For ease
of use, TreppenSchlepper shall require no installations or any other
modification in staircases whatsoever. It shall
manage and steer itself, and that means it needs some fully autonomous control
(which we shall discuss in one of the following blogs). For now,
let's focus on the energy supply only. With no wires attached we need
sufficient battery power, and a way to charge it easily. Would a Li-Ion battery pack like the one used in my Laptop do the job?  |
| laptop Li-ion battery |
According to the manufacturers spec's, such battery packs store some 50 .. 90
Wh of energy with typically 11 V rated voltage; one can buy it at Amazon or other places for somewhere between 40
and 150 USD. I'd guess these batteries are pretty robust now, with life
expectances of more than 3 years under heavy use, being quite sturdy against normal accelerations/bumps and temperatures and due to the large (Laptop) market quite
mature and cost efficient already.
The battery on this picture (right) includes 9 cells, has 87 Wh of energy, and has a size of approx. 28 x 8 x 4 cm and weights about 200g (model number 451-11695)
Let's
estimate the energy needed by TreppenSchlepper during a
day, assuming overnight re-charge.
|
physical
variable
|
estimation
|
Reasoning
|
|
Total
mass
|
70 kg
|
50 kg
payload + 20 kg System =70 kg
|
|
Number
of floors to climb
|
5
|
first
guess
|
|
Resulting
height to climb
|
15 m
|
assuming
3m/floor
|
|
Mechanical
efficiency
|
25%
|
wild
guess
|
|
Required
energy per climb
|
33Wh
|
E = m *
g * h * eta
= 70kg
* 9.81 m/s2 * 15m /0.25 = 41202 Ws =>
11,4 Wh
|
For going downstairs we would theoretically have a chance for recuperation, but certainly not with the current design. So let's just assume it requires downstairs 25% of the energy we put into it going upstairs.
This sums
up to 11.4 Wh * 1.25 = about 14 Wh for a complete up & down cycle.
With 50
to 90 Wh at disposal, it should be safe to say that is enough for 3 to 5 times going up and
down per day (or before we require re-charging of the battery).
Is that a reasonable estimation ? Let me know via comments in this blog, or directly via treppenschlepper@gmail.com
So there is sufficient energy stored in reasonably-sized batteries, but power might be a problem... Those laptop batteries are designed to deliver power over e.g. 6 hours. If we assume that TreppenSchlepper uses 5 seconds per step (which is quite slow), and have a step height of let's say 18cm, it would take 417 seconds to climb these 15m from the energy estimation, and that's without additional manoeuvring at the stair landings in between. Going 5 times up and down takes 4170 seconds, which is about 1 hour and 10 seconds. Thus, batteries will have to deliver their energy in 1/6 of the usual time , requiring 6 x peak power. Not sure if standard laptop battery packs would like that...
ReplyDelete4170 seconds is about 1 hour 10 minutes... sorry for the typo
ReplyDelete