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--/- control approach - software

--- The design of System and Control will mainly take place in the fourth Quarter. ---

17/3 Comparison

‘All for one, one for all’ ‘All can do all’
  • .Microcontrollers
  • .All slaves
  • .Feedback (re)action
  • .Quantity

+ cheap
+ redundant

  • .Raspberry Pi
  • .All masters
  • .Consensus algorithm
  • .Quality

- non redundant
- overpowered

17/3 Low tech - micro controller

Microchips are little control units designed to process. They have no processing power for complex calculations but are cheap and fast in their operation field.

The main point of this microcontroller approach is to keep the elements light. (The elements exist each of a knot or ‘joint’ and a beam/rod.) The term light refers to light in weight but especially light in intelligence. The advantage is that light is cheap. Which means the number of elements is easy to scale. The power of this approach is to give the elements the lowest intelligence as possible and to gain synergy from all light elements. That way the goal is achieved rather by quantity than quality. Than cooperation has became a way not an objective.

Electronic dimensioning To engineer a light element the level of intelligence and programming must be kept simple. That implies no complicated calculations of the complete structure. Just design electronic features that are needed. In the perspective of seeing the whole structure as the synergy of the separate elements it is logical to dimension the intelligence of the elements accordingly to the fraction of their size compared to the assembly. On a higher abstraction level could be stated that every higher level of intelligence on one element has unused potential. As a law of nature demands everything is dropping to its lowest potential.

Reach set point This approach of control is using the operation method of a servo; putting power on the motor till it moves to the set point using the feedback of the potentiometer. Basically the microcontroller will do the same: if the servos of the own joint will not be able to reach the set point than the neighbour joint will have to power his servos as well till they will be able to do that together.

Local control Hand in hand with simple intelligence and programming is simple communication. Bypassing all to all communication helps slimming down the system. Only neighbours have to communicate i.e. each one to the right and to the left. The only important conversations they have to maintain is the call for help if the set point will not be reached. In this manner the neighbours together make the neighbourhood without overall control.

Roderick Kroes

17/3 High tech – Raspberry Pi

Overall control Every element is suited with a raspberry pi. All of them are connected (Ethernet/Bluetooth). Positions of all servos are then sent to the one with the strongest sensor input. So every element can compute the position of the whole structure and takes into account all the desired positions by means of the sensor input.

Consensus The desired positions as well as the boundaries of the system are together formed to set points. Some conflicting desires might occur in the composition of inputs. The algorithm in the processor creates a consensus between all different desired locations. The result is the set points for the joints and the trajectory how to reach those set points.

Balance Another restriction is the balance of the structure. That means the trajectory must be evaluated again to abandon every point where the trajectory gets close to a tip over point.

High intelligence Several clever features can be built into this high intelligent system. The joint that has been designed has its restrictions in degrees of freedom. Those restrictions can be very easily build into the trajectory algorithm to achieve the demanded manner of movement. As well as the very important balance to be maintained can be taken care of in the programming code. Now all the joints have to pass their positions and sensor inputs communication channels have to be adapted to that as well. Ethernet or Bluetooth may be appropriate for such data traffic. Those alternatives must have a connection to the processor. Moreover the processing power have to be sufficient.

Modularity For all the elements to be the same and replaceable they are made identical. The downside however is that while one unit has the lead all other processing units are (close to) useless.

Roderick Kroes

With the support of the Culture Programme of the EU.
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