mid 70s. I’m sure it’d be easier to redesign it with modern parts. But I’m going to see how closely I can do it to the original book. Wooden PCB racks, reed-switches and all.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Small update

Took a momment out to update the RepRap wiki entry on my printer project.

http://reprap.org/wiki/Bonsai_RepStrap

I think some of the connections I made at the convention at the weekend may be a great deal of help in building them too.

I’m wondering that when the first few machines are working, that I might loan them out to a few artists to see what they can do with them. See what less hardcore engineering purposes they can find for them.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]