29_Locking System Revision

In order to simplify the locking system for the finger segments, Devin has considered using motors located locally on the segments to lock the joints.  This would greatly simplify the problem we are dealing with when the surface length of the finger changes as it curls. 

With the current design, there is difficulty in ensuring that the system will lock/unlock properly as this length changes.  The wire that routes down to the fingers to lock the joints would need to change length along with the finger surfaces, and it seems overly complicated to account for that in addition to the variance in the distance change between each finger.  Having motors locally on the segments would completely eliminate this problem.  We have been able to find motors as small as 6mmx24mm that could fit inside the finger segments and provide a force to the lock mechanisms.  

If we decide to use motors (we’ll try to decide as soon as possible as it is a critical design point) they would be controlled with PWM signals (or possibly plain DC if we can match the motors close enough to how we need them to operate).  Also, a resistor in series with the each motor’s power lines could be monitored for current spikes to indicate when the pin has been locked or unlocked (current will spike when the locking pin has been fully pushed into the pin’s port). Our current sPIC33 has enough analog inputs to handle these 8 new motor current signals, but if PWM is used to control the motors, then we will either need to use two dsPIC’s or find one that has at least 14 PWM channels..