CONTENTS

  home page
  design
  specifications
  transmission
  power
  weapons
  mistakes
  the team
  combat history
  help us
  future projects  
  gallery
  contact us
  postscript
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Overall

Specification -

• Hull mass 19k
• Length 750 mm
• Width 750 mm
• Hull depth 200 mm
• Hull material 6mm aluminium chequerplate welded inside and out

Weights - Totalling approx. 95 kg

Hull	19 kg		Wheels	8 kg
Left Motor	8.5 kg		Axles	6 kg
Right Motor	8.5 kg		Chain	6 kg
Lift Motor	7 kg		Misc	2 kg
6 Batteries	16 kg		Bearings	2 kg
Controllers	1 kg		Weapon	10 kg

Drive Motors

Manufacturer : NECO
Frames : PM714C
Body Diameter : 122mm
Body Length : 268mm
Armature Resistance : 0.11 ohms (cold) 8.7 ohms (Hot)
Armature Inductance : 3.2 milli Henries
Max short-circuit current : 250 Amps
Max current before motor is demagnetised : 160 Amps
Max power delivery per motor for 20 seconds : 2kW
Max instantaneous power delivery per motor for 1 second : 6kw
Battery Current drawn to climb 1:1 hill : 40 Amps
Controlled RMS voltage needed for motors to climb 1:1 hill : 5v



Radio Frequencies Available

Most competitions require robots to operate on the 40MHz frequency. In Britain, boats, land machines and aircraft may use these frequencies. In this country the available frequencies and channels are -

Frequency	Channel No		Frequency	Channel No
40.665	Channel 50		40.815	Channel 81
40.675	Channel 51		40.825	Channel 82
40.685	Channel 52		40.835	Channel 83
40.695	Channel 53		40.845
40.705			40.855
40.715	Channel 54		40.865	Channel 84
40.725	Channel 55		40.875	Channel 85
40.735	Channel 56		40.885	Channel 86
40.745			40.895
40.755	Channel 57		40.905
40.765			40.915	Channel 87
40.775	Channel 58		40.925	Channel 88
40.785	Channel 59		40.935	Channel 89
40.795			40.945
40.805			40.955

Channels 60 to 80 belong to the 35MHz band (Model Aeroplanes only)


Transmitter

We are presently using a modified Futaba Field Force 6 system. This set is designed for aircraft use but was supplied with a 40 MHz module. As standard, engine speed does not centre. For controling the speed of the robot we now use the left joystick fitted with a self-centring device but no friction mechanism. This means that the driver can release the sticks and the robot comes to rest.

The transmitter has both pulse coded and pulse positioning modulation selectable from the liquid crystal display. Individual models can be stored in the transmitters memory. This is useful to us since we have several models (ships, planes and cars) to control and this makes setting up easier. We nearly lost a radio controlled buggy on an aerodrome when it went out of range. At the time we were using Pulse Positioning Modulation and the buggy continued with the last known command. Clearly this could be dangerous with a 100kg robot. Pulse Coded Modulation is easily set up to immobilise the model (or send it in a circle) if the signal is lost.

Our Vantec speed controller will default to 'no power to the motors' when there is no signal. This will happen if we were using a PM receiver and the signal was lost. When a PCM receiver is used, then defaults must be set up. This is because the robot will continue with the last known signal should contact be lost. The defaults if programed into the transmitter are passed to the receiver every minute and tell the receiver what to do if the signal is lost. Should the signal fail then after 300 milliseconds, the receiver will carry out the default instructions and bring the robot to a halt.

The reason for our concern at the loss of signal is simple - the aerial might get bent or snapped off during the event! These precautions will ensure the robot comes safely to rest, without injuring bystanders or damaging itself further, until the aerial can be repaired.

Materials

Materials required for robot construction should be strong enough to survive a number of bouts, light enough to carry, easily machined and welded for construction and, above all, affordable. Aluminium chequer-plate was used for the hull of Joker

Material Strength can be expressed as...

Elasticity	The sample springs back to the original shape
Ductility	The sample does not break easily when stretched though it deforms
Resilience	Elastic but little energy is lost when it springs back
Shear Strength	a measure of strength when layers of the material slide over each other
Tensile Strength	a measure of strength when the sample is pulled
Compressive Strength	a measure of strength when the sample is pushed
Wear resistance	the quality of a surface not to wear away

If a sample is stretched, the force on the sample increases (the strain) and the sample elongates (becomes stressed). Up to a point most materials initially show a linear relationship between stress and strain (Hooker's Law) and, up to that point, releasing the force results in the sample regaining its original dimensions. The molecules of the sample do not change the chemical bonds between adjacent molecules.

When the forces are high, the bonds break and reform, the sample behaves as a plastic and the sample will suffer a permanent change of shape. The sample may then become weaker because the new bonds will be fewer and the sample becomes thinner where a neck forms.

In some materials however, the sample may become stronger. This is usually because the shape of the molecules alters so that stronger bonds can form, the metal becomes crystalline or the molecules themselves line up like fibres in a rope. Copper is an example of this. It may start off as a malleable metal. Bending it or stretching it will strengthen it. If it is stretched, the metal where it forms a neck becomes stronger and prevents further necking. This means that the metal may be drawn into wires and will resist breaking if the sample is repeatedly flexed and straightened. Heating the metal will soften it again. Such materials are said to be 'ductile'

Some metals are too hard to machine unless they are heated first. Rough treatment may restore their hardness. A blacksmith needs to constantly reheat a horseshoe to soften it so that it can be worked to the correct shape. Banging and quenching the material strengthens it. This is due to crystals forming in the metal, which strengthen it. (stones in concrete act the same way and hamper the propagation of cracks)

Large areas of crystalline substance are brittle and decrease the strength of the material. This happens in metal fatigue. Low temperatures can also fatigue a metal. Tin, for example turns into a powdery form at prolonged low temperatures (Tin disease). The hull of the Titanic may not have ruptured if the water was warm, but then there would have been no icebergs!

The elements of metals are usually alloyed with other substances, usually other metals, to alter their crystalline structure and make the resulting alloy stronger. Steel for example, is a mixture of the elements iron and carbon.

Tensile strength of some materials (MPa)

Also yield strength (MPa) and elongation (%)

Material	Treatment	Tensile	Yield	Elong
440C AISI stainless steel	annealed	760	480	13%
440C AISI stainless steel *	hardened at 330C	1970	1900	2%
5160 I-SAE alloy steel	tempered at 200C	2200	1790	4%
Titanium Alloy #	Oxygen annealed at -225C	1580	1420	15%
Aluminium Alloy 6061 T6 ~	Solution heat treat & aged	310	275	12%

*Stainless steel was used for the weapon of Joker. It is not easily cut by House Robots and can be ground into a sharp blade.

# Titanium, although light, is springy and not suitable for rigid structures. It is more difficult to weld than aluminium.

~ Aluminium is considerably cheaper than Titanium and lighter (RD 2.7 vs 4.5) and is easier to weld. This is why we used aluminium alloy 6mm tread plate for the hull of Joker

For info...

Stainless Steel contains 1.07% Carbon, 17% Chromium and 1% Manganese.
Alloy Steel contains 0.60% Carbon, 0.80% Chromium and 0.88% Manganese.

Surface Treatments

Wear resistance, and to a smaller extent, the strength of a structure is a result of the surface treatment given to the object for example -

Bead blasting, Anodizing, Precipitation hardening, Work hardening, Case hardening, Cyaniding, Carbonizing, Nitriding, Carbonitriding, Flame hardening, Induction hardening

The chosen surface treatment must, of course, be suitable for the alloy in question.

We would have bead blasted and then anodized the aluminium hull of Joker if funds had permitted. This would have endowed the surface with colour as well as toughening it.

THE WEAPON COMPONENTS

The Geared Lift Motor

We used a Parvalux PM 50 LIS (in line multi-spur D.C. totally enclosed IP 54 permanent magnet motor. This is rated at 280 Watts for 15 minutes. It lacks the internal fan of the PM60 which is rated at 345 Watts.

The motor will only need to be operated for a few seconds during a bout so is driven well over its rated power. At 24 volts the motor turns at 3000 rpm, the output shaft turns at 27 rpm and has a rated torque of 81 Nm. It shares the same gear train as the PM60, which is rated at 100 Nm. At twice the voltage it will turn at 54 rpm.

The motor was modified thus -

1. The oil was removed from the gearbox and the gears lightly greased.
2. The output shaft was reduced in length and modified to take a 7-tooth pinion
3. The box was re-assembled to put the output shaft near the top
4. Flat countersunk screws were used upon reassembly to save space
5. Suppressor capacitors were soldered across the brushes
6. The brush cover screw was replaced with a countersunk item to save space
7. The motor body was covered with insulating tape to prevent short circuits
8. A spacer was fitted to the mounting base to give clearance to the speed controller
9. The suppressing choke was dispensed with

The Torque Limiter

Joker is easily flipped due to its high ride height of 10 mm. This is of no great consequence since it runs both sides up and can turn itself over using its lifter.

The weapon sticks out some distance and could exercise some leverage on the hull and damage it. This is reduced by incorporating a Cross & Morse Torque limiter model 500M2. This has a maximum rated torque of 57 kg at 1 metre. This can obviously be tightened up further if needed. In practice the level of torque is perfectly adequate because -

1. Our favourite weapon is only about 860 mm in length
2. We would turn ourselves over if the force exceeded 30 kg at 1 metre
3. We only need to lift one end of our opponent so the force needed would be 50 kg
4. We could lift 100 kg if the load was centred on our weapon.

The torque limiter has been modified by -

1. Putting it in a lathe and removing all excess metal
2. Replacing the hexagonal setscrews with socket grub screws to save space and weight
3. Bored out the centre to 25 mm
4. Broached a key way into the centre hole
5. The clutch was fitted with a 35-tooth 1/2 inch pitch plain plate sprocket

Gearing

The lift motor is geared 5:1 through a standard chain. This means that the shaft will have a torque of 500 Nm or 50 kg at 1 metre. Exceeding the rating of the motor by, say 100% will mean that another robot could easily be lifted if Joker was glued to the arena floor. In practice, the weapon is pushed down and the front of Joker is lifted. The weapon is slid under our opponent and then raised. This will lever the weapon and our opponent off the floor. They will lose traction and the result is a victory (in theory!).

The motors were designed to run on a 24 volt supply. They will obviously run around twice as fast on 55 volts. The gearing will reduce the weapon shaft to about 10 rpm or one revolution every 6 seconds. This is a little fast in practice and when funds are available, a speed controller will be fitted to replace our relay and resistor circuit we use to control the lift at present.

The Shaft and lift