Hot Feet

Experiment 5 -Bijun Chen, Masha Karimi, Katie Micak

 

HOT FEET

DESCRIPTION:

When faced with the challenge of Experiment 5- multiples, we were most interested in creating a prototype that could be built upon in a practical way. Our goal was to also create something which could have a use beyond the classroom. “Hot Feet” was born out of the spirit of giving. Ideally, this giving would be to those who are unfortunate to spend more time than comfortable out in the cold, namely those that are homeless (though there could be many other applications or users).

 

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Hot Feet is a shoe that offers battery powered heat by closing a simple circuit. It consists of one battery that sends a charge first through the right shoe (which holds the battery) and then sends it to the left shoe, turning on both heating pads found in the insole of each shoe. The circuit is completed when the shoes are put together at two points of contact, positive and negative. After a few seconds both shoes will begin to heat up, and the battery will not be active if this circuit is not closed resulting in neither shoe creating warmth.

CONCEPT:

In creating Hot Feet we wanted to create a warming shoe that would:

  1. Be simple to use
  2. Ran off of a rechargeable battery
  3. Would be inexpensive
  4.  Could be easily replicated
  5. Inconspicuous in design
  6.  Safe and durable

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PART LIST/ COSTS:

Our total costs for 3 prototypes is around $220.00, with the highest expenses going towards the shoes and the batteries.

Part Name Quantity Cost for Each Supplier Cost Total Cost Total with Tax Link:
Shoes 3 pairs 20 Payless Shoes 60 67.8
Heating Pad 6 7.4 Creatron inc 44.4 50.17 https://www.creatroninc.com/product/5v-heating-pad-5x10cm/?search_query=heat&results=84
Conductive Fabric 1 piece14*12″ 19 Creatron inc 19 21.47 https://www.creatroninc.com/product/conductive-fabric-14×12/?search_query=conductive+&results=40
Conductive Thread 1 * 30ft roll 4.85 Creatron inc 4.85 5.48 https://www.creatroninc.com/product/conductive-thread-30ft/
LITHIUM BATTERY – 1200mah 3 17.85 Creatron inc 53.55 60.51 https://www.creatroninc.com/product/lithium-ion-battery-1200mah/?search_query=lithium+battery&results=28
Felt 1 pack 3 Dollarama 3 3.39
30awg Silicone Wire – 2M 2 pack 1.8 Creatron inc 3.6 4.07 https://www.creatroninc.com/product/30awg-silicone-wire-green/?search_query=silicon+wire&results=13
Regular thread and needles 1 box 3 Dollarama 3 3.39
Total cost: 216.28

 

 

BUILDING PROCESS:

Each person purchased a shoe that reflected their preference. Our hope was to create a prototype that could be integrated into multiple shoe designs regardless of the show structure. The shows purchased were: a running shoe, a winter boot with faux fur lining, and a casual high heel with laces.

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Once purchased we each created insoles that would contain the heating pads and created a thin boundary between the pad and the foot of the wearer. All wires were connected using simple sodered connections and conductive thread. We created the switches on the outside shoe, and sewed conductive thread from the inside to the outside of the structure at points were the feet naturally lined up and made contact.  The thread on the outside would be create the connection over both shoes and complete the circuit.

 

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CONNECTIONS/ ISSUES:

The Connections inside of the shoes were loose. Loose connections inside of the shoes had higher resistance than the actual heating pads ( P = VI = RII ) which resulted in the connections heating up more than the actual pads to the point that the heat was not bearable anymore. These heating pads require a lot of power to run and also their temperature can go as high as 60 C degrees. Running them in series requires less battery usage and also brought down the heating pads temperature to a more bearable heat. Hence we had less energy waste. If the connections are done perfectly, these shoes should function even in rain since the resistance of water over felt (material that the shoes are made out of) is higher than the resistance in conductive fabric and conductive thread. Therefore the currents would still run through the path with lower resistance. The placement of the battery on these shoes were very crucial. our initial design paced the battery somewhere on the outer side of the shoes to make sure no interfering with the comfort of the wearer’s feet. However cold weather also interferes with the battery performance. Our challenge was to find the best location for the battery inside of the shoes where it is still comfortable to be worn. Having the battery inside of the shoe resulted in the battery staying at a temperature range which prevents it from discharging quickly.

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First Image shows the parallel circuit diagram and the second shows the series circuit diagram.

POWER In the parallel format there will be a bigger power supplied to both pads. In the series diagram there will be less power supplies. hence the series diagram is more power efficient.

HEAT higher heat produced by the pads due to higher resistance there will be less heat produced by the pads.

MATERIAL Parallel diagram needs at least three points of contact to perform therefore more material to connect/wire the three conductive fabric switches on each shoe. Series diagram needs at least 2 points of contact to perform hence less material usage.

EFFICIENCY In the parallel circuit if one part disconnects the other part still performs, whereas in the series circuit it is required for all parts to be connected and perform ignorer for the entire circuit to work.

 

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SURVEY/ RESULTS:

Three users would wear the shoes for 16 hours, or two days, for the duration of the experiment. Although the prototype worked correctly, each user had different reported experiences.

Katie’s shoe worked well (at first). Heated up to a comfortable warmth quickly. Was comfortable. Day two the circuit got overloaded and caused a burn on her foot- she had to remove her shoe quickly.

Mahsa had a similar experience. Her shoe worked for quite a few hours before the connections got strained and she also received a burn on her foot, while in public.

Bijun’s shoes worked the whole time. Her connections were sound. Her biggest issue was recharging the battery, which she did do only once. The reason her show was probably successful the longest

 

SURVEY:    We created this quick survey to cover the main points of Hot Feet.

MAHSA’S RESULTS:

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Did Heated Insoles work?  Yes

How comfortable is the shoe? (1 less comfortable- 10 most comfortable)  8

Did the battery last?  Yes

Did you have to recharge the battery? Yes

If yes, how many times/ how long did it take?  I charged the battery once after the first day of experiment (first 8 hours) were over.

Do you think “Heated Insoles” would work keep feet warm for people spending long periods of time outdoors?  Yes

Did Heated Insoles warm up your feet?  Yes – and my feet stayed warm long after I took my feet apart.

How warm were your feet? (1 coldest – 10 hottest)  7

What would you change?

I would change the material that the insole was made out off. The felt insoles were too thin to hold their shape and were moving around inside of the shoes.

The Connections inside of the shoes were loose. Loose connections inside of the shoes had higher resistance than the actual heating pads ( P = VI = RI 2 ) which resulted in the connections heating up more than the actual pads to the point that the heat was not bearable anymore.

The choice of having the pads running in a series circuit worked well. These heating pads require a lot of power to run and also their temperature can go as high as 60 C degrees.

Running them in series requires less battery usage and also brought down the heating pads temperature to a more bearable heat. Hence we had less energy waste.

If the connections are done perfectly, these shoes should function even in rain since the resistance of water over felt (material that the shoes are made out of) is higher than the resistance in conductive fabric and conductive thread. Therefore the currents would still run through the path with lower resistance.

How helpful was the repair kit?

The repair kit was very handy. It consisted of:

  1. Conductive Thread
  2. Conductive Fabric
  3. Aluminum Foil
  4. electric Tape to go over possible loose connections

 

BIJUN’S RESULTS:

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Did Heated Insoles work? Yes

How comfortable is the shoe? (1 less comfortable- 10 most comfortable) 6

Did the battery last? Yes

Did you have to recharge the battery? Yes

If yes, how many times/ how long did it take? Once, exchanged to another battery

Do you think “Heated Insoles” would work keep feet warm for people spending long periods of time outdoors? Yes

Did Heated Insoles warm up your feet? Yes

How warm were your feet? (1 coldest – 10 hottest)  8

What would you change?

The number one thing I would change is the material of the insole, the one I had (felt) cannot handle daily wear and tear, it looked very nice before putting into the boots. I guess that is something we have not considered well. Secondly, I would change the style of the boots. I think my other teammates suffered less when they made theirs. Mine is very tall and has no opening, and it makes it extremely difficult to work with the insole and the connection part in the bottom; and for the top connection conductive fabric, it’s easier to work with, but I can feel the wires when wearing those. I believe the better solution to this problem would be to start / hack the boots with a zipper/button or any kind of opening in the back or side.

Using boots is a good idea because they are more likely to be worn during cold weather, with the heating pad.

How helpful was the repair kit?

It is very helpful! Electric tapes were unexpectedly helpful.

 

KATIE’S RESULTS:

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Did Heated Insoles work? Yes

How comfortable is the shoe? (1 less comfortable- 10 most comfortable) 7

Did the battery last? Yes

Did you have to recharge the battery? No

If yes, how many times/ how long did it take?  N/A

Do you think “Heated Insoles” would work keep feet warm for people spending long periods of time outdoors? Yes

Did Heated Insoles warm up your feet? Yes

How warm were your feet? (1 coldest – 10 hottest) 7

What would you change?

On the second day the when I put my feet together the heating pads turned on very quickly. After about 5 mins (and once the circuit was broken) I started to feel a slight shock or burn. It was in my right shoe, the same shoe with the battery. So it was a unsafe in its current design.

I would change a lot about construction- probably make the wires stronger or embed them in the shoe. Also create a shoe that was fire resistant.

How helpful was the repair kit?

It was helpful, but I did not use it as I was not confident that my repairs would be safe.

 

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POSSIBLE NEXT ITERATION:

Our results concluded that this type of shoe could possibly be safely, durably and successfully constructed. It could be created to be hooked into existing shoes, or be a whole new shoe in itself. I found this project to be successful simply because we did create a functional prototype that could find legs and multiple uses in the real world.

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Video for HOT FEET:

 

 

Documentary on the making of HOT FEET:

 

 

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