gamibots, pager motors, soccerballcopters, things from ebay / china

been spending money lately
mixed feelings 'bout my consumerism of things i feel like i might only use once or twice but i tell myself it's research :P

gamibot

based on
http://www.howtoons.com/?p=3484
these are super cool because you use a business card instead of a toothbrush, i have twenty extra business cards but not twenty toothbrushes and it'd be a shame to buy new toothbrushes just to chop off their heads

all it needs is a business card, tape, a pager motor, and a battery :) so cute.
pager motor placement affect movement a lot, e.g. I changed the placement a bit and this one moves faster and more forwards than sideways

anyway, to start this story off, i am co-teaching a few lessons in 4th grade for my d-lab education class. and last year when we went to China, +Cathy Wu bought a bunch of pager motors in preparation for making swarmbots. I then bought a couple dozen off of her this year in preparation for bristlebots but then realized I needed to solder leads to them. The type she bought is to the right in this picture:

I tried soldering wires onto the tiny motors (they are about 1cm long) and promptly desoldered the metal leads from motor. Well, crap.

Anyway, I ordered some pager motors off of ebay for 84 cents each and they arrived eight days from ordering from China. I expected it to take three weeks so it was a pleasant surprise. (Well, I bought from two sellers and the other packaged arrived in 10 days).

that's a bag of 30 motors! i could fit them in wallet. they come with pre-formatted messages. I wonder if these two are actually the same seller.

Details

From two different ebay sellers:

"10pcs Pager and Cell Phone Vibrating Micro Motor 2.5V-4.0VDC With Two Leads s883"

x3 = 23.63 for 30, or 0.79 each. Arrived in 10 days

x1 = 8.36 for 10, or 0.84 each. Arrived in 8 days.

I emailed them to check there were two wires coming off of them and got a pretty prompt response.

and i get reimbursed for these, so yay ^__^

Note in particular that these are from Shanghai and not Shenzhen. According to Amy, who travels to China for work a lot, and Star, 

I found better "hard hardware" streets in Shanghai TBH, & don't remember seeing tons of motors in SZ.

Yup, I think you are right. SEG looks like the place to go for electronics, but Shanghai had way more mechanical stuff. It was a fun visit, though!

soccerballcopeter

In other news I am playing poking at copters a bit for the lulz. (I have been spending more money ever since making decent money at fitbit last summer... no regrets! i think)

"Pro 6042 Flying Ball Scientific 3CH R/C UFO Remote Control Gyro LED Helicopter"
22.91 + 1.6 shipping
bought 3/26 arrived 4/4 (nine days)

all that it needed was 6 AA batteries and it even comes with two props. super cute. fits in palm.

and it flies!

uhm, I thought this would be totally harmless because it is so tiny. and it pretty much is, but i was surprised because it has a decent bite just crashing into you (i thought the soccerball shape would protect me from the props)

things from ebay/china

in another post some day, crazy cheap and awesome robots (even hexapods!) from taobao, the swarmbot entry for $10 robot competition, and cost reduction due to scaling analysis.

Also, can we just take a moment and reflect how amazing it is that I can get a functioning flying thing complete with wireless control shipping to be from China for a total of $25 USD? That's like 1.5 arduinos without batteries or anything at all. Mass manufacturing is awesome.

Servo repair with 4-40 tap, no thanks to silly proprietary servo hardware

Hexapod now has 18 working servos again! yay.

Servo Failure modes
I didn't strip the gears* on one of my servos from applying to much load to it (the way I expected my servo to fail), but rather stripped the threads on the servo to servo horn coupler.

*see http://techtv.mit.edu/videos/10523-what-is-design-an-example for a good video of designing a robot, having the gears strip, and solving that problem with rubber "shock absorbers." This video is shown near the very beginning of 2.007 Design and Manufacturing I, a sophomore build-robots mechanical engineering class.
@28:30 you see a good picture of stripped servos gears, where the missing teeth means that the servo can't turn correctly:

Anyway, I had some issues because I thought maybe I was using the wrong size screw. The servo horns and screws and splines are all some dumb not inter-compatible between manufacturers proprietary design.

So I ordered some replacement servos off of ebay.
"Vigor VS-2 standard analog Servo VS 2 vs2"
$9.98 for 2, or $4.99 each.
Probably I paid way too much but whatever. At the time I thought $5 was really cheap for a servo (now I think $3 is more reasonable price for this servo). Bought 2/9 and delivered 2/19, not bad.

At first I thought I got ripped off and the servos were stripped, but then I looked more closely and realize that there are no threads cut into the servos:

So you can use the proprietary self-tapping screws, but I realized you can just tap them with regular ol' 4-40 threads and use normal 4-40 screws instead of, if you ever lose the pack of proprietary servo stuff, hunting around for ages looking for an appropriate size screw.

left: 4-40 screw mates fine with servo horn. top: a 4-40 tap. right: A proprietary screw with mysterious thread count and pitch next to a nylon 4-40 screw.

Works well!

miniature things research (tiny steppers!) / start-lolling, start-trolling, start-rolling

stepper motors
I started looking into how tiny and cheap steppers can get, since micro servos are in the $2-3 range, and holy lady hexapods they can get tiny.

 More info here.

Turns out most tiny steppers come from vehicle dashboard instrumentation. To actually buy them
 you don't turn to mcmaster http://www.mcmaster.com/#stepper-motors/=lwy84g

Instead, a search for "nano stepper motor" reveals this:

More info here, including the fact that this stepper can be driven directly by an Arduino. 
On amazon, these cost ~$2-3 each as well. (search for "stepper motor gauge").
I just order 6 for $16.50 to have some hand to play with (randomly ordering the micro-servos a while back turned out well); we'll see how this goes. So, upcoming tiny stepper gantry?
Some more reasonable 15 cm ones cost ~$15 (vs the price on mcmaster...)

flying things