Koala 2.5 User Manual Rev 1.1
25
4.10
Motors
The Koala 2.5 has got 2 DC motors in order to drive its six wheels.
The motors have 6W nominal power. The gearbox has a reduction
ratio of 58.5:1.
Figure 4.11 : Motor block with wheels
The encoder has a 100-pulse by turn resolution. With the reduction
ratio of 58.5:1 and an internal hardware 4x multiplier, we have
23’400 pulses by wheel turn. As the diameter of the wheel with the
tire is 82.5mm (no load), this gives 90.3 pulses by millimeter. Or 1
pulse is 0.01107mm (11.076um).
Reminder: 1 revolution = 259.18mm = 23’400 pulses.
1m = 90’284 pulses
Be careful, when placing a payload on the Koala the tires will crush
and the diameter will be slightly modified. For example, with a
payload of 3kg, the effective diameter falls to 80.5mm, changing the
speed and position calculation.
The best solution when placing a payload on the koala is to perform a
travel of 1m (command “F,90284,90284”) and measure the real
distance crossed by the Robot.
Both motors are controlled via Pulse Width Modulation (PWM) at
20kHz. This technique switches the motor on and off at a given
frequency and during a given time. By this way, the motor reacts to
the average of the power supply, which can be modified by changing
the period the motor is switched on. This means that only the ratio
between on and off periods is modified, as illustrated in the figure
below:
Summary of Contents for Koala 2.5
Page 1: ...KOALA 2 5 User manual Revision 1 2...
Page 49: ...Koala 2 5 User Manual Rev 1 1 46 7 Mechanical drawings Unit is mm Figure 6 1 Top view...
Page 50: ...Koala 2 5 User Manual Rev 1 1 47 Figure 6 2 Right view Figure 6 3 Front view...
Page 53: ...K Team S A Z I Les Plans Praz 28 1337 Vallorbe Switzerland...
