Paul CrouchDo PAMs really have much benefit over motors?
Some (subjective) pros & cons of PAMs vs BLDC motors for this application:
| Pneumatic Artificial Muscles | Motors (& gearbox) |
| + Powerful for their weight/cost. + Fast. | - Have to trade speed for torque. - Do I have the budget for big enough motors? |
| + Negligible weight for muscle itself. - Weight of valves (400g each) & compressor (2.88kg). Reservoirs planned to be 2L soft drinks bottles (tested to 90psi). - Fittings, pressure sensors, regulator (all non-zero). | - Weight of motors & gearboxes or lead-screws. Small KEDA 28-30 920KV Brushless Outrunner weighs in at 57g. Larger Turnigy Aerodrive SK3 - 5055-280KV Brushless Outrunner: 570g. |
| + Inexpensive, even including cost of 3-way solenoid valves. ~£11 per DOF. + Single small compressor (85lpm) for ~£30. - Fittings & accessories should be considered (all non-zero). | + Small BLDC motor ~£9 - Larger (more torque) motors cost more. £40+ for bigger BLDCs. - Required ESCs can be costly too(?) |
| + Compliant: built-in suspension for both rolling and walking. + A degree of safety around those pesky humans. - Difficult to position and lack of rigidity would make balancing (future!) more difficult. - Limited unpowered support - collapses when not powered, so no static display or maintenance. | + Easier to position. + Gearing that isn't back-driveable would automatically lock limbs for static support. - Could be too rigid? Transfer of shock. Not compliant to terrain. |
| - Air demand could outstrip supply. Compressor choice & reservoir size have major impact. - Compressor current ~30A. | Current of multiple BLDC motors? Small KEDA 28-30 920KV Outrunner max 7A. Turnigy Aerodrive SK3 - 5055-280KV max 60A. |
I'm concerned about the speed-torque trade-off with motors; I guess that's solved with bigger motors but that has weight and cost implications. PAMs seem to have plenty of power but I'm fairly sure I'd be shortening the life-span of the solenoid valves by operating them at high rates and it would be a huge PITA to have to switch to motors, because of reliability issues, once I'd committed to PAMs.
Maybe a hybrid system? Best of both worlds or twice the weight, power consumption and complexity?
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