At this point in the design testing phase, the robot is tethered much of the time, but the engineers have tested and confirmed the use of a pair of 10 amp/hour lithium polymer batteries (about the size of a small brick) will be able to power the robot for at least a half-hour with a 20A average current draw. This includes all the motors, sensors, and controls.
Because the robot operates off a closed-loop system and uses 12 motors just in the legs (there will be another 12 in the arms and hands, as well as two in the neck), Lahr and his team needed controllers that could handle the load. "We chose maxon's EPOS 50/5 controllers for the joints, aside from two EPOS 24/5 controllers used for less demanding degrees of freedom," he said.
This closeup shows four 30mm brushless motors manufactured by maxon precision motors. (Source: maxon)
One of the main reasons the team chose to use the EPOS (Easy Positioning System) series controllers was that they came equipped to use the CANopen bus system. "Several of us were familiar with CANopen from other applications, so we were attracted by the familiar operating and programming needs of the system software from the beginning," Lahr said. This makes the EPOS embedded controllers well suited for multi-axis distributed controls that also feature electronic gearing, PVT, step and direction, and point-to-point positioning.
The EPOS controls are used in two different modes -- position control mode and force control mode. Position control allows for higher-level controllers to read position data from the sensors and closely regulate the specific position of the leg, so that corrections can be incorporated while walking. Force control mode is the latest thing in locomotion, according to Lahr. "It combines current control circuitry with load cell feedback to create a 'pure force' actuator, which allows the leg to swing freely," he said. "The EPOS controllers allow us to switch modes on-the-fly."
This is important so that the leg impact doesn't harm any of the actuators. "We can switch from position control to force control at the last millisecond, so that we can accurately control stride length and impact power," he said. An additional benefit of using the maxon controllers is that they come with EPOS Studio (a GUI-based free software package provided by maxon), which provides a simple utility to program the controllers and helps the user to bug-check software before implementing it into the CANopen system.
In general, EPOS controllers have been designed using advanced 32-bit DSP technology, which provides users like Lahr and his team the extended functionality of a miniature embedded controller. The units were specifically developed to meet demanding size and performance requirements often found in robotic, medical, and semiconductor applications.
That all makes sense, GlennA. I was just thinking the tether could get hung up in tricky environments. Yet, it would have the benefit of unlimited power. I would guess they can make tethers that wouldn't be adversely affected by fire and heat.
Rob Spiegel; I agree that a tether could be a serious restriction. But if the battery pack is only good for 1/2 hour or so, and it only carried 25 to 50 lbs or so of fire extinguisher, it is really worth the cost to develop ? If this robot can drag a fire hose behind it, it should be able to drag a tether also. Someone is doing the cost justification between an autonomous unit vs. a tethered tele-operated unit. And they may decide to build both types for further evaluation, or for different applications. Or they may continue with a tethered unit (as it is now) until the battery pack version is viable.
I would think that remote operation would be a necessity with these robots. As for having a tether for a power supply, I would think that would add vulnerability as well as restricting movement to some degree.
Yes it is impressive, Chuck. We're seeing more and more of these automated robots doing both dangerous work as well as repetitive work. The benefits of robots doing dangerous work is obvious -- saving human lives. The repetive work is also beneficial as it eliminates some of the soul-killing jobs such as tightening the same bolt 25 times per hour, eight hours per day, year in and year out.
@roddalitz. I would tend to agree with your argument but in this case it was necessary to give the robot humanoid feet. Ships engine compartments have hatch doors that are raised from the ground. To step through would require bipedal action. In this case the design may not have been based on human hubris. Though...if the robot is tethered how far can it go crossing that threshold. Hmm.
With respect I must ask whether humanoid is the most effective design? Certainly Hughey from Silent Running was far more convincing than the Star Wars robots R2D2 and C3PIO. Two legs seems like a biological accident, whereas ants and spiders work fine in most environments without issues of balance.
Rob Spiegel; Saving lives is probably the driving justification for this. There would be little concern about sending a robot into a situation that would be deadly for a human because the robot could be repaired, or replaced. There are certainly more efficient mobile platforms, but a companionway or hatch could be too difficult for a non-humanoid design to navigate. The tether may be necessary for power, and to send back video to an operator.
I don't recall the article stating if these were supposed to be autonomous or tele-robotic (remotely operated).
@ G Cabrera: I have to admit, I feel the same way, but I held back from saying so. Seeing that robot come lumbering (or tearing) across the ship, depending on how the sensors program it to respond based on environmental conditions, might be enough to send ship mates overboard, retreating in fright--and not just from an onboard fire!
I agree, Rob. Here, we have a great application for robots -- doing tasks that are just plain dangerous or that humans don't want to do. It's amazing to see how much "muscle" the new breed of robots is providing.
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