From the AtomicZombie bike building forum:
"Well, another spell in the repair dock gave me more time to think about
possible add-ons (or more correctly build-ins) to the Timberwolf
languishing in what I laughingly call my workshop. I've been giving a
lot of thought to various possible additions to Brad's basic design,
including a geared mid-drive, but mostly about how best to incorporate
electric assist right from the get-go.
The logical first idea is to use an electric hub motor on the front.
This has the advantage of simplicity, but on the other hand, it puts the
motor at the part of the trike where ground contact weight is lightest.
I don't know how much of an issue this will be, but its fair to say
that the majority of the weight in any of the Deltas is carried at the
rear, and so traction at the front wheel is a question mark.
The second idea is to use one, or two, Currie-style external motors
either directly driving one or both rear wheels, or else connected into
the chain/derailleur drive train at some point between the pedals and the
rear axle.
However, the biggest single consideration is batteries. I have the wreck
of an e-scooter that will, I hope, become a tadpole recumbent trike at
some point; its all-up weight without passenger is over 200 lbs, and of
this probably 2/3 is lead-acid batteries. I just can't see building a
Timberwolf, which with rider will mass somewhere between 135 and 150
kg., and then adding a great whacking load of lead-acid batteries. Even
if the tires would stand up to the load, it would be a tremendously
heavy vehicle.
So, we then come to the lightest currently available battery technology,
the various lithium-based types. These have an astonishing
power-to-weight ratio, but they are new technology, and as such there's a
lot of mis-information floating around. There's also the question of
cost: what form of lithium cell offers the best "bang for the buck" in
terms of watt-hours stored vs. dollars (not forgetting overall weight).
It's a basic truism that for a given power rating, using a higher
voltage means a lower current draw. Since with most types of batteries
the rate of current draw or discharge is a big factor, using a higher
voltage would allow the use of cells with less amp draw capability.
The brick wall that I keep coming up to, and banging my head against is
this: What form of lithium pack is the lowest cost for a given current
draw, and what form of lithium battery is the most flexible in terms of
series-connecting the packs to achieve higher output voltages. I have
read various "opinions" and "reports" until I'm drowning in hyperbole,
and I'm no closer to the answer: what's the best available form or
configuration of lithium battery to start with.
For example, there are a wide variety of lithium cells used in RC model
aircraft, robots, etc. There are any number of different lithium cells
available for commercial-grade power tools. There are lithium batteries
available in various ratings for laptop computers - and the list goes
on. The common denominator is that they're all expensive, and so if one
is going to bit the bullet and invest in a lithium battery system as an
integral part of the build, it would make sense to try and maximize the
power storage capacity and ease of recharging for a given dollar
expenditure.
Once upon a time, I had a shingle that said I knew something about
electrical engineering, and I suppose I still do know some parts of it.
But I'm having tremendous difficulty in separating fact from hype in
discussions about lithium technologies, and even more difficulty in
finding out how best, and from whom, to source the batteries for the
least cost without buying junk.
I've considered other options, from lead-acid, NiMH, Nickel Cadmium,
etc. - and all are expensive if purchased new. So although lithium
technology is expensive, any discussion of cost vs. weight vs. energy
storage capacity has to take into account that, unless you stumble
across a free or very cheap source, the battery pack is going to be the
largest single expense in an electric drive system for a bigg-ish delta
trike. Even if motors are purchased new, controllors likewise, the
battery is going to be the big expense, according to all the research
I've done so far."
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