A-Silicone or PU Tires?

Tested polyurethane rubber with the surface of the dohyo, with 32-07 Monitor/Slip and Friction from Testing Machines Inc.

Introduction:

Slip and Friction testing aids in the evaluation of chemicals and additives used to create or minimize the degree of friction between two contacting test specimens.

Applications:
Paper, Flexible Packaging, Foils, Rubber, Plastics, Wood,
Linoleum, Metal, Printing, Coatings, Composites

Specifications:

• Selectable speed from 5 to 43 cm/min (2 to 17 inch/min)
• Selectable travel distance from 2.5 to 30.5 cm (1 to 12 in.)
• Meets TAPPI T816, T549, and ASTM D1894

Features:

• Digital display, storage and editing of up to 100 readings, and selectable units (COF or grams)
• Settable limits
• Statistics-average, standard deviation, high/low results.
• Report printout with built in printer
• RS-232
• Static and kinetic coefficient of friction calculated in one operation.
• Direct drive arm with unique skid control.
• Sled-connecting mechanism ensures level pulling action.
• Easily interchangeable sleds.
• Full color easy to read Display

Instrument size:

Depth: 495 mm (19.5 in.)
Height: 508 mm (20 in.)
Width: 515 mm (20.3 in.)
Weight 25 kg (55 lb)

PDF product sheet:
Monitor/Slip and Friction

Product Video:

Brief test results:
* TEST REPORT *
Test Name: SL
Date: 31 Jan 2013

Sample ID: -
Sled Type: B - 200g (.44Lb)
Sled Info: -
Speed: 10cm/min
Travel: 20cm
Unit: COF

Total Meas.: 3
Rejected: 0
Static:
 -> Mean: .654
 -> SD: .089
 -> Lo: .601 (#1)
 -> Hi: .758 (#2)
Kinetic:

 -> Mean: 1.536
 -> SD: .210
 -> Lo: 1.410 (#1)
 -> Hi: 1.780 (#2)

Reading #: S K (X=reject)
 1: .601 1.410
 2: .758 1.780
 3: .604 1.420

* END *

Conclusion:
Graph bellow is found from motor parameters, by ramming the robot to the wall.

1. As expected, static is lower than kinetic friction coefficient.
2. These aren't final results, because 3 measurements at one speed means nothing.
3. It is essential to conduct full experiment at different speeds and normal loads, in order to achieve force vs speed load graph and compare with DC motor load graph.
4. Next: Full experiment conduction with PU and silicone rubbers.

Useful links:

• STATIC FRICTION IN RUBBER-METAL CONTACTS WITH APPLICATION TO RUBBER PAD FORMING PROCESSES
• Rubber Friction

Rotor Inertia Measurement

How do we measure rotor inertia?

We can calculate it out of free run.

Method:

• Connect motor to the battery;
• Measure no-load current;
• Connect oscilloscope to the terminals;
• Disconnect the battery;
• Let the single measurement appear in the oscilloscope.

Results:

We measured free run BEMF dynamic process, which is equivalent for speed.

We can approximate the achieved graph to linear, which will allow us to use approximated differential dynamics:

1. Main dynamic formula (M_din - dynamic torque, M_t.v. - no load torque).
2. Useful torque.
3. Dynamic Torque equal to No Load Torque.
4. Torque and current link.
5. EMF and angular velocity link.
6. Voltage balance equation.

Moment of inertia is equal to:

Where I_t.v. - no load current, k - motor constant, T - time, E_bat - battery EMF, r_a - armature resistance, r_bat - battery resistance.

Simulation:

Simscape electrical in Matlab, helps us to have this approximated dynamic process and calculate the rotor inertia, which is equal to 1,081e-4 kgm^2:

Conclusion:

This is quite accurate method for rotor inertia calculation, if the gearmotor has static load (friction), which linearised the exponential graph of the speed.

Cast Silicone Tires

Casted new tires with Elite Double 22 from Zhermack

A-Silicone for laboratory model duplication. Ideal for duplicating models with slight undercuts and casting investments. Use of a plastic duplication flask is recommended. Available in light green for better definition of detail.

Advantages:

• Mixing facilitated by the 1:1 base to catalyst ratio;
• High fluidity: does not require mixing in a vacuum;
• Absolute precision for faithful reproduction of detail;
• Dimensional stability over time and non-deformability, allowing a number of duplications to be made;
• Compatible with all plasters, polyurethane resins, phosphate investments and acrylic resins.

Characteristics:

• Extreme fluidity;
• Versatile, thanks to the 22 Shore A hardness;
• Light green colour.

DOWNLOAD:

• Brochure
• Instructions
• Safety Data Sheets
• Press Release

RESULT:

Center the rims in the form, and apply the mixed liquid to the gap. Polimerisation shouldn't take long, about half an hour. In the result we get newly casted tyres with perfect friction (while new).

Block Diagram

Electrical energy source ES feeds programable logic controller together with the voltage feedback. Electrical energy flows to both drivers D, which are controlled with PLC and regulate the power for the motors M, where the energy is converted to mechanical. Both motors drive a single transmission device TD, which is actually a full robot mechanical system, except motors, and a Dohyo together, energy parameters are transformed to fit the work unit WU, wich is an opponents robot system and a Dohyo ring too.
The force you need to push the opponent have to be bigger than critical friction force of the opponent's wheels and the Dohyo surface.

Conclusion:
You don't need an enormous power for motors, only slightly bigger than the product of critical friction force of your TD and prefered nominal speed (e. 10cm/s, depends on termal ability, should not overheat).