hitec_servo_b

Service please!

Preamble

Looking into servos (not to be confused with stepper motors). I’ve always avoided motors and servos, ever since my HND days and beyond. I don’t know why, I guess I just liked to concentrate on transistors and discrete logic, but now I think it is time to overcome that fear.

Quick Guides

From Which servo should I choose?

Servo Terminology:

Coreless Motor – This refers to the armature of the motor. A conventional servo motor has a steel core armature wrapped with wire that spins inside the magnets. In a coreless design, the armature uses a thin wire mesh that forms a cup that spins around the outside of the magnets eliminating the heavy steel core. This design results in smoother operation and faster response time.

Indirect Drive – This refers to the potentiometer inside the servo. The final output shaft (the part that the horn/arm attaches) has to be supported not only near the end but also deep inside the servo case. Indirect drive is when the final output shaft is not dependent on the potentiometer for support inside the gear case. Normally a bushing or bearing supports the load. Direct Drive is when the potentiometer plays a supporting role in holding the output shaft in place. Most sub-micro servos are direct drive since they are tight on space and do not have the room for an extra bushing or bearing.

Spline – This is the output shaft of the servo. It is what you attach the servo horns or arms to. Standard Hitec splines are 24 tooth with standard Futaba splines 25 tooth.

Transit Time – This is the amount of time is takes for the servo to move a set amount, usually rated at 60 degrees. Example: A servo with at transit time of .19 sec. to 60 degrees would mean that is takes the servo nearly 1/5th of a second to rotate 60 degrees.

Torque – This is the maximum power the servo can produce. It is normally rated in inch-ounces. This means that the servo can move this set amount with a 1” arm attached to the output shaft or spline. Example: A servo with a torque rating of 130 in.-oz. can move that amount with a 1 inch arm or slightly over 8 lbs. To convert in-oz. to pounds of force, divide this rating by 16. Example: 130/16=8.125 which is in pounds.

3 or 5 Pole Motors – This refers to the commutator in the motor. The commutator is where the brushes make contact with the armature. The more motor poles the smoother and more accurate the servo will operate. Most servos have either 3 or 5 pole commutators.

Nylon Gears – Nylon gears are most common in servos. They are extremely smooth with little or no wear factors. They are also very lightweight. If your application calls for long duration but not jarring motion, nylon gears are a top choice.

Karbonite Gears – Karbonite gears are relatively new to the market. They offer almost 5 times the strength of nylon gears and also better wear resistance. Cycle times of well over 300,000 have been observed with these gears with virtually no wear. Servos with these gears are more expensive but what you get in durability is more than equaled.

Metal Gears – Metal gears have been around for sometime now. They offer unparalleled strength. With a metal output shaft, side-loads can be much greater. In applications that are jarred around, metal gears really shine. There are two cons to metal gears, weight and wear. First, metal gears are much heavier than both nylon and karbonite gears. Second, metal gears wear several times that of nylon gears. How quickly depends on the loads that you place on the servo. They will eventually develop a slight play or slop in the gear-train that will be transferred to the spline. It will not be much but accuracy will be lost at some point.

See also Understanding RC Servos – Digital, Analogue, Coreless, Brushless

Video Tutorials

Yet another good introductory video from EEEnthusiast.

A good video comparing the MG996 (metal gears) and the SG5010 (plastic gears). Shame that someone seems to be doing carpentry next door.

A review of T-Pro (clone) MG996R – slow 0.2s transit time @ 6V, Original TowerPRo 0.14s but torquey 150 oz/inches.

A review of the TowerPro (clone) MG995 – The ultimate fail.

Video of a customised MG995 which has been hacked to rotate 360.

How to achieve that hack, remove the pin in the gear, remove the plastic insert which turns the potentiometer, disconnect the potentiometer and bridge two 2.5KΩ resistors. The sketch code is below, see the Sketches section below.

How to choose the right servo

Also, an excellent video on servos. Gears are made from Nylon, Metal, Titanium, Karbonite. Servo horn splines are not standard. Coreless motors have less interia than those with rotors, thereby giving the servo a faster response time. They mention an AC 32 board, but I can’t find one on eBay.

Also, batteries are important, here is a tutorial about LiPo batteries. For more information, see Power Up!

Ancillary Equipment

Battery Checker

In the final video, the battery tutorial, a  battery charge checker was mentioned

Cell Meter
Cell Meter

On eBay, RC CellMeter-7 Digital Battery Capacity Checker Fr LiPo LiFe Li-ion Nicd NiMH, for £2.89 + 0.89 (p+p)

Servo tester

Servo tester for servo & ESC Spectrum futaba hitec JR sanwa acoms

RC Servo tester ideal for Spektrum Hitec Futaba JR RC planes, heli’s 408050

Sketches

From EEEnthusiast’s tutorial: To set the servo

#include 
Servo servo1;

void setup() {
  servo1.attach(9);
  servo1.write(180);
}

void loop() {
}

To vacillate

#include 
Servo servo1;
int pos1 = 0;

void setup() {
  servo1.attach(9);
  servo1.write(180);
}

void loop() {
  for (pos1 = 0; pos1 < 180; pos1++)   {     servo1.write(pos1);     delay(10);   }   for (pos1 = 180; pos1 >= 1; pos1--)
  {
    servo1.write(pos1);
    delay(10);
  }
}

The code used in the 360° hack tutorial, which is taken from the Arduino library Servo.write() page.

#include  

Servo myservo;

void setup() 
{ 
  myservo.attach(9);
  myservo.write(90);  // set servo to mid-point
} 

void loop() {} 

Salient Points of note

  • Reaction time: – per 60°, generally 0.1s – 0.2s, the faster the better
  • Torque: kgcm-1, 1.7 to 9 or 11 (MG996), the higher the better.
  • Voltage: 4.8 – 6V
  • Size: 22.5 × 11.5 × 24.6mm to 40.7 * 19.7 * 42.9mm (MG996)
  • Weight: 12g to 55g (MG996) – Servos with metal gears will be heavier.

The servos come with either silicon fitting rings or two plastic mounting clips. The rings are better as they can deal with shock better.

Check out the Servo Database, an essential comparison site.

Servo connectors

Servos, generally, have SVG (Signal, Voltage, Ground) connectors. If you look at the plug attached to the end of the cable coming from your servo, you will see the servo connector, like so:

Servo connector

As servo boards usually have the pins in the SVG order, that means that it will support the Futaba J type connectors (but not the Airtronics, as the power and ground pins are reversed):

Futaba and Airtronics connectors

Also, Hitec and JR Radio connectors have the same pin out:

JR Radio and HiTec connectors

Servos

MG995

Specification
  • Power Supply: Through External Adapter.
  • Stable and Shock Proof
  • Connector Wire Length 300mm
  • Operating Speed : 0.17sec / 60 degrees (4.8V no load)
  • Operating Speed : 0.13sec / 60 degrees (6.0V no load)
  • Stall Torque : 9 kg-cm (180.5 oz-in) at 4.8V
  • Stall Torque : 12 kg-cm (208.3 oz-in) at 6V
  • Operation Voltage : 4.8 – 7.2Volts
  • Gear Type: All Metal Gears
  • Original box: NO
  • Color: Black
  • Item size: 40 * 19 * 43mm
  • Servo weight: 55g
  • Net weight: 66g (with accessories)
  • Package weight: 75g
eBay

It is always best to buy the servos with metal gearing, such as the MG995, as the servos with plastic gearing (SG5010) will end up breaking.

The cheapest is the MG995 Micro Servo 55g Metal Gear High Speed Digital for RC Helicopter Boat Model for £3.39

Cheapest servo
Cheapest servo

The cheapest MG995, which comes with the widest range of attachments appears to be the MG995 Metal Gear High Speed Torque Digital Servo for Futaba JR/FP Helicopter for £3.08 + 35p (p+p)

MG995 Servo with attachments
MG995 Servo with attachments

There is also 1Pcs New MG995 High Speed Digital 99 UK Gear 2BB Torque RC Servo 55g for £3.76, with additional clips.

Servo with clips
Servo with clips

MG996

Specification
  • Stall torque: 9.4kg/cm (4.8v); 11kg/cm (6v)
  • Operating speed: 0.17sec/60degree (4.8v); 0.14sec/60degree (6.0v)
  • Weight 55g
  • The dimensions are 40mm x 38mm x 20mm W excluding lugs
  • Product Weight: 55g
  • Product size: 40.7 * 19.7 * 42.9mm
  • Products Rally: 9.4kg/cm (4.8V), 11kg/cm (6V)
  • Reaction speed: 0.17sec/60degree (. 4.8v) 0.14sec/60degree (6v)
  • Operating voltage: 4.8-7.2V
eBay

The absolute cheapest is the unlabelled MG996R Micro Servo 180 Degree 55g Metal Gear for RC Car Helicopter Robot Model, for £3.09, but whether it is a M996 or not is anyone’s guess.

There is MG996R 55g Gear Servo Motor Big Torque for RC Helicopter Car Robot Arduino, £3.07

Or buying bulk, 10PCS MG996R Torque Digital Metal Gear Servo Helicopter RC Car Boat Model, £30.86

This one comes with silicon mounting rings, MG996R Torque Digital All Metal Gear Servo for Helicopter Car Boat Model New FT, for £3.34

At £3.70 each is if you buy 4 1/2/4x MG995 MG996R High Torque Servo Metal Gear for RC Helicopter Truck Model for £14.81. So, you are better off buying the one above for £3.34, plus the description is very confused.

4 MG996 Servos
4 MG996 Servos

Note that this is the MG996 not the MG995. Taken from Towerpro MG996R 10kg Servo 55g / 10kg / .20sec

This is essentially an upgraded version of the famous towerpro MG995 servo. It now has a redesigned PCB and IC controll system which makes it far more accurate. Its internal gearing and motor are also upgraded to improve dead bandwith and centering.
All specifications are the same as the previous model MG995, however this servo is far more accurate, and safe to use in aircraft which require precise servo movements and perfect centering.

The MG996’s reviews are rather bad though. TowerPro are generally badly reviewed. The HiTec servos seem to be much better received.

Amazon

A genuine MG996 Eggsnow Genuine Towerpro MG996R Servo Motor Digital High Torque Metal Gear Bearing 55g for JR RC Robot Car Boat MG996, for £7.89 (weight 61g)

Linkage for MG996

There are the 18 wheel brackets to consider, in aluminium: 2x Best uk Metalboat Steering Gear Bracket for MG995 MG996R Standard Size, £1.18 for 2, so a total of 9 x £1.18 =  £10.62

Wheel Link
Wheel Link

Or,

MG90

Specification
  • Dimensions: 23 x 22 x 12mm
  • Net weight: 17g
  • Package weight: 23g
  • Operating Speed (4.8V no load) : 0.12sec / 60 degrees
  • Stall Torque (4.8V): 10.2oz / in ( >2 kg/cm )
  • Temperature Range: -30 to +60 Degree C
  • Dead Band Width: 4 usec
  • Operation Voltage: 3.5 – 8.4 Volts
eBay

4.8V MG90 Metal Geared Micro Servo Fit Airplane Helicopter flight direction RT, for £2.11

MG90
MG90

MG90s

Specification
  • Operating Speed (4.8V no load): 0.11sec / 60 degrees
  • Operating Speed (6.0V no load): 0.10sec / 60 degrees
  • Stall Torque (4.8V): 2.0 kg/cm
  • Stall Torque (6.0V): 2.5 kg/cm
  • Size: 22.8mm x 12.2mm x 28.5mm
  • Weight: 13.6g
  • Temperature Range: – 30 to + 60 degree C
  • Dead Band Width: 10uS
  • Operation Voltage: 4.8 – 6.0 Volts
eBay
MG90s
MG90s

SG5010

Specification
eBay

Quality SG 5010 TowerPro Torque Servo Coreless For Helicopter Torques RCs for £3.22. So for the saving of 10p, it is just not worth it.

SG90

Specification
  • Dimension: 23mm x 12.2mm x 29mm
  • Net Weight: 9 grams
  • Operating speed: 0.12second/ 60degree ( 4.8V no load)
  • Stall Torque (4.8V): 17.5oz /in (1kg/cm)
  • Temperature range: -30 to +60
  • Dead band width: 7usec
  • Operating voltage: 3.0V~7.2V
eBay

Trex 450 SG90 Mini Gear Micro 9g Servo For RC Helicopter Airplane Car Boat, for £1.07

SG90
SG90

More…

From the quadraped below, the Dragoon: Custom RX-64 Quadruped, the Dynamixel RX-64 Robot Actuator from Robotis, $279.90 each

M-200-RS RX-64
M-200-RS RX-64

Hitec 645MG

The hi tec ultra torque is faster and more powerful than the rc sport rs2.
HI TEC HS 645 MG,RC SPORT RS2,STANDARD SIZE HIGH TORQUE METAL GEAR SERVO,FUTABA, £25 approx

LD-2015

Specification
  •  Size: 40*20*40.5mm
  • Speed: 0.16sec/60°7.4V
  • Stall Torque: 15kg/cm 6V; 17kg/cm 7.4V
  • Operating voltage: 6-7.4V
  • No-load current: 100mA
  • Cable length: 30cm
  • Weight: 60g
  • Power on, 0.5ms~2.5ms high level pulse, 0~180 degree change; power off, could rotate 360 degree in manually twist
  • Accessories included: Main shaft horn (4mm thickness), countershaft horn (2mm thickness)

Similar to MG996, but slightly (3mm) smaller, with a supporting second axle, LD-2015 High Torque Metal Gear Digital Servo Two-axis Servo f/ Robo-Soul Robot, £11.08

LD-2015
LD-2015

Note: biaxial means one drive shaft, one is the imaginary axis (supporting role).

vintage HS-300

Specification
  • Torque: 4.8V: 42.0 oz-in (3.02 kg-cm)
  • Torque: 6.0V: 51.0 oz-in (3.67 kg-cm)
  • Speed: 4.8V: 0.19 sec/60°
  • Speed: 6.0V: 0.15 sec/60°
  • Weight:1.66 oz (47.1 g)
  • Dimensions: Length:1.60 in (40.6 mm)
  • Dimensions: Width: 0.80 in (20.3 mm)
  • Dimensions: Height: 1.40 in (35.6 mm)

Other Hi-Tec

  • HS-303
  • HS-311
  • HS-322
  • HS-225BB
  • HS-225MG
  • HS-255BB
  • HS-430BH HV
  • HS-45HB
  • HS-81
  • HS-82MG
  • HS-56HB
  • HS-65HB
  • HS-65MG
  • HS5055MG
  • HS-5056MG
  • HS5645
  • vintage HS-646 MG
  • HS-55 equiv SG90
  • HS635HB
  • 645MG
  • HS75BB
  • HS-700
  • HS-715
  • HS-755HB
  • HS-125MG
  • HS-126MG

Other brands

  • Futuba 3003
  • ACOM AS-12

jr/ spektrum

DS8325

– discontinued

Specification

Key specs at 7.4 V: 0.118 sec/60°, 430 oz-in (31 kg-cm), weight 80 g.

eBay

JR Propo DS8325 9.6Kg.cm/0.15s

Power HD High-Torque Digital Servo DS8325HV

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6 thoughts on “Service please!”

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