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Old Jun 05, 2007, 12:44 AM
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Servo - Operating Voltage Range - (Hitec) usage with NiMH, Lipol & A123 batteries.

Originally Posted by ebill3
Here is one receiver that will take 7.5 volts. Others? Bill
Note : Fusion Instruction sheet states = Operating voltage 3.5 7.5 V* ⇒ 4 5 NiCd / NiMH cells - this to allow for the "float" charge of the stated 4-5 NiCD/NiMH which quickly dissapates and does not mean a 2S Lipol can be used without a regulator. Many servos would not survive prolonged exposure to voltages above 6.0 with digitals seen to burn out very quickly. As advised earlier, refer to the specs of each unit being used as some do not handle more than 4.8v whilst some new servos designed for the Robotics market are designed to operate up to 7.5v.
Hitec answers re 4.8- 6.0v servos and robotics 4.8 - 7.2v servos
Hitec High Voltage Servo Work with 4.8V-6V voltage
"All the HV servos have specs listed at 6.0 /7.4v... using them at 4.8v is also possible with reduced performance. - Mike."
Servo volttage & FAQ - Society of Robots
101 - Servo FAQ & picking the right servo for the job
Servos capable of no lipo regulator
The Aurora 9ch TX & Optima RX's are 2S compatible. Hitec RCD Optima 6, 7 & 9ch Receiver Manual
The Optima SPC (Supplemental Power Connection) can handle up to 30 volts. This is the optional power for the RX only. If used, it eliminates the possibility of the servo battery, if it sags, to cause a brownout. In electric flight, you can pull power (balancing connector or plug) from the main battery (up to 6s) to power the SPC. This protects against an ESC BEC brownouts too!
Only the HS-7955, 7940, 7950, and 7954 servos are rated for 2S lipo.
(A123) Peak voltage is over 7V yes, but A freshly charged 5 Cell NiCd/Mh pack is 6.75v and quickly settles down from there once a load is applied. This is much different than the A123's which start and stay at a much higher voltage.
None of the Hitec servos rated for 6V would require a regulator if using a 5 Cell Ni Cd/Mh. The 225 servos for example pack a lot of punch in a small package but their size means a smaller motor which is more susceptible than a standard size servo with similar torque to overheating if pushed hard. Torque alone should not be the deciding factor when choosing a servo.
Since the 625MG is a standard sized servo it is more capable of handling the A123's but if you're asking it to perform close to it's max then the life would be reduced. Just as any servo... if you need 100in/oz of torque and that's all you have then the servo is operating at 100% where if you use a servo with 200in/oz it's working half as hard so things like motors and amps don't get as hot and the likelihood for failure is considerably lower.
Update Oct10:
Eight new high performance servos. These servos cover three main categories - digital, high voltage digital, and robotics.
The digital servos offer superior holding power and programmability.
High Voltage Digital Servos now offer 7.4V performance. This means that you can drive these servos using a 7.4V Lipo without having to step the voltage down to 6 volts (however the servos can still work well on 6V).
This means more torque and higher speeds. Servos are offered in steel and titanium gearing.
The Robot Servos continue Hitec's advanced technology in this field. Robotics demand durability, long run times, and precision performance. Hitec has done all of that and more.
HS-A5076HB Digital AGTT Slim, Karbonite Top BB
HS-5665MH Digital High Speed HV Metal Gear, Dual BB Servo
HS-5685MH Digital High Torque HV Metal Gear Dual BB Servo
HS-7945TH Digital Multipurpose High Voltage Titanium Dual BB Servo
HS-7980TH Digital Mega Torque HV Coreless Titanium Gear Dual BB
HS-M7990TH Digital Mega Torque HV Magnetic Encoder, Titanium Dual BB
HSR-5990TG Titanium Gear Robot Servo Dual Ball Bearing (35990R) -
HSR-5980SG Steel Gear Robot Servo Dual Ball Bearing Servo (35980R)
Digital Servo - HSR (Robotic) Servo. Do Not Use for Acro or Standard Purposes.

A123 Update
"Any Hitec standard size servo can be used with unregulated A123's. - Mike."

Alan T.
Alan's Hobby, Model & RC FAQ Web Links
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Last edited by A.T.; Sep 30, 2012 at 06:05 PM.
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