Sunday, June 19, 2011

Mobile car chair

First, a little bit of backstory

From before I started going to miters earlier this year, there's been a car chair mounted on an old electric wheelchair base. Unfortunately it didn't work and didn't have a battery pack so it was hard to test. Earlier today I decided to see if I could fix it. Fortunately Shane tipped me off that electric wheelchairs often run at around 24v. I hooked it up to a DC power supply and it turned out it worked when everything is plugged in (with the power supply in place of the battery). In other words, all it needed was a battery.

Soldering the cells:

Heat shrunk & insulated the contacts

Charging the batteries:

Chair base sans-batteries

I forgot to take any pictures of it with the batteries inside and I didn't get any good pictures of it driving around (my phone crashes when I try to put it in video mode). Someone else took some video, hopefully I'll get that soon so I can post it. The chair now drives around very smoothly and has space for at least 4x the batteries I put in it for increased range. It still needs a good mount for the controls and possibly a better interface. Odds are it'll make an appearance next time miters has a booth for something.

Sunday, June 12, 2011

3d printing, new design

Change in main structure, now I'm planning on building my printer with 1/4" acrylic. It's waaaay cheaper than making it out of aluminum and will be lighter. It's also much easier to build an enclosure so I can heat it instead of just having a heated build platform. Airflow for working with PLA will be harder, I'll just have to build it into the design instead of propping a desk fan up pointed into my printer like I did with my makerbot.

Switching to t-slot construction makes designing and machining the parts far easier. Also I don't have to worry about the machine racking like I would have had to with the earlier design.

For comparison, here's the old and new designs. The shafts aren't structural, they're a part of the design I haven't put in the new version yet.



The new design is about the same size as the old one, but it's much easier to scale. It doesn't need nearly as many slots as it has. I put in so many since it's easier in Solidworks to pattern the slots like that than only putting a few in. As far as I know, the main difference will be it'll take a little longer to cut it out.

Wednesday, June 8, 2011

More door fun

Continuing on with fun things about my door. A few days ago I finally got around to turning my door into a speaker. It's actually pretty simple. Four transducers (horribly simplified, they're the part of a speaker that moves to make noise) are hot glued to my door. They're wired up in pairs in series, one is the left and one is the right channel. Both pairs are hooked up to an awesome little class D amplifier which is duct taped to my wall and plugged into my computer. In short, my door is now another audio output for my computer. My motherboard's left channel is dead so I can only use half of the transducers at the moment but I'm getting a cheap usb sound card to be dedicated to being the output for my door.

Sketchily mounted amplifier with volume control

Doorbell v2.0

I'm bored and don't feel like going to sleep yet. Guess that means it's time to catch up on some of my projects!

I fixed up my doorbell to be much less sketchy. Now, a 555 timer constantly runs at a visible duty cycle (around 17 hertz), driving a 2n7000. When the button is pressed, the voltage source is connected to a 1000uF capacitor and powers the LED. When the button is released, the capacitor discharges through the LED and another resistor to make it drain faster. I probably should have a resistor in series with the LED, but the LED I'm using is tough and a good brightness without any resistor. I'm relying on the fact that the voltage source has some internal resistance for current limiting. Here's the circuit and the new setup:
New setup outside, aluminum tape as wires. I'm great at neatly aligning tape aren't I?
I had to reinforce the connection on the inside with hot glue since aluminum tape isn't very structural.
The circuit itself. The blue LED that's on is something else.

Sunday, June 5, 2011

Motorized scooter

A while ago, I decided I wanted to build a motorized scooter. Brilliantly, I decided I wanted to build my own motor. I'm still pretty sure I could given more time but it'd be tedious and require a lot of redesigning. I might go back and try to do that in the future.

In the meantime, I've decided to switch to a brushless DC outrunner motor from Hobby King.

It should be a lot more powerful then the hub motor and I can use it with the same controlled I had bought for my hub motor. I'm switching to a belt drive and redesigning the back of my scooter a little. My current wheels are a little small so I'm springing for some nice 8" wheels from I still need to finish the design of the mount and figure out how to build it, but I might jump ahead and order everything I need for the belt drive. Almost everything else can probably either come from around MIT or McMaster so it won't take as long. Hopefully I'll be zooming around with a motor in the next few weeks.

Saturday, June 4, 2011

Sad scooter

While I was riding back from MITERs earlier tonight I noticed something strange was happening with my scooter's steering...

Didn't there used to be a nut there?

I have no idea when it happened (I didn't hear it), but the nut I had on the front wheel unscrewed itself and the screw had slide out so far the spacer on the inside of the fork (adjacent to the wheel itself) also fell out. My wheel looked like it was a few seconds from falling off when I noticed it. The fork ripped the hub up a little but it's nothing too bad, it's just superficial damage. I carefully rode it back to EC sans-nut since I was too lazy to walk it back. It should be a really simple fix. I just need to machine a new spacer, find a new nut and get some locktight or something similar to stop this from happening again. I guess I'll be walking to MITERs tomorrow.

3d printing!

The start of a gantry 3d printer. The toolhead will move on the X and Y plane and the build platform will move along Z. If it turns out as planned, it'll probably have a build area of around 10"x10"x12". Most (possibly all) of it's structure will be aluminum angles and bars bolted together. I haven't figured out a good way to keep all the joints straight yet but that shouldn't be too hard.