Push/pull systems are proportional but yield diminished throw at the ends of travel because in real time the linear distance traveled by the connector rod decreases as a function of the servo arm moving through an arc. Most of the travel in a push pull system is near the neutral position. So, while the movement of the servo and rudder are in synch with each other their movement in actual time is greater near neutral than at the ends of the servo throw. FirstFooty’s analysis in cardboard is only proof of proportionality and does not take into account the movement/time relationship.
Rusty when you look at the data sheet, it does a 60 degree rotation in 100ms. NanoMuscle only draws power for the time it is rotating and then draws limited power while holding and no power while the shaft is returning therefore the average power is much lower. The cycles from 3xAAA is 30k!
It certainly is interesting, Andy.
This might represent the first generation of a later viable servo.
My casual observations were that the muscle ‘Muscle Wire’ that had useful strength (linear MigaOne) of 2.5lbs (standard servo 40 ounces/inch?) took half a second to ‘warm up’ and 2.7 Amps to drive!
The rotating muscle one can do 2 Newtons (8 ounce/mm? - about a 4 gram servo output) but on 4.8 volts at close to 1 amp drive maximum. This drive is over the whole 60 degrees, so how do you hold on neutral at 30 degrees? Even if you could there is no zero power drain except at 0 degrees - full rudder. The ‘servo’ is likely to be driving 350mA constantly. The high number of cycles they quote may be under no load.
Ii reminds me of my old ‘galloping ghost’ single channel radio that manages to give three proportional servo outputs using one servo and mechanics, but was always driving, and oscillating the control surfaces!
As an aside, and whilst I am ‘talking’ to you - there is a request on RCGroups from a new sailor for more information on your Bottle Boats. I referred him here, but share an interest with him in asking if you have a plan or dimensions to share (principally for IT) that might get a newbee started on this quest?
It seems like a lot of fiddling just to get the rudder to swing. you only need a narrow corridor when using the usual pushrod system, but a much larger area for the whipstaff arms to swing, and you might even end up stripping the servo gears. Just more things to fiddle with (remember Murphy’s Law.) and more friction involved to tire out the poor micro rudder servo.
It seems like more of an artsy thing to me.
FYI- I have seen a similar arrangement in model military ships, but they used a cable system to move the tiller. The cable (or string) wrapped around a small drum on the multi-turn rudder servo.
I may have missed it but how do you get the tiller attached to the rudder blade, screw it to the cheek?
Mine arrived this morning set up to PC first time and no problems figuring it out even with out the manual got two extra RX units so i can swap between models - no selection of models just turn rx then tx off on model you want to stop using then turn tx on and rx of new model.
I have to say i am very impressed £28 for TX + RX and £11.50 for additional RX’s - I can see me buying these again :zbeer:
Well done R2Hobbies - it arrived in 5 days and that included the weekend!!!
