Self Balancing Unicyle (SBU)

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ianyoung
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Self Balancing Unicyle (SBU)

Post by ianyoung » Aug 10, 2017 1:07 am

I bought a Self Balancing Unicyle (SBU) from Focus Designs in the USA a few years ago and used it to get around my town (Lancelin, Western Australia) most days.

A few months ago it developed a fault of violent vibration to the point of throwing me off the SBU. I have tried to contact Focus Designs but it would appear they may have gone out of business.

Any suggestions on how to fix this problem?

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amberwolf
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Re: Self Balancing Unicyle (SBU)

Post by amberwolf » Aug 10, 2017 2:34 am

Without a more concise description of "violent vibration" (direction, periodicity, intensity, any other qualities, etc), I can only make some guesses:

It could be a position sensor, like a motor hall sensor, that is either not signalling correctly (bad sensor or magnet fault) or is not able to send it's signal to the controller (broken or intermittent connection anywhere between sensor and cotnroller PCB inside it's casing).

It could be a battery or BMS problem, where voltage drops on a cell or a sense wire causing the BMS to cut power, then the voltage rises, then the BMS turns back on, then voltage drops again, then the BMS cuts power, etc.

It could be a mechanical issue, like a bearing, causing drag or actually broken so it catches, releases, catches, releases.

Or if it's a planetary gear reduction on the motor, it could have broken teeth on one or more gears, etc.


If you can provide significantly more detail on the problem, what led up to it, how it developed over time, and how the system itself worked when it was normally operating, it may help us help you figure it out.

ianyoung
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Re: Self Balancing Unicyle (SBU)

Post by ianyoung » Aug 10, 2017 8:58 am

I suspect it is a battery or BMS problem. When the SBU was working normally it operates like a Segway ie lean forward to accelerate, lean back to brake. When the battery is getting low it gently "pushes back" as a warning to recharge.

There was no lead up to when the fault occurred. As I accelerated it violently suddered forward & backward very rapidly making it unridable. In fact the first time it happened it I did a face-plant!

I can't find any circuit diagrams but there is some shrink wrapped circuitry above the batteries (one in each fork) ... the remainder of the electronics is internal to the wheel and appears difficult to get at.

Is there at test I can do to check the batteries?

If so, where can I get replacements?

Thanks for your prompt reply.

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amberwolf
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Re: Self Balancing Unicyle (SBU)

Post by amberwolf » Aug 11, 2017 12:54 am

The first test for hte batteries is just to leave them on the charger at least overnight, and potentially for several days or longer, so that if it has a balancing BMS that can do it's job and balance any cells that are low enough compared ot others that they are triggering the shutdown under load.

Then retest the SBU and if the problem doesn't immediately recur but takes a bit of time to do so, then it is probably a battery issue.

If it immediately recurs, you can put a voltmeter (that you can hold onto and see while riding) connected to the battery main + and -, and then watch the meter as the problem occurs. If the voltage stays steady as the problem happens, it's probably not a battery issue. If the voltage jumps way up and down, it probably means the battery is cutting out and turning back on and cutting out, etc.

If the battery is the issue, then you can open it up and use a voltmeter to test the voltage of every cell group. You'd want to post photos of it so we can give you an idea where to put the meter leads to test, if you get to that point.


If the battery isn't the issue, you'd have to open up any place you can get to wire connectors, and try unplugging and replugging the connectors.

If there aren't any of those points, or it doesn't help, then it's likely the problem is within the wheel itself, as it sounds like the motor and controller might be inside it, and may require significant disassembly to open up and test.

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Re: Self Balancing Unicyle (SBU)

Post by fred_dot_u » Feb 09, 2018 9:44 pm

I realize this reply is months after the original post, but I've only now returned to this forum after many moons away.

Considering that the SBU in question provides feedback via oscillation near the battery power limits, it's likely to be version 2 or version 3. Version one beeped at such a low volume, it was inaudible over the chain noise.

I have v2 and love it, nearly 3000 miles so far. The gentle oscillation will only work if the limits of the battery are approached equally gently. Lithium based batteries have a severe drop-off as they near exhaustion. The SBU will not necessarily keep up with strong acceleration (or deceleration) if you have nearly exhausted the battery. Instead of providing a gentle reminder, it will use the remaining capacity of the battery to throw you off.

One does not have to have a nearly exhausted battery to accomplish this. One can attempt to slow too rapidly, causing a high current draw on the system, plunging the battery below the safe voltage. The result is that the controller turns that gentle reminder into a shutdown, even though the battery isn't too low overall.

I installed a CycleAnalyst on my SBU immediately and use the AH figures to limit my operation. With the provided 4AH battery, I stop if I believe my travels will reach 3.2AH accumulated. After nearly 2000 miles, the battery pack is getting tired and I'm not able to get the range I previously enjoyed.

It's great to see another SBU user here. I'm disappointed too that the company has gone out of business. I was ready to purchase v3.

If anyone has a lead on purchasing a LiFePO4 pack of 4-6 AH capacity, 36v, I'd appreciate it. The chinese sources are on holiday for the rest of the month. I've had to walk home recently for my overconfidence and I really want to avoid that again.

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