Gerot

GeRot is a gecko-inspired wall-climbing robot with Dynamixel motors. This document will guide you to control the motors with API.

We provide C++ and Python API to the robot, you can check them in Here. We take the Python version as an example.

1. Environmental Configuration

Before you using this API, make sure you have installed Python2 or Python3 correctly. Then we have to deal with USB lantency timer. USB device always has a lantency before it sends the data, it will make your control task vert slow, so you probably need to reduce the lantency. In Fact, RS-485 with its USB device is not a good way to control a robot, EtherCat or CAN will be better.

• In Ubuntu, you should run the codes below in terminnal to reduce the USB latency:

  sudo usermod -aG dialout $USER && echo 1

  sudo tee /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

  On the other way, you may change it permenantly by doing this:

  sudo nano /etc/udev/rules.d/latency-usb.rules

  Add these codes:

  ACTION==”add”, SUBSYSTEM==”usb-serial”, DRIVER==”ftdi_sio”, ATTR{latency_timer}=”1”

  Save. Finally:

  sudo udevadm control –reload-rules

  sudo udevadm trigger –action=add

  You may check the result like:

  cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

• In windows, check this, you can find it in step 20.

2. Python Package Install

1. Go to https://github.com/ROBOTIS-GIT/DynamixelSDK, clone this repo.
2. Open the repo in your terminal, then

   cd python

   run

   python setup.py install

   NOTICE: If you have installed anaconda in Ubuntu and you want to use the API with it. You have to specify the “python” above, because if you use “sudo”, you will use the originnal python in your system. Maybe you can do it like

   ~/Anaconda3/bin/python3 setup.py install

3. Go to this repo,

   cd dynamixel-egg

   then,

   python setup.py install

   now you have installed the driver package, you may connect your motor to your pc.

4. Check AMC_oneleg_newapi.py, you can specify the parameters in

   motor0 = DxlAPI(range(3), ‘/dev/ttyUSB0’)

   The first parameter is to set the motor’s ID, it should like [0,1,2]. The second one is to set the port(in Ubuntu is like ‘/dev/ttyUSB0’, in Windows is like ‘COM1’), the third one is to set baurdrate. Make sure you have make these parameters right.

3. How to Use

In the example, we test 3 motors in position control mode.

Here are the things need to be done:

1. import the package we need, like

from dynamixel.mt_dxl import DxlAPI

1. init, like

motor_group = DxlAPI(range(3), '/dev/ttyUSB0')

1. set the operating mode, like

motor_group.set_operating_mode('p')

if you want to use torque control mode, input ‘t’ instead of ‘p’.

1. turn on the motor, like

motor_group.torque_enable()

1. drive the motor with your code, like

motor_group.set_position([0, 0, 0])

each element in [0, 0, 0] is a angle in (-pi, pi).

If you want to set the torque, use motor_group.set_torque() instead, this function has to be used in torque control mode.

If everything is good, the motor moves.

1. shutdown the motor, like

motor_group.torque_disable()
motor_group.portHandler.closePort()

You can check more examples in YOUR_DIR/vary_exp/gecko_amc.py and YOUR_DIR/vary_exp/gecko_pc.py