TBM performed its own side by side testing to compare servos under similar conditions.
This is for one servo only, this is not the average of several servos.
The values we posted in the servo comparison table are the highest values we saw in the test.
Every servo has a higher torque the first time power is applied to the servo. Power drops off in torque and amps immediately and continues to drop. Servo manufacturers publish the highest value at the first instant of use because this is the highest attainable value.
The voltage that the servos were tested at were less than the starting voltage. For instance, we set the regulator for 6v, though when the servo was stalled, the voltage dropped below 6v, like 5.7v in some cases. Servo manufacturers will maintain a constant voltage of 6v for testing purposes, so their values will be higher.
We are measuring stalled torque, which is the torque available to move a surface, not hold the surface in place. If we were to first stall the servo, and then pull on the meter to try to move the servo arm, the load would go way up! It can be triple the stalled torque. For instance, if the servo read 10 lbs stalled, if you pulled on the meter to move the servo arm, the meter might read as much as 30 lbs, and the amps would increase similarly. Thus holding a control surface in position is much easier than getting the control surface into position in the first place. Some manufacturers post values somewhere in between the stalled torque and the holding torque. How they determine the numbers they post is vague, and I'm sure the methodology is different from manufacturer to manufacturer. Our method compares values attained from a similar method. It is not intended to duplicate values posted by servo manufacturers.
Amps is directly proportional to torque. However, keep in mind that gear ratios are changed so that speed is traded for torque. The motor will pull the same amps in a speed versus a torque version of the same servo (like the HS625 and HS645), however the torque is less with the faster servo. However, for the most part, if you want more torque, you will pull more amps.
Amps is directly proportional to voltage. The higher the voltage, the higher the amps, and the higher the torque and speed.
Some servos can dissipate heat better than others, so some will maintain a higher torque after 30 seconds (like on a knife edge) than others.
Voltage and amps is directly proportional to the gauge wire and plugs used. If you use HV plugs on the battery and use a power expander type unit, the power to the servos goes up tremendously on high powered servos. Just one JR8711 can't be operated at its fullest capability if a normal JR type plug is used on the battery, switch, regulator, etc. the voltage drop across those little plugs is tremendous. Imagine what the voltage drop to the servo is if a bunch of servos are trying to draw current simultaneously! Using a JR8711 without a power expander is a waste of money, because the amps can't get to the servo. It's not the wire as much as it is the plugs.
Within experimental error, losses after time/heat, and voltage drops, there are several servos which are all about the same in torque. These are the HD-1501MG, HD-9150, HS-645, HS-5645, HS-7985. The JR-8411, and JR-8611A are a little stronger. The HS-7955 is quite a bit stronger. And the JR8711 and JR8711HV are best by far, with the JR8711HV being the biggest, baddest servo out there. It is king of the hill (with a price tag to match).