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Results of Technical Review

To view a team's prototype and provide feedback, click on the links provided below.

red longboard brake orange

boxing bag

green baby gate purple drum trainer
blue bike trainer silver prosthetic leg
yellow infant warmer pink proximity locator

General comments
36 instructors and guest reviewers attended the review. Team specific comments from Professor Wallace are written on this page, below this section of comments for all teams.

Teams have shown good progress since the mockup review. The current prototypes are great platforms for testing, and they are a concrete reference point/architecture from which one can carefully design and detail a "productized" alpha prototype. In detailing, the current prototypes are closer to mockups than designed products, so there are still significant challenges on route to the alpha prototype and final presentation.

It is now critical to design and execute the devices as coherent, integrated, elegantly-resolved products, thinking carefully about efficient use of materials, ease of fabrication, cost and user safety, overall form, and human factors. Think about how the current designs would need to change to be comparable to a product that you can already buy. It is often helpful to look at details in related, real products for inspiration at this point in the design process.

For teams with key functional aspects or system integration issues yet to be resolved, it is very important to tackle these problems soon in order to avoid surprises a few days before the final presentation. The core, integrated functionality should be solidly resolved before the Thanksgiving break so that there is time for implementation, planning, testing, and preparation/practice for the final presentation. As noted in the lab notes for this week, it is critical to keep things moving and have your next design revision worked out before the break.

All teams should aim to have the prototypes completely ready and available for presentation practice by the Saturday before the final presentation at the very latest.

Your team will need to take a split approach during the final weeks, working on the prototype and at the same time designing/preparing materials for the final presentation. A large number of product development professionals will be in attendance and will review your projects, so it is a terrific opportunity.

The Team-specific comments/suggestions below from Professor Wallace are intended to help each team in preparation for the next design revision. Please consider these comments before setting priorities before the holiday, and feel free to ask if there are questions. I hope to discuss design details more when we meet on Tuesday, Wednesday, or Thursday this week to talk about your presentation setup. Please contact Professor Wallace to schedule a time for your team if you have not done so already.

You will also receive written comments from individual instructors before your lab (if you meet on Tuesday) or by Wednesday morning. Also, the average score from reviewers for each prototype, with standard deviations, is at the bottom of the page.

Team-specific comments and suggestions
red, green, blue, yellow, orange, purple, silver, pink

Red:Longboard brake
View the prototype and provide additional feedback

A lot of solid work and progress has taken place since the mockup review. You have two approaches on the table so you need to make a decision, but the good news is that it seems like you have made enough progress to make a rational, data-driven decision. After making your decision, the challenge will be to test and learn more deeply from this generation of prototypes and then carefully resolve the fine implementation details and product form to realistically implement a product. Small details in the geometry are very important, right down to the fastener selection (i.e., what type of fasteners are used to attach to the longboard).

Also, for which ever path you choose it is really important to test with a variety of wheels, and make sure that you understand which you can accommodate, if not all. It would also be possible to design the brake pad thinking carefully about having minimal performance change as it wears and in wet conditions.

Some specific comments related to each implementation approach follow.

passive mechanical

  • this seemed to work quite well and reliably. When I looked at the prototype, it made me think of something my one of my professors said at one point when I was a student (studying industrial design, prior to my mechanical engineering degrees). "This appears to be simple enough to be real". The meaning behind the statement was that successful designs for real products provide their desired benefits to users in the simplest/cleanest, most reliable way possible (ideally also with some protectable intellectual property). Appears in "appears to be simple" implied that the clean solution is actually the embodiment of sophisticated thinking.
  • there was some concern about the "throw the board and jump on" use scenario. This might be achieved using a damped elastomer spring between the two plates. Imagine a hollow, rubber wedge with a small air hole, so when compressed it takes some time to return to its original triangular wedge shape.
  • can the cables be placed/routed so that they are less exposed/prone to catching?
  • one can imagine a thumb screw-like mechanism on the cable sheath that could be use to adjust the brake pad travel, to accommodate different user preference/weights, or allow adjustment with brake pad wear.
  • pan-head screws don't seem like a fitting choice to attach the truck to the board.
  • could the hinge be designed so that any guides/posts on the back, open end become unnecessary (further simplification)?
  • is there a form language, or style that you will use to brand this as a unique product?


  • it was hard to tell how well it was working, but it did seem to be actuating, but too slowly to noticeably reduce the braking distance.
  • perhaps a spring-loaded brake that is electrically released might allow better control of exactly when braking begins once a desired delay has occurred
  • would it be the case that users would want to adjust the delay parameters/behaviors? If so, there might be some sort of UI needed for the design.
  • it seems that the brake is applied, and then released, after a preset amount of time. Are there failure modes, such as stopping on a hill, where this might be an issue?
  • details such as changing batteries, and making sure that the electronics are waterproof and shock isolated will be important to consider.
  • the membrane switch seems reliable, and affords a branding opportunity, while the original strain gauge idea would leave the board surface unchanged. Is one approach preferable for intended users?
  • aim to have printed circuit boards and soldered assemblies in a final prototype. Avoid breadboard-like implementations because they are very unrobust under use, and you can almost count on something going wrong after the device is moved around or bumped.

Green: Baby gate
View the prototype and provide additional feedback

Things seem to really come together for the final days leading up to the technical review. It seems like you now have a clear reference point from which you can design and detail a realistic gate. Be sure to use the current prototype to thoroughly test your electronics implementation and opening heuristics. Remember, above all, it must be a good gate that locks reliably and positively, and stays locked when it is supposed to! And, your added value proposition of hands-free operation.

Some additional thought are:

  • there is a lot of flex and play in many of the joints, which leads to an overall impression of not being secure. One of the gates shown in your mood board (munchkin loft aluminum), has a very nice, stiff and precise feel. I really encourage you to buy this now so that you can use it as a reference for designing joints/slides.
  • there are a number of bits for the design (mechanical latch, sensor unit, battery holder, etc.) that all seem like disparate elements. Can everything be brought together to create a coherent unified product?
  • given the "template" that you have now, can you step back and think of as many ways as possible to simplify and clean up the implementation? What is the simplest implementation to afford the user benefits you are offering?
  • sharp edges and catch points on fasteners, edges, or latches need to be completely eliminated. Sharp edges for obvious reasons, and catches points are more than just conveniences. If a small child has clothing that catches and falls, a situation might arise where the child could even be hung (this was an issue with old cribs that had posts that stuck up above the rim of the crib). Be attentive to the little details.
  • it was not clear how the top-of-stair scenario was accounted for, and clearly the gate also needs to work from both sides.
  • clear status information seems like it might be important, so that at a glance a parent can be confident that everything is as he/she thinks it should be.
  • aim to have printed circuit boards and soldered assemblies in your prototype. Avoid breadboard-like implementations because they are very unrobust under use, and you can almost count on something going wrong after the device is moved around or bumped.


Blue: Bike trainer
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You have done a lot of work on different aspects of the product. You still face a key technical challenge related to how to implement the resistive braking. It seems like the magnetic brake had significantly lower dissipative power than needed. I think that a free body diagram, imagining a bike on the desired maximum gradient you would like to emulate, would help to quantify what you are aiming for. Once you have this, you can determine the max power and then look at commercially available eddy current brakes of similar braking power to bound/see roughly how big of a system you are looking at (if you have not done this already).

While significant effort has been put into the eddy current brake, before starting the next implementation it also seems like a few-hour mockup test using the electric bike hub motor would be worthwhile. Shorting the motor leads (with no battery in system) will give you a feel for the maximum torque you could achieve with the hub motor, and then possibly use pulse-width modulation between shorted and open circuits to achieve different levels resistance. My understanding is that you are meeting with Rich Tuesday, and he could help with this test. Please let me know how this goes, or if more assistance is needed with a test.

With the above information it might help making a decision about technology and architecture (in hub, out-of hub).

Additional thoughts follow.

  • think carefully about the overall integration of the product. There has been significant effort on the braking mechanism, the user interface design, and wireless communication/control. But they seem a bit disparate. There did not seem to a clear, overall big picture/system design for the product. What is the design for holding the phone on the bars? Is the control system powered by batteries, charged by the system? While there are still open questions being resolved about the braking method, it is advisable to work on this—perhaps for a hub version and also a mounted system outside of the hub.
  • the UI mockup looked good. Could it be made even cleaner/more visual than it is now? If you have not done so already, use the UI mockup for user testing.

Yellow: Infant warmer
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This is a good first shot at how to make a realistic prototype. It seems like a lot about fabrication challenges has been learned from this version and several design details can be refined and simplified. Think carefully about how to move the details from mockup-like to real product. Always keep in mind that above all else, the device needs to be designed so it cannot fail and hurt a child, either by over or under heating. Clear status information and appropriate warnings if there are any problems are critical.

Some other thoughts and suggestions follow:

  • One of the next steps in improving the implementation is more precision/accuracy in the fabrication of the molds. One possibility would be to CNC machine the renshape for all of the molds, or even more precise/controlled execution of a manually built mold. Dust control needs to be worked out for the vacuum forming, and the use of higher melting temperature polycarbonate for the under-layer should resolve the fusing problem for the thicker sheets.
  • The method to join the different layers need resolution. It seems like two stiff, annular rings could be used to clamp the layers together and create a clean rim with integrated handle. Happy to discuss if you like.
  • The control unit could be much more integrated with the bassinet form as the current version seems out-of balance and likely to be damaged. Using a printed membrane interface (like on the firefly) seems like a clean and inexpensive way to make your display both easy to clean and waterproof.
  • The running of the individual heating wires is a bear. Perhaps consider using sheet/film heating elements to avoid this (one brand I am familiar with is called Zmesh).
  • Perhaps the bags could be eliminated and the phase change material is held directly between layers of the bassinet. It seems like top sealing, with the use of a rim clamp (described above) and silicone could achieve the necessary sealing at the rim.
  • It seems like the control/temperature regulation needs further refinement and careful testing to avoid potential injury to the occupant.
  • The implementation of the cover concept, while it works, seems like something that could snag clothes (leading to possible drop accidents) and would be hard to keep clean. The implementation, in concept, is quite similar to the segmented ipad covers (smart cover). It seems like it might be used for design inspiration.
  • while the key need is to keep the child warm, can this become a beautiful environment for the infant rather than feeling like the child is wired in a machine?

Orange:Boxing bag
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You have a clear vision for the product, a promising UI, and an interesting approach to fabricating the bag core. Now, the challenge is to take this mockup versions and both detail and execute it cleanly like a real product.

Additional thoughts follow:

  • the instrumentation rod does not seem like a user-serviceable device. This affords opportunities for different ways of implementing the bag core. For example, the cast core could be two parts, more like a pill that interlocks in the middle, so that both ends are cast and finished, and the core is not exposed on the end.
  • the instrumentation rod now should be designed as a coherent product, thinking about how it would be reasonable fabricated and assembled in volume. The current version reflects more of an engineering mockup.
  • aim to have printed circuit boards and soldered assemblies in a final prototype. Avoid breadboard-like implementations because they are very unrobust under use, and you can almost count on something going wrong after the device is moved around or bumped.
  • it seems important to have a clearly articulated and communicated model for what the senor data looks like that you are receiving, and how this is processed to provide the output information. Without this it is really hard to know what the numbers mean.
  • it seemed odd to only have a cumulative force measurement and no individual punch feedback.
  • casting jigs could be made to keep the hole for the instrumentation rod centered, and the form could be lined with polyethylene to make demoulding both clean and fast. Happy to discuss in person.
  • think carefully about the low voltage power routing issue and how to wirelessly interface with multiple bags
  • think about whether you want to make your own bag, and how it would afford branding opportunities for your product. Professional sewing help is an option.

Purple: Drum trainer
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Overall things seems to be working quite consistently, which puts you in a great position to now really design a product. The architecture for sensing on the cymbol seems quite nice. It would be great if something equally inspired could be realized for the drum and hi hat. You have a system with many parts, so quick communication of what it entails could be a challenge. It might be really useful to design the package experience for your product, so that you can open the box and see everything that is in the kit in a nicely displayed way. This could be shown digitally or physically.

Also, there seemed to be very good overall team knowledge about what your product is and how it worked.

Some other thoughts and suggestions are below.

  • design each sensor like a product on its own. Think about all the details that would be needed to make them producible in volume, and look like a product rather than a prototype (each element (sensors, control box) is a small electronic device/product with tiny details, and you can use other products as detail inspiration.
  • it would be nice to see the installation process
  • think carefully about everything that needs to be designed or part of the system, down to the wire clips
  • the software prototype is good, and would now benefit from more UI design. Also, it seems like there are many things that the system can do, so think carefully/test to decide what you would want as an initial offering. It seems like reading and writing midi is compelling.
  • I did not have a chance to look inside the control box, but aim to have printed circuit boards and soldered assemblies in a final prototype. Avoid breadboard-like implementations because they are very unrobust under use, and you can almost count on something going wrong after the device is moved around or bumped.
  • will be interesting to think about how to demo/communicate the product so that observers can really get a feel for the experience and how it works.


Silver: Prosthetic leg
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A lot of progress has been made since the mockup review, which is good. That said, there is still a way to go. It seems like we need to get a setup in lab (parallel bars?) so that you can really test a prosthetic leg. We can help you with this if you like. Also, remember that your core value proposition is a comfortable prosthetic leg. Can you test the comfort of a jamming socket liner before you have the rest of the leg? Starting to answer this question sooner than later would be good.

Arthor Petron (mentor on purple) works in the biomechatronics lab and would be a great resource. He is willing to help and he can be emailed through Purple team's page.

A few other comments are:

  • now that you have a basic architecture, it is important to resolve an overall integrated, coherent product design that includes all elements, the user interface, and battery/charging access, etc.
  • the flat bags did not seem to conform uniformly to the stump shape. Try to test the cup-shaped one (mould being printed) ASAP as this may take some iteration and the molds take a long time to print
  • try to eliminate as much tubing and as many connectors are you can. It seems that air channels could be cast in the silicone liner to replace tubing, and the motor pump unit might barb connect into the base of the cast silicone unit
  • sensing when to recharge the vacuum seems like an open and difficult challenge without an obvious answer. Is it necessary to sense? Will the leak rate be consistent enough that, just on a conservative time cycle, the device can recharge the vacuum? Perhaps this is a user tunable parameter? Should the user have the option to say... wait a few moments before pumping as now is not a good time?
  • noise seems like an important issue. It might be worth looking at sound deadening paints (used in planes, for example), which could be applied directly to the pump and the pump housing.
  • the clam shell outer socket seems like it needs to be more compliant. Also the sharp top edges, and bumps where the leaves overlap seem like they could form chafing points. Have you considered something perhaps like a stiff velcro/elastic wrap as the outer socket? Might use a back brace as a quick mockup to test.
  • once you have a more realistic socket implementation, it seems important to quantify the stability of the socket (under different loading cases and twisting)
  • if you have not already been doing so, working now to line up multiple people to test the device when you are ready might pay off.


Pink: Proximity locator
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It seems like the electronic implementation is really clean and functional, and you have a nicely thought through user interface. You have also learned a lot about casting, which is great. That said, it was not clear how everything will come together. Is it possible for the current display to support the refined user interface? You are working on a device that is jewelry-like, in what seems to be like a fairly image conscious market. It also seems like there might be a bit of a mismatch between the technology (~0.7mi line of site, and a ski resort of several miles with uneven terrain). Getting together to create a unified vision with matching technology seems like an important thing to do.

Some additional notes follow:

  • Directly 3D printing your molds (on the objet) will help you get a more refined casting. It might help to revisit the form lecture and the discussion on corner treatments (Oct. 22) to help think about how to develop a more jewelry-like embodiment. Happy to walk through some details related to this if you like. Also, the strap/clasp design has a big role in the overall feel and closely ties to how you are making the body (e.g., elastomer case with integral band, elastomer case with separate band, rigid machined with separate band).
  • the details and feel of the buttons is quite important to the overall experience.
  • the two use cases you have identified make sense. It is possible to make the setup even simpler?
  • the step from the text display to graphical interface is likely big, so starting to work/prototype on this aspect soon seems important.
  • weather proofing can be a challenge, so thinking about the details for this up front would be good. Perhaps you can purchase a moulded plug for the charging port that could be an insert into your casting?


Average reviewer score
The average reviewer score is on a scale of 0-10, where 10 is highest. The score is based on prototype operation and the assessment viewpoints outlined in the technical review description. The data are averaged from rankings provided by 36 reviewers.