A bicycle roller is a type of rolling road for bikes. The bike is placed on a frame that holds cylindrical rollers that are connected with a sturdy elastic band that ensures they all roll together. Riding the bike with it placed on the rollers provides an experience similar to riding on a road while static in a single location.
It is trivial to obtain the 'speed' of a bike on this setup.
It would be very useful to measure power generated by the rider and be able to relate this to speed.
Bicycle crank power meters can be bought for several hundred pounds that use strain guages to provide the data.
Specially calibrated rollers can also be bought which provide a graph of power to speed.
My rollers are more basic and I do not own a bicycle power meter and I enjoy a project from time to time.
I want to create a power to speed graph for my rollers but using basic equipment.
I think I could use an adapted cordless electric drill if I make a variable voltage power supply.
My thoughts are that I should measure torque by setting different voltages and also record the current.
I should then be able to use the drill to drive the rollers and (by controlling voltage &measuring the current used by the drill) calculate the power required to drive the rollers at a range of speeds by referring back to my earlier torque calculations for those voltage current values.
From there I should be able to transmit power data using a method similar to this project.
Is there anything here that I am obviously howlingly wrong about?
It seems like a lot of opportunity for calibration errors at every stage of the process. I'd aim at measuring the torque directly with bearings on the roller mounts, a lever arm, and a cheap load cell and amp. This would bypass the drill current and voltage calibrations, speed calibration curves, torque measurement calibration, and the maybe the bike-roller calibration.
I would think you could use a permanent magnet DC motor in the 6 to 12 volt and 100 to 200 Watt range with proper belts and pulleys, but what would you do with the generated current? Waste it in a big resistor?
I would beg, borrow, steal, or rent a bicycle with a power meter (hub or crank) and calibrate the speed to power on your rollers.
Do your rollers have an added resistance unit. If not, the power spinning on rollers is not very great, and may not be worth worrying about. If there is a resistance unit, then measuring the rpm of that unit and the torque required to drive it can get you to power.
Use a car alternator , the load on the alternator will represent the power being transmitted by the rider .
With some maths the losses should be calculated from the run down rate of the bike or power required to keep the pedals turning at the same rate without the cyclist .
you have a cool project in mind to measure your power output on your bike rollers! Your plan to use a modified drill and basic measurements seems clever and creative.
Be accurate ,consistent and careful