Monday, October 20, 2008

Converting Schwinn Meridian to multi-speed

I've done a trial version of converting my wife's Schwinn Meridian trike to multi-speed, using leftover parts. I've got more leftover bike parts than most--For normal people a donor bike would be the easiest way to get the needed parts. I'm planning to look for one to solve some of the problems I've found

The donor I'm looking for is a department-store 21 speed with a 3 piece crank. Ideally it would have a frame-mounted derailleur and a chain guard, but that's not critical. Better mountain bikes will have a cassette, which won't work in this application. I've seen bikes that would work for around $20. All we need are the drive train parts--if the rest of the bike is trashed, it won't affect the build. Since it is hard to fit a bike in a Cavalier, I'm taking a tubing cutter so I can chop the frame in pieces to get it home.

Like many trikes, the Meridian uses an intermediate gear system. The main chain goes between the crankset to an intermediate hub. The intermediate hub has a freewheel, a brake and a fixed sprocket. A chain runs from the fixed sprocket to another fixed sprocket on the rear axle.

The conversion is relatively straightforward. I removed the old freewheel on the intermediate hub and replaced it with a 5 speed freewheel. I also installed a low-end Shimano derailleur, the type that is held on by the back wheel.

The first step is to disassemble the trike and remove the old freewheel. This is a fairly standard BMX unit, however they neglected to add the notches usually used by a removal tool. This makes non-destructive removal difficult. I opted for destructive removal. (Even with the slots I may have gone with destructive removal rather than either buying the tool or paying to have the old freewheel removed)

The two holes are meant for a pin spanner. I don't have the right size so I used a pair of needle nose pliers with the tips ground to fit. Threads are opposite, so clockwise unscrews. On other freewheels, I've used a punch and hammer.

If you might re-use this, put something under the hub to catch the thousands of little ball bearings that will fall out. (I suspect once you see how many there are, you'll give up on putting it back together...)

Once you unscrew the ring, you will be able to lift the sprocket off the body. The aforementioned thousands of balls will fall out. This exposes the part of the body that unscrews from the hub. I used a vise, locking pliers would probably work. This is standard threads, removes by turning counterclockwise.

Ideally, I should have used a longer axle in the intermediate hub--The derailleur side needed some extra space to fit. I was able to shift it enough so there is just (barely) enough axle on each side. I'd probably want more thread engagement on a bicycle, but this doesn't hold the wheel on so stress should be less.

I need to do something here--I need just a little more space than I have, and I am at the limit of the original axle. If the donor bike's axle is longer I will use it, otherwise I will fabricate a different derailleur mount that doesn't rely on the axle nuts.

To shift the axle--Remove the nut holding the band brake in place--That will let you remove the brake itself, giving access to the cones. You will need a cone wrench (Harbor Freight's bike tool kit is a really good value, and includes the specialized bike tools needed for most bike repair) Loosen both cones from their jam nuts, move the axle over, shortening the part that sticks out on the brake side. Re-adjust the cones and tighten. (Hint: Get the adjustment close, but a bit loose and tighten both cones. Use 2 big wrenches on the jam nuts and tighten until you've removed the play)

You will need some washers or spacers to add some space to the freewheel side, so the nut is past the freewheel. You also need some washers to go between the main frame and the rear axle carrier to get a bit more space. Since the main frame is aluminum, you need to be careful not to spread it too far--Aluminum is not as forgiving as steel to being spread.

I need about 5 mm more space...I gained about 3mm. This is just enough to let the freewheel fit when the intermediate hub was positioned right, but not enough to let the chain ride on the smallest cog without rubbing and probably jamming up on the frame. Not a major problem in this application--The goal was better hill climbing, not speed, and the 4 remaining gears give one gear higher and two gears lower than the original--the ones that would be most used. I adjusted the travel screws to lock out the smallest cog. I can get the space in the frame, but unless I either get a different axle or a better way to hold the derailleur, I don't have enough space in the hub.

The next problem was the derailleur. The standard mount for this cheap type uses a special D-shaped nut that sits in the axle slot to keep the derailleur aligned. Since I had virtually no extra space, this nut was enough to rub on the freewheel. Instead, I moved the derailleur and hub back a bit, and drilled and tapped a hole in the bike frame to replace the D nut.

5 speed index shifters are rare, but 6 speed use the same spacing and will work with most Shimano 5 speed freewheels. The spare shifters I have were 7 speed. Luckily, they have a friction mode, letting them be used with the 5 speed spacing. The final version will most likely use 7 speed spacing, so I'll leave them for now.

Future plans are to change the spacing of the freewheel. If I use 5 gears with the spacing of a 7 speed cluster, I'll save another 2mm or so, which should be just enough to use all 5. There are a few different possibilities--The most likely is to salvage cogs and spacers from a 7 speed and mount them to the 5 speed body. I could also shave the existing spacers down.

Another reason to get a donor bike is the chain and front chainrings--Single speed bikes almost all use a wider chain, with wider sprockets. These will not work with derailleur parts.

I took the largest chainring of the replacement off in hopes of making it work with the old chain guard. Unfortunately the guard bracket rubbed the inner chainring, so I still had to remove the guard. I will try to find a donor bike with the proper chainrings and a guard. (I passed one by at the thrift store that would have been perfect, days before I started this project) Trikes aren't likely to go as fast as bikes, so higher gears aren't really needed--The middle and small rings from a mountain bike set are plenty--In fact, for this use, I am only using the smallest chainring, since there is no easy way to mount a front derailleur.

If you have any questions, feel free to ask--I'd like to know where I'm not clear, so I can improve these directions.

Wednesday, October 15, 2008


I'm dealing with a poorly written web application--Basically a big and moderately complex form to fill out. However it has unique features that make it extraordinarily difficult to use

  1. If you hit the backspace or Enter key, and your cursor is not in a text field you will lose all your work.
  2. Most fields will initially allow any value-however the form will not allow you to save if the values are not acceptable. It won't complain about them until you try to save, then it will inform you that you cannot save until you correct a single error--If you have two errors, it will only tell about one at a time, giving that many more chances to hit backspace at the wrong time
  3. Soeme date fields are directly editable, others require you to click on a calendar. The ones requiring the calendar will let you put the cursor in their field, but if you backspace, will delete all your work.
  4. You can make a copy of an existing similar form rather than starting fresh. Not everything will be copied--Many of the fields that would be useful to have a copy of are not, and many of the fields that will always need to be edited or changed are copied.
There are other peculiarities, but these are the most bothersome. I'm constantly amazed at the lack of usability that is considered acceptable in software.

Wednesday, October 08, 2008

Testing the user

I took a co-worker shooting this weekend. She has two guns, but had never shot either of them. She wound up bringing only one, an Arminius .38 revolver--She didn't know how to unload the other.

The Arminius is a K-Mart special sort of gun, almost literally--under another name, it was sold at K-Mart back in the day. This one wasn't obviously horrible, but it also wasn't as well-finished as a Smith or Ruger. Rather than the traditional cylinder release, you pulled the ejector, the grips are plastic, and the trigger pull is a good bit harder than I am used to.

The experience shows how important it is to test fire any gun you may be relying on for self-defense--She has arthritis, and was unable to pull the trigger double-action with one finger, and unable to cock the hammer. She had no problem with any of my guns, including my double-action-only J frame revolver. Usually I'd say a revolver is an excellent choice for a non-gun person. Not in this case, with this combination of person and gun. The only way she was able to fire it was to use the index finger of her support hand to help, and it took her several seconds to shoot.

Her other gun is some sort of mousegun-She thinks it is a Browning .25, but is unsure. I'm going to recommend that she sell them off and buy something she can shoot, in a 9mm or larger caliber.

Saturday, October 04, 2008

The Bonyard

The Google Maps view of Davis Monthan AFB is fascinating:

View Larger Map

Davis Monthan is home to the 309th Aerospace Maintenance and Regeneration Group, basically the boneyard for obsolete US aircraft. Around 4400 old military planes are parked in the desert. The low humidity helps preserve the aircraft, and the hard soil means that it isn't necessary to pave their parking areas. Google lets you zoom in enough to identify individual aircraft, and in some cases see how they have been stripped for parts. I'm not an aircraft expert, but I'm pretty sure some of the ones I can ID are from the 1950's.

Wednesday, October 01, 2008

Adapting Adapters

To re-use an AC adapter for a different gadget, you need to know the voltage, amperage and polarity of both the device and the adapter. I don't throw adapters out even if their gadget is broken--I can often re-purpose the adapter to work with a new gadget.

Adapters and most appliances that use them will have something like this:

We are concerned with Output and the funny symbol that is (on this one) in the bottom right corner.

The input doesn't really matter as long as it was designed for the US (or whatever voltage you have where you are). Output is what we are concerned with.

Voltage should match as closely as possible. Undervoltage is unlikely to harm a DC gadget, (especially one that is meant to run on batteries) although it might not work. 2 or so volts over probably won't hurt most gadgets either, but there is no guarantee. This adapter is marked 13.8v, came with computer speakers asking for 12 volts, and I used it successfully on wireless speakers asking for 15.

98% of gadgets with adapters are DC, but there are a few AC.

If no voltage is listed, but the appliance takes batteries, count 1.5 volts per battery.

Amperage (Amps, A, mA)is in some ways more flexible--the adapter should have more amp capacity than the appliance--Less is no problem at all. This is an unusually large adapter, with an unusually high rating of 1.7 amps. Most adapters are rated in mA, somewhere between 100 and 800.--1,000 mA is equal to 1 amp, so this is equal to 1700 mA. It is adequate to power anything taking this voltage with 1700mA or less current--The appliance will only take what it needs. If the gadget needs more than the adapter can supply, it will likely either burn the adapter out, or blow a difficult to replace fuse inside the adapter, without harming the appliance.

Polarity is the final concern. The symbol in the lower right corner shows the polarity at the plug--There is a negative sign attached to the C portion of the symbol, and a + attached to the center dot. This means that the center conductor or tip is the positive conductor, the outside or back is negative. AC output won't have a polarity.

If the plug fits,voltage is close enough, polarity matches, and amps is more on the plug than gadget, you are good.

Plugs are fairly easy to change--I've had cases where I had an adapter that was electrically right but had the wrong plug, and another adapter with the right plug. Swapping the two gives an adapter that works for the application. The hard part is figuring out the polarity of the plug. Any Radio Shack has multimeters, Harbor Freight has them for a few dollars--That makes verifying polarity (and actual voltage) simple.

Without a multimeter, you'll need to get creative. My experience has been that the marked wire is positive, but I won't guarantee that's always the case. (with zip cord, one wire is marked with a stripe, ridges or lettering, where the other is unmarked) That should let you deduce the proper connection. Most plugs are center positive, and most stuff under about 6 volts won't be damaged by a brief reverse polarity, but don't count on that for anything precious. If you are doing a laptop power supply, get a multimeter to be sure. If you have a Harbor Freight nearby, they have multimeters under $5.

A final method is to wrap wires to the battery clips. Most gadgets will have two obviously separate clips, and usually one or more clips that you can see are connected together. The pointed end of the battery is positive, the negative end is flat. You can usually strip a couple of inches of wire and twist it around the single clips and get your gadget running. If the clips aren't accessible, use old batteries with their ends taped to hold the wire in place.