Rotacasters: Big, Bigger, Biggest!    Send article as PDF   
Yes it ‘s another Holonomic Platform Robot, but this ones special. I built this Mindstorms Robot to celebrate a package that arrived in the post today from Rotacaster Australia. Yes, more omni-wheels to’ Beta Test’. But these are monsters compared to the original 48mm (2″) Rotacaters.

125mm Rotacaster Holonomic Platform

These new [rotacater] measure 125mm (5″) in diameter, and weigh in at 272g (0.6lb) compared with the small ones that only weighed 37g. Both sizes us a standard LEGO Technic Axel whole. These rotacaster’s provide unlimited maneuverability and bring a whole new dimension of possibilities to the design and functionality of large wheeled [mindstorms] Robots.

125mm Rotacaster Holonomic Platform

125mm Rotacaster Holonomic Platform

Due to the size of this Holonomic Platform Robot, I decided to make the instructions in two separate parts. The first part is the BASE (Large Holonomic Platform Base) which has three identical WHEEL HOUSINGS (LargeHolonomicPlatform-WheelHousing.lxf) attached to it. The BASE also houses the LEGO Mindstorms NXT Brick, and three Ultrasonic (Sonar) Sensors attached for Navigation.

Holonomic Platform Wheel Housing

The whole robot is built around a central trunk (left). This arrangement, produces 3x arms separated at 120º, from which the whole robot evolves from. Attached to each arm part, are the arm assembly branches with a Ultrasonic (Sonar) Sensor attached (Bottom Left). From the “ORANGE AXLES” (Part #55013 Technic, Axle 8 with Stop), the Wheel Housings are attached.

Holonomic Platform Base Sonar Attachment

The Wheel Housing (Left) is the final component for the Robot. The Wheel Housing also includes the NXT Motor Mounting as well. The NXT Motor is quite capable of directly driving the new 125mm (5″) Rotacaters. But beware as your robot will really spring with the large Rotacaters attached. For indoor use, it may be worth your while to gear the motor drive train down. Alternatively, reduce the maximum power output to the NXT Motors to around 75%. With a couple of modifications to the Wheel Housing (Bottom Right) you can use the standard 48mm (2″) [rotacater]’s on this robot.

Holonomic Platform Base Sonar Attachment Top

Holonomic Platforms a great fun to build and use, but this Robot takes you to the next level. These new 125mm (5″) diameter Rotacaters will allow you to leave the safety of the lounge-room floor, and head off-road. With a bit of ingenuity, a Compass or GPS Sensor the great out doors can become the domain of this Holonomic Platform type Robot.

Holonomic Platform Base

As mentioned above, these new 125mm Omni-wheels from [rotacaster] will allow you to construct robots that break away from the confines of indoor surfaces. Like the smaller 48mm [rotacasters], the quality is excellent. With a dynamic load capacity of 115kgs and a lateral load of 68Kgs, your LEGO Parts will fail before the wheels will. Due to the roller size, these [rotacaster] a quite noisy compared with the smaller wheels when traveling on hard surfaces.



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