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Assembly!
Presentation Video
ContROLL
An automatic device that limits the speed of a wheelchair going down a ramp in order to prevent uncontrolled descent and hand friction burns
Product Contract
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Storyboard
CAD Images
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Contributors
Adam Zimmermann: CAD, Physical Model Validation
Anna Haddad: User Interviews
David Hernandez: Tech Development, Frictional Disk Brake Investigation
Delaney Goetz: Tech Development
Enya Ryu: User Interviews
Gaby Ulloa: Physical Model Validation
Jacky Dong: Product Contract
Jesus Rodriguez: Tech Development
Justin Li: Physical Model Validation
Kris Vu: Tech Development
Lillian Linden: Storyboard, Presentation
Max Fan: Product Contract, Tech Development, Attachment
Satchel Sieniewicz: Tech Development
Sylvie Waft: Storyboard Drawings, User Interviews
Warren Wang: Tech Development, Hydraulics
Yuka Perera: Tech Development
Reviewer Feedback
Aditya Ghodgaonkar
Feedback
How do we know what deceleration rate to pick for different user weights? Don't want someone falling/flying off the wheelchair. What about complete stop vs. only slowing down? Can the system detect one is preferred over the other? Is there a way for the user to intervene or override?
Georgia Van de Zande
Feedback
- Does it make sense to have an acceleration max on your product contract? - How dangerous is it if the device’s battery dies and the user doesn’t realize? How are you avoiding this scenario? - A quick google search for “average walking speed” says, “The average walking pace is 2.5 to 4 mph, according to the Centers for Disease Control and Prevention.” How did you reach the 2 m/s max? is this something that users might want to set for themselves? You mentioned sometimes people might want to turn it off, but they could just set the max to like 10 m/s, and you can keep the device on always. - When someone wants to turn on/off the device, or change the speed max, can they do that while sitting in the chair? Or does it have to be adjusted before they sit?
Charlotte Folinus
Feedback
Storyboard: very pretty, but I think additional visuals or captions could have explained what was happening at each step — many images looked very similar to each other. How does product positioning on the wheel chair frame matter to your users? How does it interfere with other types of add-ons/attachments they might have, or with wearing a backpack over the back of the chair? How does it attach to multiple types of wheelchairs, or are you targeting one specific type of wheelchair? How long does the battery last? How long should it last? I couldn’t quite follow how this attaches to the chair. From the CAD, it looks like the 16 thumb screws (8x2 sides) must be unscrewed, and the entire assembly must come off of the chair frame? The physics of where you’re applying load on the assembly (through the brake pad) makes me think this will tend to rotate as it’s used — how hard would someone need to tighten the screws to have a secure fit? Would a different attaching mechanism (less prone to rotation) make it easier to install? I’m not quite sure where the box is on the chair frame, but are the thumb screws easily accessible? You mentioned that some of your users have limited grip strength — how much grip strength is required to attach to the chair? Can users adjust the stiffness of the braking? What happens if the device is misaligned on the two sides (either the user installed slightly off-position, or the frame-wheel distance isn’t exactly the same on the two wheels)? How much of a misalignment would it take for one wheel to slow down much more than the other? Communication: it would have been great to include a discussion/sketch/high level CAD model of sensing in your presentation (perhaps you did, and we didn’t get there!). I also got confused by the CAD model shown in isolation, without the brake pad, chair frame, or wheel — including some of these elements in the CAD (even if grayed out) or keeping a sketch nearby would have helped me orient myself.
Dave Custer
Feedback
The feature of switching the brake system on and off came as a surprise, and, as many of the questions from the audience suggest, invokes numerous risks. Your current images show only one contact point of the brake on the wheel; should there be two contact points 180 degrees apart so the brake device doesn't torque the wheel axle? As an aftermarket add-on, will your device put undue stress on the wheel, popping it off its axel or affecting bearing wear? I can vouch that bicycle brakes don't work so well in the rain and agree with the audience member who brought up the risk of wet brakes. What do people who get around in wheelchairs do when it rains? Is wet braking extra hard for them too? How do people who get around in wheelchairs feel about having another charging station inconveniently on a convenient surface in their lives? Can you recharge the batteries from the motion of the wheelchair? With a USB(C) cable plugged into the chair instead of moving batteries around? A power budget would help me wrap my brain around the charging specifications. My sense is that you've thought through different actuation and braking methods, whether they are always engaged or switched on/off by the user. A graphic that represents this thinking might better guide an audience in their response to your concept. Several questions asked about the control. Do you have a clear picture of situations in which a person in a wheelchair can safely descend a ramp: the speed, user mass and height, chair dimensions, slope angle, braking deceleration, braking assist available from handbraking, length of downhill travel... A graphic that shows this safe space might keep an audience from asking you about things you've already worked through.
Chuck Xia
Feedback
I curious about the user study on the pros and cons of using an electrical system instead of a manual control. Looking at the product contract, it isn't clear that the user need and product attribute lead to an electrical design instead of a mechanical one. If the challenge is grip strength, you can design mechanical system with enough mechanical advantage to cover that strength difference. I would guess that the user would want to be in full sensory control of the wheelchair when going down hill. The electrical system seems to be taking away the user's ability to control the wheel with their hand. The additional removal and charging step is not going to work with the user experiences. The wheelchair bound user needs to take it off the wheelchair, charge it, and put it back on the wheel chair everyday even if battery last 2-3 days (for example most of us charge our phone even if it is still above 25%). Then every time after charge, the user needs to attach the component to the wheelchair securely. This interaction needs more thoughts. For the electrical system, you really need active feedback. First both wheels need to be going at the same speed. Or the user will start turning while going down hill. I can't imagine the system will work well if you only have open loop control the force applied. The weight of the user, the incline, the road surface, the wheel, the brake pad, the mounting system all have an effect on the braking response between the force applied and the angular velocity of the wheel. The amount of force needed to break changes. You need a feedback control to ensure a constant velocity and also match it on both wheel. How much force do you need to slow down the wheel? How much force can the linear actuator apply? The mount system does not seem rigid enough to apply the force without slipping. With only attachment at the tube, the system can pivot around the tube. The break pad with the linearly actuator when press against the wheel, also apply an torque around the mounting point.
Lauren Futami
Feedback
I wanted to revisit a few questions I had during the mockups: How often does this scenario occur for wheelchair users? Are wheelchair users often losing control on inclines/declines? Why aren't they able to use their handbrakes for a more controlled descent? I was also unsure of the specific use case this would be used for - how steep are these inclines? I'm assuming this is for more unexpected inclines found on hills since I would expect that ADA compliant ramps wouldn't put wheelchair users in a steep incline scenario. Although the general problem you're trying to solve makes sense to me, I have no experience relying on wheelchairs and am curious if potential users would find this much more helpful than existing handbrakes. From your presentation, I wasn't sure whether or not you had a user/users to confirm this need, and if you have, then that's great(!) and I am much more convinced, but if not, I would strongly suggest doing so before pursuing this idea further.
Rob Podoloff
Feedback
I worry a bit about how you can control the amount of resistance being applied to the two wheels so that you don't induce a turning torque. I also worry whether your current mounting method can withstand the load from the wheels. Can your solenoids exert enough force?
Micki Dupnik
Feedback
It seems like this device could introduce more safety concerns than originally there. A lot of good points were brought up in the lecture about patient safety and also if user actually want something like this. You should take these into consideration if you continue down this design. Does the breaking mechanism account for user weight? How do you account that the attachment mechanism would come undone with all the vibrations a wheelchair sees. The CAD confused me a bit and I was unsure how it engaged with the full wheelchair, how mechanism works etc. I think showing an animation would've been helpful to visually explain how the mechanism works. I think you're story board needed words to help explain what is happening as well.