You are doing the conversion at your own risk. I am not responsible for any damages to the SBrick, motors, etc.
The original RC conversion was done a couple years ago with VEX remote control. After knowing the SBrick, a blue tooth device to control Lego motors via your smart phone, I think why not to use it in the Bruder CAT delta loader.
The SBrick was ordered from the official website and costed around US$60. Some Lego connecting cables were also ordered for the connection.
A Lego connecting cable has 4 wires, the outer two are for power supply and the inner two are for motor control.
Do not connect the outer wire to the inner wire and connect to a power supply, you might burn the SBrick.
Installing the SBrick on the base of the model. As the thickness of a SBrick is bigger than a RC receiver, you might have to figure out how to get enough space.
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.
The Model
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.
The Travel System
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.
The Arm Lift 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.
After completing the conversion, I enjoyed playing with it all the time and shared with others as well. However, due to very rough machining or fabrication, some of the components did not perform what they normally do. I have made some improvements as follows:
1.The Antenna
The original antenna is a wire connected to the receiver box and a plastic tube is provided to support it. It was very difficult to store it when unused. I replaced it with a retractable antenna which can be conveniently pulled out and retracted.
2.The Fuse
The Vexplorer transmitter and receiver kit used to control the machine worked very well until some time ago I smell something coming from the receiver box. I didn’t know what happened and opened it. Two tiny parts were burnt out and therefore two channels were not functioning. I believe that it was caused by the surge current of stall motors. As there is no way to order the receiver box alone, I have to order the whole kit which is a waste of money.
To avoid the new receiver burnt out again, I installed a fuse in the power supply circuit which was next to the battery box for easy replacement. The size of the fuse is 1A as it should be well enough for 3 motors running at the same time.
3. The Head Lamps
Two LED lights are installed at the roof of the cab to stimulate the real machine.
4. The Cylinders
The cylinders converted from the original plastic components were not strong enough. To save the issue, I fabricated the cylinder body from aluminum tubes. The section housing the micro motor and gear box is a 16 x 14 mm; remaining cylinder is 14 x 8mm. The cylinder rod is 8mm x 6mm of which the screwed shaft is turning inside. A small flat bearing is put in the driving shaft to provide a smooth turning. Two grub screws, one in each side of the cylinder are used to stop the turning of the motor inside the cylinder.
It took me a few days of spare time for making one cylinder. If it runs smoothly, I will modify the remaining boom, stick and bucket cylinders.
It took me almost 5 months of spare time to complete the conversion; most of the times were spent to search the internet for different solutions, ordering the parts and waiting for the shipment. I reckoned that I have spent only 1/3 of the time actually doing the conversion.
After completing the conversion, I feel satisfactory and lost. The conversion was followed in what I planned and designed. There were some hiccups including the lost shipment of the mini slip ring and wrong order of some components. I feel lost because I need to find another project to do, in addition to cycling.
The Model US$52.00
The Travel System US$72.00
The Slewing Turntable US$46.00
The Cylinders US$85.70
The RC System US$54.98
Total Costs US$310.68 + shipping
As I could not find any suppliers of above materials and parts in my country, I had to order all of them in the net, primarily from on-line shops in US (Robot Market Place). The shipping cost is expensive and I reckon it was about 30 – 40% of the costs, approximately US$100. In addition, I needed to order some materials or components as a pack even-though I used only a few pieces of them.
I made an estimate that I have spent almost US$500 on this project. I might save some shipping cost if I ordered the parts and materials one order. To order most of the above-listed parts and materials, I would recommend Robot Market Place (http://www.robotmarketplace.com). They provided very good service and prompt delivery.
I later found out that there are similar micro geared motors and mini slip rings available in China at a fraction of the cost. I presume that they are coming from the same manufacturer. I am seraching in the internet for more supplies and believe that I can reduce the total costs by as much as 25 - 50%.
I admit that I am not a RC enthusiast and know nothing about radio control system. I only understand that I require a 6-channel RC system to control the travelling, slewing and cylinders movement. There are large number RC systems available in the market but mainly for remote control of airplane or speed boat models. The 5th and 6th channels normally are switches.
After searching the market, I finally decided to purchase the VEXplorer Transmitter + Receiver Kit. It is a less expensive and simple RC system. It consists of a transmitter with 2 joysticks for 4 channels of control and 2 on-off push-button controls, one receiver for 6-channels with 2 auxiliary powers, and a battery holder.
It is a plug-n-play kit and there is no calibration or adjustment required. You simply insert the VEX 2-pins plugs into the slots of the receiver and change the polarity of the power by flipping over the plug.
Step 1
Connect the motors with 2-pins wires, secure the receiver on the floor inside the excavator model, and inserts the plugs in the slots. Change the polarity of the wires by flipping the plugs if required.
Step 2
As you would not want to dismantle the body of the excavator model every-time you change the batteries, cut out the space under the engine hoop and put the battery holder inside and connect it with the receiver.
Step 3
Stick the control pattern diagram on the transmitter for guidance of controlling the excavator model.
Now you have a complete RC system to control an excavator model. Two sets of on-off push buttons on the top of the transmitter for controlling the forward and backward travel of the two crawlers. Two joy-stick control levers for 4-channels of control. Left joy-stick left-n-right for slewing, and up-n-down for stick in and out. Right joy-stick left-n-right for bucket in and out, up-n-down for boom lower-n-raise.
There are basically two types of cylinder, hydraulic or electric. With hydraulic, you would require a motor driven hydraulic pump and distribution valve set to provide and control oil flow. It is more complicated, expensive and suitable for metal models. You would not able to make them for yourself without a CNC machining lathe but can be purchased from suppliers such as Manolo Gomez.
On the other hand, the electric type is easier to handle and you can make them for yourself using hand tools. One example is to use the hand drill bit driven by a motor with the nut fixed inside the tube. When the shaft is turning, the tube will slide in and out of the cylinder simulating the linear action. You can also purchase them from supplier such as CTI-Modellbau.
After considering different options, I decided to go for electric type and make by myself using the original plastic cylinders as the body. From the information of various conversion projects or part suppliers, I understand that the linear speed and stroke of the cylinders as below:
Liner speed: 10mm/s
Stroke: 40mm for bucket, 80mm for stick and 70mm for boom
A M4 threaded shaft is used as the driving shaft which is turning in a M4 stand-off to cause the cylinder rod moving in a linear direction. Every turn of the shaft will cause the stand-off to move 0.7mm. Therefore, you would need a motor of 900rpm to achieve a 10mm/s speed.
Step 1:
The geared motor has a 10 x 12mm cross-section area. You would need to round off the edge enabling the motor to be fixed inside the original cylinder body of 10mm diameter.
Step 2
Cut the threaded shaft to appropriate length and connected to the motor via a light hub. The light hub is made of plastic material with copper collar for set-screw. The tube of the light hub is accommodated for M3 but there is no problem to screw the M4 shaft into it, providing enough strength to hold the shaft. The shaft end is fixed with a screw nut as stopper.
Step 3
The M4 stand-off is fixed to the tube of the rod, you would need to grind-off a little bit of the edges. Then put the cylinder body and rod together. Fix the motor with plastic straps into position.
Step 4
Connect the motor with power to see if the rod slides in and out of the cylinder smoothly.
I admit that this is not a good looking option for such modification. However, if you do not want to spend money on expensive electric linear cylinders, it is the easier and economical way to achieve with only hand tools.
The slewing turntable allows the upper structure to rotate freely. In a real machine, you would have a large ring slewing gear with roller bearings, rotated by a hydraulic slewing motor and distributor to provide hydraulic oil to drive the travel motors.
In most of the conversion projects, metal ring bearing is used to provide a smooth rotation. Whereas, a large ring gear is bolted on the frame and driven by a motor with a pinion gear. The rotation speed is determined by the rotation speed of the motor and gear ration between the ring and pinion gears. In a real machine, the slewing speed is approx. 10rpm. With a gear ration of 10 times, you would require a motor with speed of 100rpm.
In scale models, some ready-to-play RC models only allowed rotating of 360 or 720 degree. The reason is the wires providing electric power to the travel motors will twist and strangle together after turning a few times. To solve this issue, you can use a mini slip ring which is generally used in the security CCTV to provide continuous power supply. It comes with 6-12-24 wires with 2A rated current. You can easily purchase it in the eBay but it is normally for wholesales as the shipping charge is not worthwhile to purchase only one unit. In addition, you can purchase through a number of suppliers such as Robotshop and Adafruit at US$17.5 + shipping.
It later turned out to be missing during the shipment and another one was ordered causing delay of the project for 2 weeks.
For the slewing gear and bearing, after searching the internet for suitable components and ways of modification, I decided to purchase a VEX turntable bearing kit with motor. VEX (Vexrobotics) is famous for supplying robot components for leisure, education and competition. Their products are pricey but well accepted by the robotic fields.
The turntable and motor are ordered through Robot Market Place together with other components. The turntable is prices at US$19.99 + shipping and the motor at US$12.99 + shipping. The pack comes with two turntables, one 4.25” dia. and one 2.6” dia. The larger one has provision to install the motor so that we do not need to worry about the alignment of the motor and the gear.
The larger turntable proves to be too large and the smaller one is a good fit. The turntable, driving motor and gear are fitted on a single PCB to provide the necessary alignment and rigidity. It was then connected to power and found out to be running smoothly. According to the gear ratio, the maximum slewing is to be 20rpm.
Parts used are:
1 x VEX turntable (60T) US$8.00 (used only the smaller one)
