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Second hand GT16, interesting mix of highs and lows


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So I bought a second hand GT16 for about 900€, it had 74 km on the clock and no real dents or scrapes. Given a new one in EU would cost close to twice that amount I took a chance, knowing full well that my frugal side could come bite me in the rear if I were unlucky. I got it on eBay from a seller with 60-ish positive comments and no negatives.

I got it pretty fast, about a week from payment to delivery, and unpacked it with some trepidation and a suspicious mind.

The positives were:

  • It had no real dents and scratches except for on the pedals.
  • It started OK, and balanced perfectly
  • The app connected without fail, and the meter matched the pictures on eBay.
  • It came with a trolley.

The negatives on the other hand:

  • The trolley was partly broken, but fixable.
  • The LEDs on the sides were not connected, and there is not even a cord to connect them to unless that is stuck in the controller compartment.
  • The mudflap is just as useless as people say, I'll have to look into what can be done about that.
  • One of the plastic dampers for the pedals were missing, I fixed it with a skateboard riser.
  • The same pedal were loose, meaning would not stay up when risen agains the shell.
  • The shell sat somewhat loose on the wheel, it seems the screws connecting the shell to the wheel were not tight enough.

Some of that is the breaks of the game when you buy second hand, but a few points were a bit worrying. Standing with my weight on one of the pedals the first time made the tire "screech" against the shell. The dreaded "cracked axle" ghost raised its head grinning my way. But as it turned out, the reason were fourfold: One - the air valve stuck out a bit too much, two - the screws to the shell needed tightening, three - the shell is not as rigid as it should be, and four - the tolerances are too small.

The last aspect is my main negative feeling about the wheel, it could well have a quarter-inch more space around the tire on all sides, where the tire meets the shell. That would make the mudflap immensely more useful, would eliminate the risk of the valve or the sides of the tire rubbing against the shell, and maybe even allow a 2.5" tire upgrade...

Also, the screws connecting the shell to the pedals, which AFAIK are the only twelve screws that hold the shell to the wheel, doesn't even have washers. Basically the screw sits directly on the shell, which seem outright stupid. A metal backing, washer or a plate, would spread the forces over a bigger area, making the connection stronger. Four of those are the bottom screws that sits below the pedals, and there is no form of metal backing there either. Sure the forces push the pedal towards the shell, but there are side-forces too.

chrome-gt16.thumb.jpg.ce15f4dec4a84fd3a0ec7c4e730b31a4.jpg

I fixed the trolley with loctite, a cable tie and some really strong weave-tape. I also added chrome strips, to avoid my clumsy self killing the beauty of the wheel. The loose pedal turned out to be a combination of the tightening screw being loose enough that the pedal axle had moved around. So when the previous owner tightened it, the flat part where the adjustment screw should grip had slipped around. Taking it apart, and putting it together correctly solved the problem beautifully. I added skateboard gripping tape to the pedals, the really rough kind. You can't see it on the pic, but there is some silver tape on the shell under the pedal to avoid imprinting the grip tape on the shell. Will get rubber stickers or something to replace it with. :D

 

Now to learn to actually ride the darn thing...

I now realise my Inmotion V3 have given me some really, really bad habits. The first half hour, in the middle of the night, were like going to the bloody gym! Today, the second day, I actually got on unassisted for the first time and rode my first ten meters before a controlled stop. Good exchange for 45min of trials, still exhausting though.

There's still a lot of familiarisation to do, and a lot of twin wheel stupidities to unlearn, but I see the light at the end of the tunnel. With this tempo I will be zipping around in no time :)

The bad habits to unlearn are: almost no leaning of the wheel before getting on; getting on first, then start rolling; going really, really slow – plus the lower center of gravity on that wheel with lower pedals and 14" wheels.

I look forward to getting used to a "true" unicycle.

I'll report more as things progress...

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Thanks for the report.

The way that these wheels are coming from the factory tells me that they really don't care that much about producing a quality product

It's almost like they spent too much money getting the production going and just had to start shipping regardless so that they could get cash flow.

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5 hours ago, Marty Backe said:

Thanks for the report.

The way that these wheels are coming from the factory tells me that they really don't care that much about producing a quality product

It's almost like they spent too much money getting the production going and just had to start shipping regardless so that they could get cash flow.

China in general and Shenzhen in particular seem to have a there-is-a-entreprenurial/engineer-billionaire-in-making-in-every-shack boom-town mentality. It is a tax exempt zone clearly instituted to complement and compete with Hong Kong.

I must admit I both admire and loathe the concept. Admire it in the audacity of the kick-starter effect it has on China as a nation exporting tech stuff to the rest of the world. Loathe it in the effect it has on the concept of quality control, cutting corners in engineering and production and exploitation of cheap labour.

I think the questionable design choices, failures in QC and rush-to-market effects are almost inevitable. The up side of that is that we get products at a price that would easily be doubled if the tech were engineered and produced in the US or EU. The down side of course being 12mm axels on old KS-wheels, insufficient cable gauge and component cooling on some GW- and other wheels, unsecured screws on my GT16, BCMs that suddenly cut out the current when stressed and so on.

To engineer a EUC and get it in production is costly. You have to either adapt or design a good controller, motor, battery packs, shell, load bearing pedal setup and so on. Some seem to have the size to handle it without too many corners cut, like Inmotion and Ninebot - where the level of engineering and QC seem more reasonable. I think Kingsong is probably in that corner and Gotway is probably getting there, but Rockwheel seem to still be a few brilliant young engineers working on a shoe-string in a garage. Even the larger firms seem to be a bit rushed, but the smaller ones are in the make-it-or-break-it zone.

Take the shells of the GT-16 as an example. It is probably no secret to the engineers at Rockwheel that the tolerances are too fine between wheel and shell. But to change this now would mean to adjust the blueprints upset the production line and throw away hundreds of ready shells. It should have been done at the prototype stage, but now it would probably bankrupt the whole operation. Not necessarily the cost of production done, but the inevitable delays, extra work and probable recalls it would create.

My guess is that if they sell enough to survive, we'll see a Rockwheel GT16-S or somesuch within the next year. A variant with some USP-changes to motivate a new model, maybe larger batteries, some cosmetic changes, and some of the teething problems engineered out of the model.

If anyone at Rockwheel sees this, these are a few things I'd like to see:

  • Better cables – the cable train between the controller and battery compartments shouldn't be a hive of loose cables. A bundle of heavy gauge (for efficiency and temperature) cables with connectors in both compartments would simplify service immensely.
  • A couple of centimeters in length and girth of the pedals – they are almost long and broad enough. But some extra space on the pedal would make for better relief for your feet.
  • More space around the tire – there should be enough space to accommodate a 2.5" tire, with at least as much room left as today with the current tire. That would do wonders for the usability of the mud-flap, and reliability in terrain.
  • Load bearing screws should be backed by metal plates. While the plastic is strong, metal is stronger. The risk of stripping threads or cracking the shell would lessen dramatically.
  • Up the thickness of the central parts of the shell a millimeter or so, it would probably cost a few hundred grams of weight, but would make the whole shell much more rigid.
  • Line the joints of the shell with silicon or rubber – this would probably eliminate creaking noises and would also heighten the splash resistance.
  • Remake the mud-flap with a better fastening to the shell, and more tolerance before it touches the tire.
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49 minutes ago, Scatcat said:

More space around the tire – there should be enough space to accommodate a 2.5" tire

I continually wonder why EUC manufacturers never choose 2.5 inch tire for 16 inch wheels after the IPS Lhotz used it very successfully. 2.5 is much nicer, even if you never go off-road. 

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That they chose a narrower tire may be because they went with 858Wh rather than 1300 or 1600. A narrower tire is more efficient in terms of range. What amazes me is more that the tolerances are so small, that even the tire present is a squeeze. It is not logical, since another six mm/quarter inch in each direction wouldn't hurt either the aesthetics or the function of the wheel, or for that matter increase the cost of production more than marginally.

But yes, with the current high-capacity batteries on the market, a 2.5" tire would be a slam dunk. Better capability of swallowing the bumps and curbs, and smoother running overall. Given we have no suspension beyond our knees, that would really be worthwhile. 

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23 minutes ago, MaxLinux said:

I continually wonder why EUC manufacturers never choose 2.5 inch tire for 16 inch wheels after the IPS Lhotz used it very successfully. 2.5 is much nicer, even if you never go off-road. 

You can always do what @Ando Melkonyan did with his ACM. He cut away the parts of the shell that were in the way and then put a 2-1/2" tire on :thumbup:

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28 minutes ago, Marty Backe said:

You can always do what @Ando Melkonyan did with his ACM. He cut away the parts of the shell that were in the way and then put a 2-1/2" tire on :thumbup:

ACM is a great example. To me ACM is ideal candidate for 2.5 tire, but Gotway chose not to use it. Why?

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I'm a bit leery of starting to cut in my newly aquired wheel... :D

But if this tire-touching-shell thingie doesn't go away with me tightening the screws, I'll have to look into it.

Have already considered dremeling away some of the excess from the mud-flap, to maybe maybe get it to work as it is supposed to.

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9 minutes ago, Scatcat said:

I'm a bit leery of starting to cut in my newly aquired wheel... :D

But if this tire-touching-shell thingie doesn't go away with me tightening the screws, I'll have to look into it.

Have already considered dremeling away some of the excess from the mud-flap, to maybe maybe get it to work as it is supposed to.

Congratulations on your new GT16 :D 

The shell on mine rubs slightly but only when riding on one foot. Do yours rub all the time? Have you tried both with the mud flap extended and retracted?

Very good idea with the silver protection trimming! Looks much better than the standard padding that everyone uses :)

Maybe one day someone will design a 3D printable mud guard similar to the Gotway Msuper one:
https://www.thingiverse.com/thing:2083438

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2 hours ago, MaxLinux said:

ACM is a great example. To me ACM is ideal candidate for 2.5 tire, but Gotway chose not to use it. Why?

I love the 2.5" tyre on the Lhotz... it gives so much control! In NZ I have to ride on the sidewalk and with the wider tyre I can ride slower than a walking pace (when I need to navigate the ignorant pedestrians).

In fact, when I jumped into my Airwheel (X8) to teach my sister to ride, it seemed quite wobbly and odd.

And then, off-road... AWESOME!!!

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I haven't tried a 2.5" EUC but IMHO the 2.125" on the GT16 is really nice. Smooth/stable in high speed, no problem creeping after pedestrians and turns on a dime :)

Who knows, maybe I will change my mind if I ever test a 2.5"...

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I should have taken photos, but was so engrossed in work I didn't... I tried to take it apart, which was very interesting and added to the "craptastic" feeling of the wheel.

The first steps are pretty straightforward, basically taking the pedals off and the covers. Then it starts getting interesting...

Someone at Rockwheel thought it an intelligent thing to do, to make a separate compartment for the cables. Sounds good eh, until you hit the wall.

cable-compartment.jpg.7563a5178891ae5a899a7a157f95b3c1.jpg

I borrowed this photo to illustrate...

Notice the minuscule hole between the battery compartment and the cable-compartment? That is where all the cables goes through. The compartment is about the size of a matchbox, and in there are the cables that's supposed to take 1500W... Adding insult to injury, it is sealed by a bit of plexi glued to the opening. I almost got it out without breaking it, i chipped one of the corners. Then working in that compartment for a full grown man, is like asking for trouble. I managed to break one of the cables in the soldering and had to get the soldering iron out to repair the damage.

In reality I can see no reason whatsoever of solving the cable mess that way, unless it's done to nail DIYers that call for warranty after f-ing up. To be frank it's counterproductive, since heavy duty cabling lies twisted in that little space, risking breakage of solderings and so on. My missing LED cable was found, so I suppose it was worthwhile.

The whole reason to take it apart was to separate the wheel from the shell, but I gave up.

After getting all the cables loose and taping them down, then unscrewing the screws holding the shell to the pedals, I tried to pry the wheel loose. No such luck.

Either there are some hidden fastenings, or you have to disassemble the shell, or there is massive amount of glue somewhere, because the wheel didn't budge a millimeter. If someone knows of some more things you have to do apart from taking the six-per-side screws away to get the wheel loose, I'd really like to know. I would be good to be able to take a look at the shell without the wheel, and see if I can do something about the tolerances. I love it, but having a wheel that touches the shell when on one foot, is less than ideal... It distracts from the beauty of riding.

 

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BTW my longest ride without having to step off on the third day was 50 meters, and I made my first controlled turn! :clap3:

Still feeling a bit like the parent the teen watches dancing, but for a total of 2:30 hours of riding, it feels like I'm on track. If things go on like this, I can sell my old one very soon.

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2 hours ago, Scatcat said:

BTW my longest ride without having to step off on the third day was 50 meters, and I made my first controlled turn! :clap3:

Still feeling a bit like the parent the teen watches dancing, but for a total of 2:30 hours of riding, it feels like I'm on track. If things go on like this, I can sell my old one very soon.

Cool.  Fun adventure, eh?

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2 hours ago, Scatcat said:

Either there are some hidden fastenings, or you have to disassemble the shell, or there is massive amount of glue somewhere, because the wheel didn't budge a millimeter. If someone knows of some more things you have to do apart from taking the six-per-side screws away to get the wheel loose, I'd really like to know.

Ecodrive just posted a link to their review today, part 2 shows some details of them taking it apart:

https://ecodrift.ru/wiki-article/rockwheel-gt16-review/

 

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Out riding for the fourth time.

592966cd6305c_2017-05-2713_43_09.thumb.jpg.26774aaaa8a884e68d61b293982ee7d6.jpg

I'm now at the point where I can ride for minutes at a time. Wouldn't trust me among pedestrians yet, but I'm getting there.

No falls today. Found a big mostly empty parking lot to practice my meager skills on. Wobbly as a duck, but reasonably in control.

Hardest parts? Well the centre of gravity is higher on this wheel. It is also very, very nimble - so much so that I find myself overcompensating a lot. Except for one aspect, accelerating and breaking needs more effort, which was scary as hell until I got used to it. ?

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32 minutes ago, Scatcat said:

Out riding for the fourth time.

592966cd6305c_2017-05-2713_43_09.thumb.jpg.26774aaaa8a884e68d61b293982ee7d6.jpg

I'm now at the point where I can ride for minutes at a time. Wouldn't trust me among pedestrians yet, but I'm getting there.

No falls today. Found a big mostly empty parking lot to practice my meager skills on. Wobbly as a duck, but reasonably in control.

Hardest parts? Well the centre of gravity is higher on this wheel. It is also very, very nimble - so much so that I find myself overcompensating a lot. Except for one aspect, accelerating and breaking needs more effort, which was scary as hell until I got used to it. ?

Sounds like you're doing well.  Keep going!  Maybe you can get in some good weekend sessions.

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3 hours ago, Dingfelder said:

Sounds like you're doing well.  Keep going!  Maybe you can get in some good weekend sessions.

Actually when I got home I realised I was getting late for an event, and just turned around and rode on...

It was quite wonderful. :)

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43 minutes ago, Lorents said:

I guess the most common way to protect your EUC are these protective bumper strips:

https://www.banggood.com/Airwheel-Electric-Unicycle-Bumper-Strip-Wheelbarrow-Protective-Strip-p-957046.html?rmmds=search

Thanks for the link, but the protection I was after this time, was some rubber or vinyl foil to protect the shell from the gripping tape I added.

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On 2017-5-26 at 8:13 AM, Scatcat said:

That they chose a narrower tire may be because they went with 858Wh rather than 1300 or 1600. A narrower tire is more efficient in terms of range.

It seems quite unlikely that this would make any notable difference. Given the same air pressure however, a wider tire has less rolling resistance and hence should give the larger range. Having said that though, even the tire construction and the used materials (and of course the profile) probably have a much larger influence than the size in itself.

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