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The BitESC is a small electronic speed controller for those little RC cars like the MicroSizer / BitChar-G. It can be used in a small RC plane to have some control over the speed of the motor. The speed of the motor ramps up or down, depending on which of the buttons on the transmitter you press. If no button is pressed, the ESC will ramp the throttle down to a stop after a few seconds. This safety net comes in handy when the plane flies out of transmitter reach.

"bitesc_164x132"

How to use

"bitesc_overview"

The BitESC weighs in at 0.3 grams, without leads, and has a size of 9 mm x 12 mm. It uses an IRLM 2502 to drive the motor and can pull 1.5 A continuous. The microprocessor used is an Atmel AVR 2343 which runs at 1Mhz.

To be able to use the BitESC, you'll first need to read about the different modifications required on either the transmitter and the reciever. You can read more about how to modify the receiver of a BitChar-G car at the following topics on rcgroups.com:

- Bitcharger conversion (ref#0)

- Bitcharger receiver mods (ref#1)

- Bitcharger TX mods (ref#2)

To get the best results, it is adviced to modify the receiver by adding a longer antenna. I use 1/8 of the wavelength, for 57MHz that gives an antenna length of approx. 63 cm. After extending the antenna, you should retune the receiver by adjusting the coil.

The best hack for the transmitter is to increase the power to the RF circuit and removing the cripple cap, if your TX has one.

This BitESC should cope easily with motor noise. I use a KP00 without a noise reduction capacitor on the Cootie and it works just fine. Although it is a very good idea to add a noise reduction cap to the motor.

The BitESC expects 5 leads to be soldered. The next schematic shows the wiring diagram. The negative of the motor is connected to the BitESC, the other lead goes to the plus lead of the battery (BAT+). The BitESC contains a small RC filter to filter out motor noise.

"How to solder the ESC"

Example

Here's a photo of my Cootie (Designed by Ralph Bradley (ref#3)), which I equipped with a BitChar-G receiver and my BitESC. The actuator is connected to the H-bridge on the receiver, which normally connects to the motor and provides forward and backwards motion. The BitESC is connected to the left and right channels. To be able to use the transmitter comfortably, you'll need to switch the controls.

"bitcootie"

Schematic

"BitESC schematic" {: dither="no" }

Making a BitESC yourself

If you want to make the BitESC yourself, the next information should get you going. Here's the link to the PCB layout. Assembly code can be found below in the article.

- PCB layout (ref#4)

Here's a printout of the assembly source.

:::ASM

; BitESC

; (c) 2004 Johan Van den Brande

.include "2343def.inc"

.equ TIMEBASE_TICK = 15000

.equ SAFETY = 25

.equ PWM_MAX = 63

.equ ESC_POS_MAX = 15

.equ esc_bit = 0

.equ down_bit = 3

.equ up_bit = 4

.equ PORTB_INIT = (1<<down_bit) | (1<<up_bit)

.equ DDRB_INIT = 1<<esc_bit

.def tmp = R16

.def esc_value = R17

.def esc_pos = R18

.def pwm_value = R19

.def safety = R20

.def timebase_l = R24

.def timebase_h = R25

.macro loadesc

ldi ZL,LOW(2*esc_values)

ldi ZH,HIGH(2*esc_values)

clr tmp

add ZL,esc_pos

add ZH,tmp

lpm

mov esc_value, R0

.endmacro

.cseg

.org $0000

rjmp main

main:

ldi tmp,LOW(RAMEND)

out SPL,tmp

ldi esc_pos, 0

ldi safety, SAFETY

ldi timebase_l, LOW(TIMEBASE_TICK)

ldi timebase_h, HIGH(TIMEBASE_TICK)

ldi tmp, PORTB_INIT

out PORTB, tmp

ldi tmp, DDRB_INIT

out DDRB, tmp

loadesc

loop:

; pwm

ldi tmp, PORTB_INIT | (1<<esc\_bit)

cp pwm_value, esc_value

brlt skip

cbr tmp, 1<<esc_bit

skip:

out PORTB, tmp

inc pwm_value

andi pwm_value, PWM_MAX

; check timebase

sbiw timebase_l, 1

brne loop

ldi timebase_l, LOW(TIMEBASE_TICK)

ldi timebase_h, HIGH(TIMEBASE_TICK)

; read input states

sbic PINB, down_bit

rjmp skip_down

; reset safety

ldi safety, SAFETY

; motor --

cpi esc_pos, 0

breq skip_down

dec esc_pos

skip_down:

sbic PINB, up_bit

rjmp skip_up

; reset safety

ldi safety, SAFETY

; motor ++

cpi esc_pos, ESC_POS_MAX

brge skip_up

inc esc_pos

skip_up:

cpi safety, 0

breq safety_powerdown

dec safety

rjmp safety_proceed

safety_powerdown:

cpi esc_pos, 0

breq safety_proceed

dec esc_pos

safety_proceed:

loadesc

rjmp loop

esc_values:

.db 0, 2

.db 4, 6

.db 8, 10

.db 13, 16

.db 19, 23

.db 27, 32

.db 38, 46

.db 57, 63

Table of refs:

Bitcharger conversion1

Bitcharger receiver mods1

Bitcharger TX mods1

Ralph Bradley1

PCB layout1

> ---

> (C) 2023 Johan Van den Brande, brewed by trash.make.site