Twinkling Lights - a 555 timer contest entry

When Jeri and Chris first came up with the 555contest.com idea, I was intrigued. I'd used the chip back in the early 80's when in highschool. I still had a bunch of them in a drawer. It was just a matter of what to do with them. When I worked on my masters project (in Computer Science), I used something called spectral synthesis which simply means combining simple waveforms to form a more complicated one. The idea there was that I was trying to render what looked like realistic landscapes including mountains and valleys. If you get enough waves sine waves mashed together, you end up with something that looks somewhat random.
I decided to apply that to square waves and use logic gates to combine those waves. I figured if I could have the right set of timer frequencies set up, and combine them as inputs to 4-input NAND gates, I could drive LEDs that would twinkle in a pseudo-random way. That is what this project is about.
First, some math. I had to figure out just how many timers I'd need to generate a reasonable number of combined outputs. It turns out using Combinations from set theory works here. Given 4 inputs, there is exactly 1 way to combine those in a group of 4. If I used 5 timers, I can have 5 unique combinations of 4. With 6 timers, 15 combinations, 7 timers, 35 combinations. I figured 15 LEDs was enough for the scope of this effort.
I used totally non-scientific means to create the base frequencies. I used a handy 555 timer calculator and found that using a 10 uF cap, 10K and 100K resistors let me get about .68 Hz output at near 50% duty cycle. So, I went fishing in my parts drawers and found some capacitors I had laying around (1uF -33uF). I varied the resistor values a little till I got some blink rates that looked reasonable.

Next, I had to wire up the NAND gates. Having the combinations printed helped a lot! I was also starting to run out of jumper wires.

So, there you have it. Ideally, I'd play around with the timer frequencies a bit. For a more artistic presentation, I'd like to see the LEDs either embedded into a poster of a space scene, or scattered across one of the kids room ceilings.
Oh, I ordered some parts for this from Digikey (one of the contest sponsors). Good Karma, no?

Electrical Panel for a Catalina 27

The robot project has been on hold for many months. The main reason is because we bought a sail boat! I should point out it is a 1976 Catalina 27 (hull # 2833). I've done a lot of work on the boat, from refinishing/fairing the bottom, to refinishing the teak and now, replacing the electrical panel. The toggle switches are all crusty and sometimes intermittent. The fuses are out dated and I'd like to add more circuits. There is a perfectly good panel available from Catalina Direct. For over $170 after shipping is factored in, I decided I'd try to do one myself. In my youth, I made all kinds of projects, and sometime even the boxes that contained them.

To start with, I measured the old switch panel and screw locations. I got that put into Adobe Illustrator. I searched on the Surplus Center web site and found these switches and circuit breakers which look remarkably like the Catalina Direct ones (and I've seen one those in person, because a fellow Catalina 27 owner I know bought one). I used the dimensions from these parts to layout the panel. I actually chose to lay it out like the Catalina Direct panel. It is a sensible layout, and adds 3 more circuits. I also was free to label it exactly the way I like. In final construction, I ended up swapping out the circuit breakers I had ordered with some nicer ones from a local electronics supplier. They were slightly smaller and had nice hardware with the. Switch order: $30 New breakers: $13

I did a search with google maps and found Recognition Experts who were able to laser engrave the panel based on my drawing. Panel: $35 The new panel material was a little on the thin side. I decided that I need to add some thing on back to stiffen it. So, I used some aluminum angle to make a piece that is bolted in with the circuit breakers. Also, once soldering the bus wires to the switches (one for grounding for the indicator lamps, and the other for the breaker protected power feed), the section with the switches was stabilized.

Total project cost was just over $80.

Finally, some wheels I like, and I think they have great potential. They are described here. Basically, 6 inches in diameter, pneumatic with steel hubs and 2 bearings. They'll absorb some of the shock so the robot won't be shaken to bits. Ryan thinks they look kinda like moon rover wheels! I researched sprockets and chains. It looks like #25 chains (the smallest ANSI standard) could work, but they are a bit small and might not take the loads well. They are rated at 140 lb working load. If I went up to a #35 chain, the working load goes up to 480 lbs. The reason for my concern is this robot could easily top around 100 lbs (rough estimate). If there are sudden loads when starting up or changing directions, that could really shock the chain. The #25 has a top end rating of 781 lbs, so maybe that will work. The other nice thing about the smaller chain is that sprocket selection is simplified. With smaller pitch comes more teeth in a given diameter sprocket. For these wheels, I wanted to have a sprocket that will mount to spacers on those bolts you see in the hub of the wheel. I also want the teeth of the sprocket to be well within the outer radius. The reasons for this are mostly so that the chain won't run too close to the ground. I also anticipate some flexing in the tires, so we can't assume the wheels are always going to be the same diameter during robot movements. I found a nice 42 tooth sprocket that fits well on the wheel. Using a 13 tooth sprocket on the motor, I get a 3.2:1 ratio. Using the spreadsheet I mentioned in an earlier post, that gives an estimated top speed of 25 MPH. I also figure I'll have 2 idler pulleys, one on each side of the motor sprocket, so that the chain contacts as much of the motor sprocket as possible. That will also give me a nice way to tension the chain.
Another thing I'm thinking about is a way to mount the batteries. I want something that will be very sturdy and maybe even provide some cushioning. I was thinking of aluminum angles at the corners of the batteries, but I think something that supports more of the battery surface would be better. Maybe an aluminum plate with a thin closed cell foam pad, with some fairly large holes cut out to let things "breathe". OK, that's it for now.

Radio Gear

A stop at a local hobby shop brought me to this radio. The Spektrum DX5e has just enough features to allow me to control this thing remotely to test the chassis. It's a digital 2.4 GHz radio, but without any of the fancy features that would have driven the cost way up. The Sabertooth motor controller I mentioned several posts back will connect nicely to the included receiver. In addition, the Sabertooth has a BEC which will power the receiver off my main batteries. One more thing checked off my shopping list!

Frame Progress

A busy summer meant that not much got done, however we were able to get some of the frame assembled. The ends are attached to the beams that hold the motors (that are mounted now). I used some angle aluminum to join the pieces instead of welding. It feels like it will be a very sturdy frame! Some sheet aluminum covering the bottom of the main area will stiffen things up further.
The wheels we purchased are probably going to be too small, and difficult to attach a sprocket to. I saw this option which would really simplify the drive train construction. By combining a sprocket and wheel, it removes one challenging bit of construction. I wish I had my own lathe! Still, $200 for wheels is a little more than I wanted to spend. I also wanted to see if I could run with a live axle (where the axle is mounted on bearings and the wheel and sprocket get mounted directly to the shaft). For example, using a sprocket like this and a flange bearing like this, the robot could run a live axle.
I'm itching to order something new... drive train... electronics... hmm.

A Decision on Power

OK, so we jumped the gun, and didn't work on the frame. Instead we did some looking for batteries. I ended up looking at the PowerSonic PS-1270, which seemed like it met our Amp/hr needs, and with 2 of them, we get the 24 volts to power the motors. I just wasn't sure if they could be mounted on their side. The reason I need to know this is that the frame is 3 inches high and these batteries are less than 3 inches wide, which means I could fit them within the frame of the robot. Ryan wanted to buy them right away (of course!), but I said we ought to call PowerSonic to ask. A nice guy answered and said that running them sideways would be no problem, just don't mount them upside down. The cool thing is that he said the PS-1290 was the same size, but in a 9AH, instead of 7! Instant increase in power density is a good thing! I thanked the guy and started hunting for them at the cheapest price. I found them for $23 each at BatteriesASAP.com So, they are ordered and on their way. Now, to find a decent 24 volt charger for these AGM battries.
Oh, anyone know a good source of sprockets and chains? I looked at a bike repair shop, but those sprockets would all require me to machine a hub adapter, since the center holes were far to large for the motor.

Frame Mock-up

Since the last post, a couple of things have happened. We ripped and cut that aluminum tube into the 1x3 channel. The wheels were ordered and came in just a couple of days ago. So, we just had to lay things out on the floor to see how everything fits! There's a box under the motors so they can be positioned properly over the inside frame members. It looks like there will be plenty of room, which is good news!
The next steps are;

• trim the frame members to fit together
• weld the frame (but leave we'll bolt the pieces on outside the wheels, for easy servicing)
• drill the holes to mount the motors
• get axles for the wheels
• find some mounting hardware for the axles
• research and acquire the gears for the motors and wheels
• get the right length of chain to connect the motors and wheels

Once we get all of that done, we can start worrying about electrical items, such as batteries, motor controller, and radio-control hardware. I'm sure we'll be tempted to just apply power to the motors to see the thing move!