Self Balancing Unicyle (SBU)

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ianyoung   1 µW

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Self Balancing Unicyle (SBU)

Post by ianyoung » Aug 10 2017 1:07am

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   100 GW

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Re: Self Balancing Unicyle (SBU)

Post by amberwolf » Aug 10 2017 2:34am

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   1 µW

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Re: Self Balancing Unicyle (SBU)

Post by ianyoung » Aug 10 2017 8:58am

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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Re: Self Balancing Unicyle (SBU)

Post by amberwolf » Aug 11 2017 12:54am

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.

fred_dot_u   1 µW

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Re: Self Balancing Unicyle (SBU)

Post by fred_dot_u » Feb 09 2018 9:44pm

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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Re: Self Balancing Unicyle (SBU)

Post by Beast191 » May 21 2020 10:22pm

Hope you guys are still out here, I am the the proud owner of a brand-new out-of-the-box, SBU V3.
It's supposed to be one of the units sold after or from the Shark Tank appearance
The box had been opened and the unit looked at sometime during it's captivity and unfortunately somewhere along the line the key for the lock mechanism was lost, even more unfortunate, the lock is in the locked position. Meaning you can't turn the power on to the unit.
I hooked the charger up and it shows a steady green light but the LED on the on-off button does not light up I'm assuming that's because the lock is in the locked position and isn't getting power? It was like opening a time capsule, the tires brand new the tred shows no tred at all.
I had seen one of these in downtown San Diego in 2013 I think, I was standing at a corner in downtown San Diego waiting for the light to change so I could cross the street and someone had stepped up next to me and my in peripheral vision it look like they were hovering. The light turned green at that moment and the person leaned forward and was off, and running it was incredible. I'd forgotten all about that moment and I don't know why it popped into my mind so I decided to go online and find it. And not only did I find it I found one for sale on eBay, I put in my bed and three and a half days later it was mine. I took the plate that holds the on-off button and the locking mechanism and it looks like it shouldn't be a problem to pull it out, but I'm thinking that since I don't have the key, what would happen if unsoldered the wires on the bottom of the locking mechanism and reversed them? There are only two wires, I am assuming, positive and negative. If I reversed their positions, with the lock in the locked position wouldn't that make the locked position of the lock mechanism the positive side of the connection the same power to the on-off button? Only now you wouldn't be able disabled the on-off button through the locking mechanism because there's no key to change the position of the locking mechanism? Any help would be appreciated I can't wait to ride this thing.....

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Re: Self Balancing Unicyle (SBU)

Post by Balmorhea » May 22 2020 1:57am

The “lock” is a key switch. If there are only two wires going to the key switch, then their polarity does not matter. Connect the two wires and it’s on, disconnect and it’s off. You can substitute any other latching switch, with or without a key. You can connect the wires directly, without a switch.

Try not to hurt yourself. If I understand correctly, the thing might date to 2012 or so. The battery is probably dead or defective for any of a number of reasons.

fred_dot_u   1 µW

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Re: Self Balancing Unicyle (SBU)

Post by fred_dot_u » May 22 2020 4:10am

Of the problems one could have with an SBU, you have an easy fix. As noted by Balmorhea, it's a simple switch. If your batteries aren't completely shot :lowbatt: , you'll have some fun ahead.

Do you have conventional pedal unicycle experience? If you use the right method to teach yourself to operate the SBU, it's a thirty minute process, best split up into two fifteen minute segments.

I had to shelve my SBU for medical reasons and I still miss the fun I had on it. I think v3 will do 18 mph, while my v2 had a top end about 15 mph. The responsiveness is nothing short of amazing. After no time at all, it will be as if you're controlling it with your mind.

Keep us posted of your progress.

p.s. SBUv2 for sale, needs batteries.

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