Introduction
For over 60 years electric shock has been used as first aid in treating venomous bites and stings in Third World countries. Using the spark plug wire of an internal combustion engine to treat scorpion stings is a folkloric remedy that dates back to at least the 1940s [1] . Later, in the 80's and 90's, studies were published regarding using shock on snake bites by Guderian[2] and Mueller[3] [4] and spider bites by Osborn [5][6][7][8] . When no medical facilities nor antivenom are accessible, first aid electric shock has been touted as an acceptable alternative. However, an adequate source and method of delivering the shock in remote 3rd world locations still remains a challenge.
The purpose of this wiki page is to to provide details of our current design as well as facilitate collaboration to improve the design. The goal is to develop a portable, robust, mechanical shock-generation device that can be used in remote locations where traditional treatments are unavailable. A small non-profit organization that is dedicated to helping the underserved in developing world locations has some monitary resources available for efforts to this effect.
More information about using shock for venomous bites or stings can be found at http://venomshock.wikidot.com/.
Background of the STAR Spring Zapper Design
The picture at the right shows the STAR Spring zapper. It is small, light weight and can be operated by a patient on him/herself. The STAR Spring Zapper was created through collaboration of four individuals whose initials spelled the word STAR. Though the design is functional, the apparatus has limitations. To bring new insight, ingenuity and energy to address these limitations the team is seeking additional design talent. The current design was engineered using the CAD drafting software Solid Edge. It is anticipated that new team members will be proficient using this tool, though proficiency using Pro E would be acceptable.
Design Overview
Our teams primary purpose is to improve the existing design for reliability, size of aparatus, and ease of operation. Although successful improvement of existing design is anticipated, exploration of a new design may be considered.
Current STAR Zapper Design Overview
The STAR Spring Zapper consists of 5 cast polyurethane parts, a magneto, 4 super magnets, two bearings, a recoil spring, an axle, and a probe. With the exception of the cast parts, all parts are easily purchased and require little or no modification. Once the molds have been created, cast parts can be manufactured in an individual's shop.
Design Criteria
The design criteria used during the engineering of this design were as follows.
- Rugged design
- Hand held
- Light weight
- No battery required
- Manufacturable in the workshop of a
- Deliver reliable and repeatable shocks
- Can be used on onesself (i.e doesn't require an administrator)
- User friendly (easy to understand and operate)
Existing Design
The existing design meets many of the criteria above. It fits into the palm of a man's hand, weighs less than a pound, doesn't require a battery, can be readily manufactured, delivers repeatable shocks, is fairly rugged and corrosion resistant. However, user trials indicate that it is not easy to operate. An injured individual in a state of panic and pain would have difficulty following the instructions. The device is too large for a small hand, and the latch and trigger mechanism is too complex to manage in a tense environment.
How it works
The complete users manual can be found here
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| #1 Arm the device. The first step (and probably the least intuitive), is to arm the device. This is done by pushing the trigger in toward the flywheel. The picture above shows the trigger correctly pushed in. This enables the ratcheting system, permitting the flywheel only to be turned in the counter clockwise direction. It will be latched every 1/2 rotation until the spring is completely wound (approximately 9 complete turns) #2 Open the handle. Using a fingernail pull the flywheel handle out of its slot. A spring mechanism in the handle automatically returns the handle to its home position. Challenge: The requirement to arm the device first, before cranking, is not intuitive. Ideally, this would be an automatic process in which the device is armed when the handle is folded out. |
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| #3 Wind the flywheel. Turn the Flywheel counter clockwise. While turning, a ratcheting mechanism keeps the flywheel from prematurely unwinding. The Flywheel winds approximately 8-10 turns before the recoil spring is completely tight. #4 Align Dots. After the desired number of cranks are turned, the flywheel needs to be stopped at a location where the ratchet will catch. The ratchet will catch at locations where the dots align. Challenge: One limitation is that there is no easy way of determining how tightly the flywheel is wound. One option is to add a clear viewing portal in the case as well as the flywheel which would allow the operator to see if the spring was wound or not. A visual indicator of the amount the spring has been wound would be helpful. Also, the ratchet system would be easier to operate if the dots did not need to be aligned. For example, at whatever number of rotations the user stopped cranking, the flywheel would stop. |
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| #5 Close the handle. By letting go of the handle, the handle automatically returns to its slot. #6 Apply the probe. The probe should be placed directly over the bite mark. The ground, which sticks out of the case, should be applied to the opposite side of the bite. #7 Pull the trigger. The trigger mechanism needs to be pulled firmly. Challenge: If the trigger is not firmly pulled, the flywheel will only unwind one revolution, and then the ratchet system catches it again. There is a lot of force being released in the spring and even at one revolution, the ratchet system can be damaged. The ratcheting/trigger aparatus needs to be modified or completely redisigned. One possibility might be to enable the ratcheting system only if the cranking handle is open. Then, when the trigger is pulled (even very slowly) and the spring is discharged, there is no chance a ratcheting mechanism will catch. |
How is it currently made
The overall goal of the existing STAR Spring Zapper design was to make it easily manufacturable in an average individual's basement. Predecessors of the STAR design required a high degree of mechanical ability as well as a well supplied machine shop.
Parts
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| With the exception of the cast parts, everything else can be readily purchased and requires little or no modification. The exception is the flywheel axle rod which needs to be cut down to 1.75" with a hacksaw from its original 3' lengh. The picture below shows all the parts that go into making a STAR Spring Zapper. |
Molds
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| Cast Parts The molds for the case were developed using an expensive 3D printing process. Once the final production design is complete, then molds out of delrin or aluminum will be created. As indicated below there are several parts that were case as well as the molds to create them. Case Mold: The case mold also includes the probe tip. This probably isn't ideal but it seemed appropriate at the time. After a 2' length of spark plug wire has been added to the magneto, a small stainless steal tip is crimped to the end of the wire. At the same time the axle that will be set in the case is placed in the mold. This assembly is placed inside the bottom half of the mold. After adding a few more mold inserts, the top of the mold is attached. Finally, a two part mixture of polyurethane is poured into the mold. After curing, the mold is carefully taken apart and the case and the molds are cleaned up. Flywheel Mold: A similar process is used for the flywheel. 4 super magnets are incased in one half of the mold. After adding the top half of the mold, more inserts are added to create different features in the flywheel. Trigger and handle Mold: There is also a mold for the handle and the trigger. |
Detailed Design
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| This picture shows the handle closed with the trigger engaged. This would be the configuration when the Zapper is completely wound up and ready to be discharged. The trigger spring's orientation serves two purposes. Once the trigger has been armed (pushed in toward the flywheel), the job of the spring is to keep trigger oriented in such a way as it readily falls into the slot in the flywheel (as the flywheel is being cranked.) This is to keep the flywheel from completely unwinding if the handle is accidently dropped. After the trigger is pulled, it now needs to be kept from falling into the slot in the flywheel. The trigger is positioned such that, once it is firmly pulled, the tip of the trigger passes over the little round bump on the case. Once past the bump, the trigger can't accidentally catch the discharging flywheel. This design works well if the trigger is pulled hard. However, when the trigger is pulled hesitantly, the flywheel starts to discharge before the trigger has passed the round bump in the case. On the next revolution the trigger falls into the notch in the flywheel and violently stops the flywheels discharge, causing wear on all the parts. The position of the round bump on the case is also important. When the trigger has been armed (pushed toward the flywheel), it needs to stay close to the flywheel the entire time the crank is being turned. As the flywheel turns, the trigger rubs across the flywheel, falling into and out of the slot in the flywheel. The round bump can't be put too close to the flywheel or, on the next rotation, as the trigger is coming out of the slot in the flywheel, it will catch on the bump and hook there. On the other hand, if the bump is put to far from the flywheel, even when the trigger is pulled hard, it won't latch on the other side of the bump and will accidentally and violently latch the discharging flywheel. |
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| This pictures shows the case & trigger but without the flywheel. The axle that the fly rotates around can be seen as well as the hook that the recoil spring catches. This picture shows how the trigger would be located if the flywheel had recently been discharged. |
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| In this picture the handle is being used to crank the flywheel. The flywheel is in an orientation where the holes are aligned so the trigger can latch. The trigger falls into this latch position on every 1/2 rotation. This picture incorrectly shows that the magnets are aligned with the magneto when the trigger is in the latched position. The super magnets are so strong that, if the flywheel was latched here, the magnets themselves would hold the flywheel from unwinding. |
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| This picture shows the case and trigger without the flywheel. The trigger is in the released position (i.e, just after the trigger has been pulled and the flywheel discharged.) |
Assembly process
Once all the cast parts are finished, cured, deburred and cleaned up, the assembly process can begin. The steps include:
- Press the bearings into the flywheel
- Assemble the handle
- Attach the handle to the flywheel
- Insert the trigger and spring into the case
- Insert the flywheel into the case
- Bolt the flywheel in place and add drop of locktite
- Test the Zapper and make sure a clean bright spark will jump 1cm from the probe tip to the ground.
