Introduction: Solar Powered, Bike Frame Pottery Wheel

By Avi Kazen
About: I'm a maker in Chicago, IL, originally from Tucson, AZ. I like things that involve electronics, art, biology, and sound.

This instructable will show you how you can build a solar powered pottery wheel out of a bike frame!

Step 1: Ingredients

Please note that many of my design choices were based on availability. Better design alternatives are certainly out there, and I will note some of these throughout.

Materials:

  • Bike frame - I recommend getting one for free. If you live somewhere with a community bike workshop, see if they have any junk frames you can use. All that really matters is that it has a seat and forks. Oh, and a rack is a convenient addition.
  • Motor - I had an old e-90 motor from a razor scooter laying around, so that is what I used. This is a 100 watt, 24V brushed DC motor. I ended up designing my power system for 12V, which I will talk about later. You can find this motor here for $25, but there are many out there that will work. One important consideration is the sprocket/chain you will be using. I designed mine using the same sprocket as the razor scooter, #25, which comes on the E-90 motor. This motor works well and spun fast enough at 12V, however it is a bit weak (will slow down some when I'm working the pots). Consider using a higher wattage motor/higher voltage system.
  • Chain - as mentioned above, I used #25. You will probably need about 4 feet, but good to have extra. Here is plenty for $17.
  • Chain breaker - you will need this to size the chain correctly. Here for $13.
  • #25 sprocket - the selection of the sprocket depends on the bike frame/head tube diameter. This is usually 1", in which case you will want a sprocket with a 1" hole. Again, my selection here was driven by what I had available. I ended up having to bore out my sprocket's inner diameter a little bit to fit on the fork stem. The sprocket I used appears to be a 55 tooth. This looks like a suitable option for $6.
  • The wheel - this is a tricky part. I used a wooden round from home depot for 5 bucks. This was easy to work with and a perfect size, but unfortunately mine was not uniformly dense which made the whole pottery wheel shake when spinning. I did my best to re-balance it, as I will explain later, but if you can find a more uniform disk to use it will save you a headache down the road.
  • Solar panel - there are many 12V solar battery chargers available for maintaining charge on car batteries. You want one that has a decent power output so it actually charges the battery. Here is the one I used for $25. If you design your system for 24V instead you will need a different one, or at least a different circuit then what I will describe.
  • Batteries - I designed my system to be 12 volts because I had two 6 volt lead acid batteries lying around. You can just as easily design this for 24 volts to get some extra power out of the motor. Get one here for $17.
  • speed controller - see the step about electronics for more details on this.
  • 3 large hose clamps - must be big enough to go around the motor and the down-stem of the bike frame. a few bucks at home depot.
  • Some wood - needed to stabilize the bike frame. you should be able to find some scrap.
  • Some brackets - I used some small 75 cent brackets from home depot
  • Various hand tools - including a hack saw, drill and a screw driver.

Step 2: Stabilize the Frame

I used some wood to stabilize the frame. While sitting on it, your legs will be on the ground to help stabilize it more, so this is mostly just so it doesn't fall over when not in use.

Use a couple pieces of scrap wood and some brackets to build supports for the frame. As you can see in the photos, I did one across the back wheel mounts, and one diagonally from the down tube. I used a tuna.soup can lid as a bracket, a resourceful trick a friend taught me.

Step 3: Set Up the Wheel Assembly

This was, in my opinion, the trickiest part of the build. I will describe my strategy, but I encourage you to be creative and try to improve where you can.

The forks:

I used the front forks, and mounted them UPSIDE DOWN on the head tube of the bike. This was a bit tricky to find all of the right pieces to make this work, but if you have access to a community bike workshop, just play around a bit with various headset components until you have something that works. This will be the spinning axle for the wheel, so the bearings should work well.

Before you mount the forks, use a hack saw to saw them off to a comfortable height for the wheel. The wheel will sit on these cutoff ends (or slightly above).

The sprocket:

The sprocket should fit on the stem of the forks. Mine was slightly undersized, so I bored it out a bit and then forced it onto the threaded end, which actually made for a nice snug fit. I also used a couple of lock nuts on each side, tightened around the sprocket, to hold it in place.

The Wheel:

The way I decided to go about this was to screw a piece of wood vertically from the back of the wheel using some shelving brackets, then screw into that piece of wood, though the forks, to hold it in place. This was obviously a very hacky way to go about this, and took a long time to get the wheel perfectly perpendicular to the axis. Careful measuring of the center of the wheel is key. Even with a perfect center, though, I still found that my wheel was off balance due to nonuniform density of the wood, which made the whole bike shake when it spun. To combat this, I screwed some extra chunks of wood to the underside of the wheel in an attempt to balance it. In the end I was able to get it pretty well balanced, but it took awhile.

One other issue I found is that the fork stem, and possible the head tube, are actually tapered. Thus, when mounting the forks upside down, it didn't fit snugly and was able to rock back and forth in the tube. This is a weakness in the design, though different bike frames may not have this issue?

Overall, I think this step is the weakest part of the build. Better alternatives could include a different choice of wheel made out of a more consistent material, a better way to attach the sprocket, and a better way to use the headset as an axle. Basically the whole thing. Maybe there is something better than forks to use. I thought about using iron pipe, because then a flange could be used to attach the wheel to the top, but I couldn't think of how to make the axle work. If you have access to a welder you can just weld it to the fork, though keeping it straight might be tough. I'd love to hear your thoughts for how this could be improved.

Step 4: The Motor and Chain

Attach your motor to the seat tube using the hose clamps. The sprocket should be level to the front sprocket from the previous step. I installed mine upside down because it seemed a bit more rain-proof that way.

After the motor is tight, install the chain. Measure the required length of chain down to the nearest link (better to be on the short side), and use the chain breaker to separate the length of chain. The chain should have also come with a master link which is use to reconnect the two free ends. Note that the chain will form a loop around the front down tube, so don't reconnect it until you have it in place. The chain should be tight once in place on the sprockets. If it is slightly too short, you can use a shim behind the motor to move it slightly forward.

Step 5: The Electronics

You have two choices here. If you are a nerd like me, and want to build your own speed controller, keep reading. If you are not, buy one of these and skip the rest of this step.

We need a way to control the speed of our pottery wheel. Since we are using a brushed DC motor, the best way to accomplish this is with a PWM controller. I am sure there are a thousand instructables out there on building these, but I wanted to build my own that incorporates regenerative breaking and low voltage cutoff to protect the batteries. I also included a voltage readout.

If you don't know the theory behind regenerative breaking, this is a very good post. Explaining PWM is beyond the scope of this instructable. Try google.

Is regenerative breaking necessary? Probably not. I have no clue how much it has boosted my battery life. I mostly did it to explore the concept, but I'm sure it is helping a little bit.

I chose to base my design around an adafruit Trinket. This is a development board based on an ATTiny microcontroller. You could use an Arduino instead. I chose the trinket for it's size.

Here are the details of the less obvious parts of the circuit:

  • I used a 5 volt trinket from Adafruit. They offer great tutorials on how to use these, and they can be programmed with the Arduino IDE. This project only called for a couple inputs/outputs, so this was a good option.
  • LM317T is an adjustable voltage regulator. I used this to regulate the voltage down to around 7V which is used to power the trinket and the speed reference. The V+ line will be noisy with the motor turning on and off, and will also drift based on the batteries charge. This would lead to inconsistent speeds if it was used to drive the speed reference directly. The Trinket has a built in regulator, which can handle up to 16 volts, therefore it doesn't really need to be after this regulator, however I chose to power it this way to further buffer the trinket from spikes created by the motor. Also note that my drawing is actually not accurate at this point. R11 doesn't really make sense here. If you use an LM317, look up the datasheet for proper use. I drew up this circuit using scheme-it after the fact to make it look nice (transcribed from my notebook). Don't know what I was thinking here.
  • The speed reference is made up by the pedal and R3. The pedal is just a potentiometer (or rheostat, since we aren't using both ends of the pot). In combo with R3 it generates an adjustable voltage divider that acts as the speed input to the microcontroller. I use R3 rather just using the full potentiometer because the range had to be attenuated (0-5V rather than 0-7V coming off the voltage regulator) and so I only needed two wires running to the pedal (rather then three if I used the the full pot). More details about the pedal will be discussed later. Alternatively, I could have just used the 5V output on the trinket and used the full pot and skipped R3, and probably the voltage regulator all together.
  • R1/R2 is a voltage divider feeding into the micro as a battery reference. This allowed me to program a low voltage shutoff. As I have mentioned, I designed my system to use 12V. Therefor I did a 1/3 voltage divider here (R1=2*R2). If you were designing this for 24 V, you should obviously drop this further, maybe R1=5*R2
  • Q1 is an NPN bipolar junction transistor to drive the half bridge. This is needed to drive the MOSFET gates with 0-12V rather than the trinket's 0-5V output, which wouldn't be able to shut off the P-channel FET properly.
  • R4 limits the current to the BJT. 1k should work.
  • Q2 and Q3 are P-channel and N-channel MOSFETs respectively, forming a half bridge. A motor can be speed controlled with a single MOSFET, but using a half bridge like this allows for regenerative/powered breaking.
  • R5 limits the current when Q1 is on, so the battery isn't shorted. A few Kohms will work.
  • R6 is to further protect the gates of the MOSFETs. Might not be necessary. I believe I used 1k here.
  • D1 and D2 are flyback diodes and are necessary for regenerative breaking.

Some tips:

  • Use female headers on your circuit board instead of soldering the trinket permanently in place, so that it can be plugged in/removed as necessary. Some of the pins on the trinket are used for the USB programming, meaning depending on the layout you might not be able to program it in circuit.
  • Find a nice waterproof project enclosure so the circuit can be weatherproof.
  • Use plugs/connectors to interface the circuit with the big components like the motor, the battery and the solar panel.

Code for trinket:

The below code implements the regen breaking and the low voltage cutoff. Since I wasn't sure how much power this wheel would be sending back towards the battery as it slows, or how much power the battery can absorb, I implemented a "deceleration limiter" to slowly ramp down the speed. Depending on your battery/motor this might not be necessary (it probably wasn't in my case either). You can remove this by changing threshold to 1024. Also, you can adjust the battery cutoff voltage by adjusting battCutoff from 0 to 1024.

const int motorOut=0;
const int pedalIn=1;
const int battIn=3;
int motorSpeed=0; // 0 to 255
int pedalVal = 0; // 0 to 1024
int lastPedalVal = 0;
int threshold = 50;// 0 to 1024 limit the rate at which the motor can decelerate. Higher number=higher rate. time it will take to do a full decel is 256/threshold seconds
const int battCutoff=700; //battery level at which to shut down system. depends on voltage divider. for 1/3 voltage divider on input from 12 volt pack with a cutoff at 10 volts, cutoff should be 3.33V or 3.33/5*1024=682
int battVal=0;


void setup() {
pinMode(Motor, OUTPUT);
}


void loop() { 
//battery monitor
  battVal=analogRead(battIn);
  if (battVal>battCutoff){ //Battery Monitor OK
    pedalVal=analogRead(pedalIn);
  }
  else{ //Battery Monitor not OK. Shut 'er down.
    pedalVal=0;
  }
  
//limit deceleration
  if( pedalVal > lastPedalVal-threshold ){ //accelerating or decelerating within threshold. allow accel/decel at pedal rate.
    lastPedalVal=pedalVal;
    motorSpeed=pedalVal/4; //adjust from speed input (0-1023) to PWM output (0-255)
  }
  else{//pedal moving faster than threshold rate. limit rate.
    lastPedalVal=lastPedalVal-threshold;
    motorSpeed=lastPedalVal/4;
  }
  
  analogWrite(motorOut,motorSpeed);
  delay(250); // 1/4 second delay in between reads for human compatible timing
}

Step 6: The Pedal

The pedal is basically a potentiometer (adjustable resistor knob) that can be controlled with your foot. My design used a lever made out of wood with the potentiometer fixed at the bottom-center of the base (just below the fulcrum). I mounted the potentiometer using a 90 degree bracket that the it screwed through. A string is fixed to one end of the lever, then wrapped several times around the potentiometer knob, then fixed to the other end of the lever. As the lever rocks back and forth, the distance from either end to the potentiometer changes, thus the string is pulled back and forth. Since it is wrapped around the knob, this results in turning the knob.

The joint for the lever was just a couple screws.

If you built your own speed controller, this potentiometer is used as a rheostat (because only two pins are used to make an adjustable resistor) and this is combined with R3 to create the speed control input.

If you bought this one, you should just extend the wires so that you can use the potentiometer it comes with.

This design actually worked better than I expected!

Step 7: Put It All Together

This is where a bike rack comes in handy. I used it to hold the battery, solar panel and speed controller. The solar panel hooks up directly to the battery, which goes to the power inputs of the speed controller. The pedal goes to the control input. Make the wire long enough so the pedal can be positioned in a comfortable spot. The output of the speed controller obviously goes tot the motor. I used some nice metal conduit for my wires which made it look a bit nicer and will hopefully protect the wires from critters/sun.

Place the solar panel over the battery/controller to give it some rain protection.

Step 8: Make Pottery!

Enjoy!

Put this pottery wheel out in the garden, or take it with you to your next maker fair and make some fresh pottery wherever!

I have yet to find the limit on my battery capacity. Every time I go out to use it, it's charged, and I haven't had it shutoff on me. I have used it for a couple hours at a time to make some decent pots, and the battery still has a good amount of charge left.

Overall this was a fun project with a very functional end product. I have pointed out some weak spots along the way, and I'd love to hear/see your ideas for improvements!