Built by Wolves for Wolves


TaunTaun Arms and Tail


TaunTaun Tail

This tail required a lot of torque to move it, and I could not locate powerful enough servos for the tail. I recommended some motors and specs to Dan, and he had some actuators made. They are essentially the same design I use for the other animatronics tails, but much bigger. 

     

The actuators consists of surplus automotive windshield wiper motors, with machined aluminum pulleys. The windshield wiper motors are right angle worm gear driven. However you can back drive them, if you try really hard.

Potentiometers where later attached to the output shaft to allowing for a full PID (Proportional, Integral, Derivative) servo loop control.

 

The original tail was made of laser cut poplar, however after shipping it to my place, the tail suffered damage and it was determined that materials stronger then wood would be needed for the tail to be robust enough. It was later rebuilt using feather light cast plastic.

 

Above are two pics of the actuator module attached to the new tail spine, hanging in the closet in my apartment, which helps give a sense of scale.


TaunTaun Tail H-bridge

Two H-bridges where used to drive the motors. They where built using an off the shelf H-bridge chip from Motorola (MC33886). 

   

Both H-bridge chips and support components needed to run them.

 

Logic interface board, its just more parts needed to control the H-bridge chips. 5-volt regulator to supply logic power to the H-bridge, Filter caps, and a 74LS08 AND chip to allow the micro to place the PWM signal on either leg of the H-bridge. 

       

The H-bridge and logic interface board connected together and a cooling fan for the H-bridge, although it never got warm.

     

Testing the H-bridge and logic interface boards with some small motors. Note the halogen light on the 12-volt battery, in case anything shorted out, it would provides a current limit (only used during the testing phase, fuses where used in the final product).


TaunTaun Tail And Arm Controller

Tail and arms servo control board. This board runs the 6 hobby servos that move the arms.  It also runs the software servo loops that control the tail. It also communicates back to the master system controller via high speed SPI.

 

The Arm and Tail controller is based on an Atmel ATmega16 Microcontroller running at 16 Mhz. 

Each servo, except for the tail servos, are powered from a 6 volt regulator (the main system runs on 12 volts).  This was a cheaper option then trying to run all the servos off a 12 volt to 6 volt DC to DC converter. 

The regulators also provide each servo with short circuit and thermal protection. For example if someone comes up and hold one of the arms from moving. That servo will attempt to move, and then draw to much current causing the voltage regulator to shut down. This protects the servo from damage. Then when they let go, the arm will begin to move again.

Both of the tail servo loops are done inside the microcontroller.

Position feedback is from a potentiometer mounted on the output shaft actuator. The voltage from the potentiometer is then sent into the micro's analog to digital converter. The micro then does a full PID loop attempting to minimize the position error between the analog voltage and the desired set point. In the process it outputs a PWM signal to the H-bridge. This then moves the motor, which moves the potentiometer and completes the servo loop.

       

Finished arm and tail control module, note the position potentiometers, the other phone cable is the high speed SPI link.


TaunTaun Arms

The arms where made from laser cut popular.  

Standard metal gear hobby servos are used to provide actuation. They are located where the muscles in the arm would be.

Bicycle brake cable is used to mimic the tendons used to move the arm.

The springs are used to offset the weight of the arms, and make it easier for the servos.

     

       

Later the smaller servo used in the wrist was replaced with the same metal gear servos used for the rest of the, cause it broke.


TaunTaun Arm And Tail Systems Testing

System testing, arms and tail, in my basement (note, this project started in my apartment and then finished in my house. I am slowly converting the basement into my workshop).

           

This was a quick mock up using a sawhorse, and it looks kind of cool. 

It was done this way to be able to program the interactions between the arms and the tail, and so I could take video of the whole system working.

The scopes are used to debug communications and the motion sequence code. 

To make all the motion sequences for the tail and the arms, a special TaunTaun version of the RTMCS is running on the laptop.

At this point I had already delivered the head, so I had to trick the arm and tail controller into working, that is what the board on the bottom right is used for.


TaunTaun H-bridge Rebuild

The arm and tail controller was sent back to me a couple times because one of the H-bridge chips would fail (not both at the same time).

The Motorola MC33886 H-bridge chip would run the motor with no problems for several weeks.  Then it would stop working correctly, only allowing the motor to go in one direction, (one side of the H-bridge had failed). After replacing the chip that had a problem, it would work fine for another week and then die again. 

This chips data sheet states it to be "short circuit protected" "over current protected" "Over temperature protected" etc... but it still died. Thus, I would not recommend using the Motorola MC33886 chip for anything.

Because the Motorola part does not work correctly, I had to build my own H-bridge.  It used good old TIP 120, and TIP 125 Darlington transistors. The aluminum bus bar acts as a heat sink and provides a good connection point for the motor wires.

   

H-bridge connected to the Arm controller board.

     

Final, system testing, the motor controller, again. 

I wired up a gear head motor with a 10 turn pot to mimic the tail, so I could check that everything was still working.

When the arm and tail controller came back it was in this plastic enclosure, so I built it into the top of the box with a cooling fan. Since the Darlington transistors are not as good of conductors as MOSFETs they get a little warm and need a cooling fan.

The fan grill is made of paperclips.

     


Finished videos:

Note: The tapping sound in the video, is my digital camera's auto focus (one of these days I will buy a Digital Video Camera, they are getting cheaper).

P5240009.MOV Tail wag axis motion test, with sound.

P5240010.MOV Tail raise axis motion test, and I hold up the battery running the tail, with sound.

taunarm1.mpg Arm motion test with servo tester.

Note: The actions are a little jerky because the gains are set a little high, this was to compensate for dampening of the fur that would later cover the arms.

P7160090.MOV Full system motion test, standing random mode enabled.

P7160091.MOV Full system motion test, running random mode enabled.


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