Stokemonkey safety notice

I sent this out moments ago via email, but I want to get the word out on all channels:

Dear Stokemonkey users, current and prospective:

Cleverchimp LLC has become aware of a safety issue relating to controllers sold with the Stokemonkey Human Electric Hybrid Drive. Specifically, if the throttle’s connection to the controller fails in a certain way, the controller may apply full power to the motor without any throttle input until the system is turned off. To our knowledge, this type of malfunction has occurred only once, fortunately with no harm done. Unfortunately, we have determined that all Stokemonkey systems sold to date have the same vulnerability. We are working on a fix with the controller manufacturer, and will send replacements free of charge to all customers as soon as we get them.

In the interim, please be aware that a faulty connection could lead to a loss of control of the vehicle and injury or property damage. Please do not seat passengers before you have turned the system on, because the problem may appear at the instant you do so. If the problem occurs as you are riding, firmly apply the rear brake to stop the motor, and turn the system off. If the problem develops, do not use the system until it is repaired.

Please feel free to contact Cleverchimp with any questions you may have. We will keep you posted via email as to when we expect the new controllers to arrive.

Todd Fahrner

Instigator, Cleverchimp LLC

3 thoughts on “Stokemonkey safety notice”

  • Allan F

    Hmm, so would it be better to downshift into the granny gear, almost immediately slowing the bike down, or up shift to the tallest gear to take away as much mechanical advantage as possible, and let the brakes do their thing?

    I’m guessing what’s best may depend slightly on the situation. But the very quick drop to the granny gear, maybe even derailing the chain in the process, seems a natural panic maneuver. On the other hand, lugging the motor and relying on good brakes seems a pretty effective course of action.

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  • Todd

    Allan, if you’re riding the bike when the problem occurs, just applying the brakes in whatever gear you’re in and turning off will take care of things — the controller will “give up” stutteringly if the motor can’t advance at all. If you go to a low gear, you’ll just need to apply the brakes harder to overcome the greater torque; conversely, going to the highest gear will load the motor hardest, making it easiest to brake. The case I worry about most is when you’re not on the bike with your hands near the brakes at all, but standing aside it as you power up. Let’s say you have a kid strapped in as you do this… small risk, unacceptable potential consequences.

    For the curious, the problem occurs when the wire or contact corresponding to the middle of the three-pin throttle connector is interrupted, with the other two intact. The fix will involve a throttle fault detection circuit in the controller that cuts power when the throttle signal is outside normal operating parameters.

    There are many other parties distributing substantially the same subcomponents in other electric bike products. I had heard of runaway throttles, but in previous cases believed it to be related only to throttles with an LED power indicator — seems the indicator signal has a tendency to leak into the control circuit, especially in wet conditions. Stokemonkey hasn’t used these types of throttles for this reason. But now we understand that it’s a more general problem that needs a more general failsafe strategy to address. I think Cleverchimp is the only one publicizing the problem and pressing a fix because the other products tend not to be sold as suitable for carrying passengers; any passenger/cargo space on regular electric bikes tends to get taken over by batteries.

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  • [...] last year we identified a safety liability with Stokemonkey. We have since tested several potential fixes, and rejected most as unreliable. [...]

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