minnemike said:
With this frame and old American style BB I'm going to need an adapter to make it fit a middrive. And it'll have to be eccentric offset if I want a design that sits too close to the BB like a bbs02.
They do make adapters. There's a thread here somewhere on BB standards, from a few years back, that lists some of them.
Of those, I guess my only worry is overkill if I'm targeting 750-1000w cruiser with at least enough to get up and over some hills with a 3 speed.
If you want to know if it will make the hills, you will need to determine the amount of torque needed to climb the worst case hill in question with the total weight in question.
Then see if the system you want to use can produce that amount of torque with the gearing you want to use, while still maintaining the minimum speed you need up the hill.
Then see if the IGH itself can handle the amount of torque the motor will be putting out with the gearing you'll use to it's input, so you don't shear it's protection pin or whatever weak point is designed into it to prevent destruction.
A total amount of power *can* translate into whatever torque you want..but it may not be able to do the speed you need at the same time, with available gearing options.
I'm not afraid to spend a grand if I can get exactly what I need.
Whether that will be enough depends on your needs. Sometimes that's just the *battery* cost.
Have you defined your necessary range, at a certain speed? And defined the hill slope and length? Those will help determine the wh/mile you will probably use, and then the range gives the total wh needed for battery pack capacity. Then the max amount of power helps determine the amount of power the battery must be able to output, and thus it's construction or size.
Knowing those lets you figure out how much it might cost for just the battery, which is the heart of the system. That means it must provide all the power you use, and so must be good quality and of *at least* enough capacity to achieve your goals.
If you think you might ever have detours, or windy days, you should account for this by adding some amount (say, 20%) to the battery capacity.
Since capacity *and* performance drops with age, you may also wish to add some amount (say, another 20%) to the battery capacity to account for aging, so that it still will do what you need as it gets older.
Another consideration is that a fair number of people discover that the power they thought they would need isn't enough, either to do what they wanted, or just isn't enough fun after awhile.
So getting a battery with significantly more performance capability than you actually need is a good idea, if you think this applies to you.
