Build pack onto and around frame tube, rather than inside?

fatty

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In the interests of stealth, we've seen small packs inserted into frame tubes, and commercial ebike frames are built with a recess or box section to house packs.

On conversions, where possible (hardtails), packs are braced within the frame triangle.

Otherwise, packs are cantilevered from a frame tube. This is obviously not ideal, especially a flat pack or mount against a round tube.

Has anyone built or considered building a pack of cylindrical cells as a (partial) shell directly onto and around a frame tube? Each radial segment would be a parallel string, with multiple "rings" connected in series longitudinally down the frame tube to reach system voltage.

-No cell holders or pack structural members necessary -- strong and light.
-Since the resulting pack would be a simple cylinder, it would be easy to protect with a sectioned fiberglass tube.
-The frame tube would look much oversize, but otherwise the lines of the frame would be maintained -- not stealth, but not conspicuous.
-Since the pack is built onto the frame, removing it would not be possible without complete disassembly. But since every cell is accessible, replacement of a single cell would be easy. Battery theft would also not be a concern.

Thoughts?
How would you make parallel and series connections?
 
fatty said:
-No cell holders or pack structural members necessary -- strong and light.
If you don't have cell holders, what is the structure ? I.e. how are the cells held to the frame ? Would this method work for non-cylindrical tube frames ?
 
serious_sam said:
If you don't have cell holders, what is the structure ? I.e. how are the cells held to the frame ? Would this method work for non-cylindrical tube frames ?
-The frame tube itself provides the structure -- that is the novelty of the idea.
-Attach with normal adhesives used, say hot glue.
-Would work with any profile tube, but cylindrical/ovalized tubes are most challenging for mounting a flat pack to.
 
There was a post with a recubent that had square tubing where they were trying to cram batteries inside the frame.
There are hub motors with controller and battery inside the hub motor.
People have cut into existing frames to weld in their battery box design.
 
markz said:
There was a post with a recubent that had square tubing where they were trying to cram batteries inside the frame.

I think I remember that one.
This is sort of the inverse of that idea: instead of using the frame the contain the batteries like an exoskeleton, the frame tube would serve as a backbone to build the pack onto.
 
Sounds highly vulnerable. It can be hit from all sides. You cushion them from the frame for both vibration and impact, but they can be split apart. Then a good hard cause around the outside, not just a neoprene sleeve. Just sounds dangerous having that beam in the center. Maybe you need feet between every battery to anchor the case to the tube so it doesn't allow any compression on impact. I don't know about this. Tape a single battery to the spot on the frame, hit it with a hammer or a pipe or whatever, this is the effect you're risking.

71hy20ZKclL._AC_UL115_.jpg
 
Dauntless said:
Sounds highly vulnerable.

I donno -- it's all relative. Cylindrical metal cells, glued and then taped around the frame tube, then encased within a fireproof structural fiberglass tube sounds dramatically safer than most garbage Chinese packs of reject/harvested cells and poor assembly, let alone naked LiPos taped to a frame.
 
Interesting, are you describing arranging the cylindrical cells encircling the frame tube, parallel to it?
 
Grantmac said:
Measure the frame then 3D print cell holders which snap around it with the cells arranged radially.

Well, I think one of the advantages to building the pack directly onto a cylindrical backbone is that it wouldn't require cell holders. The bare cells could be mounted directly to the frame tube.
 
Unless the outer casing you use on the setup completely constrains the cells, vibration may eventually loosen them so they can move around, and heating/cooling may allow them to move very slightly within their heatshrink wrappers. If that happens, they may either split the wrappers or wear thru them, and if this then allows contact between different groups, you may have a fire (that you may not be able to put out).


Another issue is frame flex. Unless it is a completely rigid frame with thick heavy tubing, most frames will flex a little while riding, and some of them flex a lot (especially unsuspended or hardtail types, and the longer the frame is, the more it will flex). This flex may lead to separation of cells from each other if the interconnects are not also flexible, and may lead to separation of cells from frame if the adhesive used is not flexible enough.

Hotglue is a terrible glue. Most of the ones I've seen or used cease to actually stick to the surface they're applied to after varying amounts of time, regardless of surface prep and type, and that's in a pretty constant-temperature environment (within a few degrees) just sitting there, no vibration. On a bike, there's a lot of vibration, flex, and temperature change (especially as the cells heat and cool during use/etc), which will accelerate this process.

Silicone adhesives tend to attract and hold moisture, which tends to lead to corrosion.

Whatever adhesive is used is only going to be holding onto the bike's paint, and the cells' covering. If those aren't sufficiently well-bonded to their respective material surfaces, then the adhesive is only holding paint to covering, and not cell to bike, once that bond breaks.

If you use cell holders in halves or thirds or whatever that encircle the frame and lock together once placed on it, then slide cells into them like into a revolver chamber, then the material of the holders is the limiting factor, rather than paint, covering, and adhesive. There is then only one potential failure point rather than three, before cells begin to risk touching each other or otherwise being "loose" inside the enclosure.


You'll also have to waterseal the enclosure itself at each end to the bike frame, in a way that water can't flow along the surface of the frame thru any part of the enclosure and wick into the battery itself. (unless this is always used in a dry environment with zero rain).
 
What is the need for stealth in the USA? Most places allow a decently powered e bike. In any case, to my eye, every time I see fat looking frames I see a factory e bike.

Stealth remains about the same as it was 10 years ago, hide the motor behind panniers, which have the battery inside. Then everybody who rides a bike sees how fast you ride up a hill, and knows you have a motor. The rest of the population remains clueless, about almost everything except their phone, and the dumb stuff they just read on social media.
 
Yes, because you have an experienced eye but to the casual person out n aboot they'd have no clue unless the ebikers riding gives them away.

Whats the need for stealth in the USA, many reasons. The primary one I'd say that anything that sticks out gets scrutinized more. An old rusted out car will get their plates run more often then a late model non rusted out car. But your last paragraph is spot on. Thats why reasonable riding is the name of the game. Every area is different, even within a same city, and every rider has a different "history" on file if any at all.


dogman dan said:
What is the need for stealth in the USA? Most places allow a decently powered e bike. In any case, to my eye, every time I see fat looking frames I see a factory e bike.

Stealth remains about the same as it was 10 years ago, hide the motor behind panniers, which have the battery inside. Then everybody who rides a bike sees how fast you ride up a hill, and knows you have a motor. The rest of the population remains clueless, about almost everything except their phone, and the dumb stuff they just read on social media.
 
amberwolf said:
Unless the outer casing you use on the setup completely constrains the cells, vibration may eventually loosen them so they can move around, and heating/cooling may allow them to move very slightly within their heatshrink wrappers. If that happens, they may either split the wrappers or wear thru them, and if this then allows contact between different groups, you may have a fire (that you may not be able to put out).

Another issue is frame flex. Unless it is a completely rigid frame with thick heavy tubing, most frames will flex a little while riding, and some of them flex a lot (especially unsuspended or hardtail types, and the longer the frame is, the more it will flex). This flex may lead to separation of cells from each other if the interconnects are not also flexible, and may lead to separation of cells from frame if the adhesive used is not flexible enough.

Hotglue is a terrible glue. Most of the ones I've seen or used cease to actually stick to the surface they're applied to after varying amounts of time, regardless of surface prep and type, and that's in a pretty constant-temperature environment (within a few degrees) just sitting there, no vibration. On a bike, there's a lot of vibration, flex, and temperature change (especially as the cells heat and cool during use/etc), which will accelerate this process.

Whatever adhesive is used is only going to be holding onto the bike's paint, and the cells' covering. If those aren't sufficiently well-bonded to their respective material surfaces, then the adhesive is only holding paint to covering, and not cell to bike, once that bond breaks.

You'll also have to waterseal the enclosure itself at each end to the bike frame, in a way that water can't flow along the surface of the frame thru any part of the enclosure and wick into the battery itself. (unless this is always used in a dry environment with zero rain).

Good points to consider, but not insurmountable.

In fact, my experience with hot glue on a (isopropanol-cleaned) bike frame has been the opposite -- I used it thinking it would be somewhat removable (as is the intention here), but it turned out to be a major recovery project. But then, I wasn't using hobby-grade glue, but an industrial high-temp, high-strength glue. I think I would actually use a low-temp, low-strength glue to hold the cells in place, and then wrap the entire pack in a self-fusing adhesive tape (which would also waterseal). Since every cell is directly adhered to the frame tube, the load isn't cantilevered out like it would be with a big LiPo brick, or even a shark pack.

Overall, I think this idea resolves mechanical retention/stability relative to existing single-tangential-line frame mounts.

I think the bigger challenge would be making the electrical connections while on the bike. If already planning for a single string of large 40152 cells, this mounting approach may be more attractive due to the easy M6 thread.
 
markz said:
Whats the need for stealth in the USA, many reasons. The primary one I'd say that anything that sticks out gets scrutinized more.

Agreed. Panniers invite scrutiny (theft) entirely unrelated to electrification.
Most sheeple wouldn't scrutinize an oversize (padded?) frame tube.

In any case, I agree that it's not fully stealth, but that's not the objective. It would just be less obvious/ostentatious.
(Although it could be stealthier if the pack was built with thin 18650s.)
 
fatty said:
... and then wrap the entire pack in a self-fusing adhesive tape (which would also waterseal).
Promising idea. The stretchiness and rebound of the tape should help keep the batteries tight to the frame tube down to mildly cool temperatures. Be aware there are several variations of quality and properties of this kind of tape. The samples I experimented with* (wire/connector wrapping and waterproofing) started to deteriorate, crack, and tear after less than a month of non-constant summer sun, implying low UV resistance so might require an additional covering.

The wrapping technique would also make a difference in its resistance to water ingress. Starting the wrap from the bottom towards the top would normally keep the water shedding over, instead of working its way into, the "seams."

*Might be different than what you may be thinking of. This tape is not really "adhesive," but yes it does fuse to itself.
 
99t4 said:
implying low UV resistance so might require an additional covering.
Yeah, it would be trivial to cover the tape with an off-the-shelf fiberglass tube.

99t4 said:
The wrapping technique would also make a difference in its resistance to water ingress. Starting the wrap from the bottom towards the top would normally keep the water shedding over, instead of working its way into, the "seams."
Yep, bottom to top and back to front.
 
How many cells would you get in a string, along the short length of the downtube? You'd be limited to something like 10S.
 
serious_sam said:
How many cells would you get in a string, along the short length of the downtube? You'd be limited to something like 10S.

Yeah, I came up with 10s rings using only the down tube as well, so rather than only parallel, the rings would have to be a combination of parallel and serial, or use the top tube.

I was also thinking of a series-only 1p24s of Headway 40152s..
 
fatty said:
I was also thinking of a series-only 1p24s of Headway 40152s..

Assuming that the down tube was 40mm in diameter then one is looking at four rings of six cells each.
That would be 120mm (4-3/4 inches) in diameter by 608mm (24 inches) long with a weight of 11.52Kg (25 pounds).
That is minimal without any casing or terminations, bms (24S = 76.8 volts), etc.
I suspect that is going to be a fairly long for a down tube.
Also not very stealthy :?

H,mmmmm ..... just thinking ....
Three rings of six would be 18S ... leave two out to make room for BMS, switch, etc.
That would cut the length down to 18 inches and be a more common 16S1P=52 volt configuration.
 
LewTwo said:
Assuming that the down tube was 40mm in diameter then one is looking at four rings of six cells each.
That would be 120mm (4-3/4 inches) in diameter by 608mm (24 inches) long with a weight of 11.52Kg (25 pounds).
That is minimal without any casing or terminations, bms (24S = 76.8 volts), etc.
I suspect that is going to be a fairly long for a down tube.
Also not very stealthy :?

Yeah, I came up with 11.5kg for maybe 1kWh -- not very compelling, but the screw terminals would make in situ assembly easier. And definitely not stealthy. But as above, 18650s would cut down the bulk quite a bit.
 
fatty said:
Yeah, I came up with 11.5kg for maybe 1kWh -- not very compelling, but the screw terminals would make in situ assembly easier. And definitely not stealthy. But as above, 18650s would cut down the bulk quite a bit.
See edit above ... (17 pounds)
 
LewTwo said:
H,mmmmm ..... just thinking ....
Three rings of six would be 18S ... leave two out to make room for BMS, switch, etc.
That would cut the length down to 18 inches and be a more common 16S1P=52 volt configuration.

Nah, LFP 24s is nice because the ~87.6V charge voltage is just under the common 90V controller max, while being divisible by 6 for convenient balance charging. Could always use the top tube too...
(I'm not planning a build like this, just brainstorming)
 
LewTwo said:
H,mmmmm ..... just thinking ....
Three rings of six would be 18S ... leave two out to make room for BMS, switch, etc.
That would cut the length down to 18 inches and be a more common 16S1P=52 volt configuration.

That might actually work for me ....

LiFePO4 Layout 08 (Headway 40152) 00.jpg
 
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