6V vs. 4.6V torque
05-07-2003, 01:16 AM
#2
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6V vs. 4.6V torque
If you assume the servos don't burn out with the extra current, torque will be proportional to voltage.
If the motor is stalled, the resistance seen between the supply inputs is the winding resistance + driver electonics resistance. The supply current will be proportional to Ohm's Law more or less. Motor torque is proportional to current, so torque will be proportional to voltage to a first approximation.
If the motor is stalled, the resistance seen between the supply inputs is the winding resistance + driver electonics resistance. The supply current will be proportional to Ohm's Law more or less. Motor torque is proportional to current, so torque will be proportional to voltage to a first approximation.
05-07-2003, 01:44 AM
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6V vs. 4.6V torque
Originally posted by sideshow
So at 6 volts there will be 20% more torque? Or whatever the % works out to be?
No idea what a first approximation is.....
Bob
So at 6 volts there will be 20% more torque? Or whatever the % works out to be?
No idea what a first approximation is.....
Bob
The first approximation means the analyis does not take acount of things like heating (increases Ohmic resistance, reduces the gain of FETs, increases the gain of bipolar transistors) fixed voltage drops due to forward biased diodes and transistor saturation and so on.
Look at the published figures for other servos to get an idea of what happens in real life.
05-07-2003, 08:24 PM
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6V vs. 4.6V torque
If the Li packs can't push the amps then you won't get the torque. Also the voltage will drop. If the voltage to the receiver drops below 3.8 V, then it will go into battery failsafe.
The message here is that the battery must be able to supply the required current to the servos.
Servos draw current in response to load. So if the load is the same, then current will be similar whether you have 4.8 V or 6 V. If the servos are blowing back at 4.8 V, then 6 V may enable them to hold on, but only if the battery can maintain 6 V with the extra current.
I've seen the thread in the Jet forum, and my preference would be to bite the bullet and use standard size servos if you don't think minis will be adequate. If a servo can't do its job at 4.8 V, then at 6 V your safety margin is less than 20 %. The larger servos will have more efficient motors (more torque for the same current) and bigger gears which are more tolerant of abuse.
It does seem that by being careful with the application, the minis can be made to work in a Bobcat, but there does not seem to much margin if things go wrong.
The message here is that the battery must be able to supply the required current to the servos.
Servos draw current in response to load. So if the load is the same, then current will be similar whether you have 4.8 V or 6 V. If the servos are blowing back at 4.8 V, then 6 V may enable them to hold on, but only if the battery can maintain 6 V with the extra current.
I've seen the thread in the Jet forum, and my preference would be to bite the bullet and use standard size servos if you don't think minis will be adequate. If a servo can't do its job at 4.8 V, then at 6 V your safety margin is less than 20 %. The larger servos will have more efficient motors (more torque for the same current) and bigger gears which are more tolerant of abuse.
It does seem that by being careful with the application, the minis can be made to work in a Bobcat, but there does not seem to much margin if things go wrong.
