Introduction

This page describes my design (and step-by-step construction instructions) for a lightweight mountain bike 'cockpit'. The main feature the cockpit enables is continuous, GPS based and moving map topo navigation.

It includes an etrex, a Palm model Tungsten T, a strong LED headlight a cell phone and a central power source.

The centerpiece of the cockpit is a palm Tungsten T. It's loaded with topo maps and software that enables it to connect to the etrex. Using pathaway software, it displays the relevant map, and centers it on the screen based on location sent from the GPS. The end result is a clear view of where we are on the map. There are numerous other features of the software, like heading, estimated time of arrival, tracking a route, recording and storing a path and much more.

The design goal is a navigation system that is light, dependable and inexpensive. Its benefits are:

• No need for cumbersome paper maps, enabling continuous ride as it is very very obvious where the bike is on the map, including heading, speed, altitude, and a multitude of other data.

• Two screens - the etrex screen and the palm screen, provide a wealth of information, with the Tungsten T complementing the information missing on the etrex.

• In addition, the Tungsten T other features can be used, for example playing audio through headphones or its small speaker for the genre inclined.

• The Tungsten T collects many more trackpoints, and has virtually unlimited memory compared to the etrex, resulting in much more accurate tracks.

• A central power source, located in a seat pack, feeds and charges the etrex, Tungsten T and when needed, a high-intensity flashlight. . Power distribution is controlled via a set of toggle switches.

Throughout the remainder of these page I'll describe the system components. If you intend to build this, I strongly suggest you read this through at least once, see how it applies to your needs, skills (soldering, electricity, cutting aluminum) and bike. There is no one way to do anything, and this is no exception. I will likely modify this system as I did thus far. However, having said that, I can say that the state of the system right now is good enough - it is terrain tested, dependable and works well.

The Parts

1 - The Palm Tungsten T: Being totally unfamiliar with handheld devices until this project, I chose this palm model mainly because of the following reasons: it has a reflective type LCD, which I read performs better in sunlight. It has sufficiently high-resolution (320x320) and a color screen, a must for topo maps It is more compact than other models and uses less power than most palms. It can be had for less than $100 on ebay. Having said that, I'm not absolutely sure it is the best decision - in retrospect, I'm not very happy with the software its running - PathAway. I've been using Oziexplorer for quite some time, and it has a CE version, however, it runs on PocketPC OS only. In retrospect, I would have looked closer at handhelds running Windows Mobile OS a lot closer than I did. Using Pathaway means I need to convert back and forth from Ozi to Pathaway using a software called GPS Babel - it works, but the whole process is cumbersome. Even worst, Pathaway doesn't support Israeli datum (Ozie does), which means I need to re-calibrate every map I have, which is a drag. Also needed is a protective case, such as the aluminum case shown here, that's made specifically for the palm Tungsten T. I bought the T, the case, cradle, charger, cable and a 128MB SD card as a bundle on ebay for around $100 Also needed is a palm universal connector. This will be used to connect the palm to the etrex. You can get the connector, or rip it from an old cable. I got mine in Israel from BNC
2 - etrex GPS -  and a plug that connects it to the outside world. Elsewhere on this web I describe how to make your own plug. This would be very much needed here as you'll read later on. You'll also need a handlebar bracket for the etrex. Again, the plug can be bought in Israel from BNC
3 - The power pack : The power pack is composed of four C size rechargeable batteries, that are stored inside a seat wedge pack. I modified  a large size  wedge saddle pack that has expendable compartment along the lines of this  Avenir Bigmouth. It's large enough to contain the batteries, plus bike tools and other stuff I recommend against the quick release types - I got one and it broke after a few rides. Instead, get the one with strap around. Also, you'll need two C cell battery holder, or one four cells holder. I found that gluing two twins make for a more compact set for the pack. Also needed are three small toggle switches. Finally, some Velcro, electrician tape and zip ties are needed. The switch base needs a strip of aluminum.

The construction takes a good few hours, and lots of tools. It is a perfect weekend project, but it took me a few iterations to identify and remedy the weak links of this system. There's no one way to do this, of course, so I'll describe the end result and the pitfalls I encountered on the way.

Always keep in mind that anything that is even slightly loose, rattles or exposed will strongly tend to come apart when in the bush. Everything should be constructed with that in mind.

Construction of the power pack

Start with gluing the two battery holders back to back. I used hot glue, because its strong on plastic, yet is not too brittle like superglue. I guess epoxy is equally suitable. Solder in series the holder outer jacks to create four batteries in series holder. Solder the external jacks to about six inches of wire and solder a connector to the other end. I used an audio mono connector. They click on hard and stay together. Tape Velcro (wooly side) to the bottom of the battery holder (shown right in picture) Add washers to the springs. It will hold the batteries much tighter and improve contact. I've found this important. The pack needs a modification to prevent the battery holder from moving about. First, a Velcro needs to be sawn to one side, and pulled through a metal ring on the other side. The metal ring is fitted through the side of the pack by making a couple of holes in the fabric. The idea is that this will push the batteries hard against the back. Next, a small hole on the top needs to be made for the wire and connector to go through. Finally, I've added two strips of Velcro on the bottom (hook side), to help hold the battery pack in place. The end result is a battery pack that is tightly held inside the wedge pack. The bottom picture shows the seat post. Notice the metal ring, through which the Velcro strip goes through to hold the battery pack, and the connector held by the pack's post Velcro. All these ensure the batteries will stay in place, no matter how hard you ride. I've gone through several iterations and tried the below ideas, all of which were less than stellar: Tried to store the batteries inside the seat post, using the frame as one wire (similar to the wiring in a car). I drilled a small hole at the top of the seat support for the power wire to go through. Although this was by far more elegant than my final solution, implementation was difficult, as the batteries rattled and my innovative ideas to make holders for them so that I could still slide the seat up and down didn't work too well. I also found that using the frame as wire wasn't great, as there's no good connection to the headset. Maybe the annodization of some parts are the cause for that. Tried placing the batteries on the front, below the stem. Found that they go through more rattling than in the back, and I didn't like the idea of loading the front wheel with more dead weight. Below the seat is very close to the bike and rider center of mass. .

Construction of the palm holder

This is not an easy part to make if you don't have the right tools. Basically what's needed is to make a cutout in the case cover and glue a clear plastic over it. In addition, a loop needs to be installed for a Velcro strip (yup, another one!) to hold the cover shut tight. Start with marking the cutout needed. Measure the screen size, add two millimeter or so around the edges, and use an accurate ruler to find where it's located. I used a drill and a fine jigsaw to make the square cut. Next, cut and glue a piece of clear plastic to cover the cutout. I used superglue for that. Next, drill two very small holes, around the middle. Shape an office paper clip to a rectangle, thread it though the hole and cut the excess and bend the two ends at the inside. Cover with hot glue to protect the T. This will be used for the Velcro strip that holds the cover tightly shut. Next, peel and glue three long strips of Velcro on the back of the case, wooly side. Cover as much of the case back as possible. These strips will hold the case and the palm to the base, so the more of it, the better. Finally, peel and glue a small piece of Velcro on the top left corner, so that when the cover is open during riding, it won't scratch or rattle on the handlebar. The end result a case that hold the palm very firmly inside. The following trials disappointed: Tried the case without the paperclip loop and Velcro strip (more on this later), just using the factory built clicking cover. It opened up very quickly on the trail, no matter how I tried to adjust it. Tried the case without the cutout window - it makes the entire project mute because every time I wanted to check my position I had to stop, open the cover and figure out what am I looking at. The cutout window is really important. It's enough to glance once in a while to keep a mental track of where you are. .

Construction of the Switch Base

• Start with cutting a rectangular strip  of thick aluminum that is wider than the palm case. It's length need to be from the stem screw on your bike, to the handlebar top screw, plus at least a couple more inches. I got the material from an old aluminum case.
• Next, place the palm case on the strip, around the middle of the strip in both dimensions, and mark its outline using a pencil.
• Next, place the strip on the bike, center it over the stem. Now move it about half an inch forward and mark the position of the stem bolt. The palm outline should be where you'd like the palm to end up at.
• Drill out a hole in the strip the size of the stem bolt, at its location. Unscrew the stem bolt and the round stem holder, place the strip below the stem holder, push the bolt and stem holder through and screw the bolt over the strip again slowly, making sure the strip is about centered over the stem. As the bolt is tightened, it will make a clear round dent mark on the strip.
• Next, bend the strip upwards and then back to create a step, as shown in the picture at the bottom. Mine didn't come out that nicely because I didn't start out with this - found I needed this step later on. It's needed so that the palm connector will have some clearance above the bolt.
• Next, draw nice symmetric curves from the bolt plate to the edges of the strip.
• Mark where the strip goes over the handlebar screw, and bent the strip down 90 degrees towards the slot made by the two halves of the handlebar-stem holder.. Mark a notch around the bolt, and measure how high the handlebar holder is above the handlebar.
• Cut the strip length and cut the notch over the handlebar bolt. This is shown on the second picture below. Make the final cut of the strip along the marks, and file the edges smooth.
• Next, make the cutouts for the switches, and bend them down. Drill appropriate size holes for the switches and screw the switches in. The switch position I used is: top left for the etrex; bottom left for the palm; top right for the LED light. The bottom right cutout shown in the photos is a mistake.

.Picture 1

Picture 2

Picture 3

The next step is the wiring. Basically this is divided into two issues: palm-etrex wiring and the power distribution wiring. The wiring diagram below describes all that's needed.

• I used a piece of an old USB cable to do the wiring between the palm and the etrex. I cut the wire insulation in the middle and separated the power wires in order to route them through the switches.
• I used the metal aluminum base as the ground wire. This was handy for the headlight lamp, whose ground is the body and was connected to ground through the bike frame, via the same bolt that is used to tighten the front of the switch base.
• In assembling the palm connector, the pin numbering goes like this. Holding the connector so the two slots are on top, and the gold pins away from you (solder pins close to you), top left pin is number 1, 2 is under it. 16 is bottom right pin.
• etrex connector has VCC close to the cable.
• I used hot glue on the solders inside the palm connector to make sure nothing shorts while riding rough terrain.
• I've put plenty of insulation tape on the palm connector, to assist in holding the shell together. Also, I've taped a piece of rubber on its underside so to cushion it above the stem bolt.

Finally, I've sawn a piece of cloth and Velcro (again!) that goes from the bottom of the switch base, up through the palm cover loop and closes on the Velcro to hold the palm cover shut tight against the switch base.

Integration

In integrating all the elements, its important to keep the abovementioned principle in mind - build everything so it lasts the rough trails.

• I used audio mono-connectors for the wire from the battery pack to the switch base. I found they are hard to connect, but stay together a lot better than other connectors I've tried, e.g. USB.
• Use zip ties on the power wire and route it through frame members that stay together as the bike moves, not those separated by the rear shock.
• Before connecting the devices, check and double-check voltages and polarities at the connectors.
• The LED light is rated for 3.6v, but can easily take the 5.2v the C batteries supply. Same for the etrex, though I've read that the newer (revision3) etrex must take 3.3v. If that's the case for you, you'll need to route separate wire for it, feeding from the third battery. I've never tried that though.
• This system endured several very rough trails and has taken a couple of spills! One was a wheelie that I ended up on my back, with the bike on top of me (didn't disengage pedals quickly enough). The other was a jump that ended with a crash and the etrex side of the handlebar planted. The etrex took a hit on the connector but everything survived. Velcro works in outer space, and it works wonderfully on my bike - thank you NASA (and for the fleece warmers too, while I'm at it)
• Make everything easily detachable. It takes me now less than a minutes to assemble/disassemble the entire 'cockpit':
  • The etrex via its handlebar bracket - just unplug and release.
  • The palm via its case. Just release the plug and cover-holding Velcro and pull the case off the base.
  • The cell is simply stored in a pouch. It's not chargeable via the batteries because it uses a higher voltage and can retain charge much longer than the other devices. I'm thinking of changing that in the future.
  • The switch base usually stays on the bike, but can also be easily disconnected from the power cable. Then, a single screw needs to be unscrewed (the stem screw) and the handlebar screw needs to be released.
  • The headlight is mounted on an old light mount, so a single screw releases it as well
  • The battery pack can be disconnected from the power cable (audio mono connector) and after a bit of struggle with the Velcro, pulled out of the wedge pack