After completing the CAT excavator rc conversion two years ago, I was busy pursuing my other hobby, cycling of which I completed three overseas bike tours in less than 20 months. While planning another bike tour in January 2015 and it is too hot and humid cycling in the summer, I decided to find something to do indoor. After watching the video by SmallHaul about his RC conversion of a Bruder CAT delta loader, I decided to do the same by myself.
The conversion should be simpler than the excavator conversion as it only involves three movements, i.e. travel, arm lift and bucket curl. However, the challenge is how to put all components into a confined space.
I ordered the model from Amazon at US$22.00 + shipping. It took almost two weeks to deliver, as I was using the cheapest freight, I had no complaint.
Bruder is using interlocks to assembly all their construction toys, without using a single bolt or nut. It took me over an hour to figure out how and then strip down the loader into components.
SmallHaul was using Tamiya twin motors to drive the loader, I used micro geared motors instead. These micro geared motors are versatile and come with different Voltage (3 – 12V), RPM (78 – 3000 @ 12V), torques and shafts. They are small with only 25x12x10mm (LxWxH) and perfect for this project. This type of motors will cost you US$20 each at any U.S. online robot shop, I purchased them in Taobao at only US$3 – 5 each. The quality was not so consistent so I purchased one more sets for spare.
The tracks are driven by the elevated wheels. I used RC car wheel connectors to connect the motors and wheels. The material at the wheel hub was removed to house the connectors. They were secured on the wheels with glue and a M4 screw. It costs me only US$0.5 each instead of expensive prop connector that other people are using. To avoid the slippage, small rods (2mm dia.) were inserted beneath the wheel surface which acting as teeth to engage the wheels and belts. A bracket was made to house the motors and then bolted on the inner sidewall of the loader body.
By considering the weight to be lifted including the bucket, I had considered using high torque servo motor to lift the arm. However, the servo motor was too bulky and left no room to install other components, I decided to use the same micro geared motor set-up I used for the excavator conversion. A bracket was made to hold the geared motor at the base of the loader, of which the motor drives a M4 shaft to push the cylinder rod connecting to the lift arm. According to my experience with the excavator conversion, I would need a 1,000 rpm motor to achieve a 10 mm/s linear speed of the push rod.
The
Bucket Curl
I had also considered using servo motor to
curl the bucket. However, it was either
too bulky or too fast. I need a motor to
turn at 30 – 40 rpm or approx. 0.5 revolutions per second. I used the slowest micro geared motor I can
get i.e. 60 rpm @ 12V, bolted to the bucket coupler. A pivot arm was attached to the motor driving
shaft and bolted to the lift arm. The
motor was hidden inside an aluminum tube and wire in the lift arm for better
outlook.
The RC System
I used the VEX system to control the movements. It comes with a transmitter, receiver, signal splitter, antenna and battery box. I also ordered four controllers to drive the motors. I also installed a circuit to have a power switch, fuse and power supply to the front lights of the cab. It took long time to figure out how to put all these parts and components into the tight space.
Most of the RC components were installed in
the base of the loader, including the receiver and signal splitter. As the orginal battery box is too big, I
replaced it with a cassette. All other
components such as the motor controllers were squeezed into the tight space at
the back of the loader.
Conclusion
The conversion looked simplier than the excavator, however it was more difficult in term of space, components selection and the execution of the plan. For example, the space at the back of the loader was just enough to house the motors, battery cassette and motor controllers. As most of the conversion were using servo motors, I did not have any reference and tried a number of the micro geared motors for the travel and arm lift. Eventhough, I was still unable to find suitable motors and required higher speed motors to achieve the desired travel and arm lifting speeds. So, there will be continuous improvement in this conversion.
For SBrick conversion, please click this link:
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