I still have a backlock of the past two years – but with this project I actually did quite a nice job documenting it.
Best of all it’s
and you can get all the CAD files on github.
Now to the build. Since I’m not big on baking cookies for Christmas – I invested my time in a project I was thinking about doing for some time: Building an electrified kickboard. This is the result:
The ingredients are:
from the shop:
- a cheap (used) kickboard from ebay : 37€
- better wheels (110mm, rubber instead of PU) : 33€
- 63mm 3kw outrunner + cheap „100A“ ESC : 100€ (+ 19€ customs)
- a cheap servo tester
- a horribly expensive push potentiometer : 20€
from the parts bin:
- some parts from maedler.de
- 12 and 40 teeth pulleys
- the appropriate toothed belt
- two used 3S 5Ah Li-Po batteries (from my 60km/h RC car)
- some wire
- a day of CAD work
- a day of milling aluminum (and some minutes on a lathe)
- a day putting it all together + some soldering
I took the easy way – just to get the thing functioning (let’s deal with a microcontroller + programming later – if I need to) – and just soldered an extension cord + push potentiometer to the servo tester.
Also I desoldered everything unneeded from the servotester – but the better/faster method would have been just to cut the unneeded parts with pliers.
Next I sat down at the computer and let my ideas form in CAD. (This is the 3rd iteration)
First milled parts taking shape (these are the right and left axle mounts)
There is a mechanism for tensioning the belt by sliding the motor mount.
It looks nice enough … doesn’t hold up to the torque though – and so I had to redesign it later.
The process of milling the back plate:
The program used (XpertMILL):
and the finished part next to the original one:
The „gas pedal“ fitted to the handle:
A video of the first motor test:
As a quick hack to get moving I made a big Y-cable to fit the batteries into the left and right trouser pocket with a really long cable down to the esc.
A test ride (video suffering from vvs)
She is having trouble keeping the front wheels on the ground during acceleration 😉
The process of building the new battery pack from used Makita battery packs with 18650 cells:
balancing the Frankenstein pack:
Lasercut insulator rings and leads soldered across the top (3p configuration)
Soldered into a 7s 3p pack:
Fitted to the kickboard:
For safety I should still put a 2mm aluminum sheet under the cells.
Some links and data:
Quite useful for calculating the drive train is http://smarthost.maedler.de/
The measured no load rpm of the motor is 1295 which according to 4.2V*6*170rpm/V *12 / 40 = 1285 rpm … sounds legit.
This yields in 1295U/min * 11cm * pi / 100 cm/m / 1000 m/km * 60 min/h = 26.85 km/h @ no-load … or estimated 26.85 km/h * 0.8 = 21.5 km/h – theoretical.
The top speed – measured – is 22km/h with 6S, or 26km/h with 7S.
Energy consumption is about 13Wh/km (gunning it).
The battery pack holds 3.7V*3*7*2.5Ah=194.25Wh nominal … but since these are used and abused cells from Makita power drills the actual value should be lower.
Theoretical range is therefore about 15km – the real range is yet to be tested.
Max load was 38A – that would be 1kw of power to the motor – with a 100kg person on it and I guess the limiting factor are the cells and worn down T5 belt that will be replaced with an AT5 belt and pulleys.