SUPERB DESIGN - In the main you can't beat nature. Sclerotin is a component of insect exoskeletons, the structural material of their body. It is formed by cross-linking protein molecules, a biochemical process called sclerotization. Technically it amounts to a form of tanning. The resulting material adds physical stiffness to the toughness of an insect's chitinous (cellulose like) body parts. It is particularly prominent in the thicker, armoured parts of insect and arachnid integument, such as in the biting mouthparts and sclerites of scorpions and beetles. Combined with calcium carbonate, as in the shells of crustaceans and molluscs, chitin produces a stronger composite that is harder and stiffer than pure chitin and is tougher and less brittle than pure calcium carbonate. These bio-materials are the building blocks of life.

CHRISTMAS ROBOT ANT PROJECT - RUNNING SMOOTHLY

The suspension system of the Christmas Robot consists of three part legs with: traction pads (rubber & spikes), springs, shock absorbers and linkages - that connects the chassis of this robot (a vehicle) to its feet and allows greater tolerance to surface irregularities between the feet and the ground on which the robot stands.

Suspension systems serve a dual purpose - contributing to the vehicle's terrain handling capability, including acceleration, cornering and braking. The aim is to keep the vehicle and any cargo safe, by reasonably isolating the motors and control electronics from bumps and vibrations.

These goals are generally at odds, so the tuning of any suspension involves finding the right compromise. It is important for the suspension to keep the feet in contact with the land surface as much as possible during a walking (or running) cycle, because all the ground forces acting on the vehicle do so through the contact patches of the feet. When speaking of suspension, we normally think of a car - and for this article there will be many analogous examples.

Suspension systems can be broadly classified into two subgroups: 

1. Dependent, and 

2. Independent.

These terms generally refer to the ability of the opposite end of an axle to move independently of each other, but in robots there may be no suspension system at all between four or more wheels. Our suspension system is fully independent.

Suspension attachments must match the frame design in geometry, strength and rigidity. In this case the rotational frequency is 900rpm, or 15 cycles per second. Both sprung and unsprung mass is therefore critical as is the attachment points.

We will now take a look at all the components of the suspension of this giant animatronic ant - and decide what components to use as we consider the technology that gives us movement over land.


SPRING RATE

The spring rate (or suspension rate) is a component in setting the robot's ground clearance (ride height) or its location in the suspension stroke. When a spring is compressed or stretched, the force it exerts is proportional to its change in length. The spring rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used in performance applications where loading conditions are more extreme.

Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the robot from the ground. Cars that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate close to the upper limit for that vehicle's weight. This allows the vehicle to perform properly under a heavy load when control is limited by the inertia of the load. For example, riding in an empty truck used for carrying heavy loads can be uncomfortable for passengers because of its high spring rate relative to the weight of the vehicle.

SPRINGS - Here we see a tension coil spring and a compression coil spring.

LEAF SPRINGS

A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. A leaf spring takes the form of a slender arc-shaped length of spring steel of rectangular cross-section. A leaf spring can either be attached directly to the chassis of a car at both ends or attached directly at one end. In our case the spring attaches to the upper leg. How much of the leg is spring and what it will be made of is what comes next.

BIOLOGICAL INTERFACE - These are cheetah blades, in effect, high performance leaf springs. They worked so well that paralympian Oscar Pistorius got into a dispute with the IAAF. The London (August) 2012 Paralympics we're focusing on the most talked-about equipment used at the games - carbon-fibre prosthetic blades inspired by the hind legs of a cheetah.

Developed by Icelandic company Össur, the blades caused controversy a week earlier when "blade runner" Oscar Pistorius (above) was beaten in the T44 200m by Alan Oliveira. Pistorius later claimed the Brazilian had started using longer blades, giving him an unfair advantage.

The blades were again in the spotlight, when Jonnie Peacock, the British single amputee, beat both Pistorius and Oliveira in the T44 100m final with a time of 10.90 seconds.

NIKE - South African double-amputee sprinter Pistorius previously used regular track spikes with his blades and had to glue or tape the plates on in a process that took a couple of hours before each race and meant they were never quite the same twice. 

For the London 2012 Paralympics, Oscar Pistorius used the Nike Spike Pad as worn by "Blade Runner".

The Nike Spike Pad is designed to adhere directly to the Össur Flex-Foot Cheetah blades, using just contact cement to reduce weight while maintaining strength and stability. It also takes only 30 minutes to attach both of them now.

Nike innovation director Tobie Hatfield developed the design over the course of several months by reviewing high-speed video of Oscar running on a treadmill to identify the impact point of his blades during each stride and get the spike receptacles in exactly the right positions for traction and consistent performance.

The spike plate is made of carbon fibre with a thermoplastic polyurethane coating, while the midsole pad comprises two pieces of foam with two different densities: softer at the back to cushion landing and harder at the front for take-off.

Pistorius' participation in able-bodied international sprinting competitions in 2007 raised questions about his use of running blades, and the IAAF amended their rules to ban the use of "any technical device that incorporates springs, wheels or any other element that provides a user with an advantage over another athlete not using such a device." After initial studies, Pistorius was ruled ineligible for competitions under these IAAF rules. After further research was presented, the Court of Arbitration (CAS) ruled that his running prostheses were not shown to provide a net competitive advantage over biological legs. In 2012 Pistorius qualified for and competed in both the 2012 Olympic Games and the 2012 Paralympic Games using his running blades, becoming the first amputee sprinter to run in the Olympic Games.

COIL SPRINGS

A coil spring, also known as a helical spring, is a mechanical device, which is used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material (spring steel) formed into the shape of a helix which returns to its natural length when unloaded.

A torsion or compression spring is where the material of the spring acts in torsion when the spring is compressed or extended. The quality of spring is judged from the energy it can absorb.

WEIGHT TRANSFER

Unsprung weight transfer is calculated based on the weight of the robot's components that are not supported by springs. This includes foot pads, lower legs, dampers and other components.

Sprung weight transfer is the weight transferred by only the weight of the robot resting on the springs, not the total vehicle weight.

SPRING TRAVEL

Travel is the measure of distance from the bottom of the suspension stroke (such as when the robot is supported from underneath on a show stand and the legs hang freely) to the top of the suspension stroke (such as when the robot's upper leg can no longer travel in an upward direction toward the body).

Bottoming or lifting a leg can cause serious control problems or directly cause damage. "Bottoming" can be caused by the suspension and leg, etc. running out of space to move or the underside of the body or other components of the robot hitting the ground.

BUMP STOP

The "bump-stop", which protects the suspension and robot (as well as the onboard components) from violent "bottoming" of the suspension, caused when an obstruction (or hard landing) causes the suspension to run out of upward travel without fully absorbing the energy of the stroke.

Without bump-stops, a fast robot that "bottoms out" will experience a very hard shock when the suspension contacts the bottom of the frame or body, which is transferred to the workings and every connector and weld on the steel frame. In the case of cars, factory vehicles often come with plain rubber "nubs" to absorb the worst of the forces, and insulate the shock. When a desert race vehicle, that routinely absorbs far higher impact forces, may be provided with pneumatic or hydro-pneumatic bump-stops. We'll be using simple rubber blocks during development.

DAMPING

Damping is the control of motion or oscillation, as seen with the use of hydraulic gates and valves in a vehicle's shock absorber. This may also vary, intentionally or unintentionally. Like spring rate, the optimal damping for comfort may be less than for control.

Damping controls the travel speed and resistance of the vehicle's suspension. For example, an un-damped car will oscillate up and down. With proper damping levels, the car will settle back to a normal running state almost immediately. Most damping in modern vehicles can be controlled by increasing or decreasing the resistance to fluid flow in a shock absorber. We don't have much room to play with conventional shock absorbers if we are to remain anatomically accurate.

BIOLOGICAL INTERFACE - In this spectacular photograph of Amy Purdy by Paolo Kudacki, we see the snowboarding paralympic medalist and her prosthetic lower legs and feet. Here is a fine example of bio-engineering where suspension is put to good use to give Amy a chance to show her skills on the slopes. Metal is allied to bone to achieve this performance.

A cheetah's frame is also bone based. The flexibility and speed of the cheetah is astonishing, given that their frame or skeleton is made from calcium. Bone is one of the strongest materials found in nature. Ounce for ounce bone is stronger than steel - a bar of steel of comparable size would weigh four to five times as much but is only twice as strong. In tensile strength bone is rather like cast iron, although around 1/3 of the weight, in bending stress it behaves like steel. But it is the design of a bone that is important for strength. For example, many bird bones are hollow, with struts or trusses (cross walls) that crisscross for structural strength.

FLEXIBILITY

Flexibility, for example, in modern cars comes mainly from rubber bushings. These are subject to decay over time. For high-stress suspensions, such as off-road vehicles, polyurethane bushings are available. They offer more longevity under greater stresses at the expense of limiting flexibility.

Due to weight and cost considerations, structures are not made more rigid than necessary. Some vehicles exhibit detrimental vibrations involving the flexing of structural parts, such as when accelerating while turning sharply. Flexibility of structures such as frames and suspension links can also contribute to springing, especially to damping out high frequency vibrations.

For most purposes, the weight of the suspension components is unimportant, but at high frequencies, caused by ground surface roughness, the parts isolated by rubber bushings can act as a multistage filter to suppress noise and vibration better than can be done with only the foot pads and springs.

The head and tail of the ant may contribute to overall flexibility, as may rubber mounted motors and transmission - though that is not a priority for the development prototype.

LEG MASS v COST - Aluminium legs in 28.5mm tubing is likely to be around £35 + delivery, whereas, titanium in 25 and 19mm tubing will run to £138 + delivery. The price for carbon fibre will be significantly higher because of the moulds, but we need leg patterns anyway for film special effects. Please note that this photograph is copyright © Jameson Hunter Ltd 2015. You will need permission from Jameson Hunter to be able to reproduce it. 

GEOMETRY - Careful design of the leg is important if we are to avoid another actuator for the lower leg. We are thinking about a two-stage spring loaded system at the moment - with shock absorption. Amputee athletes use a similar system for high speed track events. Please note that this photograph and the subject drawing are copyright © Jameson Hunter Ltd 2015. You will need permission from Jameson Hunter to be able to reproduce it. 

AXLE MOCK UP - December 27th - More progress. Working in steel is time consuming when prototyping demands constant fine adjustments. Once the angles are all worked out it is not so bad - working them out means many cups of tea and coffee - to gather ones thoughts. Please note that this frame is Design Copyright and that this photograph is Copyright © Jameson Hunter Ltd 20 December 2015. All rights reserved. You will need permission from Jameson Hunter to be able to reproduce it. 

This website is Copyright © 2023. The design of the Robot Ant on this page is design copyright © December 15 2015, all rights reserved - Jameson Hunter Ltd. IMPORTANT NOTE:  Under no circumstances may our products, or those of Jameson Hunter Ltd, be used by any military or law enforcement organization, for any warlike, combat, or peacekeeping crowd control purposes. Anyone purchasing one of these units will be required to sign a binding undertaking (Deed) to that effect. Any unit found to have been purchased by proxy, will be confiscated, along with civil remedy in respect of breach of contract, that all parties in the chain will be vicariously liable for - to include damages for vehicles developed from our designs without our consent - and possible fraud issue from the deception. In addition to copyright theft, the law of passing-off applies.