Custom wheel frame/shell

[esaj]

The shell of the wheels is mostly just for holding the switches, wiring, mainboard and batteries, and of course for aesthetics. Plastic is fairly good material for this because it's cheap and light, and the plastic (ABS?) used in the shells are fairly durable, ie. doesn't break that easily on crashes. However, upon investigating the shell of the Firewheel further, I found out that the crash it took when the battery cut out had actually broken one of the "poles" (or whatever they should be called) that are used for the screws holding the shell-halves together. It's not that critical, as the shell can still be fixed, but while the Firewheel shell is nice to ride because it's slim, it's also a huge pain in the ass when it comes to dismantling and rebuilding the wheel. This is mostly just a design issue with Firewheel, because some genius decided it's a good idea that all the compartments are accessible from the inside only. So why not design a custom-shell?

Designing an entire shell-half as a single piece isn't exactly easy, and getting it right in one go is pretty much impossible. As I don't have access to a 3d-printer that could make large enough pieces, I'd have to either make a  modular-design from several pieces that somehow lock themselves together, creating lots of vulnerable points, or pay for printing the prototypes somewhere, until I "get it right". The original shells are likely done with injection-molding, which is cheap and fast for large batches, but the mold still first needs to be designed and done, which isn't that cheap, and makes no sense for a few items. Different thing if I were to make 1000 or 10000 pieces

The modular shell isn't a bad idea in itself, as if the battery- and mainboard-compartments and wire channels were their own pieces, it would help with testing different designs (ie. where to put things) if you could move them around. This leaves the question about how they're actually attached and held together.

The way I chose to approach this was with a separate internal frame, that acts as a "scaffolding" onto which the other parts are to be attached. The material? Flat metal bar, steel to be exact  Yes, it's heavy. With preliminary calculations of the simple bolted-design using straight 3 x 40mm bits of bar, like shown in the first design below, the total weight of the frame came around 3kg. Of course using less thick or less wide bar drops the weight, but on the other hand, the frame should be rigid enough not to bend (at least badly) on a possible crash.

There are two basic designs I have come up with so far (meaning today), and they're both fairly simple:

This one is the simple one (from construction point of view); it's only straight bits that are to be bolted together (or of course they could also be welded, then the bars wouldn't need to run on top of each other at places). Cheap also, as the bolts and the flat bars cost next to nothing. The sideways-running flat bars are meant to be L -shaped at the ends for through-bolting. The bent pipes there are just for show, as I was thinking how to make the frame more rigid, but might be needed. The picture is of course not to scale, just a quick mock-up of how the bars would be placed. They're attached to the pedal frame itself with the same bolt-holes that the usual shells attach with, and one side must have a hole for the motor cable. @vee73 actually suggested that the "triangle" could be turned upside down and make it a "flat top", that might work too. Then all the batteries and the mainboard could sit there also, keeping it fairly simple.

As for covering the frame, I was thinking of either some form of plastic sheet, or for more hardcore, metal hole plate or grate :

 

It's not going to look pretty either way, but on the other hand, I don't really care, as long as it's nice to ride. The actual compartments and wiring would be on the outside of the frame cover (whether it's plastic, hole plate or grate), the compartments are small enough to be 3d-printed to get them as a single piece of plastic. Through-bolt attachment again (glue on wire channels?), with care taken on the battery compartments that the batteries themselves can't hit the bolts (or move around in general, by padding them inside the compartments like is done currently any way). Also the compartments could be further protected from the outside by crash bars (like in motorcycle engines). Main thing that they aren't in the way of my legs, so the wheel stays thinner in the middle ( of course some sort of padding needs to be placed there.

 

 

 

Another design, which is aesthetically more pleasing (of course the frame will be covered by the "actual" shell)

Nevermind the purple-thing in the background, it was an earlier attempt at modelling this, as Tinkercad isn't exactly the best tool for this    The hard part here is getting the flat-bars bent fairly precisely, they can then either be bolted or welded together. 

Also covering the frame has more limited options, as the covers need to bend enough, if the round form is to be kept, otherwise it isn't of much of use (if it's boxy outside, but round on the inside).

 

The simplicity of a taller "box" is also an option, that way it would be fairly easy to stuff everything on top of the tire, kinda like vee has done with the MSuper:

I'd just make it thinner in the middle, so I wouldn't have to stand on the edges of the pedals.

 

Thoughts? How would you make a custom shell / frame for a wheel?

Ps. If anybody calls a wheel with a paint job and decals "heavily modded" after this, I'm going to ban you  Well, not really

 

 

Edited September 20, 2015 by esaj

[Tilmann]

Forget Steampunk - I'll go with the Flintstone's design, tie two 2 by 4's to the sides for pedals and skip the wimpy shell thing 

 

[Gimlet]

Would it not be a lot simpler to take a glass fibre mould from an existing shell after adding any extra blocks for more switches, batteries etc. and the make one in either glass fiber, diolen, kevlar, carbon fibre or preferably a carbon kevlar mix?

I've made canoes using all these materials in the past and if you use an epoxy resin rather than the standard polyester resin when you lay up the finished case it will be stronger, lighter and harder wearing than most other easily workable, available materials.

It also gives you a lovely finished pattern if you use clear resin.

http://www.fibreglast.com/category/carbon-kevlar-hybrid-fabric

Edited September 21, 2015 by Gimlet

[esaj]

Would it not be a lot simpler to take a glass fibre mould from an existing shell after adding any extra blocks for more switches, batteries etc. and the make one in either glass fiber, diolen, kevlar, carbon fibre or preferably a carbon kevlar mix?

I've made canoes using all these materials in the past and if you use an epoxy resin rather than the standard polyester resin when you lay up the finished case it will be stronger, lighter and harder wearing than most other easily workable, available materials.

It also gives you a lovely finished pattern if you use clear resin.

http://www.fibreglast.com/category/carbon-kevlar-hybrid-fabric

Interesting, although making the mould out of glass fiber might be quite hard due to all the details (of course many of those are unnecessary and even unwanted ), if taking the mould from the inside. Maybe a big pile of plaster (or urethane?) would work better? The "poles" on both sides must line-up and be of correct height or the shell cannot be closed properly (if using the original as model), and the halves aren't identical. Of course if the mould would be made from the outside, it would be a lot easier, but then I'm not sure how I'd get the halves to stay together.

 

 

Edited September 21, 2015 by esaj

[Gimlet]

The normal method is to add any extra bits you want to the plastic shell, smooth it down really well, wax it with release wax then lay your fibre glass and polyester resin on the outside.

Once your mould is made you trim it, smooth it and release wax it apply a gell coat and then lay up your woven matt and epoxy resin. Once that has hardened you can use thin plastic card to position all the internal partitions and alloy or plastic tube for your posts. Epoxy them lightly into position using a temporary positioning template made up on the original shell. Stiff card is good for this.

Then reinforce the posts and coat the card partitions in more of your chosen woven material making a reasonable sized attachment flange to the shell. Lumps and lugs can be made using epoxy putty and reinforced with offcuts and threads from the material. Finally release each half from the mould, trim the fit with sandpaper and files, drill holes for the fixing screws and you're done.

Edited September 21, 2015 by Gimlet
predictive text!

[esaj]

The normal method is to add any extra bits you want to the plastic shell, smooth it down really well, wax it with release wax then lay your fibre glass and polyester resin on the outside.

Once your mould is made you trim it, smooth it and release wax it apply a gell coat and then lay up your woven matt and epoxy resin. Once that has hardened you can use thin plastic card to position all the internal partitions and alloy or plastic tube for your posts. Epoxy them lightly into position using a temporary positioning template made up on the original shell. Stiff card is good for this.

Then reinforce the posts and coat the card partitions in more of your chosen woven material making a reasonable sized attachment flange to the shell. Lumps and lugs can be made using epoxy putty and reinforced with offcuts and threads from the material. Finally release each half from the mould, trim the fit with sandpaper and files, drill holes for the fixing screws and you're done.

Might try this (too) over the winter... fiber-glass -mats and -fabrics are cheap, carbon fibre seems to run close to 60€ per square meter. One minor problem might be that the missus probably would tell me to go do it in the garage, due to all the chemicals and fiber-glass dust, and that's uninsulated and unheated, so it's probably going to be < 0 celsius in winter, not sure if epoxy-resin likes that  

Edited September 21, 2015 by esaj

[Gimlet]

No it won't work in the cold. You'll have to put a heater out there.

Polyester for the mould is much cheaper than epoxy resin but it does stink. Epoxy is supposedly more toxic but has very little smell and I found I had no reaction to it when crawling up inside the two canoe halves to resin them together.

You would probably find that 1 square metre of of carbon kevlar hibred weave would just about give you two layers on each shell half, I always like to turn the second layer at 45 degrees to the first for maximum strength, and enough offcuts for the internal partitions.

Pure carbon fibre is stiffer but can be a bit brittle in a canoe when you slam into a rock so a wheel crashing onto a concrete kerb will probably have the same effect.

[RichieV]

One word: LEGO

[esaj]

No it won't work in the cold. You'll have to put a heater out there.

I know, I should have put the "minor problem" in quotes

Polyester for the mould is much cheaper than epoxy resin but it does stink. Epoxy is supposedly more toxic but has very little smell and I found I had no reaction to it when crawling up inside the two canoe halves to resin them together.

You would probably find that 1 square metre of of carbon kevlar hibred weave would just about give you two layers on each shell half, I always like to turn the second layer at 45 degrees to the first for maximum strength, and enough offcuts for the internal partitions.

Pure carbon fibre is stiffer but can be a bit brittle in a canoe when you slam into a rock so a wheel crashing onto a concrete kerb will probably have the same effect.

Never done moulds before, but I did read a couple of tutorials and watched some videos. Definitely doable, also found some cheaper (although lighter = less thick) carbon fiber and some other fabrics, waxes, gels etc. stuff used in making the molds and final pieces. Definitely something I want to try over the winter, it could actually work pretty good. I could probably alter the shell shape somewhat to get the battery compartments placed a bit differently and to make more room for the wiring. Still, I want to try the metal frame too  Well, I'll probably have a good 4-5 months of time when the weather won't permit riding (unless I go all vee-style ).

One word: LEGO

I think I have my Legos somewhere in the attic   Could be useful in trying out designs... or build the shell from Legos?   

[Gimlet]

You must have noticed that most wheels have two identical shell halves so you only need to make one mould, you can then use the same materials as the mould and cast a cheap trial just to get the hang of it. But for the finished product $60 for a metre of good quality carbon kevlar hibred material isn't too bad. Like I said pure carbon can be a bit brittle unless you use multiple layers whereas you'll probably get away with just two layer of carbon kevlar, especially if you use epoxy resin.

[esaj]

Well, after lots of doodling and trying to learn to use some free CAD-software, I took the plunge and got some materials this wednesday & set to work. In the end, I did decide to go with aluminum (4x40mm, 4x30mm and 2x30x30mm -"edge") and the inverted triangle. I've now used a couple of evenings/nights at it, and gotten something done, although I have very little experience working with metal (plus bad workmen always blame their tools, but apart from the "Dremel-clone" -mini-sander and an electric drill, this is all done with cheap hand tools)... here's a few pictures to tease you, I'll try to get around to write more about my plans some day, when I got the energy   

 

Edited October 2, 2015 by esaj

[esaj]

Got some more work done today on this (about 6 hours). I put all the pictures (except a couple out of focus) I've taken so far into an imgur-album, didn't bother to pick out any specific ones: http://imgur.com/a/dVNBq

One of the first things I had to do was get one broken bolt out of the pedal-frame. Guess vee had broken it either during changing the shells or in some crash. I tried to cut a groove into it and get it out just with a screwdriver, but in the end I had to drill it out and re-thread it.

First I tried to measure the positions of the screws and then make them on the aluminum-bar, but that didn't work out too well. I then used pencil to trace the positions and use a drift (is that the correct word? That pointy piece of metal for hitting "starting points" for drilling with a hammer...) to mark the positions:

All the tools I've used have been an electric drill, drift, hammer, couple of clamps, small miller-drill bit, 4mm and 5mm drill bits, mini-sanding machine ("Dremel-clone") with cutting discs, couple of hacksaws, measuring tape, different sized & shaped files and straight edges (plus some miscellanous stuff like screw drivers etc. basic tools). I was actually looking at blade for my miter-saw that's specifically made for cutting aluminum (and other non-ferrous metals), but was put of by the price tag (65 euros), as I probably have no use for it after this project. In hindsight, it would have saved several hours I've used for sawing the pieces, and then I'd have all the angles exactly and all the cuts straight...   But, there aren't that many pieces to cut anymore, so probably not much point to get one now (unless I start over ). I really, really wish I also had a pedestal drill, bench grinder & angle grinder, and maybe few more toys to make life easier with this...

 

I must have destroyed about 15 of those cutting discs doing the holes for the motor cable... had to do it twice, since the first piece was the one with the bolt-holes off, I milled them bigger to get the positions right, but discarded the entire piece and started over, as it was too loose after the holes were enlarged. 

In the latter piece I still haven't drilled the last hole (the one which had to be re-threaded), need to carefully get the position correct. Although it could probably work just fine with just 5 bolts too. I cut the hole for the motor cable so that it can come out and "loop" back behind the bar, the connector is so large that the hole would have to be too big (the bar would probably bend or break due to so little material being left on the sides).

Made those angled pieces today to keep the diagonal supports in place, they're bolted straight to the pedal frame also, the piece laying on the top is meant to be later on cut to provide another horizontal support, probably 2-sided (so two pieces, both in front and behind of the vertical wider beam.

The "box" on top is starting to get its shape. Although it may look big in the picture, the height from pedals to top will be under 60cm (<2 feet), when putting my foot on the bricks, the top comes up to about just above my knee. The "box" is about 15cm (6 inches) wide. Front-to-back, the deepest length is about 42cm (<17 inches). I don't have a scale, but based on average aluminum weight (I don't know the exact alloy the bars are made from, they were sold just as "aluminum"), it should come in around 3kg (with the missing supports and the rest of the pieces for the box). On top of that comes the casing for the mainboard and batteries (which themselves weight 3kg alone), and the carbon-/aramid-fiber -shells (which I won't be probably making for a while yet, and probably will try first with cheap glass-fiber & resin just to see if it's doable in general).

That's it for now, tomorrow I'll try to use more time on the app, to finally get vee's wheel & phone back to him, like I originally was supposed to a couple of weeks back, before catching the flu...

 

Edited October 4, 2015 by esaj

[EUC Extreme]

Looks pretty high.

[esaj]

Looks pretty high.

True, it will be about the height of the 18" King Song, except slimmer (King Song is 19cm wide vs. 15cm on this). Of course, it becomes wider once I get around to making the shells (2cm more on both sides, and it's the same width as KS 18"). Also, as it will be "top-heavy", it's probably going to be different to ride. Another thing affecting the riding will be that while the gyro will "see" the same angle no matter how far from the axis it is, the accelerometer will likely get higher values (higher angular acceleration), as it's distance from the axle, around which the top part turns, will be higher. No idea how this is going to affect things (in the worst case, it's going to overshoot the corrections, causing that rocking back and forth).

Edited October 4, 2015 by esaj

[Jag_Rip]

Heavy metal stuff!

what are you going to use that huge amount of space for? A full golfbag? Small kitchen? Unless you want to go for several kWh's of power I'd slim it down a bit. But interesting to see, its not that complex to do it, if you got the hand-eye-measurement coordination mastered.. wich I dont.

[zentype]

Amazing stuff. I'm going to be keeping an eye on this project to see how it develops for sure. Like Jag_Rip, I don't have the skills do do something so ambitious... You mentioned "paint job and decals" in your first post. With me, it's just "decals" lol.

Just think what you could do with a high end 3D printer... 

Edited October 5, 2015 by zentype

[esaj]

Heavy metal stuff!

what are you going to use that huge amount of space for? A full golfbag? Small kitchen? Unless you want to go for several kWh's of power I'd slim it down a bit. But interesting to see, its not that complex to do it, if you got the hand-eye-measurement coordination mastered.. wich I dont.

Amazing stuff. I'm going to be keeping an eye on this project to see how it develops for sure. Like Jag_Rip, I don't have the skills do do something so ambitious... 

It's really not that hard to make, as there's nothing but separate pieces of aluminum and through-bolted connections. Getting the pedal-frame holes correct was probably the hardest part, otherwise it just takes a lot of time with all the cutting required (and like I said, I'm using just a hacksaw, got cheap and didn't buy the non-ferrous metal-cutting blade for the motorized miter-saw ). I haven't worked with metal since the elementary school, and never was any good with shop-classes, so if I can do it, anyone can. Originally I meant to use stainless steel, but it turned out that stainless steel is a lot more expensive (at least in the local shops) than "plain" steel. Like 3-4 times more expensive than plain steel or aluminum. It would have also been heavier, but I could have used less support structures, as it doesn't bend as easily, and could have asked my neighbour to weld parts of the frame once I got it "correct", not that easy with aluminum. But on the other hand, aluminum is so much more light, that the extra supports don't bring that much more weight... but as I'm still going to add more support, the total weight of the frame alone will be above 3kg. Earlier I thought that an MSuper would be too heavy wheel for me, and now this is going to be around the same weight probably  Except larger...

The box will be housing four battery packs (at least for now, probably could fit even more) and the mainboard (which is a bit larger with the metal-plate than in most wheels) + secondary PCB. I might decide to slim the top down later on by bending the upper parts of aluminum bars together so the top "arches" a bit (which might need a blowtorch or something to heat up the metal to do properly), if I see the need to... I think it looks bigger than it is in the pictures (not that it's really small either ):

The measurements of the box are roughly length x height x width = 420x210x150mm (16" x 8" x 6"). A single battery pack is about 145x130x25mm (5.5" x 5.1" x 1") and the mainboard with two large capacitors and the plate is around 200x100x30mm (7.9" x 3.95" x 1.2"), haven't measured the secondary PCB, but that's so small that I can tuck it away pretty much anywhere (and doesn't have any sensors, so the position won't matter). The way I've thought I'd place them is something like this:

The packs & mb probably aren't 100% accurate in scale, but close. So the red / see through blocks are the battery packs and the bluish one is the mainboard. The mainboard can be of course only in the "correct" position or the gyro won't work like it's supposed to (so I can't place it lying on it's side for example). This way the parts should be fairly balanced, no more weight on either side. The yellow parts (except the pedal frame) are a quick & rough mock-up of the shell-shape I had in mind (although not that "flat", just didn't bother to try to model it more precisely in Tinkercad), with air-intake/exhaust at front and back for cooling... of course the battery packs and the mainboard must then be separately housed inside (with padding around the battery packs to prevent shocks), to protect them from moisture and crap from getting into them and using something like finned aluminum cooling blocks coming through the housing (but that's not necessary at least for now, as the temperature outside is so low). For winter-riding, the front and back must be closed with something. But I'm getting ahead of myself, as first I need to finish up the frame and test that it's actually rideable   Initially I'll just create a simple box inside the frame from some old floorboard-laminate I have laying around and use pieces of wood for building simple inner housings for the battery packs & PCBs.

I've also got a couple of lights coming for this project: http://www.aliexpress.com/item/1-125W-3000LM-Cree-U7-Car-Motorcycles-LED-Fog-Light-DRL-Blue-Circle-Universal-LED-Driving/32462932543.html  Should work with 12-80V DC voltage, so should be possible to power directly from the batteries (47-68V), but as they're spot-lights, I might need a diffuser to spread the light a bit. The front of the top-side will have that inclined part where I attach the voltage display(s), still looking for temperature displays (if possible, I'd like everything to power themselves directly from the batteries, but might need a separate power source for those, probably a 9V battery).  Also might need a winter-tire (so have to order one outer tire and maybe couple of spare inner tires), and battery heating, if I'm going to ride this during the winter...

 

You mentioned "paint job and decals" in your first post. With me, it's just "decals" lol.

Nothing wrong with paint jobs & decals, it's just that someone posted something like "heavily modded Ninebot, OMG it's cool"-topic in the Ninebot forums and I was expecting to see something like Gotway MSuper-mainboard modded into a Ninebot (I've seen a video of a guy riding a Ninebot at 30+km/h and looking the speed at Gotway-app), or something like this project and it was more like a couple of decals and separate light & camera attached... My face was like: Sees topic:  Opens topic and starts video:  Nice looking wheel, but what has he modded?  Waiting...  Oh.    Guess I just understand the terms "modding" and especially "heavily modding" bit differently (ie. more like actually modifying/rebuilding/swapping the structural/electronical/other internal parts and/or firmware of the wheel).  Maybe my way of defining a mod could be "if it doesn't void the warranty, it's not a mod"?

 

Just think what you could do with a high end 3D printer... 

Like I've mentioned before, my cousin has a cheap 3d-printer (so not high end), but it's limited to something like 200x200x200mm parts at maximum, so no good for making entire shell-halves (that would need something like 500x500x200mm or even more). I do know a couple of 3d-printing services that can make larger parts, but designing the shell-halves so that they fit and actually close up properly isn't that easy, and getting many, many prototypes done before it works could cost a lot. Plus, I want to use a lot sturdier material than "just" ABS-plastic for the shells, that's why I've planned to go with epoxy-laminated carbon fiber and carbon/aramid-fiber for the final shells (first run with cheapest fiber glass & epoxy resin to see how difficult it is to get right ).

 

 

 

 

[OleTC]

 

The measurements of the box are roughly length x height x width = 420x210x150mm (16" x 8" x 6"). A single battery pack is about 145x130x25mm (5.5" x 5.1" x 1") and the mainboard with two large capacitors and the plate is around 200x100x30mm (7.9" x 3.95" x 1.2"), haven't measured the secondary PCB, but that's so small that I can tuck it away pretty much anywhere (and doesn't have any sensors, so the position won't matter). The way I've thought I'd place them is something like this:

 

Really interesting project. Maybe You'll find place for a Thermos/sandwich-holder, inside the frame, so You can store coffee and lunch in the Wheel.

Am following this with interest.

Regarding the weight, it appears a Little overkill to me, to use carbon-cloth, since the weight-addition will be negligible, related to glassfiber. And carbon, though very strong and rigid, is known to splinter, so.... But maybe You have other arguments for it.

Happy Work with this project.

[Sholphin02]

Hi Esaj.......amazing project. I'll follow with huge interest.

Also, could you post the link to the "video of a guy riding a Ninebot at 30+km/h" ? => I'll be glad to learn how he did the trick of achieving this speed on a 9b1

[esaj]

Also, could you post the link to the "video of a guy riding a Ninebot at 30+km/h" ? => I'll be glad to learn how he did the trick of achieving this speed on a 9b1

I've only seen it in Facebook... Not shown how it's done, but it looks legit (ie. probably not done with someone riding on a Gotway next to to the person shooting the video, otherwise they'd have to stay pretty close to each other so the Bluetooth-link wouldn't disconnect)... My guess would be Gotway mainboard (and maybe battery?) inside a Ninebot, otherwise NB-tech, as the 18" motor is too big to fit inside Ninebot shells, and the 14" would probably be too small (the shell would hit the ground)?

Finally found it again:

https://www.facebook.com/groups/ElectricUnicycle/permalink/821027567995208/

Edit: Also when he stops, the leds don't seem to be showing the battery status but just stay lit with blue color (isn't original Ninebot showing green/yellow/orange/red with the leds being lit lower the lower the battery is?).

Edited October 7, 2015 by esaj

[esaj]

Made some progress again:  http://imgur.com/a/9j29g

The bottom of the box is now reinforced with 4x40mm and 4x30mm bits.

Motor cable "shield plate", this is bolted on top of the long part with the hole for the motor cable. Idea is to reinforce the weak spot (the thinner strips around the hole for the cable.

Adding horizontal-support for the angled pieces & the motor cable plate.

Reinforced enough? I guess?

Similar horizontal support added for the other side.

Although not exactly light, it's not very heavy either... supporting it in the air with two fingers.

Attached to the motor... The motor-cable plate (not seen in the picture, this is the other side) still needs a bit of milling around the bolt holes that go to the pedal frame (although I broke the milling-drill bit earlier , have to use a crappier bit now) , and the groove in the plate might need to be enlarged a bit (the cable fits, but is maybe a bit tight). Then I need to add a couple of bits to the "box" for supporting the "floor" of the part which houses the components, but after that, I should be ready to start building the housings & installing parts.

 

Edited October 7, 2015 by esaj

[Tilmann]

Hi @esaj, so you're building the Flintstones wheel in earnest, huh? You never fail to amaze me . Great project!

I was about to suggest to replace the gyro sensor on the mainboard with one on a little breakout PCB as those can be bought for pocket change and many small video camera gimbals use such a design (for the ever so popular MPU-6050 sensor, see http://www.ebay.de/sch/i.html?_from=R40&_sacat=0&_nkw=mpu6050&_sop=15; there are breakout boards for more advanced types like the NBO055 available, too, but run about 30 Euro). Connecting the sensor with a flexible cable to the main PCB would give you much more design flexibility as only the sensor has to be mounted in the original orientation (as long as you can't adapt the firmware).

But then I looked up some descriptions of the electrical interconnection, which is an I2C bus, and my idea may not be as smart as I thought. The english Wikipedia page (https://en.wikipedia.org/wiki/I²C) doesn't say much with regard to physical limitations, but the german text (https://de.wikipedia.org/wiki/I²C) explicitly warns, that the interface is not very robust against EMV and "longer" cables and data may be distorted without detection. (Original text: "Das Protokoll des I²C-Bus ist von der Definition her recht einfach, aber auch recht störanfällig. Diese Tatsache schränkt die Verwendung auf störarme Umgebungen ein, wo weder mit Übersprechen, Rauschen, EMV-Problemen noch mit Kontaktproblemen (Stecker, Buchsen) zu rechnen ist. Auch ist er ungeeignet zur Überbrückung größerer Entfernungen, wie es beispielsweise für Feldbusse typisch ist.)

Another discussion about using bicycle computers on our wheels mentioned, that due to electrical interference from the motor, wireless models can't be used. That's why I would be concerned about the reliability of an external gyro. Too bad. 

 

[esaj]

Hi @esaj, so you're building the Flintstones wheel in earnest, huh? You never fail to amaze me . Great project!

Although slow, it's been pretty rewarding so far... nice to work with my hands for a change, instead of banging out code   It's gone surprisingly well (at least so far), although the "quality" of my work is nowhere near a professional metal worker and my tool set is fairly limited. Luckily it's not the kind of project where (sub-)millimeter precision is needed everywhere, and I can alter the design when need be. Hopefully by this time next week, I've already test-ridden it at least once.

But then I looked up some descriptions of the electrical interconnection, which is an I2C bus, and my idea may not be as smart as I thought. The english Wikipedia page (https://en.wikipedia.org/wiki/I²C) doesn't say much with regard to physical limitations, but the german text (https://de.wikipedia.org/wiki/I²C) explicitly warns, that the interface is not very robust against EMV and "longer" cables and data may be distorted without detection.

Nice idea with the gyro, although even if there weren't problems with interference, soldering the cabling to a board with lots of surface mounted components and very small holes/pads might be beyond my skills. And my "supermarket" soldering iron isn't exactly a precision tool either  Of course I do have that one broken mainboard which could be used for practicing, might be useful later on...

If hobby16 comes out of hiding and gets his telemetry -hardware project  done, with this frame it should be no problem to fit it inside   Modifying the app to support the protocol should be a breeze with current architecture.

[Tilmann]

Nice idea with the gyro, although even if there weren't problems with interference, soldering the cabling to a board with lots of surface mounted components and very small holes/pads might be beyond my skills. And my "supermarket" soldering iron isn't exactly a precision tool either  Of course I do have that one broken mainboard which could be used for practicing, might be useful later on...

If I remember correctly, that broken mainboard is still functioning, but may not always start up at first attempt, right? So it could be used for a proof-of-concept shot, hmmm.

The soldering part may not be as bad as you would think looking at that flimsy sensor package with 24 pins. I am fairly sure, you only need max. 6 wires, probably only 4:

Of course, you need to remove the sensor from the mainboard. SInce you may happily destroy it in the process, that should be doable.

You certainly need to connect the blue ones. I don't know, if the pink ones are needed. Attaching those 4 to 6 wires to the mainboard is likely the hardest part. With a bit of luck, you can trace the connections on the PCB and find easier connection points, than the original SMD soldering spots.

Soldering the breakout PCB with the new sensor is a piece of cake:

So, if the win in design flexibility is worth it and you can keep the cable fairly short, it's probably worth a try. I'm just afraid it's next to impossible going back and re-mounting the MPU-chip were it was on the mainboard without expensive SMD equipment.

[jayjay23]

AD0 seems to be a address selection PIN, so in theory you could maybe attach two MPUs at the same time:

I2C ADDRESS

AD0 = 0 1101000
AD0 = 1 1101001

For INT it depends on the controller, but I would somehow guess that the workflow of calculating balance in a wheel makes it not necessary to let the MPU be the triggering part for starting calculations, so my guess is you will likely not need it.