Portable Workout Generator That Generates Electricity!

Many students often have hectic schedules that are so filled with activities that they usually don't have a dedicated period to themselves to engage in activities that keep them physically active, or sometimes they do, but getting to the gym when they become free at night becomes impractical, and even the most basic habits like charging your phone can become forgettable. Sometimes, short periods of free time become apparent throughout the day, such as waiting in study rooms for a friend or even between meetings. I wanted to be as productive as possible with my time, so I have designed a prototype portable cable workout machine that is mountable to turn those short periods into workout sessions. For the foundation of this build, I wanted to to be able to adapt to multiple different types of excersise to train multiple different muscle groups, the cable based workout machines such as cable towers or cable row machines tend to be versatile in this, as depending on the position they are set up, they can train multiple different types of muscle groups in the body, whether it be triceps, lats, or shoulders, etc. This kind of flexibility made it an optimal choice for designing a versatile workout machine, and to top it off, it turns that exercise into usable energy that can charge your devices! It does this by spinning a flywheel, which conserves kinetic energy due to its higher inertia, and then that energy transfers to an overdrive gear ratio that multiplies the RPM tenfold, spinning a motor extremely fast, which in turn generates electricity that can be stored in something like a power bank. This project doesn't replace wall outlets; it just helps charge up your devices when you forget to plug them in. But otherwise, this project of mine is more about converting our energy into electrical energy that is storable in a power bank. My hype for this was for this is that it's supposed to be a fun way to stay active while charging your phone on the go! This project, in my mind, was simply about spinning the shaft of a motor while I worked out, but wow, it turned into a series of designs and complex mechanisms trying to achieve that, which really pushed me to pursue making this project work.

Energy can never be created or destroyed, so I set off trying to conserve as much mechanical energy as my body could provide the machine and convert the majority of it into electrical energy. But trying to design a system to be efficient yet portable made me question the very usability of the project. I first attempted to create iterations of different mechanisms that could convert the linear reciprocating motion of a cable into a one-way rotational motion because I wanted the build-up in torque in both directions to apply to the rotational movement of a 3D printed disk, which would result in it increasing its RPM for every pull and return stroke. This initial disk's RPM would be multiplied by overdrive gear ratios, which would spin the shaft of the motor, generating voltage and electricity while still being efficient in transferring that energy with minimal losses due to friction or heat. To achieve such a thing was so complicated that I'd studied mechanical linkages and their association with Grashof's law, proofs, and attempted to mimic mechanisms that could achieve it on YouTube. I made 3 prototypes and all of them failed due to either having generated too much friction or requiring more energy just to end up with the spin being abrupt or non-continuous. Eventually, I ended up realizing that the overall efficiency of converting the input of the exercise into usable energy would be lower than if I tried to harness it through one way, which is the pull stroke. I successfully made a mechanism that could harness the mechanical energy into usable energy by harnessing the pull stroke with a one-way rotational clutch, allowing the RPM to increase for every stroke. When the return stroke was engaged, the motor would almost instantly stop, which prompted voltage cutoffs. Implementing a flywheel was the right choice but portablity would be on edge, to genearate consistant voltage while making the system compact, I made a small flywheel with metal balls inside the flywheel, increasing the overall mass, which lead to a increased inertia, which lead to a increased spin time on the motor due to the inertia of the flywheel, allowing the voltage to be more consistent so that the inputs of devicecs could be satisfied with a more consistent voltage flowing through them.

I started this project late September, and now it's the beginning of January, after a lot of iterations due to experiencing a lot of friction issues in my prototypes due to the large overdrive ratios that demanded lots of torque for a hell of a lot of speed. Here, I made a 5th prototype that can generate voltage and can be mounted to desks, and it's what I'd like to present to you today. I want to show you how I made it, and get feedback from you as to what I can improve in the next iteration!

Mechanical Parts and Tools

1. 3D Printer
2. M3 screwset/toolkit
3. M6 screwset/toolkit
4. M2 screwset/toolkit
5. M3/M6 hex drivers or allen keys
6. (1) One-Way Clutch Bearing
7. (1) Spiral Return Spring
8. (11) 608-2RS Bearings
9. (Various sizes and amounts) Stainless Steel Balls Kit
10. Friction Lubricant or Grease
11. (1) 1-inch wide, 3.25-feet-long hook and loop strap
12. (1) 1KG PLA (any color)
13. (1) 1KG PETG (any color)
14. Soldering Iron and Solder
15. Pliers (for stripping wire)
16. Multimeter
17. Hot glue gun and sticks

SOFTWARE

For this project, I used Fusion 360 exclusively to design the parts! You will not require this, but if you ever want to make modifications of your own, you can modify all of these parts in Fusion 360 and improve this design to be better!

3D Printed Parts (PLA)

1. The files attached list parts as PLA indexed with a number. These parts should only be printed once. There is a total of 29 PLA parts.
2. Some parts may require a Brim and Support. Allow auto brim and support for better results

3D Printed Parts (PETG)

1. The files attached list parts as PETG indexed with a number. These parts should only be printed once. There is a total of 7 PETG parts.
2. Some parts may require a Brim and Support. Allow auto brim and support for better results

Electronics

1. (1) Low KV Brushless Motor (Must Be this Specific Motor)
2. (6)Diodes
3. (2) Low ESR Capacitors
4. (1) USB-C Input Charge Power Bank
5. Female USB-C Charge Port
6. (1) USB-C Cable Male to Male

There is a total of 36 3D printed parts that need to be printed using a 3D printer. Some parts in PLA, some parts in what I recommend is Carbon fiber PETG, but PETG works just fine.

Some key tips for prepping for this project would be:

1. Lower acceleration speeds (if applicable to your slicer), overall and initial layer print speed reduced to 25mm/s.
2. Layer height for small parts should be very low; for PETG parts, I recommend printing them at 0.15mm or lower per layer.
3. Layer height for the majority of PLA parts could be printed as high as it does not matter for them, I'd recommend 0.15mm or above for every layer; even small PLA parts are ok to be printed in that range.
4. This is my preference, but I prefer to manually set my supports since my slicer always overdid it for me in the past. I'd recommend a Top Z distance of 0.25-0.3 and the same for the Bottom Z distance if applicable to your slicer.
5. All parts were printed at 10% infill with a Gyroid infill pattern except for PETG1, which was printed with the same infill pattern but with a 50% infill. Not required, but I would reccomend a infill higher than 10 percent for specifically PETG1

Some things to keep in mind is for this build to make it easier, I not only mention the file name while building them, but parts of that are made of different material is printed in different colors. For this build, I printed the Carbon Fiber PETG components with a brown color and the PLA components in a while color.

I WILL ALSO HIGHLY RECOMMEND FOLLOWING THE PHOTOS! THERE IS A LOT TO HELP GUIDE YOU!

Starting off with building the Retractable Cable Drum, I will list the STEP file name that was listed in this Instructables supply section as we go along! For this step, we will build the output gear of the cable drum.

1. First, grab PETG1 and take the notched circular end, and push it through a bearing. It will be extremely tight, but it is necessary later, so put it aside for now.
2. Take PLA14 and PLA15 and slide their hexagonal female and male inserts together; it should be a loose fit, so it won't be as painfully hard as before. Sorry about that :(
3. Now we bring back PETG1 with the bearing hanging around the notched end, press fit the hexagonal part of PETG1 into the hexagonal insert of PLA15
4. Nicely done, now we have the output gear of the retractable cable drum.

For this step, you will need 3 bearings, an M2 screw with a length of 10mm, a spiral spring, PLA1, PLA2, and PLA3, as well as any 2 parts of [PLA9, PLA10, PLA11, and PLA12]. You will use all of them, but for now, I will take PLA9 and PLA10 for this step. But again, it doesn't matter which of the 2 you pick.

PLA1 will act as the main plate for all the gears within the mechanism. I will refer to PLA 1 as the mainplate. It will help to mount everything in place before we add the footplate to keep everything together. Place PLA1 on its flat side and notice the 2 holes on the side opposite to where the circular cage is. Place 1 bearing per hole, and then place PLA9 and PLA10's cylindrical counterparts through the holes of the bearings. So that the hexagonal parts face upwards toward the roof.

Now take another bearing and place it in the center hole of the circular cage on the main plate, then put the narrower side of PLA3 and place it through the center of the bearing. It should be a very loose fit with the wide circular part of PLA3 pointing upwards. Now place the spiral spring in the center, but check for rotations. Essentially, we want the spring to compress or get smaller when the cable is pulled. Take the end of the spring and pull on it to figure out the direction of rotation that leads to the spring becoming compressed. Flip the spring on both sides to figure out which direction is correct. For me, it was the clockwise rotation of the spring that led to it being compressed. Knowing the correct side and rotation. Place the spring in the circular cage, and you should see a small hook. The spring latches onto this hook by pressing it inward to the plate. Once pressed, plug PLA2 on top of the hook. Screw down an M2 screw of 10mm length into the top of PLA2. This will secure the spring in place.

For this step, you will need PLA13, PLA5, PLA7, PLA8 Bearings, a 1-inch wide and 3.25 feet long hook strap, and the completed output gear made previously.

Connect the hexagonal insert and plug from both PLA5 and PLA13 to create the cable gear, then plug 1 bearing into each of the 2 gears' bearing holes. Then, proceed to wrap the cable around the circular axle. Keep in mind the rotation of the cable gear when you pull the cable; you want to wrap the cable parallel to that motion. So in my case, since the spring compresses clockwise, I know that this gear has to rotate counterclockwise, so I will wrap the cable counterclockwise, as it is the direction the cable gear will spin if the spring gear spins clockwise, which it will due to the spring requiring to spin clockwise to compress.

Insert PLA7 and PLA8 down the hexagonal shafts of PLA9 and PLA10; now the pulleys are connected to the main plate (PLA1). Slide the completed cable gear down the axle nearest to the circular cage and the pulleys with respect to the rotation; it will unwind, for if the spring begins to expand, it will permanently deform and possibly break the other components when you pull the cable from the cable gear.

Place the completed output gear on the second axle on the main plate. It will take a little bit of struggling, but once it's in, it will be difficult for it to pop out due to the inverted shape of the teeth locking onto each other. Then grab PLA4 and press-fit its slotted end into the slabbed input at the center of the spiral spring; the end of PLA4 should press on to PLA3, and just like before, the spring gear (PLA4) should rotate clockwise. Place a bearing into the bearing hole of PLA4.

These gears inside the retractable cable drum are called Herringbone gears. These gears mesh nicely and more quietly, while the sharp shape of the inverted teeth cancels out axial forces, which forces the gears away from each other, which makes it effective in this setup. When they intersect and mesh together, the main plate is filled with quiet gears that do not slip, no matter how hard you pull on the cable, making an efficient energy transfer machine and still provide alot of resistance for the muscles!

For this step, you will need PLA16, PLA20, PLA29, (2) M3 16mm Screws and (2) M3 20mm Screws

First, grab PLA16; this is the sub plate. I will refer to PLA16 as the sub plate from now on. Now align the main plates (PLA1)' bearings, the male hexagonal shaft that sticks from the center of the completed cable gear, and the bearing's inner race of the spring gear (PLA4), to the sub plates' female bearing, hexagonal insert, and connect the bearing peg to the inner race of the bearing embedded in PLA4. This will take some effort to get it right due to the loose fit of the pulleys, but push down until there is no resistance. Ensure the subplate is not wobbly.

Grab PLA20, this is called the foot plate. I will refer to PLA20 as the foot plate, and now we can flip the mainplate and subplate assembly upward. If you applied the subplate onto the inserts of the mainplate correctly, it should stick without falling apart. The foot plate sits below the legs of the subplate and main plate, so lift both slightly to slide the foot plate (PLA20) through. Align the plate with the curves and edges with both the mainplate and subplates curves. If aligned correctly, if you look at the sides where the sides of the footplate extrude a little upward, (2) M3 holes should be aligned with the holes of the main plate (PLA1).

Only on the side where the main plate is, which is one of the sides of the foot plate, should be screwed in. There are screw holes on the opposite side where the subplate will be, but for now, we will leave it open. Take (2) M3 16mm Screws, and screw them into the holes only on the side of the footplate where the mainplate is. Finally, grab PLA29, and you'll notice protruding oval and circular shapes from one side and a long side of PLA29. The long side has (2) M3 holes, which should rest on the circular platform on top of the sub plate (PLA16). Align the protruding shapes sticking out of the shorter side of PLA29 to the female inserts of the main plate (PLA1). It should just sit there long enough to allow you to screw (2) M3 20mm screws on the longer end of PLA29 into PLA1 to make the top sides of the main and subplates connected and stable.

Nice job! We completed the retractable cable drum! After this, we will work on a second footplate that has the electronics portion and the flywheel!

Now we will step aside and make the flywheel. For this step, you will need PLA18, PLA19 (4) M3 10mm screws, (40) 5.5mm stainless steel balls, and (45) 6mm stainless steel balls.

Place PLA18's hexagonal side onto the table, while the circular insert side faces upward. The outer ring of balls is meant for the 6mm stainless steel balls, while the inner ring is meant for the 5.5mm balls. You will need (45) 6mm balls to fill the outermost ring of the flywheel and (40) 5.5mm balls to fill the innermost ring of the flywheel. Do not pick up the flywheel, as the balls will fly out. Once accomplished, grab PLA19 and align the most outer M3 screwholes with the screwholes on PLA18's circular insert side. Again, as you put the balls through this side should already be facing upward. Grab (4) M3 10mm screws and secure the Lid(PLA19) onto the flywheel(PLA18).

Nice job on making the Flywheel! Let's put this aside for now.

For this step, you will need PLA23, (2) M3 15mm screws, (1) M6 8mm screw, PETG4

This second plate holds the majority of the electronics as well as the flywheel. To begin assembling it, we need to prep it by attaching it to the cable drum. It will act as the "foot plate" for the electronics instead of the footplate for the retractable cable drum.

Grab PLA23 and observe the side walls protruding from the plate. 1 side will have M3 screw holes, and one side will not. Align the footplate screw holes along with the side of the cable drum where the output shaft (PETG1) is sticking out. Grab (2) M3 15mm screws and screw the second plate into the output side of the cable drum. This is so we can set up the flywheel and the electronics next to it.

Now grab 1 M6 8mm screw and PETG4. I'd recommend looking at the photos to see where PETG4 is mounted. On the farthest side, mount PETG4 with 1 M6 screw; you will notice you need 2, but this is intentional, as we will come back later on. So this allows PETG4 to rotate on the second foot plate.

This step will explain the wiring done with the parts

For this step, as clarified in the supplies list. The electronics are SPECIFIC. Especially the motor selected here. This circuit requires 6 diodes to form a rectifier circuit, 2 capacitors to create a parallel circuit that filters the generated voltage. An output terminal where I used a female USB-C connector. ALSO THE MOTOR COMES WITH A SMALL TIE, KEEP THE TIE SO IT MAKES ORGANIZATION BETTER AND MORE COMPACT. (I would recommend tying up as much excess cable as possible to make the system more compact. I did this for testing purposes, but feel free to cut the wire down so you do not need to use the tie or have the excess wire stick out.)

Below is a simple explanation of how this works, called "Understanding", but if you want the instructions to make the circuit directly, just scroll down to the "Wiring" paragraph.

Understanding: Essentially, without going into crazy science, the motor, when spun, generates a "back EMF," but for now, we will refer to it as voltage being generated by the motor, as it is essentially acting as our main generator in this setup. So this motor is called a BLDC motor, and it generates AC voltage when spun. A rectifier essentially corrects this AC voltage to DC voltage, which is something many handheld or portable circuits require, such as power banks or phones. The motor has 3 wires called phase wires, for this setup, its ok to wire them between any end of the rectifiers. To get a better explanation, I would recommend taking a look at the photos. Rectifiers are commonly seen in items such as power bricks, which we use to charge our devices. In our case, we can call our motor an unpredictable wall outlet. It has surges of AC voltage running through it, and a rectifier takes those surges and turns them into a usable DC voltage that can charge our devices. You can see 2 capacitors connected to the positive and negative terminals of the rectifier in a parallel configuration, so the capacitors positives are linked together and the capacitors negative leads are linked together. This increases capacitance and allows the capacitors to store more energy through the bursts of energy we will generate for every pull we do on the machine. Finally, the ends of the capacitors are connected to an output terminal. This terminal is where you would plug in a device to be charged. For this setup, I wired a female USB-C connector to the terminal.

If you wish for a better understanding than this, I have linked a few photos that express my thoughts on motor backemf generation, current, reverse polarity, a more in-depth view on how rectifiers work as well as a better understanding of why the system was so unstable due to the requirement of such a large torque for my wanting of a higher RPM. I hope you can read my handwriting:(

Wiring: For this circuit, place the diodes out as shown in the photos. In one of the photos, I have mapped out the circuit with green and blue wires. Green represents positive, while Blue represents negative. Now, yes, this is confusing because the diodes are clearly marked, but is what you're thinking right? The negative side is the striped side? Yes, but stay with me. First, create 3 pairs of diodes, each having 2 diodes each. Wire them in series or connect one positive side of a diode to another diode's negative side. Check the orientation of them in the photo. Now with your 3 pairs of diodes, which have their 2 diodes each connected, connect the 3 pairs in a parallel configuration, essentially, if you look at the pairs, the ends of the pairs have one end sticking out with the striped side and the other end with a no strip side. connect them. Now connect the phase wires to the middle leads of the rectifiers, between the pairs of diodes. The picture can help. Now, spin the motor with your hands, and for safety purposes, use a multimeter and measure the voltage difference between Rail 1 and Rail 2. You can identify these rails by looking at the pictures above; one of them will list the rails I am talking about. The rail producing a negative voltage will be marked as ground, and the one producing a positive voltage will be marked power. In my case, the green wire in the photo was positive, and the Blue wire was negative. Connect 2 capacitors in parallel, their positive leads and their negative leads. Connect the positive leads of the capacitors to your defined positive rail and the negative leads of the capacitors to your defined ground rail. Now connect the female USB-C connector to the positive and negative leads of the capacitors. This completes the circuit.

For this step, you need your completed circuit, the second footplate (PLA23) with PETG4 slightly screwed on it, PLA28, (2) M6 20mm screws, PETG5 and PETG6.

Attach PETG6's hexagonal peg into PETG5's female hexagonal insert. Now pay close attention to the bottom side of PETG5's protruding oval and circular shapes. These shapes go into the motor; they clamp onto the motor while spinning, so you need to line them up onto the motor so they can actually do that. Align the circular and oval pegs with the inserts made into the motor bell. Bring the rectifier + capacitor portion of the electronics below the motor, and you will notice a square-shaped extrusion downward below the motor mounting points. This is intentional so it can act as a dish to hold these electronics. Both the rectifier and capacitor can fit, but since I was in my testing phases, I chose to make sure my capacitors stick out. You do not need to mimic that action. Grab PLA28 and align its legs with the screw holes near the square dish. The M6 holes should align perfectly, which should allow you to screw (2) M6 20mm screws down. This holds down the electronic portion, make sure to have the output terminal ( which is the USB-C female connector) stick out as it will be mounted elsewhere. Now the motor can be mounted to the motor mount plate on top of the second footplate. The motor comes with M4 screws. Mine came with 2, so I screwed the M4 screws diagonally for better distribution.

This step can be skipped if you chose to cut off the excess motor wire and connect the motor to the rectifier with the shortened cable. I simply added this because I was still testing the capabilities of the motor in other experiments.

For this step, you need PLA26, (2) M6 8mm screws, the tied-up portion of the cables, and PLA27.

Grab PLA26 and the tied-up portion of the cable. Begin pushing the tied portion through PLA26. PLA26 is flexible, so slightly push against the walls. This helps the tied portion maintain a tighter shape so it can fit through and stay within the barrier when you actually mount PLA26 on the second footplate (PLA23). Now that the tied portion of the cables is prepped, mount PLA26 with the open wall portion of the rectangular barrier facing the motor. Use (2) M6 8mm screws to screw down the barrier on the plate. This helps secure the cables without them interfering with other components, and to top it off, you can seal it with a very small amount of hot glue and the Lid for the barrier, which is PLA27. It's a very loose fit, but it was meant for easy access. To keep it in place, use a small amount of hot glue to secure it. Don't go too far with the glue.

For this step, you need the one-way clutch bearing and PETG2.

Coat a very small amount of glue in the inner race of PETG2; this helps ensure that not only does the indented area of the bearing stay in place, but the rest of the bearing's outer race maintains a better grip on the outer shape of PETG2. Align the indent of the outer race of the one-way clutch bearing with the protruding indent of PETG2. It should align well, and with the hot glue drying rapidly, you need to push down quickly. It will be very tight and difficult, but in the end, the clutch should be well aligned with PETG2. Put this part aside for now, as we will need this later.

For this step, you will need PLA25, the output terminal (USB-C female connector), and (2) M6 8mm screws.

Slide the output terminal through PLA25's large hole; it should slide very easily with no resistance, then apply hot glue around it to keep it inside. For easier removal, I would recommend only gluing one side. Unfortunatley for this step, I forgot to take a picture to indicate where on the second foot plate this part is mounted. It is the area right below where the motor, along with PETG5 and PETG6, sits. I would recommend briefly removing the motor along with the connected PETG parts to mount PLA25 properly. Use (2) M6 8mm screws to screw it down to the plate.

For this step, you will need PLA24, and I would recommend (2) M6 8mm screws, but I ran out due to using them in another project. I ended up using (2) M6 10mm screws, just not screwed all the way down.

Grab PLA24 and next to the charge port, as well as where the small hex gear (PETG6) points to, Mount PLA24 onto the circular female insert of PETG6. The insert should help pinpoint the M6 holes underneath it, which should align well. Secure down PLA24 to the second footplate by using (2) M6 8mm screws. Now the motor gear should be able to spin with more stability and not fall off.

This step could be slightly more difficult; we would recommend following the pictures for additional guidance. For this step, you will need PETG7, (1) Bearing, Flywheel One-Way Clutch Insert, the Completed Flywheel, and (1) M6 8mm Screw.

Grab PETG7 and before inserting the bearing into the bearing hole of PETG7, coat the walls of the bearing hole with hotglue, a small amount to make a tighter fit. Press down the bearing into the bearing hole and leave it aside.

Grab the Flywheel One-Way Clutch Insert that was completed previously, and on the subplate where the output shaft sticks out (PETG1), if you look closely, the shaft has a circular shape with a protruding rectangular shape that sticks out. Very small, but it aligns with the indented rectangular cutout of the inner race of the one-way clutch. First, ensure that the hexagonal shape spins in the direction the output shaft spins WHEN the cable is pulled, and continues to spin in that direction when the return stroke engages. You can test this by holding PETG7 and continuously rotating it in the same direction the output shaft rotates, WHEN the cable is pulled, if the flywheel one-way clutch insert rotates in the same direction as the return stroke after the pullstroke is disengaged (you basically let go, you stop pulling the cable toward you), the clutch's oreintation is incorrect, to correct this, simply flip the flywheel one-way clutch insert and run the test again to ensure it continues rotating in the same direction of the output shaft when the cable is pulled, and continues to rotate in that direction even after the return stroke is engaged. The reason why it won't rotate without you holding the hexagonal part in the opposite direction is that the inertia is too low for it to overcome that force, which is why the flywheel was implemented, and because of that, it conserves its rotational motion and power for much longer periods of time.

Once you are able to confirm the correct orientation, pull out the clutch insert and coat the output shaft of the cable drum with a slight amount of hot glue. Then, align the inner race of the clutch with the protruding indent of the shaft. It will be extremely tight, but press down until the shaft's face is level with the face of the bearing. Try not to push all the way down to the subplate's surface, as this will cause more friction issues.

Grab the flywheel and orient the hexagonal insert side to the hexagonal clutch; it should align nicely and be a firm fit. Press it down and then grab PETG7 from before. Align its semicircular female insert with the semicircular peg that sticks out of the flywheel. It could be troublesome trying to fit it, so if you want, briefly remove PETG4 to insert PETG7. Ensure PETG7 meshes with PETG6. Screw back on PETG4 and then rotate it so its peg enters the bearing's inner race of PETG7. Then use (1) M6 8mm screw to finally screw the other side of the PETG4. Which secures down PETG4 completely. PETG4's purpose for being added is to help push the gears down because in earlier prototypes, they would constantly push each other. We will refer to this as the Gear Tensioner.

For this step you need PETG3, PLA21, PLA22, (2) M3 15mm Screws.

First, screw PLA21 and PLA22 into the holes on the side of PETG3, and the threads should be able to mesh nicely. The first time will be slightly tighter, but then screwing on and off again will reduce the amount of force required to get them to clamp down on a desk. With the completed desk clamp, align the screw holes of the second footplate with the screw holes of PETG3; the screw holes will be near the square dish where the electronics reside and in front of the charge port. Use (2) M3 15mm screws to mount the desk clamp to the second foot clamp. You will notice 2 holes left unattended on the clamp and the first footplate, but there is no reason to install them.

Now the setup is mountable!

Congrats, you've made it to the end! A finished prototype of the portable cable workout generator that actually generates electricity and can charge a power bank!

There is alot of improvements that can be made, and I will continue working on it to improve it, for now try coming up with your own unique ideas to make this a better project!!! You can hear my own thoughts on what to improve below!

Reflections and Considerations

Something I'm going to keep in mind for the next prototype is to design a gear tensioning system that can automatically adjust the tension to ensure the gears mesh easily without the need for manual intervention to tension the gears. To be honest, it was the most stressful part because, although the tensioner (PETG4) was very effective, it required a lot of force and precision to keep the gears meshing properly.

The Low ESR capacitors were effective, but also chosen because of their lower equivalent resistance. To better absorb larger spikes for longer run times, I'm going to replace the 2 capacitors with 1 large capacitor that has a much higher voltage capacity and greater capacitance, preferably greater than 2200uf. My reasoning for this is that the 10V 1000uf capacitors I had on hand, unfortunately, would not be able to sustain greater pull strokes, which generate more energy. I may probably go for a Low ESR 35V 2200uf capacitor as a general scope of what I'm aiming for, or higher.

For this build, I had an overdrive gear ratio that increased the RPM of the motor by 10 times, this is so I could qualitatively test if my math was right or off for I had made a few calculations before hand and had an estimated overdrive gear ratio that increased the flywheel RPM by 16 times, should the flywheel hold a consistent RPM of 120 (I have a picture of my calculations on this step should it interest you). This build, from my observations, had a lower average Flywheel RPM due to the torque impulses generated by the large overdrive ratio; however, the calculated voltage and current generation for the 10 times RPM increase was not far off, which I'm happy about. If I went with the which would result in smoother consistant voltage generation without pulling faster but harder slowly. My reasoning for this is that I want the workout machine to increase muscle growth and endurance by pulling something with a much tougher resistance, but with a more consistent speed and strength. The issue is this will create slipping, since it spins 10 times faster, it requires 10 times more torque to spin the flywheel, this introduces 10 times more force on the teeth experience, which causes increases in axial forces, shear forces, and this causes slipping and ejection of the gears. To fix this, my next prototype will probably implement a belt system where the gears do not make contact with each other, but indirect contact through belt drive to eliminate those conditions, and as a bonus, implement a screwable, adjustable belt tensioner that doesn't require manual intervention. Hopefully, this helps me keep my hand away from the gears in the next prototype.

For the next prototype, this is most likely not a definite application, but I wish to introduce other forms of mountability, like open-air suction cups to mount to walls, so more types of workouts are possible in areas without a desk, as well as work on a smaller overall form factor now that I know the system is functional and works. My printer can allow smaller gear module sizes, but again, I do need to watch out for torque impulses generated by gears, as it is currently the biggest issue in this project. Lastly, I would like to start aiming for smaller and more compact prototypes. This prototype was not heavy, but I wish for it to fit in a backpack while being lightweight, so that it feels normal when you go to school. At the very least, begin trials for prototypes being more lightweight and compact.

Thank you for sticking around my portable cable generator project! I still have a lot to learn and continue improving, which is what I hope to do with this project!