I always liked Dickels MD#3, but I don't have the time to craft it out of styrene, so it's mostly printed and uses left over parts from other robots. The base was an idea to make a small omni directional drive with small servos for steering and encoders and cheap motors for the drive. There wasn't enough space in that design. Now its the right size base for the MD#3 body I replaced the stepper motors with mini servos that reduced complexity. I had some 3.2-volt lithium batteries from another project I run the motors on a 6.4 volts battery pack and the Arduino on the 9.6-volt battery pack to reduce noise
Bentley has 3 Arduinos
a mega in the base to control the steering servos and drive motors
a nano in the chest for the servos
and another nano in the head for radio coms to the joystick
I use I2C for comms between the arduinos.
update 7/7/18
There have been a few changes since the last update.
The radio control has been removed due to it being unreliable.
The Omni base was changed to a differential control.
A Raspberry Pi running ROS is used for control.
The Omni base had one really major problem the motor gearing was too high the
RPM should be around 50 RPM these were 200RPM. with tight wheel angle,
the motors would stall due to lack of torque increasing the power resulted in a
jerk and rapid movement. The cheap motors were structurally week and
flexed this was a bonus as it acted like a suspension. When we swapped
the Omni base for a differential drive with wheel encoders,
the movement problems come down to tuning. The cheap servos I had laying around
are very noisy and tend to jitter they will need to be replaced with better one's
if this project continues
Update 12 May 18
During the last week, Bentley took his first steps. The drive system is not omnidirectional yet I just set power and steering direction, so he drives like a car this puts the wheel under strain in turns. The servos in the head moved too fast they had to be slowed down which give a more natural look. I'm still waiting on some parts that are on the slow boat from China one of which is a new battery for the MCU the old AA's don't last long and cause system instability when the voltage drops the first sign is the comms between the arduinos slow down.
drive around
- Actuators / output devices: 4 x SG90 Servos
- Control method: via joystick
- Power source: Battery
- Target environment: indoors
This is a companion discussion topic for the original entry at https://community.robotshop.com/robots/show/bentley