I have a variety of Tower Pro 55g hobby servos (mg946r, mg996r,mg995r).
Are these all permanent magnet motors and likely to have a linear torque speed curve?
If so, then do I get the most power from these servos at half speed/ half torque?
Any rule of thumb to use? I'm interested in making a quadruped that could do more than crawl.
How do you run them half torque?
Half speed I can see, you control where they are moving to via the servo pulses you send it.
I think it's gonna draw whatever current it needs up to the stall current of the motor at the heart of the servo to try and move to that position tho, no? I don't see a max current value at any website, they all just carry the same as in the above link, with maybe a little more, such as:
Tower Pro MG-946R Digital High Torqe Servo
Model: IM120713006
Availability: Discontinued
•Operating Voltage : 4.8~7.2V
•Operating Speed : 0.20sec/60degree (4.8V)~0.17sec/60degree (6V)
•Torque : 10.5kg/cm (4.8V)~13kg/cm (6.0V)
•Dead Band Width : 5usec
•Temperature Range : 0~+55℃
•Cable Length : 33.5cm
•Servo Type : Analog Servo
•Brand Model : Tower Pro MG-946R
CrossRoads:
TowerPro MG946R Servo Specifications and ReviewsHow do you run them half torque?
Half speed I can see, you control where they are moving to via the servo pulses you send it.
My thinking on this is that you design for half the stall torque by adjusting the loading on the servo. You can do that either by picking a servo geared there or by changing the leverage the servo works against.
Something on PM magnet torque/speed here:
http://curriculum.vexrobotics.com/curriculum/speed-power-torque-and-dc-motors/dc-motors
The design I have drives the limbs through a link and I can change the load on the servo by changing either the servo horn length or changing where it is attached to.
I took a course in motors years ago (they were giant motors), but I remember plotting torque/speed curves. Power = Torque * speed. If you design at stall torque there is no movement and hence no work done. If you design at no load speed there is no torque and also no work done, So maximum power transfer must be between the two. Power determines how fast a vehicle moves (top speed) and torque determines how fast it gets started, or whether it can even start.
At least that is my thinking on this, but I have been wrong before!