P18318: Automatic Extend-Retract Hydraulic Restraint System for Amusement Rides
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Detailed Design MSD II

Table of Contents

This page documents the continued design work which was conducted in MSD II. This means that analysis and other information presented on another page is not repeated here. Preliminary detailed design work can be found here and or detailed design phase work from MSD I can be found here .

Team Vision for Detailed Design Phase

Bill of Materials and Budget

Bill of Materials

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There may have been adjustments made since the last upload of the Bill of Materials screenshot. For those with access to our google drive, our live document of the current BOM (and drawing tree) can be found here: https://docs.google.com/spreadsheets/d/1Cn9PnJ_VQP_LwmslyDjRNAAasP80ypYWoP_nLyGFiMM/edit#gid=837229667

Budget

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The current budget is missing some of the hardware and other components which are called out in the bill of materials. We approximately spent $25 total on all hardware used for the project. The budget also does not include parts the team did not pay for. This includes any components machined by ACM as well as the motor which was purchased by ACM. For those with access to our google drive, a folder with a live document of the current budget can be found here: https://drive.google.com/drive/u/0/folders/1Xi2s3LzJmakuykeSPs2D1KwC3Fu5o5rI?ogsrc=32.

Models and Drawings

During design and assembly, part numbers are to be tracked according to this document: https://docs.google.com/spreadsheets/d/1Cn9PnJ_VQP_LwmslyDjRNAAasP80ypYWoP_nLyGFiMM/edit#gid=0

The document details the method for acquiring the part, what material it is, and where is is intended to be manufactured. It also tracks which CAD file the part corresponds to.

Some of our CAD models can be seen below. The majority of our content for detailed design is considered private. Those with the required access can view this information | here.

Overall Assembly and Sub-assembly CAD Images

Overall Assembly (183180100)

Front Right Back Left Top
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Bottom Section Isometric 1 Isometric 2 Isometric 3
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Butt End Sub-Assembly (183180200)

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Screw, Rod, Piston Sub-Assembly (183180300)

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Purchased Part Information

The following items are components which are being purchased from outside vendors or supplied by our customer:

Engineering Calculations and Design Considerations

Accumulator and Manifold

While it was not largely covered earlier in the design process, it is important to note that we opted not to design a new accumulator and valve system (with solenoid) as well as manifold (we did have to design an intermediate manifold component). We will be using these components straight from the original hydraulic cylinder that ACM sent us.

Hydraulic Seals and Groove Dimensions

All seals were sourced from Grizzly Seals’ standard seal catalog. Each type of seal requires certain dimensions for grooves, gaps between mating parts, and recommended pressures which are specified in the catalog. All seal grooves and faces were dimensioned based on these requirements. Most sealing surfaces required a surface finish of Ra = 32 microinch. These surface finishes are called out on the drawings. Part tolerances were defined such that the seal geometry will remain acceptable away from nominal dimensions.

Butt End

Insert

Motor Mount Bracket

Intermediate Manifold

Rear Cover

Piston

Rod

Motor

Unfortunately when we went to purchase the motor we previously specified (see MSDI Detailed Design page), the price had more than doubled and the lead time became longer than a semester. This led us to have to find a new motor and we opted to use a similar Crouzet 8989B102 which can be found here. The most notable difference was this new motor produced less torque and greater RPM, which made us have to change the belt drive system we planned to use.

Belt Drive System

Ball Screw

Our selection criteria for our ball screw can be found here.

Several companies were reached out to in order to find the most desirable screw. We opted to go with components from Thomson Linear, and completed the purchase through Kaman Automation, a local distributor. Thomson offered a ball screw that best fit our needs and a compatible ball nut and end support. They also offered custom machining of the ball screw to fit our needs. The components we purchased can be found at the links below.

Inner Barrel

Outer Barrel

Cylinder Gland

Positioning Rod System

Originally the cylinder system was going to have internal positioning rods that were put in place to prevent the nut from spinning without ever moving laterally along the rod. Due to difficulty of machining the seal groves in the holes for the rods through the piston, the system was removed. It was determined that this was doable as the piston is connected to the rod and rod end, which would be fixed to a restraint arm and prevented from rotating. The design of this original system can be found below.

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Filters

Before adding filters to the design, tests need to be done to see how they impact the flow and determine their effectiveness. There isn’t enough time to complete these tests without significantly impacting the design progress. Therefore, filters will not be in the cylinder prototype. If time allows, the filter test will still be done and a recommendation will be made as to whether or not they should be included in further design iterations.

Electrical System Designs and Schematics

Electronics

Amusement park PLC

Amusement park PLC

Our original idea was to use a buck converter that was previously brought up in MSD I. Through some research, some buck converters don’t always supply proper voltage to the microcontroller which could limit full functionality of the microcontroller. Therefore further testing needed to be done to determine if these buck converters could be used in an isolated environment, away from the PLC user interface panel like the one shown above.

Another part of this system that needed to be isolated from the PLC are the signals that the ride attendee will send from the control system to the motor that will be operating the hydraulic restraint. This system design consists of 4N35 optocouplers to isolate the 24VDC signal and output a lower voltage signal to the microcontroller.

Based on the efficiency analysis of buck converters and isolation from optocouplers the circuit above was produced. From testing in PSPICE the performance of the buck converter was proved to be more efficient when a current of 1A or more was drawn. This could be a major flaw because if the buck converter wasn’t supplying a consistent voltage with very minimal ripple voltage then the microcontroller won’t be powered successfully.

Efficiency of the buck converter circuit from TI WEBENCH

Efficiency of the buck converter circuit from TI WEBENCH

The aim is to shoot for at least 90% efficiency to power the microcontroller properly. Based on the graph above, the buck converter circuit should provide an efficient supply voltage.

The optocouplers proved to be very efficient. When the circuit was tested in PSPICE, it was able isolate the 24VDC signal and output a low enough signal to not damage the microcontrollers inputs.

To prepare for a buck converter that might not work well with our system small transformers were researched. Not many transformer options were found to drop the voltage from 24VDC to 9VDC that were small enough to be used in our system. Instead, voltage regulators were designed into the system. While they might not be as efficient as a buck converter they offer a very consistent voltage supply. The above design was tested in PSPICE to simulate voltage regulation. From testing, the voltage regulators were able to step down the voltage from 24VDC to 12VDC, from 12VDC to 5VDC, from 5Vc to 3.3VDC. The separate voltages were chosen to supply enough voltage for the isolator circuit, and other sensors that will be applied to the entire system.

Crouzet Motor 8989B102

Crouzet Motor 8989B102

A 8989B102 Crouzet motor with lower torque was selected because of the price increase of the previous selected motor. It has a current rating of 4.9A and a supply of 24VDC. This will be controlled by an H-Bridge circuit device called a DROK L29.

DROK L298 H-Bridge Motor

DROK L298 H-Bridge Motor

The control circuitry can output 7A which is enough to power our motor. Which can supply a range of voltage from 6.5VDC to 27VDC.

Inrush Current Limiter

Inrush Current Limiter

While doing research on DC motor, I found that they are prone to having an inrush current spike when powered up. To prevent that I we will use a current limiter called an NTC Thermistor which is rated at 7A. As the 7A is being reached the thermistor starts to increase resistance to limit the amount of current being drawn by the device, in this case a motor.

Current Sensor Adafruit INA169

Current Sensor Adafruit INA169

To help monitor the current being drawn by the DC motor, a current sensor “INA169” by Adafruit will be put in series to the motor in order to help control motor operation with the controller. This device can be monitored up to 5A of current, which is suitable for our DC motor.

To also prevent any damage to the internal mechanics to the hydraulic cylinder and/or motor, a current limiting circuit was designed to prevent any over-current being sent to the motor if more torque is required. It will be attached to an optocoupler circuit to help notify the controller as to when the circuit starts to limit current.

Force Sensor SEN-09376

Force Sensor SEN-09376

To simulate a ride restraint making contact with a passenger, a force sensor will be used. This will send a signal to the controller to stop the motor if a minimum of 5 lbs of force is applied.

Rotary Switch PT65503

Rotary Switch PT65503

To simulate PLC signals to the optocoupler, 3 switches for ‘forward’, ‘reverse’ and ‘stop’ will be installed onto the device. Each will output 24VDC to the optocoupler when switched on, which then sends a signal to the controller as to which signal is actuated.

Arduino Uno R3

Arduino Uno R3

To help control the entire system, the controller that will be used is an Arduino Uno R3. It is powerful enough to control the H-Bridge, read signals from the machine operator, force sensor, and current sensor.

Software

The program in the Arduino will be constantly reading input signals that the ride attendee would be operating. It will also be reading a force sensor that we are assuming to be on a ride restraint to detect contact with the passenger in the forward/close direction. A signal that will be read in both directions will be the motor signal, which will be from the current limiting circuit, as soon as the current starts to limit the voltage to supply to the motor will drop and that will force a signal to the controller to be high. This will then shutdown any motor operation going in reverse or forward direction.

Test Plans

After review of the schedule and scope of requirements, the list of tests has been condensed. The following tests will not be performed:

Listed below is information pertaining to test plans that have been developed.

Max G-Force Test

Weight System is Able to Move

Manufacturing and Purchasing Plans

Most of our manufacturing and purchasing information is included in the above sections. All machined parts will either be made in house at RIT by both our team and the shop staff, or outsourced to ACM's shop. Components which need to be purchased are included in our budget as well as in a list below the above drawings table.

Plans for next phase


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