Schlagwort-Archive: ev

K2 Kickboard ev mod – analog to pdm controller

After I avoided programming my own microcontroller to get the thing rolling in as little time as possible (sidetracking kills a lot of drive) – I finally decided it was time to take it on.

Actually the realisation that the cheap servo tester assumes the poti position when powering up as middle position convinced me that it was necessary to write my own speed controller – since I can’t (or at least not realiably/comfortably) use the braking functionality of the alien power sytem esc.

Also this way I can – or at least I can try to – write my own soft-start routine so people don’t fall off the back.

@phrewfuf encouraged me to program the arduino nano I tucked in a box some months back for when the time was right 😉
Since he didn’t send me the code I just set down myself today and took the first steps.

Also I had to wildlarize the freaking busted poti I pulled out of a part drawer. If you’re  not familiar with the term:

„widlarize“ (invented by Bob Widlar): You take the bad component to the anvil part of the vice and beat it with a hammer। It will make you feel so good, for no damaged parts will appear in your latest application।

It sucks so hard wasting time and money with  broken components that I consider not reusing old parts – or at least not the parts lying around shackspace 😉

Here is already another poti hooked up to an analogue pin linked to the pin the servo is connected to:

#include <Servo.h>

//onboard led
int ledPin = 13;

//servo pin
int escPin = 3;  // servo signal connected to digital pin 3
Servo escServo;

int potiPin = 7; // potentiometer wiper (middle terminal) connected to analog pin 3
int potiVal = 0;     // variable to store the value read from the poti

void setup()
  pinMode(ledPin, HIGH);
  //initial Servo Position

void loop()

  potiVal = analogRead(potiPin);    // read the input pin
  potiVal = map (potiVal, 0, 1023, 0, 180); //convert input range to servo range



Next up I need want to get interrupts working.

K2 Kick Pro Kickboard mod with 3kw outrunner

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:

from the parts bin:


  • 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:

shrink wrapped:

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

The data:

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.