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29-09-2009 15:50



 Two wheeler


  Motor control


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Robots - Two wheeler - Rebuilding the base.
With the robot showing at least some will to cooperate it was time to rebuild the base of it so that incremental encoders could be fitted to the wheels. This will let me measure the actual speed of the wheels.
A new baseplate was designed and cut out of 3mm aluminum plate. Except for the holes around the perimeter used for stacking the various levels quite a few  mounting holes where cut in it so that circuitboards, sensors and what not could be mounted to it.
Here's a couple of photos showing the manufacturing of the base plate.
The first photo shows the raw aluminum plate mounted on the machine table. The second one shows all the holes drilled, on the third all milling operation have been done and the last one shows the finished plate cut out.

The next three photos shows the other three parts needed (two each). The first one shows the inner support bracket where the encoder will be mounted. The second one shows the outer support bracket and the third one shows the motor mount.
This shot shows the finished parts. You can see the wheels retrofitted with pulleys for standard T2.5 belts, inner and outer support bracket with it's bearings, the wheel axles and incremental encoders.

With all the parts ready it was time to put them together.
Here's two photos showing the parts for the motors. The first one shows the motors, mounting brackets and pulleys. The second one shows the two motors with pulleys mounted.
In the following three shots you can see how the wheels are mounted to the base. The black thing on the inner support bracket is the encoder mounting plate, the actual encoder is snapped on to this plate and the encoder disc is then fixed to the shaft with a small set screw. There is a square hole in the base plate right next to the inner support bracket that's supposed to line up with the connector on the encoder so that the cable from it can be routed thru the base plate.

The first of these two photos shows the base with the wheels and motors mounted. The second one has the encoders and IMU mounted. The IMU consists of two boards, the lower one  (closest to the base) houses the accelerometer and gyro and the upper board is the amplifier board. This board is needed since the impendance at the output of the sensor are a little high seen from the PIC's A/D. By placing the IMU in between the wheel like this it is very close to the robots center of rotation.
The motor driver IC's where moved from the solder less breadboard to a some what more permanent veroboard mounted on top of the base deck. This board is now replaced by an etched PCB containing its own PIC microcontoller.

Copyright 2006 Henrik Olsson. All Rights Reserved.
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