Issue No: 1 Doc No: VSSC:MVIT:ASMG:MDAD:DR:110:2016 Date : 28 – 07 – 2016 Security Classification: Restricted Copy No: Control Status: Universal launcher for ATVP- Preliminary Design Document Aerospace Mechanisms Group Mechanisms & Vehicle Integration Testing Entity Vikram Sarabhai Space Centre Thiruvananthapuram Prepared by Task Team Approved by Chairman, Task Team
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Elevation drive system consists of a driving shaft with two synchronised drive systems (one on each side as redundant) and each drive unit consists of a
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planetary reduction gearbox with worm gearbox for inherent self-locking, plummer block for housing the bearings, flame proof AC servo motor with closed loop control and built-in fail safe brake .
Estimation of torque demand:
Normal rotation speed = 450/min. = 0.013rad/s =0.125 rpm [90O in 2 min]
Acceleration time = 10 s
ω = ω 0 + α t where ω 0 = 0 rad/sec
Angular acceleration (α) = ω/t
Angular acceleration (α) = 0.0013 rad/sec2
Torque due to acceleration = 1.525 x105 kg-m2 x 0.0013 rad/sec2
Frictional torque = 0.5µFd = 0.5 x 0.0018 x 210000 x 0.22 = 41.6 Nm
Torque due to wind (25 m/s) = 12290 Nm (Refer Appendix: A)
Torque required to rotate the boom with rocket =520*9.81*2.27=11.579 kNm (for RH-300 elevation) & 7.984 kNm for RH 200 elevation Total torque required for
rotating the boom = acceleration torque + frictional torque+ wind
torque + torque due to rocket weight
= 198+41.6+12290+11579 = 24108.6 Nm
Assuming a factor of 2, Torque = 48217.2 Nm (say 50 kNm x2 Nos)
6.2.1. Gearbox specifications: A combination of planetary and worm gear box is used for elevation drive system. Gear Ratio Required Input speed (Motor speed) = 1500 rpm Output speed required = 450/min = 0.125 rpm Gear Ratio Required = 1500/0.125 = 12000
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Stage – I (Worm Gearbox) Gear Ratio = 70 Motor speed = 1500 rpm Output speed of gearbox = 1500/70 = 21.43 rpm Stage – II (Planetary Gearbox) Gear Ratio = 180 Output speed of gearbox = 21.43/180 = 0.119 rpm = 430/min Torque Calculations Torque requirement = 50000 Nm Input torque required at Stage – II gearbox = 50000/180 = 278 Nm Assuming a gearbox efficiency of 70%, the output torque required for Stage – I Gearbox is 397 Nm Input torque required at Stage – I gearbox = 397/70 = 5.67 Nm Assuming a gearbox efficiency of 40%, the motor output torque required is 14.2 Nm. Assuming a driver efficiency of 70%, the motor torque required is 20.25 Nm at 1500 rpm.
Gearbox Size : ~ 400 X 700 X 700 mm (Stage – I (Worm Gearbox) : ~Dia 600 X 1000 mm (Stage – II (Planetary Gearbox)
Weight : <700 kg (for two stages)
Rated torque for Stage – I : >2000 Nm (for 10000 rpm-hours life)
Rated torque for Stage – II : >50000 Nm (for 10000 rpm-hours life)
Design criteria : AGMA standards / DIN
Tolerance : DIN 4 or better
Qty : 02 Nos
Interfaces:
Mounting: Foot mounted Planetary and Worm gear box with
Output: Splined shaft preferred
Input : Splined shaft preferred
6.2.2. Motor and Control system Specifications 1. Category : Programmable A/C Servo motor (Siemens
make) with position and speed feedback, with brake 2. Make : Siemens
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3. Rated Power : 3.3 kW 4. Rated Speed : 1500 rpm 5. Rated Torque : 24.5 Nm 6. Static Torque : 27 Nm 7. Mass : 27.5 kg (without brake) 8. Margin on Torque = (27/20.25) -1=0.3 9. Qty : 02 Nos
Control system:
1. Type: Servo control system with programmable position, speed and acceleration meeting the accuracy requirements specified in Section 4
2. Programmable from a remote PC 3. Final drive position sensor (optical encoder of accuracy 0.5 arc minute or
better). It is preferred to have the feedback sensor on the boom for better positioning accuracy.
6.2.3. Shaft A cylindrical stepped shaft of dia 260 mm is firmly attached to the boom at the hinge location through splines (Fig.8a). The maximum stress observed is 203MPa and the angular deflection is 0.164deg. The sag observed due to the weight of the boom is 0.313 mm. The boom is laterally restrained using a coupling as shown in fig. 8b. Shape: Dia 260mm with spline at boom location, reduced to Dia 240 stepped down
to dia 220 at bearing locations and interfaces for gearbox coupling
Material : 15CDV6 steel
Qty : 01 No
Attachment details : Ref Fig 8b
6.2.4. Spline Selection
Involute sided splines of 300 pressure angle is selected for the application. The spline selection is carried out as per IS standard 3665 The configuration of spline arrived at is 260x244x31x 7HE / 7he IS:3665
Major dia of Internal Spline : 260mm
Minor dia of Internal Spline : 244mm
Major dia of External Spline : 258.4mm
Minor dia of External Spline : 242.4mm
Module : 08
No of Teeth : 31
Length of Spline : 200 mm on each side
Design Margin (Stress based) :835/160 – 1 = 4.2
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6.2.5. Brake specifications:
From Section 6.2 the torque required to hold the boom in position is estimated as 23869 Nm at the boom location. Since it is difficult to accommodate a brake with 23869 Nm braking torque in the proposed configuration, it is decided to keep the brake at the worm gearbox output shaft. A normally closed (fail safe) heavy duty disc brake is preferred. From literature it is found that heavy duty disc brakes are available and typical specifications are given in figures 9a and 9b.
Holding capacity of brake required = 23869/180
= 133 Nm
Type : Disc Brake, NORMALLY ENGAGED, electrically released (with manual release option)
Manufacturer : Pintsch Bubenzer (Or equivalent)
Supply : 3 Phase AC
Power : 450 W
Current : 0.8 A at 400V
Disc Dia : 630 mm
Braking torque : 2200 Nm
Mass : 110 Kg
Margin on Braking Torque : (2200 X 2/133) - 1 = 32
Two disc brakes on either side of boom is provided
6.2.6. Elevation drive bearings selection
Spherical roller bearings have two rows of rollers, a common sphered outer ring raceway and two inner ring raceways inclined at an angle to the bearing axis is considered. The centre point of the sphere in the outer ring raceway is at the bearing axis. Therefore, the bearings are self-aligning and insensitive to misalignment of the shaft relative to the housing, which can be caused, say, by shaft deflection. Spherical roller bearings are designed to accommodate heavy radial loads, as well as heavy axial loads in both directions.
Based on the load ratings, SKF Part No: 23044 CC/W33 (Spherical roller
bearings with cylindrical bore) is selected
The load ratings and dimensions of the selected spherical roller bearing part number are highlighted in the catalogue reproduced in Fig. 10. Design Checks Weight on bearings = 21+0.5/2 =10.75 tons = 107 kN Load due to Thrust misalignment (30) = 3.382 kN
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Radial load expected = 107 + 3.382 = 110.38 kN Margin on radial load = 1220/110.38 - 1 = 10 Axial Load expected (due to 25m/s wind) = 2.72kN (Appendix: A) Speed =0.125rpm (limit 2000rpm) Qty = 02 Nos Hence the bearing selected is safe for operations 6.3. Pedestal / Support system
6.3.1. Shaft Support/Plummer block assembly:
The boom shaft is supported on 2 spherical roller bearings each of which is assembled on plummer block housing. The plummer block selected is a SKF standard part with part no: SNL 3044 G which suits the selected spherical roller bearings (SKF Part No: 23044 CC/W33). The important housing dimensions and its associated components of the selected part are highlighted in the catalogue reproduced in figures 11 and 12. The assembly details are shown in figure 8b. 6.3.2. Load capability of Plummer block housings
The load capability of housing and attachment bolts are highlighted in the catalogue reproduced in Fig. 13. Radial load acting on plummer block housing (P00)= (210000+5050)/2 + thrust misalignment(3.38kN) = 110.9 kN Axial load acting on plummer block housing = 2.72 kN [Wind Load- refer appendix: A] Margin of safety on radial load = 520/110.9 -1 = 3.68 Margin of safety on axial load = 168/2.72 -1 = 60 Tensile load on housing (on bolts) (without preload) = 2.72+3.38=6.1kN (Upward wind load+ thrust misalignment) Load capability for cap bolts (M24 x 4Nos) (1800 load) = 380 kN Plummer block Qty : 02 Nos 6.3.3. Pedestal support system
The entire bearing housing, gearbox and motor is supported on a 50mm thick
plate mounted on the Pillar Fig. 14. The Pillar and Plate are designed to take care of
the axial and lateral loads of the boom and the reaction loads of the gearbox motor
assembly. A box type monocoque construction is adopted for the pillar design and
the details are given below. FE analysis were carried out using shell elements and
stress & deflection values are found to be within limits.
6.3.3.1. Loads ( with a factor of 2)
Axial a. Self weight of boom/2 + Bearing/housing + Gearbox (2) + Rocket
wt/2+ Plate wt + motor + brake :127.53x2= 255.061 kN
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b. Gearbox/Motor reaction torque : 50kNm
Lateral a. Wind Load from Boom : 2.72kN
Overall size : 1.5mX1.35mX0.7m box made of 50 mm thick plates (Fig 14)
Material : Structural Steel
Stress : 16.7 MPa
Deflection : 0.137 mm.
Interfaces : Plate to Pillar M24 Bolts (16+ 12 Nos) (hole locations are shown in fig 14)
: Pillar welded to Base Plate.
Qty : 02 Nos
6.4. Azimuth Drive System
6.4.1. Base Plate
The entire assembly mentioned above is supported on stiffened plate
mounted on Slewing Bearings. The Base Plate is designed to take care of the axial
and lateral loads from the Pedestal assembly and the reaction loads of the azimuth
drive gearbox. A skin stiffened construction is adopted for the Base Plate design and
the details are given below (refer Fig. 15). FE analysis was carried out using shell
elements and the stress & deflection values are found to be within limits.
Loads
Axial a. Loads from Pedestal assy : 373.466x2 =747 kN
(with a factor of 2) Lateral
b. Wind Load from Boom : 2.72kN c. Azimuth Gearbox/Motor reaction torque : 2.06 kNm
Overall size : Top circular plate of dia 3500 mm (30 mm thick) Fig 15
: Bottom circular plate of dia 2500 mm (20 mm thick)
: 20 Radial stiffeners and circular stiffeners (16 mm thick)
Material : Structural Steel
Stress : 44.2 MPa
Deflection : 0.504 mm.
Interfaces : Base Plate to Slewing ring M30 Bolts at 2540mm PCD 60 Nos Base Plate to Pedestal support assy - welded connection
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Qty : 01No
6.4.2. Slewing Bearings:
The entire assembly with Base Plate is assembled to Slewing Bearings for azimuth drive. The configuration selected is having an outer race with external gear and is fixed to the foundation. ROTHE ERDE make KD 600 model with external gear fixed to foundation is considered as a candidate bearing for this application.
1. Type: Servo control system with programmable speed and acceleration
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2. Programmable from a remote PC 3. Final drive position sensor (optical encoder of accuracy 0.5 arcminute)
6.4.6. Azimuth Brake specifications
From Section 6.4.3 the torque required to hold the azimuth sub assembly in position is estimated as 12290 Nm. A normally closed (fail safe) Heavy duty disc brake is preferred. From literature it is found that heavy duty disc brakes are available and typical specification is given below (Refer Figures 18a & 18b)
Braking torque required : 12290/16 = 768 Nm
Type : Disc Brake
Manufacturer : Pintsch Bubenzer
Supply : 3 Phase AC
Power : 450 W
Current : 0.8A at 400V
Disc Dia : 710 mm
Braking torque : 5490 Nm
Considering two brakes for redundancy
Margin on braking torque: 5490X2/768 -1= 13.3
In addition to this mechanical lock need to be provided for holding
7.0. Modal Analysis
The entire assembly is analysed for finding the modes and the first mode is 3.6 Hz. The first mode is dominated by the torsional mode of the shaft (Fig 19a). The second mode (4.8 Hz) is mainly due to the lateral bending mode of the shaft (Fig 19b).
8.0. Instrumentation
Instrumentation details will be furnished in the next release.
9.0. Surface Protection
Surface protection to be implemented as per the following standards
1. IS: 8062 (Parts I to III): Code of practice for cathodic protection of steel
structures.
2. IS:8062 (Part I)—1976, Cathodic protection signifies protection of a metal
structure from corrosion in an electrolyte by making the structure the
cathode so that direct current flows into the structure from the electrolytic
environment.
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3. In addition to the above, zinc rich primer coating is to be applied as per IS
standard.
4. ISO 12944: 1998, Paints and varnishes – Corrosion protection of steel
structures by protective paint systems.
10.0. Foundation
Foundation required for supporting the launcher will be designed by CMG.
Foundation shall embed an interface ring for assembling the slewing bearing. The
top surface shall be 150 mm above the ground surface. Conduits with cable carrier
shall be provided for cable routing, starting from the center to radially outward at
450,1350,2250,3150.
11.0. Thermal analysis
Thermal analysis of the system under exposure to rocket plumes to be carried
out to assess TPS/cowling requirements.
12.0. Acceptance Tests
After assembly and integration of all sub systems at TERLS/VSSC, the
following acceptance tests need to be carried out. Separate acceptance test
document will be brought out.
12.1. Load Tests
After satisfactory completion of installation, load test is to be conducted to
design limit load by simulating required conditions. During this test, deflection and
strain measurements of the launcher, No load currents & Full load currents of both
the motors and current values of all four brakes has to be monitored.
a. The tip deflection with RH200/RH300 in position shall be measured. It should
be less than 14.4 mm for the design limit load.
b. Twice the motor mass shall be kept at the rail tip and the launcher
survivability shall be demonstrated.
12.2. Frequency Measurement
Axial and lateral frequency of the launcher shall be measured. Acceptance
criteria are that the frequency of the overall system should be more than 2.3 Hz in
both directions.
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12.3. Acceptance Trials
The drive systems are the main elements of the launcher. After installation of
the launcher, the party shall demonstrate the working of both drive systems
12.4. Brake Trials
After installation of the launcher, effectiveness of the elevation drive and
azimuth drive brake shall be demonstrated. Brakes also shall be tested for two times
the holding capability, to verify the margin.
12.5. Safety systems
All safety interlocks and limit switches for drive systems shall be
demonstrated through various trials.
12.6. Calibration
Measurement accuracy of elevation and azimuth angle shall be within
specification. All the instrumentation systems shall be calibrated and calibration
reports shall be supplied to VSSC.
12.7. Alignment checks:
Alignment is one of the important criteria for acceptance of the total
system. In every stage of erection, alignment has to be checked for proper leveling,
angular deviations, parallelism etc with theodolite. The specifications for guiderails
alignment is given below
Straightness of each rail (Vertical & Lateral axis): ± 0.5 mm / meter and ± 1.0
mm for total length of 13 m.
Parallelism of rails: 222 + 0.0, - 0.1 mm for total length
No deviation will be accepted
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13.0. Summary The preliminary design of universal launcher for RH 200 & 300 are presented.
The subsystems required for the launcher are identified and configured. Counter
balance mass is provided to minimise the drive torque requirement. Provision for
tuning the counter mass is included to take care of the fabrication deviation.
Preliminary structural analysis is also completed and is meeting the functional
requirements. However the stiffness of the beam need to be finalised based on
dynamic analysis considering the wind conditions and clearance study while the
rocket is sliding. Efforts are taken to identify commercially available standard
components/ systems for the launcher design. Foundation design and cowlings for
the systems to be taken up in the CDR phase. Regarding the gearbox for elevation
drive a customised integrated gearbox with worm input and planetary output can be
considered.
14.0. References
1. MOM Task team 2. IS 875 (Part III): Code of practice for design loads for buildings and structures
(wind loads) 3. IS 3665: Dimensions for involute sided splines 4. IS 8062 (Parts I to III): Code of practice for cathodic protection of steel