Hybrid Robot (Robocon 2016)

The Hybrid Robot was a part of the Robocon 2016 problem statement which was required to perform various tasks such as pole climbing, driving ecorobot using a propeller, propeller picking and placing, line and wall following.

  1. Two wheel drive robot (Maxon motors for driving).
  2. Carries a slider arm (removable) on both sides having wind propeller as an end effector.
  3. Pole climbing mechanism: It should grip a pole using a three wheel pole climbing assembly. And by driving the wheels using Maxon motors, the bot should climb the pole.
  4. Carries replaceable propeller picking and placing arm.
  1. The important constraint for the design of hybrid bot was its dimensions. Under all circumstances, it had to fit in 1m cube.
  2. Weight constraint was: Weight of Hybrid bot + Ecobot < 40 kg
  3. Hybrid bot has an arm extending in horizontal direction of length about 40cm. Hence there was very less place for the chassis to fit in the dimension constraints.

Designing Softwares: Solidworks, Inventor 2016, Autocad 2016

Materials Used: Basic chassis structure was built using Aluminium boxes (square extrusions). Other materials are listed below:

  • Nylon – At specific places in the assembly.
  • Carbon fiber propeller as a wind blower.
  • Mild steel – for wheel shaft
  • Aluminium I - section extrusions, sheets
  • Slider extrusions

Manufacturing Processes Used

  • Lathe
  • Waterjet cutting
  • Laserjet cutting
  • Holes on the boxes were done with a great accuracy using vertical drill having coordinate display.
  • Welding (TIG – for aluminium parts)
  • Joining assembly of the Al boxes was mainly done by aluminum connecting plates (called Chepi)

Specifications

  1. Weight ~ 13kg
  2. Ground clearance = 10.5mm (14mm with grip)
  3. Height ~ 35cm
  4. All aluminium boxes were joined by TIG welding.

Problems with the design

  1. Bending strength of the upper part of the chassis was less compared to lower one. When it gripped the pole, pneumatic pistons used to give outward force due to which chassis expanded. This caused deformation in chassis.
  2. Middle pneumatic piston position was higher than those of side pistons. Thus there was an anticlockwise torque given by the pole to the chassis (seeing from side view shown in the above picture). Most of the weight was on backside, which added the torque in anticlockwise direction. Hence the chassis tilted in the vertical plane while pole climbing and could not climb properly.
  3. Height of chassis was small. Thus during start of climbing the wheels encountered the bolts at the base of the pole, due to which sudden disturbance occurred in pole climbing motion.
  4. Welding caused lots of deviation (~5mm error) from the actual design dimensions.
  5. Truss structure which joined the upper chassis with lower chassis was poor which caused deformations
Figure 1: 3-D, top and side views of the hybrid robot

Major specifications

  1. Weight (including all components) = 24 kg
  2. Height (excluding slider arm) = 35 cm
  3. Ground Clearance = 14mm

Manufacturing of chassis

This chassis was composed of aluminium boxes (18.5mm square cross section). However, unlike previous chassis it was not welded rather it’s every box was joined using aluminium sheets (Chepi). According to the joint each chepi was designed and cut using Waterjet. Holes in the corresponding boxes were done by setting the relative coordinates in the vertical drilling machine.

Various chepi designs are as follows:

Figure 2: Chepi for standard joints
Figure 3: Chepi for T-joints
Figure 4: 3D joint using chepi
Figure 5: Some special joints

Sub assemblies

Lower chassis and driving assembly

Maxon motors were used for driving the Hybrid robot. Plastic wheels of diameter 115mm were used along with bat grip over them for proper traction


The mount used for the wheel is shown in the figure on the right. The front support of maxon motor was made by bending aluminium sheet, while back support was made of nylon. Mild steel shaft (dia. = 6mm) was used. Bearing casing was made of nylon with outer covering of Al sheet.


Figure 6: Design of motor mount

Figure 7: At front side Omni wheels were used rather than conventional caster wheel. The assembly gave better performance and was stronger than caster wheels.

Pneumatic assembly

Figure 8: Three similar assemblies were used in the pole gripping mechanism. An aluminium wheel was coupled with Maxon motor. Grip was surrounded over the wheel to get better traction.
Figure 9: The assembly has another support made of 2 aluminium I-sections and 1 box also called as Triple Decker
Figure 10: Pneumatic assembly on hybrid robot

Lower pneumatic assembly

Small pneumatic pistons were mounted at base of the chassis having nylon rollers. Purpose of this assembly was to stabilize the bot during pole climbing. This pneumatics were actuated after the bolts on the pole are crossed by the bot during climbing to avoid the interference.

Figure 11: Lower pneumatic assembly

Slider arm

Slider arm has a carbon fibre propeller as an end effector to give wind power to the Eco Robot. It is mainly made of aluminium extrusion on which the wheels slide with the nylon assembly.

Figure 12: Mount for slider assembly
  1. Stronger support structure minimised the deformation of bot to a great extent.
  2. The middle pneumatic assembly was at lower position w.r.t. the side assemblies which almost vanished the effect of tilting during pole climbing.
  3. The problem of interference with the bolts on the pole was solved by increasing height of pole climbing mechanism and hence increasing the height of robot.
  4. The manufactured product was accurate as per design since the chassis was assembled using Chepis rather than welding.
  5. Enough space was now available for other components inside the chassis.
  1. Due to joining components such as chepis, nut-bolts, etc. the weight of hybrid robot increased drastically which brought load on pole climbing motors during climbing.
  2. The support of pneumatic assembly i.e., the triple decker was not a perfect sliding support. The assembly was able to move slightly about the axis of piston, due to which the Al wheels rotated in a tilted axes. This caused rotation of the bot about the pole during pole climbing.

Mechanical Team Robocon 2016 IIT Kanpur

  • Y13: Siddharth Tanwar, Abhinav Ranjan
  • Y14: Saurabh Dharme, Sarthak Mahapatro, Labhansh Agrawal, Animesh Shastry
  • Y15: Apurv Anand, Raman Pratap Singh, Abhishek Sahoo, Aalap Shah, Anubhav Mittal, Nishkarsh Agarwal

The content on this page has been taken from the report by Saurabh Dharme (sdharme) which is available here: documentation_hybrid_bot_2016.pdf