Electric Moped Update #5: The Rebirth

She’s alive! Alright, so my last post was a little dramatic but I’m feeling a lot better about the project now. A week later I ended up caving in and buying a replacement motor for the moped after realizing how long my walk to school this summer would be without it (and just how out of shape I am).

Motor Mount

The motor came in pretty quick but before I could mount it I had to make a new motor mount because the last one melted. So this time I’m going to weld it out of aluminum to fix those annoying melting problems. It should also help to suck some heat out of the system and give me some more practice on the TIG welder. The main face I cut out at the Frank Innovation Zone using the waterjet to make sure all the holes are precise enough, the rest of the parts were hand cut because they just needed to be close.

The weld came out bad, like really bad. I can’t seem to get a hang of this TIG stuff. But the weld still looks plenty strong so I’m going to use it. I also designed an impeller to combat the heating problem I described in the last post. This one should suck air through the motor and cool off the windings (should be better than stopping every five minutes to blow on the motor).

After grinding a flat spot on the shaft of the motor to hold the sprocket in place(making sure to cover all openings with tape to make sure no metal shavings got inside), I bolted the motor to the mount, attached the fan, and bolted the whole thing to the moped frame. It worked perfectly as a straight drop-in for the old printed mount.

Speed Controller

The speed controller I’m using is a cheap $20 E-bike controller from Aliexpress that was recommended on an endless sphere discussion board (great place for finding electric vehicle-related information). These cheap chinesium speed controllers don’t have too much documentation and most don’t even have labeled cables. After browsing a few forums and blogs I found Charles’s website where he has an awesome write up on his experiments with these Chinese controllers and a lot of documentation on some other really cool projects. It was really inspiring to see someone else out there, trying to document their projects like I am. His translated wiring diagram made it really easy to setup this controller although I still don’t know what some of the wires do but I was still able to get it working without them so they must not be important.

Sensorless Operation

He found that the speed controller has both a sensorless mode and a sensored mode. If it detects a hall effect sensor it will use sensored mode for startup torque and then switch to the sensorless mode for higher rpm. If no sensor is detected it will just run in sensorless mode but will have trouble starting and will need a little push to get going. Under this reasoning and with the mopeds’ sensor still not here yet I set up the speed controller in sensorless mode. This did work but was very glitchy. What would happen is when the moped is first powered on I’d give it some throttle and the motor would make a grinding sound as if it were fighting itself for a second and then start spinning. If I let off the throttle and let the motor stop and then tried to give it throttle again the motor would again make a grinding sound but not be able to start spinning again. Sometimes it wouldn’t even start spinning the motor the first time. I found that if I reached down and spun the motor a bit while giving it throttle it would take off. I think this is due to the zero startup torque Charles was talking about with sensorless and because the moped has a clutch on the wheel allowing it to free coast without spinning the motor there was no way to jumpstart the motor by pushing the moped. At this point, I think the hall effect sensor should be all I need to get it working flawlessly.

Sensored Operation


I ordered the hall effect sensor from Jason at his web store and installed it just as I had done before with the electric bike and expected that to be it to get it working annnnnd I would be wrong. After adding a 3d printed mount to attach the sensor to the motor mount I installed the sensor but noticed the motor behaved oddly. There was definitely plenty of startup torque now but when the motor rpm got to a point where it would normally transition to sensorless it would instead shudder and make a grinding sound until you brought the rpm back down to sensored speed.

This was ridable but not at all fast or comfortable. The shuddering eventually got to the point where it would no longer even start. Initially, I chalked this up to the low voltage protection being too low and trying to stop the motor when the battery voltage sagged under load. After more testing, I found it acts the same with a fully charged battery as a dead battery disproving this theory. Then I thought the shuddering was due to the maximum e-rpm Charles found while trying to run a high KV motor with one of these speed controllers. I figured it got to a point where the motor was spinning too fast for the speed controller to catch up so it was turning on the motor at the wrong time causing the cogging. But after unplugging the sensor the motor returned to pre-sensor behavior. At this point, I was more confused than a Texan in a snowstorm as to what was going on. I hadn’t thought it was the sensor because startup was so smooth but after sliding the sensor over a little bit the cogging lessened. After fiddling with the sensor for a half hour I finally got it in the right spot. Startup torque was strong and it would smoothly transition to sensorless mode. Finally, I soldered the sensor to the speed controller and set it up in lower speed mode to try and avoid the max e-rpm issue. Wahoo all good to go now to see if it’s reliable. Update coming soon!

Electric Moped Update #4: The Death of a Beautiful Thing

The Straw That Broke the Camels Back

I killed her, the moped’s dead… after making the big investment and buying a new power system I ran her a little too hard and the motor went up in smoke. So a little explanation, I’d been riding the moped with the new power upgrade for about a week. The power increase alone was amazing and it wouldn’t even blink when I pointed it up the steepest hills. I could run the new motor all over campus without the motor every getting warmer than a Canadian summer. Alright, you may be asking “how the hell did you manage to kill it then?”.  Well here’s the thing, the motor controller I was running is only rated for 80 amps (far below what the motor is rated for) so I wasn’t worried about pushing the system too hard because I figured the motor controller would be the first to go and I’d just drop the new bike speed controller in to replace it. Well, it turns out I drastically underestimated what the little motor controller could handle (when I figured it would be the weak link). I took the moped out with my roommate Colin to tour an apartment that we’re looking at renting this summer. Of course, both of us were squished onto the little bike and from the prior week’s stress testing, it had shown it can handle the load. The little guy handled the trip like a champ easily taking us both halfway across town and up way too many hills. It didn’t even blink when we got lost (twice). I checked the motor when we got to the apartment and it was barely warm, well below the 80c operating temperature. What killed it was the ride back to the dorm. We decided to take a more direct route back home, one that included a massive hill…

When I saw the hill I was worried right away, but going back to my earlier assumption of the motor controller I figured the worst that could happen is a ruined controller that I’ll be replacing anyway. Well, the moped put up a good fight, it hauled both colin and me all the way up the huge half-mile hill screaming bloody murder all the way. At the very crest, it met its end having sacrificed itself to get us up that godforsaken incline. At the time I thought it was just the motor controller that had gone out. It wasn’t until several days later when I sat down to install the new bike speed controller that I realized the motor was wrecked.

Motor Heating/Cooling

Now the biggest enemy to electric motors is heat. When an electric motor gets too hot the rare earth magnets begin to degrade and eventually the insulation coating the motor windings will melt causing an electrical short and a ruined motor. The heat generated by a motor is directly related to the amps flowing through its coils.

Joule’s first law, also known as the Joule–Lenz law,[1] states that the power of heating generated by an electrical conductor is proportional to the product of its resistance and the square of the current. (Wikipedia)

This means that the amperage you let flow through an ohmic system (any motor), causes an exponential increase in heat generation. This is why most electric vehicles run high voltage because you can get away with a high wattage system that draws fewer amps and thus produces drastically less heat. The power of a motor can be increased by increasing the motors’ cooling. Yes, this decreases the efficiency of the motor as more energy is being converted to heat than to motion (an optimized system that produces little heat in the first place is ideal) but who doesn’t want more power out of a smaller cheaper motor? (*Cough Cough* every Honda civic owner ever). Now the hard part is how to get the heat out of the motor, this part’s a little difficult. The motor I’m using is what’s called an outrunner motor.


What that means is the stator (the copper wirey bit that electricity flows through) is surrounded by the rotor (the magnetic bit that spins).  This produces some pretty interesting heat issues. All the coils are on the inside and this is where the heat will be generated. The rotor (the outer bit) doesn’t actually come in contact with the stator so heat can’t be transferred through conduction (the most efficient way to transport heat) to the rotor which has a larger surface area and can dissipate heat to the outside air easily. Because of this, the heat is mostly trapped inside the motor. The only heat that escapes from the stator is from the convection of air through the motor or through heat radiated to the rotor. Now there are two main ways to increase heat dissipation from the stator; increase the airflow through the motor and thermally connect the stator to the rotor. The second option helps the most because thermal energy is transferred more readily through conduction than any other form of heat transfer, a heatsink can then be attached to the rotor drastically increasing surface area and thus heat dissipation (Fourier’s Law explains why this works so well). This thermal connection can be accomplished by sealing the motor and filling it with oil (its non-conductive, non-corrosive, and can act as a lubricant). Heat from the stator is transferred to the oil and the oil transfers the heat to the rotor. Now as ideal as this is it’s hard to seal a motor that’s been designed to be air-cooled and is covered in holes like the RC plane motor I’m using.

Alright, so increasing airflow it is then. These RC airplane motors are designed to be strapped to the front of a plane rocketing through the air with a big ol’ prop blowing back on them, not fixed inside a slow-moving moped. In this case, to increase airflow I could add intakes that channel air from the outside and forces it across the motor like the ones you see on supercars.

Or even simpler, could attach an impeller to the end of the motor that would suck air through the center. An impeller works by using centrifugal force to throw air out of the motor. This air creates a vacuum that sucks in more air producing airflow through the motor.

Now here’s the thing. I didn’t have any extra cooling on the moped motor. All of my experience with these Turnigy SK3 motors is from the one I have on the electric bike which has both an impeller and is exposed to elements getting plenty of airflows. I realize now that my concept of how much heat these motors can take is skewed because I didn’t factor in this extra cooling that the e-bike motor has. My misunderstanding of the robustness of the 80 amp airplane motor controller and of the ability of my motor to dissipate heat are the two largest factors that aided in the untimely death of this poor motor. May she rest in pieces…


You thought I was going to ruin a motor and not take her apart? HA! After a striped sprocket grub screw, several glued in and striped Philips head screws (why not hex?!), a little heat gun work, and a whole lot of finesse I finally got the rotor off. Upon close inspection of the coils, I noticed visible bubbling in the wire enamel coating and a complete melt through in one of the wire bundles that is most likely what killed it. This melt through shorted the wires in the bundle making the motor unusable. The bundle that brunt through is suspended in air and does not come in thermal contact with anything. This lack 0f contact is most likely what caused the group to overheat. Because the group is suspended it can’t conduct heat anywhere easily so it became the thermal weak point of the motor. All other wires look good most likely because they were able to dissipate heat into the steel core.

Did I mention the motor heat completely warped and broke the 3D printed motor mount? Alright yeah, I printed it in PLA but still! Probably going to have to weld a new one to handle the heat.

Can We Re-build Her?

That would be a no… at first I thought I could simply pull out the wire and rewrap the stator but after a couple of hours of struggling to pull/cut out the wire and far too many little wire cuts to count I gave in to the fact that I can’t revive the poor motor.


So she’s dead for now. I lost quite of bit of money that I can’t afford to lose in this “learning experience”. It’s going to be a while till I can afford to order more parts to get the moped up and running again. She was awesome, absolutely awesome for getting around campus. With how small and nimble she was yet still having plenty of power to get 2 people mostly up hills. After this failure, I am beginning to doubt my knowledge and skills. I’ve been working on the electric bike for almost a year now and it’s still not running consistently (sitting in the shop now with blown MOSFETs). Now I can’t even get this project working that was going to be pretty straightforward. It’s like I just can’t do anything right. Either that or the universe REALLY doesn’t want me to have an electric vehicle. I started writing this post out of sheer anguish and depression because I thought maybe I could prove that it didn’t break just because I made it. Definitely feeling a little better and optimistic now that I’ve typed this out. Hopefully, I can find a way to make enough money to get her going soon.

This is Connor, Signing out!

Electric Moped Update #3: Power Upgrade 1.0

Finally, the part I’ve been dying to do, POWA UPGRADE! Being a poor college student  (the kind who frets over buying ramen in a cup over packaged ramen because of the 20 cent difference) I had a hard time bring myself to spend the money on the parts needed to upgrade the mopeds power system. After a few weeks of riding it around campus and then pushing it up every little bitty hill, I came upon I finally caved in and ordered the parts I needed. I figured I’d be using the moped for at least the next 4 years to get around campus so the investment would be well worth it.

  • BLDC Motor (sk3 hobbyking)
  • Electric bike Speed Controller (aliexpress)
  • sprocket (banggood)
  • keyed Throttle and Voltage readout (amazon)
  • hall effect sensor (equalsZero Design)

Motor Mount

To mount the motor I designed a 3D printed part that matched the mounting holes of the original motor and placed the shaft of the new motor in the exact same place as the old one.  I added holes underneath the motor to attach the hall effect sensor for better startup torque. With the 3D printed motor mount testing I did with the Mostly Printed Electric Bike I’m sure this new mount can stand up to the same load and same motor heat.

After grinding a flat spot on the motor shaft so the sprocket grub screw would seat properly I bolted the motor to the new mount, screwed on and adjusted the sprocket, and bolted the whole assembly where the old motor used to be. The chain rolled onto the new sprocket without error and it all fit perfectly behind the plastic chain guard. I’m a little concerned about how close the motor is to the wheel, there is definitely going to be some water and dirt thrown up by the wheel onto the motor but for now, I’m going to call it good until I can make some kind of mudguard.


Now because I’m extremely impatient when it comes to getting projects done and the bike speed controller hasn’t come in yet (that’s what I get for ordering cheap from China) I’m going to jerry-rig the electronics for not just so I can have something to get me up some hills.  I have an 80 amp speed controller left over from my initial work on the Electric Bike that I’ll use to power the motor. I stopped using it because it had zero startup torque and once when it got out of phase at high speed it locked up the motor sheering every spoke on one side of the bike’s wheel.  The problems I had with this speed controller on the bike shouldn’t be a problem on the moped because of the clutch on the moped that allows it to still coast even if the motor is stopped. Plane speed controllers require a PWM Servo signal to operate so I connected the speed controller and potentiometer throttle to an Arduino and wrote a little code to convert the potentiometer value into a PWM signal the Motor Controller can read. Snagged a 5v regulator out of my parts bin to power the Arduino, ran the positive side input to the throttle switch to turn everything on, and wham bam shang a lang we are all good to go!

In Use

Well first off the power increase after the upgrade is HUGE. The thing accelerates faster than a bullet. Because of the zero startup torque getting going is a little odd but once it’s moving the throttles pretty smooth as long as you don’t jerk the throttle. Every once and a while the motor will lose phase and stop spinning if I jerk the throttle too hard, but with a little finesse, it’s not too hard to get it spinning again. The torque with this gearing is pretty awesome and doesn’t even slow down when I try to climb the steepest hills around campus. The plane motor controller can only handle up to 24V so I’m only running the motor off one of my 24V cells, at the current gearing that comes out to about a 15mph top speed. It’s not too bad but it is a little slow for my taste. I’ll be able to run the full 48V when the E-Bike speed controller comes in doubling the top speed. Pretty happy with how it is right now but it’s not quite as new user-friendly as I’d like (every person who’s tried it jerks the throttle and the motor makes a horrible suicidal noise). The bike speed controller should be a good upgrade for usability and top speed.

Electric Moped Update #2: HeadLight Install


So I’ve gone to pick up a friend a few times from work up the hill with the moped. whenever I do it’s always pitch black and with almost no street lights. when you have two people going down a hill, on pitch black roads, with brakes that don’t exactly work, on a child’s moped, well, it’s just not a good mix. So I’ve gone through the process of adding a 24v truck flood light to the moped so then I can at least see what I’m going to hit before I hit it. The light’s super bright (almost too bright… lol nawww) and easily lights up where I’m going.

To add the light I removed the fake plastic light on the front and after drilling a hole in the center bolted the new one on where it was. I then mounted a switch next to the handlebars to turn on the light. The light runs off one of the 24v cells with the switch interrupting the circuit (its rated for high amperage and the circuit is short so I didn’t worry about using a relay). I also added an automotive fuse on the positive side of the light because I don’t exactly trust my wiring job and no one likes a shorted battery under their butt. It’s been working great so far but I’ve definitely had a few people think I was a motorcycle coming at them when I have it on.

Electric Moped Update #1: New Battery Install

The first few modifications of the moped were aimed at getting it running again with as little work as possible. When I bought it both tires were flat, it wasn’t running, and I was missing the charger. It should just take a little air to get the tires fixed, they probably haven’t been inflated since it was assembled by Walmart. The Lead-acid battery in it is most likely dead and that’s probably why it’s not running but I’ll have to see if it just needs to be charged or if it’s completely dead and needs to be replaced.


I was pretty sure the battery that came with the moped had been ruined when I bought it so I was sure I was going to have to replace it somehow. I got the seat off when I got back to the dorm and checked the two batteries voltage. each 12v battery came out to 5v  (normally anything below 10.5v means the battery has been damaged) so the batteries definitely needed to be replaced. The moped is a 24v system. My electric bike runs off of a battery pack that puts two 24v batteries in series for a 48v supply voltage. If pop this on the moped and only run one of the 24v cells it should work perfectly and give me some extended range. The bike battery is pretty big so I ended up cutting a hole in the storage compartment of the moped to fit the battery in I then soldered on two xt90 connectors so I can connect the battery to the mopeds power system. the original plan was to try running 50v but when I tried it the smell of smoke filled the air and the motor started acting pretty crazy. But when I tried running 25v again it works fine without any sign of damage (odd….) so for now, I’ll just leave it at the slow 24v and I just put a loop key in the extra xt90 plug to act as a key for the moped. The battery also doesn’t fit perfectly so I use a rolled up t-shirt jammed between the battery and the frame to stop it from rattling around.


For now, both tires are flat so I need to see if I can inflate them or patch the tubes. looking closer at the wheels the valve stems are at a really steep angle almost like the tubes shifted after being ridden flat. I tried to shift the tube back in place but couldn’t get it to move without taking the tire off. Didn’t have a tire wrench so I ended up using a flat head to get the tire off (yeah I know a bad idea). The front tire was an easy takeoff but I’d punctured the tube trying to get it off. I didn’t have a patch at the time and really just wanted to get it going so I ended up cutting up a rubber glove and super gluing it over the hole (I’m writing this 5 weeks later and it’s still holding). The back tire was a lot more difficult. I had to dismantle the chain guard and chain tensioner and loosen the bolts holding it on to get it off. I didn’t have the right tools in my dorm room so I used a crescent wrench and it was an absolute pain to get the little bolts and nuts off with it. Once I had the wheel was off I tried to get the tire off but it was next to impossible. I ended up taking it home with me for spring break to get some help from my dad. finally, both of us managed to get the tire off. The tube was destroyed so I picked up a new one from Fred Meyer and popped it on. bolted the wheel back on when I got back from spring break and after reattaching the chain guard and tensioner she was all good to go.


Moped Initial State & Reasoning

I have been looking for a simple platform for a simple and small electric vehicle for getting around campus that doesn’t need to go too fast and doesn’t break the bank (Pullman Hills are killer).  For a while now I’ve had my eye on the one of the razor electric vehicles because they’re normally really cheap second hand and already have the mounting points built in for a motor. This would be a nice change from my 3D printed electric bike whos motor mount was retrofitted to a frame not built for a motor, leading to some problems with the mount slipping and loosening (at one point slipping and shearing every spoke off one side of my back wheel). Now I understand that these razor vehicles are not built for adults or for the power I want to put in them but I figured the welded steel frame could easily handle the weight.  Now to how I got the Moped.

Having been looking for a razor vehicle for a while on online classifieds and garage sales I managed to find a floor model razor pocket mod that was highly discounted at my local walmart  during a one in the morning walmart run with one of my friends(had not expected to find a discounted model at a normal store). When I saw it at the store it was discounted to $80 and I was jumping at the chance to get it. When I tried to ask someone what was wrong with it all the guy I found would tell me is that a kid was riding it the week before. Finally I caved in and walked it up to the desk to checkout. After ages the employee checking me out found a tag on it to scan. When I got out at and checked the receipt I realized he only charged me $60! After I got back to the dorm I opened her up to see what was wrong. The two 12v batteries in it where completely dead probably from kids riding way past dead and both tires were completely flat probably from sitting so long once the battery dead.


Future Plans

The end goal is to have a little electric bike for getting around campus that I can toss in the back of the car when I want to take it somewhere.  It should be able to get up pullman hills without a problem, have a moderate range, and be able to be ridden at all times. To accomplish this I’m going to modify the battery compartment to accept the same battery I have in my bike, replace the low powered brushed motor with a higher power brushless motor, add a higher power and variable 50v speed controller to replace the 24v brushed one, and finally add taillights and headlights to increase night visibility. I’m looking forward to working on this project and seeing where it goes! Check back for updates!

Mostly Printed Electric Bike Design

I decided to build my Mostly Printed Electric Bike for two major reasons:

  • I wanted a senior project where I could push the bounds of my knowledge while also growing what I know
  • I wanted a lightweight powered vehicle to get around my new hilly college campus at WSU Pullman

My design criteria was that it could travel on walking paths and the road, be relatively fast, be electric powered to minimize noise complaints and avoid the college’s fuel storage rules,  be able to charge in my dorm room, and finally be capable of long distant trips to the neighboring town of Moscow Idaho should the need arise. After coming up with several ideas i decided on building either an electric longboard or an electric bike. I decided on the electric bike due to its higher stability at high speed, smaller turning radius, and higher potential for large battery storage.