Daily Archives: August 26, 2012

Random thoughts on Wreck-Free Sunday

Well I don’t have anything coherent planned for today, just a few random thoughts.

Last night my church selected Hestia as our patroness for the coming church year. The problem is finding 6 virgins to tend the eternal flame out of a committee of 4 ritualists, with half of those being males and a different half being over 50 YO. That kinda makes us fresh out of virgins. On a related note we missed having Lakshmi as our patroness by a single point for the selection process. A few food items or a few votes would have swung the process either way.

Here in the Beautiful Suburbs of Hell the citizens are an important unpaid part of the PD and streets department. Both are reliant on citizen input to fix problems whether those problems are drivers that drive like they have the only vehicles on the roads or roads that are changing from paved to potholed gravel. I mentioned that I can do camera enforcement of road infractions if I buy the cameras and install them on the bike, well I also need to tell the Streets Department where the dangerous pavement is. Part of the problem is that what is most dangerous for a bicycle is a complete non-issue for a car, cracks and steps along the direction of travel. Those can trap a wheel and throw a bike (and rider) to the ground in a heartbeat.

Fun stuff I’m up to is I have a few parts that I’m using to improve the altermotor assist bike. Since I never mentioned this bike before, the short story is I’m converting a junkyard car alternator to a brushless motor that adds power to the drivetrain of the bike and has no additional drag when it isn’t assisting. The idea is to climb easier, or faster with the same amount of human power, so only about the same power as a human can produce is added to the mix. The original setup had a small sprocket attached directly to the converted alternator pulling the chain so that it saw the gears used on the back but not the front. There were 2 problems with this method. The first was that there was a limited range of RPM that could be used, and all of them were very low. This kept the motor below the speed where it developed the most power at the voltage used which caused a big current drain and also caused the cranks to spin too fast when the motor was activated in the middle and granny gears on the crank taking those gears away from use with assist. So, to get better power and use less electricity I needed to get the motor speed up above power peak at the voltage used and also do something so that I have granny gears even with assist, so that no matter how steep the climb I have the option of adding assist. The plan is to use the same sprocket on the motor driving a jack shaft with 3 output cogs and one input cog for human power and one for assist. This reduces the pedal speed to human levels and also gives granny and mid-range choices for both the rider and assist as both power sources have a single input that feeds through a choice of 3 outputs. I’m still building this so I’m not sure about the ratios yet for the motor side of the shaft. The human power side of the shaft uses a 48 tooth chainring to a 16 tooth cog on the shaft, with an 11 tooth small cog up to a 22 tooth big cog with a 16 tooth middle cog, converting that to what the equivalent crank would be is 33 granny, 48 mid, and 66 big going to a 20″ drive wheel. The equivalent for a full-size bike would be 25, 37, and 50. I still haven’t figured the power peak or the speed that happens at with the motor as I’m building a new controller that will run at full power. The old controller would only run at a maximum of 95% power because of using the power switching process to run a circuit that allowed the high-side FETs to be saturated when turned on. Also I was running the motor at such a low speed that the controller would lose commutation (knowing which phase of the motor to turn on). The new controller uses different high-side FETs that don’t require that circuit to function at full efficiency. This will allow the motor to be run at 100% without any worries about burning up the FETs in the controller. I think the free-spin RPM at the voltage this system runs at will be something between 800 and 1000 RPM. But I’m not sure because there are 2 parts to the equation, the power applied to the rotor which controls the magnetic field in the motor with a stronger field making a slower motor but more torque, and the Kv of the stator windings which I have no idea what it will be because that is a measured variable that I haven’t measured yet. Incidentally that power applied to the rotor is the main reason why this project exists, when there is no power applied to the rotor there is no drag from the motor, which means that a single control lets me select assist or no assist with no drag.

And that’s what has been banging around the inside of my skull this week.

PSA, Opus