Projects of Passage

Twinkling Lights - a 555 timer contest entry

2011-02-28T19:03:00.000-08:00

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

2009-08-25T18:56:00.000-07:00

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.

2009-01-25T15:06:00.000-08:00

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

2008-11-30T18:29:00.001-08:00

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

2008-10-26T08:40:00.000-07:00

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

2008-06-05T07:23:00.001-07:00

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

2008-05-16T11:13:00.000-07:00

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!

Designing the Frame

2008-04-04T15:46:00.000-07:00

Been thinking about the frame size a lot lately. We thought about using an aluminum I-beam that is 3 inches high. The motor would mount nicely in the middle section and the wheels being 5 inches, would stick out 1 inch above and blow the frame. Sounds pretty good.
Shopping for I-beams, we found that the options were limited and we couldn't find a 3 inch that didn't have a pretty huge dimension for the horizontal parts. So, we visited a local store that has a customer counter where they sell odd bits left over from customer orders. We found a 3 inch square aluminum tube, 6 feet long. So, if we rip this, we'll end up with some 3x1 channel which will work out just fine!
To the right, you'll see a frame that is 21" x 24". The motors are drawn in to scale as are the wheels. Now, I need to get that tube ripped and make detailed drawings of the frame pieces. I'd like to weld as much of it as possible so that it will be strong. I might still bolt on the side pieces that cover the wheel mechanics.

The Motors are Here!

2008-03-19T14:37:00.000-07:00

They've arrived right on schedule! I think they'll do nicely! We've been eyeing some wheels also. They have an aluminum hub and polyurethane "tire" and some nice roller bearings in the hub. I think we'll be able to attach a gear to these via some metal spacers attached to the hub.
With these wheels (at 5 inches diameter) and these motors, we can go 33 mph with a 2:1 reduction. But, Ryan thinks we should shoot for a slower top speed. So a 3:1 reduction yields 22 mph.
I did some research on motor drivers that integrate with a R/C receiver. I found this one, "Sabertooth dual 10A motor driver for R/C". It can more than handle the power needs of these motors, though I really don't know what they will draw at full load. We've also been talking about how to construct a frame. We've been talking about aluminum I-beams. Not sure where to get these yet. We'll do some more research and report what we found. Also need a source for gears and chain, but I'm sure we won't have any problem finding those!

In the Beginning

2008-03-19T10:43:00.001-07:00

Ryan and I have been building with LEGOs for years. Robots came naturally because seeing your creation move under its own power is way cooler than having something static. Recently, we went to see a FIRST Robotics regional competition. While there were many fully functional robots there that had interesting solutions to the task, there was also a rookie team there. Their robot merely drove around the course, but that did score points for the team! The inspiration here is that any project has to start somewhere. We've decided to make a driving base that is both sturdy and fast. Our inspiration comes from both the FIRST robots and from Battlebots.
To get started, we needed to understand some design requirements. Initially, I wanted to decide on a top speed. I drove the car at 30 MPH and asked Ryan if that was a good speed for a robot. He thought 20 might be fast enough. I suspect he is the wiser of us! Last week, I worked out some calculations that started with wheel diameter and derived motor speed given different speeds and reduction ratios. The results is this spreadsheet, which does the later, but also allows you to calculate the top speed based on wheel diameter, reduction ratio and top motor RPM.
We started with a 6 inch wheel (seems like a good size) and started shopping the surpluscenter.com web site. We found a nice motor that has a top RPM of 4500 and draws about 1.5 amps at 24 volts. I figure that two of these ought to provide enough power for a nice differential drive platform. The motors should arrive today.. yea!! parts!!

Welcome

2008-03-16T15:23:00.000-07:00

Since I'm just starting out with this blog, I think it would be a good idea to tell what its going to be about. My son, Ryan, is 8 and really likes building things. I'm trying to show him some real projects that demonstrate real world principals. We've been building robots with LEGO Mindstorms for a little while now and going over some basic circuits knowledge. The idea of building a battlebot type project gets both of us excited, so we'll be using this blog to post the project status.