Week 11

     This week we finalized our design for the motor module, as Deliverable 5 and the final presentation/packet were due at the beginning of Week 12 (December 5). We had officially decided on using an off-centered mass spun by a motor, and during class we discussed different placement options (i.e., at the ankle or mid-calf). We were also initially thinking about placing two motors on each leg; one on the lower leg and one on the thigh. However, we spoke to our tech adviser during the week and he brought up the fact that having two motors may cause issues. Unless the motors are perfectly in sync, then we might end up with undesired cancellation (or additive) effects. 

Discussing placement options for the motor module on the thigh.

     We also did some preliminary calculations on the toque and power required for different frequencies and rotation weights, in order to help us determine what type of motor we'd need to order. Later in the week, Dr. Gordon let us borrow a motor and tachometer for testing. We wanted to spin an off-center mass and see if the results were as expected (meaning that our predictions for our actual motor would also likely be correct). We found the motor Dr. Gordon gave us to be too slow for our purposes. We borrowed an RC plane motor from a friend, and found that it was too fast; therefore we know that we want a motor that is somewhere in between the two sizes. 

     We were unable to spin a mass with the current set-up, however. We plan on mounting a motor to a wooden board sometime during the next week and repeating the test, as we feel as though this will be much easier than trying to hold the motor (and therefore, pose less threat of injury). 

Jake trying to hold onto the spinning motor.

Using the tachometer to measure RPM.

RPM of the RC plane motor (~90 Hz).

     This week we also worked on Deliverable 5, the presentation, and the packet. The figure below shows our current plan for the whole body. We will detail the work done since the midterm and our future plans during the presentation.

 

New proposed scheme for the entire body, including elastic bands and the motor modules. 

We hope to order all of our parts before Christmas break and start constructing the prototype (and finishing critical module testing) immediately after Christmas break. This can be seen in the updated Gantt chart below. 

Updated project Gantt chart.

Week 10

     This week during class we continued researching the cross-sectional area and modulus of elasticity of bone by discussing and reviewing some of the articles found during the previous week (see Week 9's blog post for reference). We also spoke with our professor, Dr. Gordon, and discussed our direction for the future. He told us that our Deliverable 5 was due sometime before the end of the semester, and that we could submit it early if we wanted feedback before including it in the final report packet. We also downloaded the STL file for a femur (also shown in Week 9's post) and opened it in Solidworks. We were able to closely estimate the cross-sectional area of the femur by taking a "slice" of the femur in Solidworks. It was found that the cross-sectional area was within the size range we found reported in research papers and internet searches,
     We also met as a group during the week to brainstorm ideas for how we want to target the legs, since astronauts do not move them very often while in space. We had two major strategies: overpowering (where the device or suit moves the leg) and frequency-based (where we would be trying to achieve a minimum strain delivered at a specified frequency). Concepts were generated under these two main strategies and can be seen in the pictures below.

Concepts for the frequency strategy.

Concepts for the overpowering strategy.

It was decided that the following considerations would be important for ranking the concepts. Group members were asked to rank the concepts individually over break. 

Important considerations when ranking concepts. 

Below is an example of one group member's rankings shown in a decision matrix:

Decision matrix created by one group member.

Week 9

     This week during the class meeting time, we discussed our current state of the project with Dr. Gordon and what we should do to move forward. Our Deliverable 5 has been postponed until the end of the semester, as we need to redesign or add onto our current design in order to address the issue with the legs. (Our current design requires the legs to move, but we have learned that astronauts do not move their legs very often while in a zero gravity environment, rendering our current design largely ineffective.)
     In addition, Dr. Gordon wants us to research further into the amount of load needed to sustain healthy bone. In order to determine this, we decided to also look at physical and mechanical properties of bone, such as the cross-sectional area, modulus of elasticity, etc. We spent several hours researching this, but did not have much luck. Most of the articles we found either did not give the information, or were not accessible. Dr. Gordon suggested that we might be able to find CAD files of bones, from which we could find the cross-sectional area. Below is an example of a femur we found on the NIH's 3D Print Exchange Website (http://3dprint.nih.gov/discover/3dpx-000168). The model was created from a CT scan, meaning that it is probably very accurate (even though the sample size in this case is only 1). A model of the tibia and fibula bones are shown as well.

STL File of a Human Femur found on the NIH 3D Print Exchange.

STL File of a Human Tibia and Fibula found on the NIH 3D Print Exchange.

     During the week, we met as a team to try and figure out what we needed to research still, and also to discuss options for targeting the bone. This was not a formal brainstorming session, but the following options were suggested:

Possible options for targeting the legs.

     Of these suggestions, we deemed that motors might be the most practical to use. The following sketch shows an early idea of how they might be implemented in conjunction with the current design.

A sketch of the leg showing a motor being used to move the leg.

     We also found some research articles that suggested that either a large load could be applied less frequently, or a smaller load could be applied more frequently in order to maintain healthy bone. The amount of strain needed to be applied and the frequency will determine the type of motor(s) we purchase, should we choose to go that route, but we need to find and finalize the modulus of elasticity first.
      The following papers were found when researching this topic:

"The Longitudinal Young’s Modulus of Cortical Bone in the Midshaft of Human Femur and its Correlation with CT Scanning Data"

Abstract: This study was concerned with establishing the regional variations in the magnitude of the longitudinal Young’s modulus of the cortical bone in the femoral midshaft and with investigating whether a relationship existed between the Young’s modulus of bone and the CT number. Were such a relationship to exist this would provide a noninvasive method of assessing the quality of bone in the regions of fixation of implants to bone. The data would be of considerable aid to designers of implant stems to withstand the stresses arising at its interface with the bone. Five pairs of fresh frozen human femora were used. Several beam-shaped small specimens were methodically harvested from each pair and were used to measure the longitudinal modulus adopting the three-point bending test, which was carried out with a specially constructed and validated apparatus. CT scans of the bone were obtained, prior to harvesting the specimens, and the CT number was measured at locations corresponding with the specimen sites. The results indicate that in the femoral midshaft the cortical bone has an average Young’s modulus value of 18600 ± 1900 MPa. This agrees well with data obtained by other researchers using different experimental methods. Statistical analyses revealed no regional variations in the value of the longitudinal modulus of the bone. No correlation was found between the bone modulus and the CT number. Thus a noninvasive method for establishing the bone properties still remains a challenge.
Link: http://link.springer.com/article/10.1007/s00223-002-2123-1

"Elastic modulus and hardness of cortical and trabecular bone lamellae measured by nanoindentation in the human femur"

Abstract: "The mechanical properties of bone tissue are determined by composition as well as structural, microstructural and nanostructural organization. The aim of this study was to quantify the elastic properties of bone at the lamellar level and compare these properties among osteonal, interstitial and trabecular microstructures from the diaphysis and the neck of the human femur. A nanoindentation technique with a custom irrigation system was used for simultaneously measuring force and displacement of a diamond tip pressed 500 nm into the moist bone tissue. An isotropic elastic modulus was calculated from the unloading curve with an assumed Poisson ratio of 0.3, while hardness was defined as the maximal force divided by the corresponding contact area. The elastic moduli ranged from 6.9±4.3 GPa in trabecular tissue from the femoral neck of a 74 yr old female up to 25.0±4.3 GPa in interstitial tissue from the diaphyseal cortex of a 69 yr old female. The mean elastic modulus was found to be significantly influenced by the type of lamella (p<10⁻⁶) and by donor (p<10⁻⁶). The interaction between the type of lamella and the donor was also highly significant (p<10⁻⁶). Hardness followed a similar distribution as elastic modulus among types of lamellae and donor, but with lower statistical contrast. It is concluded that the nanostructure of bone tissue must differ substantially among lamellar types, anatomical sites and individuals and suggests that tissue heterogeneity is of potential importance in bone fragility and adaptation."

Link: http://www.sciencedirect.com/science/article/pii/S0021929099001116

"The elastic properties of trabecular and cortical bone tissues are similar: results from two microscopic measurement techniques"

Abstract: "Acoustic microscopy (30–60 μm resolution) and nanoindentation (1–5 μm resolution) are techniques that can be used to evaluate the elastic properties of human bone at a microstructural level. The goals of the current study were (1) to measure and compare the Young’s moduli of trabecular and cortical bone tissues from a common human donor, and (2) to compare the Young’s moduli of bone tissue measured using acoustic microscopy to those measured using nanoindentation. The Young’s modulus of cortical bone in the longitudinal direction was about 40% greater than (p<0.01) the Young’s modulus in the transverse direction. The Young’s modulus of trabecular bone tissue was slightly higher than the transverse Young’s modulus of cortical bone, but substantially lower than the longitudinal Young’s modulus of cortical bone. These findings were consistent for both measurement methods and suggest that elasticity of trabecular tissue is within the range of that of cortical bone tissue. The calculation of Young’s modulus using nanoindentation assumes that the material is elastically isotropic. The current results, i.e., the average anisotropy ratio () for cortical bone determined by nanoindentation was similar to that determined by the acoustic microscope, suggest that this assumption does not limit nanoindentation as a technique for measurement of Young’s modulus in anisotropic bone."

Link: http://www.sciencedirect.com/science/article/pii/S0021929098001778

"THE MATERIAL PROPERTIES OF HUMAN TIBIA CORTICAL BONE IN TENSION AND COMPRESSION: IMPLACATIONS FOR THE TIBIA INDEX"

Abstract: "The risk of sustaining tibia fractures as a result of a frontal crash is commonly assessed by applying measurements taken from anthropometric test devices to the Tibia Index. The Tibia Index is an injury tolerance criterion for combined bending and axial loading experienced at the midshaft of the leg. However, the failure properties of human tibia compact bone have only been determined under static loading. Therefore, the purpose of this study was to develop the tensile and compressive material properties for human tibia cortical bone coupons when subjected to three loading rates: static, quasistatic, and dynamic. This study presents machined cortical bone coupon tests from 6 loading configurations using four male fresh frozen human tibias. A servo-hydraulic Material Testing System (MTS) was used to apply tension and compression loads to failure at approximately 0.05 s-1, 0.5 s-1, and 5.0 s-1 to cortical bone coupons oriented along the long axis of the tibia. Although minor, axial tension specimens showed a decrease in the failure strain and an increase the modulus with increasing strain rate. There were no significant trends found for axial compression samples, with respect to the modulus or failure strain. Although the results showed that the average failure stress increased with increasing loading rate for axial tension and compression, the differences were not found to be significant. The average failure stress for the static, quasi-static, and dynamic tests were 150.6 MPa, 159.8 MPa, and 192.3 MPa for axial tension specimens and 177.2 MPa, 208.9 MPa, and 214.1 MPa for axial compression specimens. When the results of the current study are considered in conjunction with the previous work the average compressive strength to tensile strength ratio was found to range from 1.08 to 1.36."
Link: http://www-nrd.nhtsa.dot.gov/pdf/esv/esv20/07-0470-O.pdf

     This week team members also updated their ethics papers as the final draft is due at the beginning of Week 10.

Week 8

     This week during class, we discussed some of the articles we had researched the previous week. We would like to look into the bone's response to mechanical stimuli more, and see if there is a minimum threshold required to prevent bone loss. We also got the thumbs-up for using the Instron tensile test machine, so we ran some tests on our elastic bands.
     The elastic bands were cut into strips that were 10 cm long and 1.5 cm wide. Each elastic band (there are five different ones) was cut up to provide three samples for testing. Shown below are pictures of this process.

Shown are the small elastic band strips used for tensile testing.

The Instron machine pulling one of the black elastic band samples.

Testing the different elastic bands.

     Isaac later compiled the data gathered from the tests and organized them into an excel file. Shown below are plots generated for each different color band.

This is an example of one of the results from a black elastic band.

Black elastic band results.

Blue elastic band results.

Green elastic band results.

Red elastic band results.

Yellow elastic band results.

      During the week, we met as a group to delegate duties and discuss Deliverable 5. We started on some Solidworks, updated the excel mathematical model, and constructed the critical module test using elastic bands.

Version 1 of the harness drawn in Solidworks.

Version 1 of the ankle brace drawn in Solidworks.

 The critical module test utilized several different bands in order to provide sufficient load. We tried to make the elastic band module as similar to the spring model as possible (in regards of things like anchor point locations and force) so that fair testing and comparison between the two methods would be possible.

This was for the inside of the arm. It contains two black bands and one blue band, all stacked on top of each other.

This is the outside of the arm. Bands were attached to the wooden model via duct tape.

The final product.

Example of the math model for the constant force spring system.

Moment about the inside of the arm using the spring system.

Moment about the outside of the arm using the spring system.

Using both the inside and outside spring system.

Moment about the inside of the arm using elastic bands.

Moment about the outside of the arm using elastic bands.

Using both the inside and outside elastic band system.

     Our team had some questions about the architectural design portion of the Deliverable, so we emailed/met with our professor. Dr. Gordon said that he was surprised we hasn't asked for an extension on the deliverable, and told us that he would prefer we wait to submit the deliverable and focus on doing more research. The research should concentrate on whether there is a minimum force needed to stimulate the bones and should also provide alternative/additional options for targeting the astronauts' legs. (This had always been a point of concern, and Jake had emailed a former professor and astronaut who confirmed that astronauts do not use their legs extensively while in zero gravity). 

Week 7

     This week we spoke with Dr. Gordon about our project budget. He said that our budget would likely be around $500-600. We also further defined what we could use for anchor points and guide loops. We decided that a fully-body harness would be essential to our project, as we think that this would make an excellent (and comfortable) place to anchor our bands and/or springs. We decided that (if budget permits) using braces might be a good option for further anchor points since they are already designed for specific body parts and are made to be comfortable for long periods of wear. An additional benefit of using braces is that many braces have Velcro fasteners, meaning that they can be put on and taken off quickly and easily. Any sort of "guide loop" could then be mounted to these surfaces. We would ideally like two knee braces, two ankle braces, two elbow braces, and a pair of gloves. (This would allow us to reach the more distal portions of the body.)
Below is an example of what we are hoping to use.

This diagram shows the different braces we are looking into using, as well as the harnesses we are considering. If  budget permits, we would like one the body harnesses shown, rather than the standard climbing harness on the right (which lacks the upper body section). 

Brainstorming on budgets and attachments. 

     In addition, Isaac started working on a CAD model that will be submitted with our Deliverable 5 (due Monday of Week 8). This will include a simple "person" and will show where the device is located on the body and the different attachment points. This will need further developing.

Isaac using Solidworks to create a CAD model for our project.

     Finally, we were hoping to use the tensile testing machine to get pull profiles for our elastic bands, as this is necessary prior to performing the shakedown testing. However, this was delayed another week as necessary paperwork needed to be filed and approved in order to receive training on the device. However, Dr. Gordon informed our group that since our project won't be able to be truly tested, it is more research-intensive than some other groups. He pushed our due date for Deliverable 5 back one week (to Week 8), which allowed us to concentrate on research rather than testing and building. This research will continue until Thanksgiving, but below is a summary of some of the research performed this week:

"The influence of static and dynamic loading on marginal bone reactions around osseointegrated implants: an animal experimental study."
Link: http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0501.2001.012003207.x/full  

Although the bone-implant contact was not significantly different for the dynamically loaded versus the statically loaded and control implants, bone loss was observed at a close distance from the implants when they were loaded dynamically. This supports the hypothesis that excessive load can indeed trigger bone resorption through the induction of micro-damage in the bone.

"Mechanical Signaling for Bone Modeling and Remodeling"
Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3743123/pdf/nihms-281049.pdf

"Loading results in adaptive changes in bone that strengthen bone structure. Bone's adaptive response is regulated by mechanotransuction. We found that applying loading to the forelimbs of rats improved bone strength by 64%. Interestingly, the improvement in bone mineral content (BMC) in these rats was only a modest 7%. Consequently, mechanical loading adds mass but also causes the cross-sectional shape of long bones to become more structurally efficient." In adults (after growth has been cmpleted, "the effects of exercise shift from bone building to prevention of bone loss. In the adult skeleton, exercise reduces bone turnover by reducing bone resorption. Our studies employ a machine that applies axial loads to the forelimbs of rats or mice. In the rat ulna, where bone growth is directed to regions of high strain energy, improvement in function is dramatically improved. After 16 weeks of loading, the rat ulna will sustain 100-fold more loading cycles before failure." The article also includes information on the signaling pathways and specific cellular components/proteins that may cause bone growth. "Studying the effect of mechanical stimulation on resorption in animal models has been much more difficult than studying the effects on formation, and consequently, our understanding of the mechanisms involved is less developed. Part of the problem is that most of the animal models developed for studying the effects of increased loading on the skeleton are designed for addressing cortical bone in rodents. Because rodent cortical bone does not undergo Haversian remodeling, resorption data are scarce." It also says that bones may become desensitived to mechanical loading and produce less osteogenic activity. < This needs to be looked into more!!

"A threshold of mechanical strain intensity for the direct activation of osteoblast function exists in a murine maxilla loading model"
Link: https://goo.gl/S00H2u

"The purpose of this study is to clarify precisely what intensity level of mechanical strain is necessary to accelerate bone formation. The mice in the loaded group were subjected to continuous loading with 191kPa using the appropriate weight ingot for 30min/day on seven consecutive days." They tested for inflammation/swelling that resulted from the loading at two different locations: one close to the loading side and one farther away. They found that osteoclast number increased in both regions, but was much higher at the closer location. 

"Bone Formation"

Link: https://www.ncbi.nlm.nih.gov/books/NBK10056/

"As new bone material is added peripherally from the internal surface of the periosteum, there is a hollowing out of the internal region to form the bone marrow cavity. This destruction of bone tissue is due to osteoclasts, multinucleated cells that enter the bone through the blood vessels (Kahn and Simmons 1975; Manolagas and Jilka 1995). Osteoclasts are probably derived from the same precursors as macrophage blood cells, and they dissolve both the inorganic and the protein portions of the bone matrix (Ash et al. 1980; Blair et al. 1986). Each osteoclast extends numerous cellular processes into the matrix and pumps out hydrogen ions onto the surrounding material, thereby acidifying and solubilizing it‡ (Figure 14.17; Baron et al. 1985, 1986). The blood vessels also import the blood-forming cells that will reside in the marrow for the duration of the organism's life. The number and activity of osteoclasts must be tightly regulated. If there are too many active osteoclasts, too much bone will be dissolved, and osteoporosis will result. Conversely, if not enough osteoblasts are produced, the bones are not hollowed out for the marrow, and osteopetrosis results (Tondravi et al. 1997)."

"Benefits for Bone From Resistance Exercise and Nutrition in Long-Duration Spaceflight: Evidence From Biochemistry and Densitometry"

Link: http://onlinelibrary.wiley.com/doi/10.1002/jbmr.1647/pdf

“These data document that resistance exercise, coupled with adequate energy intake (shown by maintenance of body mass determined by dual-energy X-ray absorptiometry [DXA]) and vitamin D, can maintain bone in most regions during 4- to 6-month missions in microgravity. This is the first evidence that improving nutrition and resistance exercise during spaceflight can attenuate the expected BMD deficits previously observed after prolonged missions.  2012 American Society for Bone and Mineral Research. It is well recognized by researchers in exercise physiology and bone biomechanics that bone needs to be optimally overloaded to have a stimulatory effect, which cannot always be provided by aerobic exercises."

"Rodent Research Contributes to Osteoporosis Treatments"

Link: https://spinoff.nasa.gov/Spinoff2016/hm_1.html

“We know that sclerostin production in bone is regulated by mechanical loading, but what we didn’t know was if you completely unloaded the skeleton’s bone formation pathway, which is essentially what happens in microgravity, whether our molecule that blocks sclerostin would still result in increased bone formation and bone strength. “If you take a human or an animal and put them in microgravity, they will lose muscle and bone at rates that are incredibly fast, much faster than a patient on Earth suffering from osteoporosis. They’ll lose bone at a rate 10 times faster in space than that individual. “For instance, static strains do not engender adaptive responses [8,9] whereas dynamic strains which change at high physiologic rates (as in impact loading) engender greater adaptive responses than those which change more slowly [10–13]. The on/off points therefore relate

to a strain-related stimulus rather than a particular strain value [9]."

Pharmaceuticals Solutions; "Mice Studies in Space Offer Clues on Bone Loss"

Link: http://www.nasa.gov/offices/oct/feature/mice-studies-in-space-offer-clues-on-bone-loss/

“One experiment focused on sclerostin, a naturally secreted protein that tells the body to dial down the formation of new bone. The mice were injected with an antibody that blocks sclerostin, essentially telling the body to “let up on the brake,” explains Chris Paszty, Amgen’s research lead on the project. That allowed the rodent bodies to keep regenerating bone tissue, resulting in increased mineral density and improved bone structure and strength. The results were encouraging: the mice injected with the antibody showed increased bone formation and improved bone structure and bone strength, similar to what was seen in the mice who remained on Earth.”

"Animal Experimental Measures of Functional Strain and Adaptation in Bone"

Source: Mechanical Strain and Bone Cell Function: A Review

P. J. Ehrlich and L. E. Lanyon

Department of Veterinary Basic Sciences, The Royal Veterinary College, London, UK

"These human exercise studies also support the data from animal studies that local loading induces local site specific changes in bone architecture [15–17]. Regardless of whether tensile or compressive forces were applied, the bone responded to intermittent, but not static loading. The first study to combine these approaches was that of O’Connor et al. [10] who used a pneumatic actuator to apply bending loads to sheep radii through metaphyseal pins. This study demonstrated a significant correlation between maximum strain rate and the degree of bone hypertrophy. This inference has been confirmed by a number of subsequent studies [11,19,32]."

Week 6

     This week was midterm week for many of our other classes, so we chose to work on things individually and did not meet together very often as a group. On Monday we presented our mid-semester presentation and then watched and reviewed the other five groups. This session was treated like a "design review" and allowed feedback from other groups on the planned designs. The mid-semester packet containing Deliverables 1-4 and a second peer evaluation were also due.
     We met as a group on Tuesday night and clarified what our next steps will be. Before we can finalize what method we will use and create detailed designs, we need to complete our shakedown tests. We emailed the tech adviser to see when Bourns Lab was open, as we wanted to get pull profiles on the elastic bands that we bought (the force for each is not specified). Once this was done, we could finish constructing our shakedown model, test the two and compare the results, and then move forward.

Our elastic bands are only categorized as ambiguous things, like "extra heavy" or "medium."

     Our adviser let us know what days the lab was open and two team members went to try to use the tensile testing machine (Isaac and Max). However, they found out upon arriving that specific paperwork is needed to operate the machines, and as such, they were not permitted to continue. Because of this, our shakedown testing has been delayed another week and we hope to use the machine during class time with our professor present.

Our team was not permitted to use the machines in Bourns Lab.

     A mathematical "model" was also constructed this week. It was created in Excel and models the shakedown devices we created (or is roughly the size of an arm). This includes different angles, forces, positions, and moments. The preliminary results can be seen below.

     Finally, we researched the topic further and also each worked on our ethical paper assignment (the draft). This included choosing an engineering failure pertinent to our field of study, analyzing why the failure occurred, identifying ethical issues, and then getting someone else from the class to peer review and edit the paper before submission.

Week 5

     This week we received the items we ordered for our shakedown testing (our constant force springs and elastic bands). We decided to go to the engineering lab and start constructing the wooden "arm" described in the Week 4 blog post. As we are not technically certified to work on our own in the lab yet, we had Wes help us.

The wooden boards modeling the upper and lower arm were cut to be roughly the same length as Isaac's arm. 

Wes helped us construct the model.

A hinge was used to connect the two boards. Small holes were cut out so that the hinge was in the center of the boards, rather than sticking out. This mimics a natural elbow joint.  

We also drilled holes on the top of the boards at 2 cm intervals. Currently we are using eye hooks to guide the string and act as anchor points, and the different holes allow the placement of the anchor points to be adjusted. 

Wooden boards connected by a hinge.

This picture shows the holes drilled in the two boards.

Once the "arm" was built, we attached the spring system. Our constant-force spring was housed in a 3D printed casing, and the end of the spring could be pulled out (similar to the way that tape measures can be used). One issue we found is that the spring can recoil on itself and then not return to the casing. This issue seemed to be mostly resolved when we attached the spring to the board, but bears further testing, as this may be a potential issue that causes us to move away from the design altogether.

Example of the spring recoiling and getting jammed. 

The spring system was composed of two springs, acting opposite each other (such as two opposing muscles). In other word, as one spring was "contracting," the other one was lengthening. Parachute cord (or paracord) was tied to the end of each spring and threaded through the guide holes until they were anchored. As stated before, screw eye holes were used to provide the guide holes and anchor points. The spring casings were taped to the end of the "upper arm" board, as their placement on the actual body would likely be near the shoulders.

Constructing the model.

The final model of the spring system.

We finished building the model for the spring system. Rather than having to deconstruct the system whenever we wanted to test elastic bands, we constructed a second "arm." We did not yet attach the elastic bands, as we are considering testing their pull profiles first, but we will do so next week.
     Next week, we will use the force transducer to test the moment generated about the elbow joint for both models. We will also test how changing the anchor points affects the moment and attempt to find  comfortable (natural) neutral points for the user.

Materials to be used for shakedown testing.

    The rest of the week, we worked on the mid-semester presentation and packet that are due on Monday. These are essentially summaries of our problem, what we have done to this point, and our future designs.

This is our presentation cover slide.