Building a Trainer

January 1, 2011. Even with several layers of clothes and warm gloves, riding at 18 mph at 40 degrees F is not too much fun. (I got a nice break today, New Year's Day, with a high of 57 F! I went for a nice ride.) To stay in shape, I decided to build a trainer for my old 10 speed. A trainer is a bike stand with a tensioning system to provide resistance. I looked at some examples on the internet, then went to my pile of scrap angle iron.

I lay some pieces of angle iron on the garage floor by the bike, tried to estimate what lengths I would need to provide a solid base. I cut and welded three pieces together:

I continued cutting and fitting pieces together. I rolled the bike into the frame as it grew, clamped pieces, marked the metal where I would need to weld it together. I used a long lag screw through the first axle hole to approximate the location of the second axle hole:

I test fitted the bike when I had the basic frame done:

Satisfied with the tight fit, I clamped, then welded cross pieces to improve rigidity:


It works. Now it needs some resistance because it is very easy to pedal with no load on the back wheel.

Digging through boxes of junk, I found the radiator fan from the old Honda Civic that I converted to electric. The heart of the electric fan is a DC motor. When you turn a DC motor, it behaves as a generator. I hooked a voltmeter up to it and gave it a spin. It generated some voltage, so I machined a plastic wheel from an old caster to become a drive wheel for the motor. I made a simple mount for it and clamped it to the bike frame:

I hooked the generator up to an old headlight bulb. Lighting the bright light puts a load on the generator, makes it hard to turn. This gives some resistance to the back wheel. Works!

January 8. I put a netbook computer and DVD player in front of the bike, with small external speakers. Clear picture, plenty of volume to overcome the whine of the little generator:

This setup is plugged in to an AC outlet right now. I need a power inverter to connect to the DC generator. Then I will be able to power my entertainment system with the bike generator.

January 13. I got an 80 watt power inverter from Harbor Freight to convert 12 volts DC from the generator to 110 volts AC, to power the netbook, speakers and DVD player. This picture shows some details:

These things sit in front of the bike on a little shelf:

Along with watching whatever I put in the DVD player, I have keep an eye on the voltmeter and the speedometer. If the voltage drops much below 12 volts, the DVD player shuts off. I have to pedal at about 20 mph to keep the voltage up high enough. The computer has an internal battery to keep it powered up if the voltage drops. I will look for a similar solution for the DVD player. Here is the whole setup:

January 20. I parked my electric car next to the bike and wired in the 12 volt auxilliary battery to the inverter and generator through a blocking diode. This gives me a more constant voltage to the inverter. I don't have to worry about the DVD player cutting off if I slow down a little. As I ride, I trickle-charge the car battery. This is something I have to do anyway to keep the auxilliary battery charged during the winter.

Frebruary 12, 2011. I found a bigger fan motor in an old van ready for the junk yard:

The motor is bigger than the Honda motor and it drove a bigger fan blade so it should put out more power. I cut it off the old housing and found a rubber wheel in my junk drawer that fits after adding a shim to the motor shaft. I made a bracket for it that bolts to the bike frame using the brake bolt and nut. I blew out the blocking diode testing it. It must put out more power! Instead of replacing the diode, I wired in an on-off switch (not shown). I extended the wires to the car battery. Now I can simply get on the bike, turn on the switch and ride:

To get more resistance, I added a 25 watt incandescent lamp. If I really want a tough workout, I can put a 40 or 60 watt bulb in the lamp. I also mounted a cheap voltmeter on the bike with a nylon zip tie.

This is a great trainer. It really wears me out.