Thursday, February 16, 2006

New Remote Unit

I replaced the previous keychain remote unit (about the size of a jumbo pack of cigarettes) with a new one not much bigger than a matchbox. The new one also has the advantage that it's a simple push-on push-off unit, rather than one designed to drive a power door lock switch.

(Note for new readers: The remote doesn't really do anything other than power up the electronics. Controlling the thing is strictly hands-free thanks to the weight sensing controller. But it's a little tricky to step onto the board when it's active, and bending over to flip a switch is just too undignified).

I bought the thing from All Electronics, a company in Van Nuys whose previous store (in downtown LA) I visited a few times when I was in college. The store is definitely worth a stop if you're in the neighborhood, and the catalog and web site are also worth a look if you're looking for fun, cheap electronic components and doodads.

Thursday, February 09, 2006

Robot Marketplace

I just placed an order with The Robot Marketplace, a company that sells parts for so-called combat robots (radio-controlled robot gladiators, basically).

I'm buying some "wet noodle" 12 AWG wire, which should be great for things like battery interconnects, along with a handful of Anderson PowerPole housings and contacts. I'll have some extras left over for whenever I get around to putting together the magic circuit board. Before I do that, however, I need to find a place that will sell me the PCB contacts in quantities of less than 100.

Wednesday, February 08, 2006

Test Ride

It turns out the bigger battery pack was just what the doctor ordered: a slope that used to reduce the 3WDM to an embarrassing crawl is now hardly noticeable. Not that I'm about to take the thing up Alabama Hill, but the trip back from work should now be possible without the thing pooping out half way up F Street.

The first draft of the battery mounting consists of eight footman fittings with some webbing and associated buckles. I'm not particularly happy with it, since the batteries still move around much more than I'd like. Part of the problem may be the cam-style clasps I'm using, which depend on introducing a bit of slack into the webbing to stay closed. That, in turn, allows the pack to slide around along the length of the board, which just now disconnected one of the front weight sensors.

I also need to make the pack wiring a bit more reliable. The two major issues are semi-adequate insulation, and the fact that the wires I'm using are quite stiff. The problem with the latter is that vibrations will eventually cause something to fail if the wiring can't flex easily. This weekend I'll try and pick up some nice, floppy 10 AWG wire and a 10k Thermistor at the nearest electronics store (a tossup between Vancouver and Mount Vernon). I'm also thinking of re-doing the wiring on the ends of each stick in the pack by snipping open the heat shrink tubing, soldering on the wires, and putting on a new piece.

Then I just need a better method of strapping the cells to the deck and I should have a good, solid pack.

Tuesday, February 07, 2006

New Magic Box

I'm starting design work on a magic box (really more of a magic circuit board) that will integrate the features of the current hand-soldered circuit board, the main relay, the protection fuse, and the servo amplifier evaluation board.

It will have connections for the battery, motor phase windings, motor hall effect sensors, and weight sensors. It will also have a connection for an on/off switch (currently provided by the keyless entry receiver) and a dedicated connection for the battery charger. Finally I'd like to add outputs for the four status LEDs (currently on the evaluation board and not visible while riding) and a brake light output based on the state of the current monitor on the servo amplifier. I'm still deciding how much room for future expansion I want to put on it.

I'll probably use the PCB123 service to design and fabricate the board. Finally I'll conformal coat the whole thing to make it waterproof, and probably put some kind of a box around it to protect it from scrapes with the ground.

This should clean up the underside of the board a great deal and make the 3WDM that much more durable and reliable.

Monday, February 06, 2006

The Batteries Have Landed

I am now the proud owner of 30 10Ah D-size NiMH Cells. Here's a picture of 10 of them:

I've spent the last couple hours soldering them together in sticks of six volts (5 cells). The solder tabs make this relatively easy, and the heat shrink tubing should enhance the conductivity by forcing the cells together:

Here's the nearly-complete pack, shown roughly where it will go on the (underside of the) board:

I still need to solder on the interconnect wiring, seal the ends up with silicone, and position the thermistor for the charger's temperature sensing. Plus I'll need to figure out how I'm going to affix the pack to the board. I'm leaning toward using the industrial-strength velcro that held the previous pack in place.

Finally it will need a full charge before I taking it for a test run around the block.

Wednesday, February 01, 2006

Just Bought Some Batteries

I just ordered up 30 10Ah high-discharge-rate tabbed NiMH cells. The pack weight should be around ten pounds and they should fit neatly under the deck.

The present pack (five 7.2V 3000mAh packs) seems to sag a lot on modest slopes. The new pack should be at least three times stiffer under load (probably more, since the cells are designed for high current), and give roughly three times the range (which translates to around 10 miles, or about an hour of riding time).

Unfortunately I have to build up the pack myself. The good news is that I can configure them however I want, and they have tabs, which should make soldering them much less dicey. I'm leaning towards six sticks of five cells each, with three sticks nestled under each side of the deck towards the front of the board.

That should leave room at the rear of the board for the servo amp, op amps, and keyless doohickey.