Test

drive

The most influential decision for the design of the joint is the way the joint is driven. In this document we argue the different drive and the best suitable on for our design needs.

Criteria for the drive

1. Handle high torques/forces (or high speed with a gearbox)

2. Power/weight ratio

3. Accurately controllable

4. Size

5. Sharing energy

6. Maintaining position

7. (Degrees of freedom (+/- 180°) (actually possible for every drive))

8. Accessible for testing

Drives

• Mechanical

1. Powerful or high speed 2. ± 500 W/kg (helicopter engines) o Fuel weight 3. Not accurate 4. Torque depended 5. Hard: Fuel line through the tubes 6. Hard: changeable gearbox? 7. Accessible (helicopter engines) but expensive Extra’s: • Low efficiency • Safety hazard: explosion possibility • Weight mainly in joint • Emissions, not sustainable

• Hydraulic (to big)

1. Unlimited high forces/speeds 2. ± 800 W/kg (SAI, but very heavy) o Fluids weight 3. Good controllable o Not accurate, speed varies 4. Big (efficient when big) 5. Hard: Fluid line through the tubes 6. Hard (almost not possible) 7. Specially made (expensive) Extra’s: • High efficiency • Safety hazard: high pressure fluids

• Pneumatic (low forces, hard to share engery )

1. low forces, high speeds (special gearbox needed) 2. ± 450 W/kg (bosch) 3. Good controllable, but not constant speeds 4. Low weight, small 5. Light tube of air through tube, but length motor and cyclinder can’t be to large! 6. ? I think: easy but pressure drop? 7. Specially made (expensive, not accessible) Extra’s: • High efficiency • No safety problems • Noisy

• Electrical

1. High forces/speeds 2. ± 3780 W/kg (himax, lightest (0.45kg)) 3. Good controllable and accurate 4. Small and depends on needed torque 5. Easy: wire through tube 6. Easy (but overheating) 7. Broadly accessible (cheaper) Extra’s: • All weight in the joint (scaling problems) • No Safety when electricity loss • Efficient

http://www.designnews.com/document.asp?doc_id=230452 http://en.wikipedia.org/wiki/Power-to-weight_ratio http://www.rcheliwiki.com/Power_to_weight_ratio http://www.inmoco.co.uk/electro-mechanical_vs_pneumatic_actuators