The package from Sculpteo finally arrived today and now I see what took so long:
Stamp on my package from Sculpteo
That’s right–despite having an office in San Francisco, they printed my piece in France and shipping it from there! Obviously this is not an option for faster shipping than Shapeways. It is cool to see the completed piece just as I designed it though:
But, it looks like I’m still trying to find a reasonable way to get things printed fast and cheap.
I was wrong about shipping from Sculpteo. They did send me email this morning telling me that my order has shipped. Of course, there is no tracking number as they already told me. But I’m hoping that regular mail will get from the Bay Area in a couple of days. Their projection when I ordered was as late as April 25th, so I certainly hope it doesn’t take that long. Good to know it’s on the way…
Since it will be a while before my new coil design is ready, I took the take to get my test platform setup:
This gives me a switch so I can turn each coil on and off independently. It also lets me turn them all off and adjust the voltage accurately before applying power to the coils again.
Just like on my spinner platform, these switches made things work much better! I don’t have the coil secured (waiting on my new coil design with mounting points for that), but I was still able to learn some things.
First, using the coil that is slightly larger than the other, I did tests to see how much current I can push through there. And again I kept my temperature probe on the coil so I could monitor if it was getting too hot. Better picture here:
I ended up with this:
My notes from things I tested:
- Switching between the two coils, I was unable to get the nail to move back and forth, no matter what voltage I used. (I later learned this may be due to the length of the nail.)
- It takes a long time for the coils to cool. Even brief pulses at 15V cause the temperature to shoot up to 130°.
- I tried using a scale to measure how much force the electromagnet exerts. Most of the tests, I got absolutely nothing. While playing with 20V, I noticed that I got a strong pull right when the end of the nail was coming out of the coil. I measured that at 60 grams. (I’m not sure what force that is–I suppose the equivalent force that it takes to pull 60 grams against gravity.)
- At 10V, there is no noticeable pull on the nail. I’m not sure how little I can feel, but I’m sure this is quite light.
Checking in with the Shapeways design specs, I see that the flexible plastic is only heatproof to 176°F. This is clearly a problem as it quickly gets that hot at the minimum voltage that I felt a significant pull.
I need to try either other wire sizes, better heat sinking materials, or a different design.
I haven’t done a lot with the spinner lately. My last test was to make a straight horizontal line that was not along the axis. I had problems with that which I attributed to not having enough high resolution timers, so I set it aside to play with my electromagnet tests. But, one thing that was still bugging me was having to use alligator clips to turn the motor on and off. That didn’t make a consistently good connection and the motor speed was clearly unstable at time. So, I finally hooked up my 69¢ switch:
If you look close, you can also see the horizontal line test. In fact, now that I look at it, the right hand side actually looks like I expect. It’s a pretty straight line. The left side is also straight, just not horizontal. Hmmm… I wonder if my real problem is just with my algorithm for calculating the line. There may be some hope here yet…
But the switch works much better than my old technique. The motor reliably turns on and off and runs at a constant speed now! So future tests will go much more smoothly.