introducing my electric kick scooter project "kicksurfer"

[tatus1969]

I have been working on this during the last two years by now, and it is time to stop hiding in a cabinet.

It all started some years ago when I was commuting to work, and realized that my trip consisted of 20 minutes in a regional train, plus 10 minutes walking to get there from home, plus another 15 minutes from the train station to my work place. In total that was 50 minutes of walking every day. Buying a foldable bike was an option then, but they are quite heavy and bulky especially when you have to lift them on a stairway. A colleague recommended me to use a kick scooter, they are very light (down to 6kg) and foldable. Said and done, but after some time using it each and every day, my hips and knees started hurting more and more. I realized that this kind of exercise was good for my condition, but not for my bones. Next natural step: electrification of my scooter.

As I am not a construction engineer, I decided to use an existing kick scooter model and upgrade it. My choice fell to this one:


OXELO Town XL susp
https://www.decathlon.de/city-roller-scooter-town-7-xl-mit-federung-chrome-id_8298992.html?gclid=CJfX7c2Z8tICFYYaGwodspUEQw

With 100€ it is a bit pricey, but I it is very well designed and doesn't all apart after the first few 100 kilometers. It is fully suspended and it has a stable folding mechanism. It also has lowered board, which reduces the required leg work during riding.

Because this is a quite popular model, there are almost identical Chinese copies of it, you can find them on ebay. They sell for roughly half the price.

At the beginning I developed my electric conversion kit just for my private fun and use. I have been using the prototype model for more than a year now, and the first battery is still alive after countless kilometers. And I realized that it would be the same fun each and every time that I step on it for a ride, that feeling does not seem to degrade. I get a lot of interest and positive feedback from people almost every time I come to a stop. All this helped me make my decision: make this a commercial product, and sell it to other enthusiasts.

That was when the kicksurfer project started. It was clear from the beginning that it would be a conversion kit for DIY'ers. It should be as simple to build as possible, and the price should be as low as possible. And, most importantly, it should be as convenient as possible.

As simple as possible: apart from the scooter and the kit, you only need a cordless screwdriver, a set of metal drills, a ruler (if available: caliper), and a hacksaw (if available: multifunction rotary tool). Build time should be less than two hours, but that is yet to determined.

As cheap as possible: targeted kit retail price (per lot of 100 kits) is 449 euros. This includes everything you need: motor, battery, controller, charger, all construction parts.

As convenient as possible:
- smart: no levers, no handles - the controller senses the driver's actions and reacts on that
- standard mode: the driver kicks once, then the system permanently maintains the resulting speed - kick once, surf home
- street-legal mode for Germany: works like a Pedelec by only boosting each and every foot kick from the driver
- automatic brake detection: keeps down torque during braking and maintains speed thereafter
- automatic startup and shutdown: no power switch
- safe: driver detection ensures automatic torque cutoff when the driver steps off the scooter
- intuitive: feels exactly like a regular kick scooter, but with any friction removed
- speed: 2 to 20 km/h
- range: 10km (to be verified)
- charging time: 1.5 hours
- weight: 8kg

As of today, most parts of the kit are ready but there is some remaining work and money that I have to invest:
- battery pack transport test per UN38.3
- plastic injection mold tool for battery/controller housing, currently it is a 3D printed part - much too costly
- find and evaluate a suitable and safe charger, current model has CE mark on it but that is in fact China Export - currently negotiations with two different manufacturers
- create mass test tool for controller board (needle bed adapter)
- add missing firmware features like configuration and firmware update via Bluetooth
- create PC / smart phone apps
- create step-by-step construction guide
- draw public attention and get funding for first mass production lot

Most recently I have set up a website for the project:

https://www.kicksurfer.de

It has just started and and I have to apologize that the main page is still empty. Both account management and blog system are running. If you are interested in this project, I would be happy if you would sign in for updates - I will regularly post updates in the blog section: https://www.kicksurfer.de/index.php/blog/

Latest post:

https://www.kicksurfer.de/index.php/2017/03/25/board-rev-4-is-finished-ordered/

[tatus1969]

Update: the pre-series batteries have arrived, using Sony US18650NC1 cells.Here are some pictures:






According to the manufacturer, the indidivual cells do pass all UN 38.3 transport safety test. The question was, would the pack meet these requirements as well. I made a short circuit test, and got this (I have to admit, expected) result:


I had hoped that I could stick with my decision of having all protection measures on the controller board, but that proved wrong. To my excuse, I only learned of UN 38.3 from my negotitations with the battery pack manufacturer. Before that, the plan was do construct the packs such that an accidental short circuit during transport was prevented. But the rules apparently do not care about that.

So I had to swallow the pill and make a separate BMS board. It is already ordered, here are some first rendered pictures. It supports remote monitoring via I2C, has all necessary protections (short, over/under voltage, overcurrent) and includes a balancer.







Of course this also means another redesign of the controller board, as all the charging/balancing can be removed.

[tatus1969]

An update of my work on the BMS system. I have been stress testing it the last few days (over charge / discharge, short circuit, over temperature), and it behaved well in all situations. I had a problem though with the way the ISL94203 switches the power FETs in certain conditions. It can happen, for example at an overvoltage after charging, that the discharge FET is off and the charge FET is on (and vice versa). If you connect a load now, then the body diode of the discharge FET takes all the load current. The Intersil support staff was quick and competent to help me out and solve that.

A picture from testing short-circuit. Yellow = pack voltage, blue=voltage across 1mOhm shunt. The pack shows an impressive 250A short circuit current, and the MOSFETs sately interrupt that after 400us.


A picture of the test setup (from left to right)
- DIY electronic load 300V 50A 250W
- Gophert CPS-3205 (used as CC/CV charger, and to run the fan at the back of the e-load)
- Hantek DSO5062B (pimped to 250MHz)
- Hantek CC-65 current clamp probe
- Adafruit FT232H I2C-USB adapter
- the battery under test
- Voltcraft ME-42 multimeter



The scope is showing the e-load's response when the BMS enables its output. As the e-load did not see any voltage before that moment, its FET is fully open, resulting in a short circuit when the battery activates. The e-load needs 100us to react to that and regulates thereafter, so this picture is also showing its step response. All this happens once per minute (I need to switch off the load regularly to measure the no-load voltage for ESR calculation), so the short-circuit current capability of the system (> 250A) is tested alongside.
Closeup of the battery


Screenshot of configuration and monitoring tool


Discharge curve (at 5A) showing battery voltage and current, temperature, and calculated pack ESR

[David Chamberlain]

Just wanted to say I think it's a really cool looking project. Especially removing the hand controls I've seen on other products is a good thing and should definitely be your no.1 selling point.

I see that oxelo have a page for electric scooters with zero products? But in the picture it looks bulky and heavy and non-folding.
https://www.oxelo.co.uk/electric-scooters-idfam65

Not sure if you've considered this, but perhaps pitch your product direct to oxelo? Looks like they would have no problem with the injection molds and assisting with the safety requirements. Seems like a good fit as you've designed your drive train around their products anyway. I'm sure some sort of deal could be struck where you can still sell in kit form while licensing it to them for manufacture. Having said that they might not like the kit idea because it would promote the purchase of cheaper Chinese products creating a direct competition for their own ones.

[Zero999]

I have been working on this during the last two years by now, and it is time to stop hiding in a cabinet.

It all started some years ago when I was commuting to work, and realized that my trip consisted of 20 minutes in a regional train, plus 10 minutes walking to get there from home, plus another 15 minutes from the train station to my work place. In total that was 50 minutes of walking every day. Buying a foldable bike was an option then, but they are quite heavy and bulky especially when you have to lift them on a stairway. A colleague recommended me to use a kick scooter, they are very light (down to 6kg) and foldable. Said and done, but after some time using it each and every day, my hips and knees started hurting more and more. I realized that this kind of exercise was good for my condition, but not for my bones. Next natural step: electrification of my scooter.

As I am not a construction engineer, I decided to use an existing kick scooter model and upgrade it. My choice fell to this one:


OXELO Town XL susp
https://www.decathlon.de/city-roller-scooter-town-7-xl-mit-federung-chrome-id_8298992.html?gclid=CJfX7c2Z8tICFYYaGwodspUEQw

With 100€ it is a bit pricey, but I it is very well designed and doesn't all apart after the first few 100 kilometers. It is fully suspended and it has a stable folding mechanism. It also has lowered board, which reduces the required leg work during riding.

Because this is a quite popular model, there are almost identical Chinese copies of it, you can find them on ebay. They sell for roughly half the price.

At the beginning I developed my electric conversion kit just for my private fun and use. I have been using the prototype model for more than a year now, and the first battery is still alive after countless kilometers. And I realized that it would be the same fun each and every time that I step on it for a ride, that feeling does not seem to degrade. I get a lot of interest and positive feedback from people almost every time I come to a stop. All this helped me make my decision: make this a commercial product, and sell it to other enthusiasts.

That was when the kicksurfer project started. It was clear from the beginning that it would be a conversion kit for DIY'ers. It should be as simple to build as possible, and the price should be as low as possible. And, most importantly, it should be as convenient as possible.

As simple as possible: apart from the scooter and the kit, you only need a cordless screwdriver, a set of metal drills, a ruler (if available: caliper), and a hacksaw (if available: multifunction rotary tool). Build time should be less than two hours, but that is yet to determined.

As cheap as possible: targeted kit retail price (per lot of 100 kits) is 449 euros. This includes everything you need: motor, battery, controller, charger, all construction parts.

As convenient as possible:
- smart: no levers, no handles - the controller senses the driver's actions and reacts on that
- standard mode: the driver kicks once, then the system permanently maintains the resulting speed - kick once, surf home
- street-legal mode for Germany: works like a Pedelec by only boosting each and every foot kick from the driver
- automatic brake detection: keeps down torque during braking and maintains speed thereafter
- automatic startup and shutdown: no power switch
- safe: driver detection ensures automatic torque cutoff when the driver steps off the scooter
- intuitive: feels exactly like a regular kick scooter, but with any friction removed
- speed: 2 to 20 km/h
- range: 10km (to be verified)
- charging time: 1.5 hours
- weight: 8kg

As of today, most parts of the kit are ready but there is some remaining work and money that I have to invest:
- battery pack transport test per UN38.3
- plastic injection mold tool for battery/controller housing, currently it is a 3D printed part - much too costly
- find and evaluate a suitable and safe charger, current model has CE mark on it but that is in fact China Export - currently negotiations with two different manufacturers
- create mass test tool for controller board (needle bed adapter)
- add missing firmware features like configuration and firmware update via Bluetooth
- create PC / smart phone apps
- create step-by-step construction guide
- draw public attention and get funding for first mass production lot

Most recently I have set up a website for the project:

https://www.kicksurfer.de

It has just started and and I have to apologize that the main page is still empty. Both account management and blog system are running. If you are interested in this project, I would be happy if you would sign in for updates - I will regularly post updates in the blog section: https://www.kicksurfer.de/index.php/blog/

Latest post:

https://www.kicksurfer.de/index.php/2017/03/25/board-rev-4-is-finished-ordered/

Very nice project, what motor did you use? I know you said brushless hub motor but is it a custom part or off the shelf?

I can see how uncomfortable it must be using an ordinary scooter. I don't think it's the exercise which is causing the pain but the twisting motion. I'm reasonably fit and once my bicycle chain broke,  had to use my bike as a scooter to travel 3 miles and I did ache a bit afterwards. If I was in your situation, I'd just buy two cheap bicycles: one to travel from home to the train station and another from the train station to work. I'd invest in decent locks for them both and that would be it but that's not as fun.

[tatus1969]

Just wanted to say I think it's a really cool looking project. Especially removing the hand controls I've seen on other products is a good thing and should definitely be your no.1 selling point.

Thanks, yes it's a novel. I was a bit too slow though, these here were first: http://www.micro-mobility.com/de/produkte/e-micro-one But that one is much more expensive, and it only helps during the kick. And they do not detect the driver, so it wants to escape when you jump off it.

I see that oxelo have a page for electric scooters with zero products? But in the picture it looks bulky and heavy and non-folding.
https://www.oxelo.co.uk/electric-scooters-idfam65

As I am a DIYer, my heart beats for this idea. And that will get lost if I sell the idea to them. I want to try first and see if I can launch it myself. If that doesn't work out, I will probably try to sell it to them.

[tatus1969]

Very nice project, what motor did you use? I know you said brushless hub motor but is it a custom part or off the shelf?

It is a COTS part from uumotors, customized in voltage and cabling. I was taking a video presenting all parts, editing that is almost finished...

I can see how uncomfortable it must be using an ordinary scooter. I don't think it's the exercise which is causing the pain but the twisting motion. I'm reasonably fit and once my bicycle chain broke,  had to use my bike as a scooter to travel 3 miles and I did ache a bit afterwards. If I was in your situation, I'd just buy two cheap bicycles: one to travel from home to the train station and another from the train station to work. I'd invest in decent locks for them both and that would be it but that's not as fun.

I was riding an ordinary kick scooter before that project. The result: two killed pair of trousers, and hurting hips and knees. I also had that two-bike idea, but what I have now is just a lot more fun. And I realized it is a perfect combination of convenience while still being active.

[tatus1969]

Here are some measurement results from testing the battery packs. The Sony cells run surprisingly hot, but I have meanwhile received the datasheet. Sony seems to keep that confidential. Most importantly, I needed to know the temperature limits. These are
- charging: 10 ~ 45°C when topped to 4.25V
- charging: 0 ~ 60°C when limited to 4.15V
- discharging: -20 ~ 80°C down to 2.5V

Ambient temp was 22~23°C during the tests. They go up to 40°C during charging, which is too close to the 45°C limit. I will measure the capacity loss when I stop charging at 4.15 instead of 4.25, because that would allow a much wider charing temperature range.

Charging pack at 5A


Discharging at 10A


Measured capacity:
Charged energy = 129.4 Wh
Discharged energy (@10A) = 114.7 Wh
Efficiency (@10A) = 88.7 %

The datasheet states a capacity of roughly (2750mAh * 3.6V * 12) = 119Wh, that is quite close.

[tatus1969]

Short update on the Li Ion charging characteristics: i reduced the cutoff voltage from 4.20V to 4.10V. This results in a capacity loss of 11%. I was hoping for a smaller figure, because this is beyond acceptable for me. But interesting. When I consider a charging voltage span of roughly 1.2V (3.0V -> 4.2V), then 0.1V is only 8.3% less voltage.

[tatus1969]

A batch of three charger prototypes from the first of two suppliers have arrived, and I took the time to test them for performance, reliability and safety. They do have some remaining issues, but I am happy that the first prototypes are close to acceptable. The biggest issue is that the certifications documents that I had received beforehand are related to a very similar model, but apparently not for the ordered one. That is what you have to expect when dealing with Asian manufacturers. I cross fingers that this was just a mistake. The documents were good and the approval is from a certified institute, but that doesn’t really help…

The most important target specs are:
– 25.2V +-1%
– 5.0A +-5%
– short-circuit protection
– universal AC input with C13 socket
– continuous operation at 10 ~ 35°C

Here are some teardown pictures of the unit.

Top view:


Bottom view:


Casing removed:


Heat sinks removed:


PCB view from top:


PCB view from bottom:


The unit is well designed in terms of clearance.

As the main transformer is a crucial part to ensure safety, I sacrificed one unit and took that component apart.

Before teardown, outer insulation sheet removal reveals EMI shielding:


Outer section of primary winding:


Secondary winding:


Inner section of primary winding, plus auxiliary:


Although I had to criticize that not all primary winding ends had received silicone tubing, the unit can be considered well constructed, because a) its low voltage side is earthed, and b) the secondary is triple-insulated. In fact, the insulation is thicker than the wire width.

The performance measurement results show that the unit is working as expected.

Test setup:


Output voltage versus output current at minimum and maximum AC input voltage:


Transient behavior, no load to full load @240V (the large glitch is caused by the electronic load, it produces a 100µs short before stabilizing the load current):


Transient behavior, full load to no load @240V:


Power up with no load @240V:


Power up with 3.7A load @240V:


Also the temperatures are reasonable and promise an acceptable lifetime:


This picture shows the measurement points. “Temp CASE” represents the hottest spot measured at the case. All temperatures were taken with an IR thermometer. To obtain realistic results, the unit was operated for 60 minutes with the casing assembled. After that time, I quickly removed the top cover and measured the temperatures at all internal locations within 10 seconds.

[jbb]

Thorough!

Well done remembering the transformer - it's easy to forget about it.

What would you estimate the creepage path between the primary-side terminations and the secondary at?

[tatus1969]

Thorough!

Well done remembering the transformer - it's easy to forget about it.

What would you estimate the creepage path between the primary-side terminations and the secondary at?

Thanks 

Creepage is maybe 2mm, but clearance is less, maybe 1mm, as you can see in this picture showing the secondary winding in view of the primary terminals. They rely on the fact that the secondary winding is made from triple insulated wire (type TLW-B), with VDE / IEC60950-1 approval. I have read further and the manufacturers of these wires sell them as reinforced insulation, so they could even have spared all extra insulation for the primary. This page gives some information: https://www.furukawa.co.jp/makisen/eng/product/texe_feature.htm

[ez24]

Following 

[ovnr]

Awesome stuff in general.

An update of my work on the BMS system. I have been stress testing it the last few days (over charge / discharge, short circuit, over temperature), and it behaved well in all situations. I had a problem though with the way the ISL94203 switches the power FETs in certain conditions. It can happen, for example at an overvoltage after charging, that the discharge FET is off and the charge FET is on (and vice versa). If you connect a load now, then the body diode of the discharge FET takes all the load current. The Intersil support staff was quick and competent to help me out and solve that.

Mind sharing your findings? I'm in the same boat (having to do a pack controller). It's a shame there seems to be no integrated charger/balancer ICs.

[tatus1969]

Awesome stuff in general.

An update of my work on the BMS system. I have been stress testing it the last few days (over charge / discharge, short circuit, over temperature), and it behaved well in all situations. I had a problem though with the way the ISL94203 switches the power FETs in certain conditions. It can happen, for example at an overvoltage after charging, that the discharge FET is off and the charge FET is on (and vice versa). If you connect a load now, then the body diode of the discharge FET takes all the load current. The Intersil support staff was quick and competent to help me out and solve that.

Mind sharing your findings? I'm in the same boat (having to do a pack controller). It's a shame there seems to be no integrated charger/balancer ICs.

The standard topology is a smart battery pack with BMS and a current limited DC power supply. That is very economic because the latter are dirt cheap. Maybe that is why the chip makers haven't come up with a one chip solution. How is your design partitioned, don't you need a power supply as well?

The problem with the ISL chip is that it switches both FETs individually, i.e. when overvolting during charge it only opens the charge FET (T1). When you now connect a load, then the body diode of this transistor is taking the load current. The FET is only activated when the overvoltage condition is over. With nominal load current this may not be a problem because the voltage drops uickly, but consider a short circuit in this situation. The same happens with the discharge FET correspondingly. Don't ask me why they do that. Luckily they have added two configuration bits that solve the OV/UV situation.  When you set CFODOV, then the charge FET is turned on when a load is detected during overvoltage. DFODUV does the same for the discharge FET when charging in undervoltage. I checked both, it works but there is a delay of serveral 100us to it.

Another problem is when you set different temperature limits for charge and discharge. There are no cinfiguration bits, and the situation is typically not removed quickly. Therefore they have a modified version, ISL94202, that behaves correctly also un these situations.

All this is only an issue when you have only one port for charge and discharge, and have both FETs in series. Use ISL94202, and set these bits.

[ovnr]

The standard topology is a smart battery pack with BMS and a current limited DC power supply. That is very economic because the latter are dirt cheap. Maybe that is why the chip makers haven't come up with a one chip solution. How is your design partitioned, don't you need a power supply as well?

Thanks, I appreciate it.

As for mine: In short, non-removable pack but I still need cell balancing after all. A design constraint is that it must support quite flexible charging (from both microUSB and 12V from a vehicle), charge time be damned. So I'm planning on using one of TI's buck-boost charger ICs.

[ali_asadzadeh]

tatus1969 that's a great project, how much the Asian  charger  manufacturers charge you? where did you order them?

[tatus1969]

tatus1969 that's a great project, how much the Asian  charger  manufacturers charge you? where did you order them?

Thanks  As I have the idea to sell the kit when ready, I can't tell the purchase price, but I plan to sell the chargers for around 30€.
The manufacturer is GVE, www.gve-cn.com/

[jbb]

Short update on the Li Ion charging characteristics: i reduced the cutoff voltage from 4.20V to 4.10V. This results in a capacity loss of 11%. I was hoping for a smaller figure, because this is beyond acceptable for me. But interesting. When I consider a charging voltage span of roughly 1.2V (3.0V -> 4.2V), then 0.1V is only 8.3% less voltage.

Sorry for being late to the party...  I hear what you sat about 11% capacity being too much of a sacrifice for you (especially if you adjust the end of discharge limit as well).  But it might not be for everyone. Would you consider allowing an end user to choose between 'maximum range' with wider limits and 'make the battery pack last longer' with tighter limits?

[tatus1969]

Sorry for being late to the party...

Not really, this project is currently on hold, because I started a small side project for it, a battery spot welder (https://www.kicksurfer.de/index.php/product-category/kspot-welder-kit/), which went bigger than anticipated. But that will be cut and dried by September, and then I expect to be able to concentrate on this again. My suppliers are already knocking on my door...

I hear what you sat about 11% capacity being too much of a sacrifice for you (especially if you adjust the end of discharge limit as well).  But it might not be for everyone. Would you consider allowing an end user to choose between 'maximum range' with wider limits and 'make the battery pack last longer' with tighter limits?

Thanks, that would indeed be a good idea. But the matter is a bit more complicated. According to the battery manufacturer, I need to reduce the charging current when hot and >4.10V. My charger cannot do that, it has a simple CV->CC charging curve.

I already decided to use a different cell type. That is + 1€ per cell, but it also has higher capacity, much higher rated discharge current, and therefore I can expect a higher lifetime as well. That makes it in fact cheaper on the long run.

[ali_asadzadeh]

Realy cool project

[tpowell1830]

---------------- BLANKED INTENTIONALLY ----------

The most important target specs are:
– 25.2V +-1%
– 5.0A +-5%
– short-circuit protection
– universal AC input with C13 socket
– continuous operation at 10 ~ 35°C

Great project! I like the 'no-controls' approach. However, aren't you limiting your consumer base with the above (in red) spec targets? There are many countries that exceed this temperature parameter. Dozens of different AC inputs.

[tatus1969]

---------------- BLANKED INTENTIONALLY ----------

The most important target specs are:
– 25.2V +-1%
– 5.0A +-5%
– short-circuit protection
– universal AC input with C13 socket
– continuous operation at 10 ~ 35°C

Great project! I like the 'no-controls' approach. However, aren't you limiting your consumer base with the above (in red) spec targets? There are many countries that exceed this temperature parameter. Dozens of different AC inputs.

Thanks :-) Unfortunately, this one is currently on hold in favor of another project: https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here

I plan to continue this one as soon as time permits, because the no-controls approach is (still) a unique selling feature and i don't want to waste that. The C13 socket is not the wall plug side, this refers to this one here:



The +35°C limit is for the charger that I had torn down above. Meanwhile I have prototypes of better ones from Meanwell, they have also better temperature ratings.

[tpowell1830]

Yes, I know, that is not the one we use in my country.

[ovnr]

Yes, I know, that is not the one we use in my country.

Tatus put in the wrong image - that's the female version of the plug, as seen on the back of UPSes and the like.

The C13 socket is common across the world; just use a C13 to whatever cable, like you use for your PC.