KEVOS® MAKEOS · Power Transmission
Friction Wheel Drive Check (Tangential Force, Normal Force Needed, Contact Stress, Speed Ratio)
For a friction wheel (traction) drive between two rollers, how hard must they be pressed together to carry the power without slipping, and is the contact stress within limits?
Check of a friction (traction) drive of two cylinders pressed together: the input torque and the tangential force at the driver, the normal force needed to carry it without slip from the friction coefficient and a slip factor, the contact half-width and peak contact pressure of the two cylinders (as the Hertz contact stress tool for line contact), the output speed and the load on the shaft bearings, against the allowable contact pressure.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Power | kW | Power transmitted. |
| Driver speed | rpm | Speed of the driving roller. |
| Driver roller radius | mm | Radius of the driving roller. |
| Driven roller radius | mm | Radius of the driven roller. |
| Friction coefficient at the contact | Friction coefficient between the rollers (dry steel on steel about 0.15; traction fluids less). | |
| Slip safety factor | Factor on the normal force against slip. | |
| Contact | ||
| Contact width | mm | Width of the contact along the roller axes. |
| Modulus of the driver | GPa | Elastic modulus of the driver. |
| Poisson’s ratio of the driver | Poisson’s ratio of the driver. | |
| Modulus of the driven roller | GPa | Elastic modulus of the driven roller. |
| Poisson’s ratio of the driven roller | Poisson’s ratio of the driven roller. | |
| Allowable contact pressure | MPa | Allowable peak contact pressure for the roller materials and life. |
Method and formulas
- Driver torque = 9549 P ÷ n; tangential force = torque ÷ R₁.
- Normal force = SF × tangential force ÷ μ.
- Line contact of two cylinders: half-width b = √(4 F R ÷ (π L E*)), peak pressure 2F ÷ (π b L) (as the Hertz contact stress tool); output speed = n₁ R₁ ÷ R₂.
- Example: 318.31 N tangential needs 3,183.1 N pressing force; contact pressure 418.76 MPa.
Limitations
- Rigid rollers with a uniform line contact; misalignment concentrates the load at one end.
- Creep of about 1–2% lowers the output speed slightly.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a friction wheel drive for a feeder or turntable
- Check rollers on a friction-driven conveyor
- Find the spring force for a roller drive
Who it is for
- Machine designers
- Design engineers
- Automation engineers
What you get
- Torque and tangential force
- Normal force needed and contact stress
- Output speed and bearing load
Interpreting the result
- Friction drives need a pressing force many times the transmitted force, which loads the bearings heavily.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2301–2309, 165–168. Topic reference; no source tables or recommended settings are reproduced.
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