Archives mensuelles : juillet 2015

BMS, how to make your wheel safer

Most unicycles use bicycles’ BMS (Battery Management System) which has a overdischarge cut-off circuit (T1) to prevent the battery from discharging under the LiIon recommanded voltage. It’s a feature usefull for off-the-shelf bicycles’ batteries but for monocycles, it’s
1) unecessary since the mainboard deals quite well with voltage warning
2) utterly, incredibly stupid since a cutoff by the BMS results in a faceplant for the rider. In other words, the wheel’s designer prefers to protect the battery by hurting the user!!! Many many users have been harmed, especially when the wheel is cold (under 10°C), since the batteries’ internal resistance increases and triggers the cut-off more easily. Continuer la lecture

Keep the Gotway quiet

The buzzer on my Gotway 14″ MCM 2S 340Wh is very loud. It’s a piezzo device, powered by a 25% duty cycle 3.3 khz square signal. The signal’s amplitude is 65V (the battery voltage !), no wonder it’s loud, and super duper annoying for you and certainly much more for pedestrians.

Unfortunately, as it has been said at length on the forum, the buzzer can’t be cut off because the GW has no tactile warning like tilt-back or vibrations on any other wheels. Without the beeping, you can overspeed (which can happens even at… 6km/h when the battery is near flat) and then, the wheel WILL shut the power down and throw you off. Yeah, as unbelievably stupid as it seems, it’s totally true : the wheel shuts the power down when riding to… protect you, nice logic, no ?

To reduce the volume and to make a Gotway ride more bearable, I don’t do the 100 Kohm potiometer-series-connected mod, it’s has been out there since the Gotway exists as a testimony of the super duper annoying buzzer (Gotway, please, do something !!!).

Here is my way to tone down the buzzer : a screw.


A2 Generic – BMS shunt

The A2 wheel is a generic X3 clone. The wheeler had a power cut because of a defective cell. After the shunt, no more power shutdown, even if the defective cell has not yet been replaced. All that happens then is a much less powerfull wheel because the defective cell (to be replaced) behaves like a short, leaving a battery pack with lower voltage, though a much more preferable and manageable situation than a sudden cutoff. More evidence of the criminally stupid idea of integrating a cutoff circuitry in an electric unicycle.

P.S. The wheel electronics is accessed from outside, which is a good point ! Mainboard is a X3 generic, with the same ridiculous heat sink which doesn’t sink anything and needs to be added a big aluminium plate.

Shunt by connecting B- to P- :

Continuer la lecture

eWheel – shunt BMS

L’électronique de la eWheel est accessible depuis l’extérieur, sans nécessiter le démontage des deux demi-coques, contrairement à ce qu’on trouve dans le design original de la Solowheel ou de l’Airwheel qui s’ouvrent sur la roue. Un bon point pour l’eWheel, qui a quand même besoin d’un shunt sur le BMS pour la sécuriser.

BMS shunté en reliant B- à P- (trait rouge) : Continuer la lecture

A2 Générique – shunt BMS

L’A2 est un clone générique de X3. Le wheeler avait eu une coupure électrique par le BMS à cause d’une seule cellule LiIon grillée. Après le shunt, plus de problème de coupure.  On peut encore rouler, mais bien sûr avec beaucoup moins de puissance, en attendant le remplacement de la cellule HS. C’est quand même une situation bien plus gérable qu’une coupure brutale par le BMS, preuve une fois de plus de la stupidité criminelle de mettre un circuit de coupure de courant dans le BMS. A noter que sur les Solowheels, d’après Shane Chen lui-même, le BMS ne coupe jamais le courant mais envoie un signal à la carte-mère pour signaler d’éventuels problèmes.

P.S. L’électronique s’accède par l’expérieur, en ouvrant des trappes et ne s’ouvrent pas vers la roue comme dans les Airwheels. Un bon point pour l’A2 ! La carte-mère est celle d’une Airwheel X3 générique, avec le même radiateur ridicule qui ne dissipe rien et qui a besoin de l’ajout d’une grosse plaque d’alu.

Shunt en reliant B- to P- :

Continuer la lecture