The Saga of the Pump

The Gado robots are designed to pick things up and move them around. Obviously, then, picking things up is a pretty crucial feature; moving things around without first picking them up doesn’t really get you anywhere.

Both the Gado 1 and Gado 2 do their picking-up using suction; they press a suction lifter (kind of like a suction cup) against some materials, turn on a vacuum pump, and lift the materials up.

The original machine literally used a home vacuum cleaner, controlled using a neat device called a Powerswitch Tail and connected to the lifter by a maze of tubes and fittings, to generate a vacuum.

There are some obvious problems with this:

• It’s a hack. Home vacuums are designed to pick up dirt, not to connect to suction lifter cups. Going from a nonstandard, unthreaded vacuum cleaner hose to a 1/4 cup was no small feat.
• Home vacuums are large
• Home vacuums are noisy; not so great when you’re working in an archive or library
• Home vacuums are expensive; even cheap models cost at least $30
• Home vacuums use 120v house current. The highest voltage in the Gado is 12v to run the motors, so turning the vacuum on and off requires a relay (the Powerswitch tail)
• Home vacuums, when controlled by a relay, are either on or off; on the Gado 1, you cannot change the strength of the suction

Obviously, the Gado 2 needed a better way to handle suction. Luckily, Sparkfun carries a vacuum pump which is cheap, runs on 12v, is small, and has 1/4 inch hose barbs already (photo credit: Sparkfun).

I thought this would make finding a new pump for the Gado 2 easy. So far, I’ve been wrong.

When I was originally sourcing parts for the project, Sparkfun had several hundred of the pumps in stock. No problem, right? Who orders a vacuum pump anyway? Naturally, when I went back to actually place an order at the start of the project, all the pumps were gone. I had no idea when they would be back in stock, so I had to find an alternative.

From a datasheet on Sparkfun, I was able to find the actual manufacturer for the pumps , Ningbo Forever Electronic Appliance Co. They had a bunch of vacuum pumps listed as ready to go. Oh yeah, and they’re located in Zhejiang China.

I don’t speak Chinese, and I had no idea if they spoke English, but I needed the pumps, so I decided to try them out. My first email response was actually not bad:

Sure, the grammar is not fantastic, and “yours faithfully” is a bit too intimate for a business transaction, but the basic idea came through just fine. I kept emailing, and eventually determined that five pumps would cost me $35, plus $60 for freight. It’s a small order, and buying in bulk would make the freight charge far more worth it, but this seemed like a fine start.

The next fun part was actually getting the money there. After about an hour at Bank of America filling out forms, I had successfully wired some cash to Ningbo. This is harder than it seems; exchange rates between the dollar and the Chinese currency are set by the Chinese government, and B of A doesn’t allow you to do conversions, so I had to wire the money in dollars. Sending dollars to China is apparently a big hassle, and can take a long time; it also means adding a $45 wire transfer fee to the price of the items you’re ordering.

Since I had no idea how long it would take to get my pumps, I figured I’d better have a backup plan, so I began researching other cheap vacuum pumps. I ended up finding a cheap little air pump at All Electronics, the KPM27H.

These pumps are the same ones used in Keureg single-serve coffee machines, and my pump had apparently been ripped from one, which explained its $5.25 price tag. They are designed to push air, not create a vacuum, but I figured I would just run the pump in reverse, and everything would be fine.

When the pump arrived, I wired it up to a 12 volt supply, and sure enough, it pumped air out just fine.

I reversed the voltage…and it kept pumping out air. No change, no suction.

I decided to see what was up, so I opened up the pump. It turns out that instead of using an impeller or a fan, the pump uses an ingenious serious of diaphragms. When the diaphragms are pushed in, they force air out of the pump.

They are all connected to a central rod, which is connected to an off-center cam on the shaft of the pump’s motor.

As the shaft spins, each diaphragm is pushed down in sequence, creating a continuous flow of air.

The catch is that it doesn’t matter what order you push the diaphragms in; if you run the motor backwards, it just presses them in a counterclockwise order, and the pump behaves the same way.

So, I was back to square one. Then I checked Sparkfun, and…the pumps were back in stock! One should be in the mail to me today, with five more (hopefully) arriving from China in the next month or so. Let’s hope they work!