Electric Unicycle Terminology

[esaj]

This is by no means anything "official", or complete, and everyone's welcome to chime in to propose new/missing/alternative terms and/or corrections. The point is to explain and make the terms less ambiguous and to help with understanding especially some of the more technical topics and discussions here.

The usual term used for the electric unicycles has usually been an "EUC" (for Electric UniCycle). John Eucist has explained the reasons for using this term pretty well here:  http://forum.electricunicycle.org/topic/119-why-am-i-calling-electric-unicycle-euc-for-short/ , so I don't see the need in repeating. More informally, most people refer to them as "wheels" (wheel in singular form).

EUC Parts

At simplified level, you could say an EUC typically has four parts: Tire/pedal assembly with a motor in the hub, a mainboard, a battery or batteries and the shell keeping everything together.

Battery Battery is the part of the unicycle that stores the energy to move the motor and power the electronics. Most wheels use a battery pack made of Lithium Ion -cells (of which there are many different chemistries, brands and models), typically 16 (around 48-67V empty/full) or 20 (60-84V) cells in series  to get the high voltage required to drive the motor, and one or more of these packs to gain high capacity. The total capacity of the battery packs are usually shown as Watthours (Wh), and on average it seems 10-20Wh are needed per kilometer ridden, although this may vary between different EUCs, riders and riding conditions. EUCs with higher battery capacity (usually done by adding more 16/20-cell series in parallel and/or using higher capacity cells) don't only go for longer on single charge, but they usually keep their torque high longer even when the battery has depleted more.

BMS  (Battery Management System) This is a printed circuit board (PCB) usually located inside one or more battery packs (although in some cases, like at least some IPS models, it can also be integrated directly into the mainboard). The BMS takes care of controlling battery charging, cell balancing, and has some protections (which can sometimes be even dangerous 2017 update: dangerous BMS overdischarge protection problems seem to be a thing of the past), like overdischarge- (low voltage/undervoltage), overcurrent-, short circuit-, and overcharge-protections.

Firmware Firmware is the piece of program in the mainboard that has all the logics for the wheel: alarms, speed limits, tilt-back, motor driving logics, balancing the wheel, communicating with a possible mobile phone app over Bluetooth or such, different types of monitoring and alarms (overspeed, overheat, low battery, over-tilt...) etc

Hall-sensor Hall-sensors are sensors that can detect a magnetic field. There are such sensors inside the motor that are used to detect the position and RPM of the motor. The mainboard logics need this information to drive the motor. Also the electrical current sensing of the mainboard is commonly done with a chip based on the hall-effect, which is also needed for certain types of motor driving algorithms like Field-Oriented Control and to detect situations where the power output is nearing the limits

Mainboard This is the "heart" of the electric unicycle, typically a single printed circuit board (PCB) inside the unicycle, although sometimes there may be more than one board (for example, Firewheels have two boards, the secondary PCB controls things like lights and battery display). Mainboard has things like the one or more MCUs (MicroController Unit, the "brains" of the wheel), power feed for the motor, step-down switching-mode power supply for other electronics, combined gyroscope/acceleration sensor (often called IMU, Inertial Measurement Unit, or MPU, Motion Processing Unit) for balancing and usually something like a Bluetooth-chip for app-support, LED control, possible display control etc.

Motor  Motor is the thing that moves the EUC. Typically these are 3-phase BLDC/PMSM (Brushless Direct Current  / Permanent Magnet Synchronous Motor) outrunner hub-motors with direct drive (with the exception of some geared EUCs, like certain older Rockwheels, secong gen Gotway M10's) that is placed in the center of the rim of the tire. Motors have rated and peak power ("wattage"), and the general rule of thumb is "bigger is better". Bigger wattage does not necessarily mean more speed (although that's possible too), as the different motors can be built with different things in mind (speed vs. torque), and there may be maximum speed limitations in the firmware, but higher powered motor can usually keep you balanced in more extreme situations, like going over a bump or a pothole at higher speed. Especially heavy riders should look for high powered (800+W rated?) motors. 2019: Probably more like 2000W = 2kW?

Pedal Pedal is the part on top of which you place your feet when riding. Typically made of aluminum or steel, there are various shapes and sizes (unfortunately commonly a bit too small for western feet), and they affect the riding comfort of the wheel substantially (especially on longer trips). Also the pedal clearance (height from ground) plays a role in riding, as low clearance can cause the pedal to hit the ground while leaning. The part connecting the pedal to the motor is commonly called Pedal arm, although other names have also been used.

Shell Shell or shells are the plastic covers within which the other parts (mainboard, batteries, tire/motor-assembly...) are enclosed. Older wheels used to have a single shell made from two parts, more modern wheels commonly have 4 parts to the shell, the "inner shell" that usually only covers the motor and to the outside of which the batteries and mainboard etc are connected, and separate "outer shells" that protect the electronics and the batteries. The difference is that the ones with separate inner and outer shells are much easier to work with if having to do repairs or such and have better ingress protection (preventing moisture/water from entering the electronics / batteries).

Strap Strap is a piece of ribbon that usually comes with the wheel. The point is to attach the strap to the wheel handle (or similar), so you can prevent the wheel from falling over or getting away from you when dismounting during practice. Most people stop using this after initial learning, although some keep using it, as it can prevent the wheel from keeping rolling on by itself in case of a dismount. 2019: Not that common nowadays, nobody mentions straps anymore.

Tire Tire (or is it tyre?) usually refers to the outermost rubber part of the tire, but can sometimes be also used to mean the inner tube ("inner tire"). Probably pretty much everyone knows what these are, so not that much point in explaining further...

 

EUC "tech-talk"

Cut-off or cut-out  There are actually (at least) two types of cut-offs that can occur with an EUC: the first is what I've called "mainboard induced cut-off" or sometimes I've also used the term "[motor] shutdown" or "[high/max]-speed cut-out", and the second is the BMS cut-off.

• (2017 notice: most wheels nowadays don't seem to no longer cut the power at high speed, "overlean"/"overpowering" near the top speeds or board failure is more common cause of such falls) Mainboard induced/motor shutdown/high-speed cut-out/max speed cut-out: In this type of cut-off, it seems that the mainboard firmware decides to cut the power to the motor for some reason (at least overspeed/too much current passing through the board or the wheel has tilted more than 45 degrees). When the mainboard does the cut off, the wheel doesn't usually totally power down, but keeps playing a warning sound or something to tell the user that the wheel must be reset before it can be ridden again. I have also thought that this might ALSO be BMS-related, if it's the overcurrent/short circuit protection of the BMS triggering, as those don't seem to latch, but release automatically? So the entire wheel would turn off for a split second...
• (2017 notice: this seems to be pretty much a thing of the past, at least in the mainstream big-name wheels, like KingSong, Inmotion, Gotway, Ninebot...)  BMS Cut-off is caused by the overdischarge (undervoltage) protection circuitry in the battery BMS triggering, and usually cuts ALL power to the wheel immediately. This can be particularly dangerous, as it can occur very unexpectedly, causing the rider to fall almost every time. Typically the protection is latched, so if your wheel shuts off and doesn't turn back on until you've plugged it in charger, it was probably because the overdischarge protection had triggered.

(2017 EDIT: Link to BMS-shunting thread removed, not necessary anymore)

Reset Resetting a wheel means turning it off and back on. Many wheels require you to do this, once the motor shutdown has triggered, although some automatically reset when turned back upright after a fall.

RPM (Rounds per minute) RPM is a measure of the turning speed of the motor, how many total rounds (turns) the motor does per minute.

Shunt Shunting a wheel means bypassing the discharge-side protection circuits in the battery BMS to prevent the BMS cut-off.  Not needed in wheels made after something like late 2015/early 2016?

MOSFET "Metal Oxide Semiconductor Field Effect Transistor" , a type of power transistor used in the mainboard (usually in a group of 6 or 12) that's responsible of driving the motor by controlling current flow in the 3 phases. Commonly referred to when speaking of the technical details of mainboards, or when someone has a burned board (one of the most common reasons of failed board is burned MOSFETs).

EUC Riding

Idling Idling is the term for staying pretty much in place by moving the EUC back and forth. This is taxing for the motor (constantly changing direction) and eats up your battery fast, but can be useful for example to wait for a traffic light to change or such.

Leaning Leaning refers to using your body to move your center of gravity and control the EUC. You lean forwards and backwards to accelerate/decelerate or change direction. To turn the EUC, you usually lean to the direction you want to turn to (left or right), somewhat similarly as with motorcycles or bikes at faster speeds, although you can also use your hips to "swivel" around for tight in-place turns, at least in slow speeds. 

Out-lean or overlean Out-lean / overlean is a term used to refer to a situation where the rider leans (usually) forwards so much that the wheel cannot keep him/her balanced anymore (not enough torque), and usually ends up with the rider dismounting (or falling). Out-leaning usually occurs near the top speeds or in uphills, where the wheel motor cannot keep producing enough torque to keep the wheel upright as the rider keeps leaning forward. Usually it occurs only after the full tilt-back (but not always, especially when accelerating fast, the wheel may not have enough torque to tilt-back), so most people shouldn't be able to do it accidentally, unless it's due to low battery (if the tilt-back is based on speed).

Overpower Overpowering a wheel refers to similar situation as with out-lean and is often used as a synonym, but seems to be more commonly used to describe a situation where the wheel cannot keep you balanced on level ground, for example when hitting a pothole that causes the wheel to tilt too much to forward or simply out-leaning.

Overspeed "Overspeed" used to mean the speed where the mainboard cuts the power to the motor. This was (at least mostly) with older, pre-2016 wheels. Nowadays (November 2017) most wheels will let you push it all the way to the end, but once you hit the max speed (which is at least somewhat dependent on the battery charge state), the voltage difference between the battery and the motor back-EMF (voltage induced by the turning motor) is too low to cause enough current and thus torque, and the rider ends up overleaning the wheel.

Power braking This is a pretty "unofficial" term, used to mean the type of braking where you push the wheel in front of you with your legs while simultaneously leaning back and pushing the pedals down to brake as fast as possible. Requires some practice, but not that difficult, and a useful skill when you need to stop "on a dime". Be warned though, on occasion this has led to the mainboard burning the mosfets, although it's not common, especially in the higher end power-wheels anymore.

Tilt-back Tilt-back is a safety measure, where the wheel starts to tilt the pedals backwards at higher speeds to warn and prevent the rider from leaning more forwards. While it is possible to lean more and try to get more speed, it might not be wise, as you can overpower the wheel. Most wheels have this (many wheels let the user adjust the tilt-back speeds with app), but some older ones don't have it at all (for example older Gotways and Firewheel).

Edited April 30, 2019 by esaj
2017 update

[John Eucist]

Thanks so much @esaj !  What would this forum (and the world euc community) do without you?  Pinned (although you could do it yourself too). 

[Rotator]

Great! Thanks.

[Jason McNeil]

Good addition to the eWheel performance post I made about a month back.

I would recommend there be something in the section on 'Out-lean' how the pedal-tilt-back helps with a feedback mechanism that prevents riders from going beyond the max speed capabilities of their eWheel. In my opinion, this is really important topic that, especially newbies, should be aware of. 

Edited July 27, 2015 by Jason McNeil

[esaj]

Good addition to the eWheel performance post I made about a month back.

I would recommend there be something in the section on 'Out-lean' how the pedal-tilt-back helps with a feedback mechanism that prevents riders from going beyond the max speed capabilities of their eWheel. In my opinion, this is really important topic that, especially newbies, should be aware of. 

Good point, I also had forgotten to add tilt-back in terms altogether... added tilt-back & overspeeding, and mentioned tilt-back in out-lean.

[mengke]

Bravo... Will just share this page...

[BobbyDee]

Nice post. That helped me get up to speed as I wait for the delivery of my first EUC/Gyro-wheel.

[AlanR]

@esaj would you identify the mosfets that need to be shunted to prevent BMS shut-off please in the photo below!?

The factory says it will replace my generic's PCB to satisfy their warranty obligations!! - I'm not holding my breath - they have been evasive and unhelpful so far.

Even if I stuff up the EUC is unusable now anyway!

I'm expecting a N1E+ any day now.

[ElectricWheelEric]

Please correct the spelling 'tire' to 'tyre'. Also, an euc is not a bike, why using pedals? You're not pedalling at all. Footrest or similar would be more appropriative. The rest is perfect! Thank you very much @esaj!

 

 

[esaj]

1 hour ago, AlanR said:

@esaj would you identify the mosfets that need to be shunted to prevent BMS shut-off please in the photo below!?

The factory says it will replace my generic's PCB to satisfy their warranty obligations!! - I'm not holding my breath - they have been evasive and unhelpful so far.

Even if I stuff up the EUC is unusable now anyway!

I'm expecting a N1E+ any day now.

While I'm not qualified enough to tell people which mosfets to shunt and which not from a picture alone, I can tell you this:  Don't shunt any of those, those mosfets are the motor driving half-bridges!! That's the mainboard, the mosfets that are to be shunted are in the BMS (Battery Management System) -board that's inside the battery pack (yeah, the shrink wraps need to be opened, at least a little bit). Hobby16 has a nice collection of BMS-pictures from various wheels here, with instructions: http://forum.electricunicycle.org/topic/459-electric-unicycles-bms-problem-and-solution/   The easiest solution, if available and easily recognizable, is to shunt between P- and B- with a thick wire, no need to solder the mosfets, so no risk of shunting the wrong mosfets. Do read about the dangers too (since the discharge-side protections are gone after shunting, you really don't want to short the battery by accident...)

 

22 minutes ago, Azuro said:

Please correct the spelling 'tire' to 'tyre'. Also, an euc is not a bike, why using pedals? You're not pedalling at all. Footrest or similar would be more appropriative. The rest is perfect! Thank you very much @esaj!

Hmm, is "tyre" vs. "tire" some  UK vs. US -English difference again, like "colour" and "color"?   

The "footrests" have been pretty commonly called "pedals" in the forums, I think people know what's being meant by pedal even if they themselves call them footrests.. you don't "pedal" a cars' gas pedal or aircrafts' rudder pedals... although many sources say pedals are "foot-activated levers" (which isn't that far off, there is a lever-effect between the pedal and the EUC itself), I picked just the one source that best supports my use of it (Merriam-Webster)  

pedal

: a flat piece of metal, rubber, etc., that you push with your foot to make a machine move, work, or stop

The definition's pretty much spot-on, you push the pedals of an EUC to make it move or stop  

 

Edited December 5, 2015 by esaj

[SlowMo]

39 minutes ago, Azuro said:

Please correct the spelling 'tire' to 'tyre'. Also, an euc is not a bike, why using pedals? You're not pedalling at all. Footrest or similar would be more appropriative. The rest is perfect! Thank you very much @esaj!

There is a saying "Put the pedal to the metal". 

[AlanR]

@esaj  Thanks for the reference - on the BMS modification - hopefully I can identify the relevant connections!

[Jimicycle]

Thank you esaj to put them together!

A suggestion about Hall sensor.

The new generation control board use Hall sensors to detect motor current. May be use Hall position sensor and Hall current sensor to distinguish them.

 

[esaj]

12 minutes ago, Jimicyle said:

Thank you esaj to put them together!

A suggestion about Hall sensor.

The new generation control board use Hall sensors to detect motor current. May be use Hall position sensor and Hall current sensor to distinguish them.

 

True that, I'll try to get around to update the list a bit...

[Knoxious]

Hi there,

 

Can someone show a video of power braking? 

 

I've tried but only seem to out lean and incur shut down. 

 

If be keen to see the technique of this. 

Thanks! 

Edited April 7, 2016 by Knoxious

[steve454]

On 4/7/2016 at 6:45 PM, Knoxious said:

Hi there,

 

Can someone show a video of power braking? 

 

I've tried but only seem to out lean and incur shut down. 

 

If be keen to see the technique of this. 

Thanks! 

Have you searched Youtube?  That is an interesting question, I am about to search Youtube but even if I find one I don't know how to post it.

[Mono]

On 08/06/2016 at 0:45 AM, steve454 said:

even if I find one I don't know how to post it

copy paste the link and type in a space (and/or enter). 

On 08/04/2016 at 1:45 AM, Knoxious said:

I've tried but only seem to out lean and incur shut down. 

You can't really prevent this by a specific technique apart from braking more gently. Generally, keep the upper body vertically upright and the knees flexible. To brake rather don't lean back, but push the wheel with your legs in front of you. 

Edited December 26, 2016 by Mono

[Mono]

EUC = Extreme Unicycle Championship

http://e-u-c.info

 

[Lorents]

You should add Face plant to the EUC riding section 

[Hoverboard UK]

Thank you for the posting, but it would be great if there were images in the starter post or references to You Tube videos.

[Darren]

the content describe detail function of every part of EUC. Especially, the end of  this content tell riders why your E-wheel shut down and you falled.

very very useful topic

[sanman]

I was looking at some of the products on the IPS website, and I was wondering what "IP Level" means.

Is that term specific to that manufacturer, or is that an industry-wide term?

[MaxLinux]

37 minutes ago, sanman said:

I was wondering what "IP Level" means.

Ingress Protection (IP) and what it means
The IP Code (or International Protection Rating, sometimes also interpreted as Ingress Protection Rating) consists of the letters IP followed by two digits and an optional letter. As defined in international standard IEC 60529, it classifies the degrees of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water in electrical enclosures. The standard aims to provide users more detailed information than vague marketing terms such as waterproof.

http://www.dsmt.com/resources/ip-rating-chart/

 

Edited August 1, 2017 by MaxLinux

[richardson121]

Thank you so much for sharing this post it's very informative for me and other's person. Thank's a lot. 

[esaj]

Ok, this post was near to 2 years old. Updated some stuff that has changed since:
-Only mentioned 16-cell series as common battery configuration, nowadays 20S is also very (if not even more) common
-Stroke out the warnings about BMS cut-outs, these seem to be a thing of the past, now we deal with melting wires, broken gyros and whatnot...
-Ninebot was the only one offering "over-the-air" -firmware upgrades at the time, now most mainstream manufacturers have those
-Hall-sensor based current measurement seems to be more common place than plain current sensing resistors nowadays
-Suggestion of minimum of 500W+ motor for heavy riders updated to 800W+
-Mention that modern wheels usually have separate inner- and outer-shells
-Firmware-based power cut on overspeed seems to be a thing of the past, overleans/overpowering still exists, as well as burning boards
-Removed the link to BMS shunting, anyone buying something newer than late 2015/early 2016 wheels shouldn't need to do this anymore? Do note me if that's not the case
-Added "MOSFET" in technical terms, as it comes up every so often
-Redefined "overspeed", somewhat 

-Clarifications of some terms, other minor fixes

Anyone know of other terms that should be added?

Edited November 10, 2017 by esaj