Araldite as filler between frame and bracket?

[MarkLeeds]

Don't turn that into a science project - you just have a small gap.

Go to a Home Depot or Lowes and get a foot of PVC shower pan liner sheet off the roll.


showerPanLiner.png


The roll is 48" wide so you'll get a huge 1' x 4' piece for about $5.
This stuff is 40mil (thickish but much thinner than inner tube), very dense, and pretty incompressible. I use this to mount all manner of stuff on the bike. You can wrap a layer or two, or cut overlapping sized rectangles to put under a layer to get an odd shape fill. This stuff is amazingly rugged and abrasion-resistant -- my go-to stuff for mounting, shimming, insulating heavy battery items, etc.

The thing is the batteries have a combined weight of maybe 5kg. If I clout a rock a speed the forces will be significant given the downtube is only around 1mm thick and a don't want to ruin my nice mtb - hence the cogitation

I like the idea, unfortunately its pretty difficult to cut hold of an off cut online here in the UK (i've spent a few minutes searching ebay and amazon), i'll try and pop down to my local hardware shop tomorrow.

 

[teklektik]

The thing is the batteries have a combined weight of maybe 5kg. If I clout a rock a speed the forces will be significant given the downtube is only around 1mm thick and a don't want to ruin my nice mtb - hence the cogitation

The new battery box forces on your downtube from impact are going to appear at the very ends of the battery clamp - not under the clamps. Any reinforcement that you add under the clamps is a wasted effort because it's not going to relocate the stress riser at the edge of the clamp where there is an apparent discontinuity of member thickness (tube vs clamp+tube). To do any good, you'd need to extend it beyond the clamp, etc. Frankly, a quick search of ES should indicate that there are no reported downtube failures for any reason. This isn't a compelling technical argument, but it should serve as an indicator that the many yahoos who've build crazy bikes before you never had this particular issue....

...here in the UK...

Really gotta go to your ES Profile and fill in 'UK' as the location so you get better advice. Right now we just know you're somewhere on the planet (probably...)

 

[flat tire]

So the purpose of this reinforcement is to increase the crashworthiness of your battery! You'd better have tesla-level armor surrounding those batteries or a crash severe enough for your battery pack to break the frame could result in more pressing outcoming like 1) a ruined battery pack 2) 1, but by fire.

 

[MarkLeeds]

So the purpose of this reinforcement is to increase the crashworthiness of your battery! You'd better have tesla-level armor surrounding those batteries or a crash severe enough for your battery pack to break the frame could result in more pressing outcoming like 1) a ruined battery pack 2) 1, but by fire.

I'm hoping the batteries will be ok as they're enclosed in a 3mm thick aluminium boxes. I am a keen off road enduro motorcyclist and crashing is one of the things I do best! Hence they obsession with durability. Here's a pic of my battery boxes

https://imgur.com/a/00UlI

 

[MarkLeeds]

The thing is the batteries have a combined weight of maybe 5kg. If I clout a rock a speed the forces will be significant given the downtube is only around 1mm thick and a don't want to ruin my nice mtb - hence the cogitation

The new battery box forces on your downtube from impact are going to appear at the very ends of the battery clamp - not under the clamps. Any reinforcement that you add under the clamps is a wasted effort because it's not going to relocate the stress riser at the edge of the clamp where there is an apparent discontinuity of member thickness (tube vs clamp+tube). To do any good, you'd need to extend it beyond the clamp, etc. Frankly, a quick search of ES should indicate that there are no reported downtube failures for any reason. This isn't a compelling technical argument, but it should serve as an indicator that the many yahoos who've build crazy bikes before you never had this particular issue....

...here in the UK...

Really gotta go to your ES Profile and fill in 'UK' as the location so you get better advice. Right now we just know you're somewhere on the planet (probably...)

Updated my profile, sorry about that. The surface area of where my clamps touch the frame is 12mm (width). I was thinking of making the sleeves at least 4 times wider, maybe the maximum allowed by the space available. I know your're saying re the lack of reported failures, I've spent a bit of time searching. It seems most of the serious offroad builds mount the battery back on their backs which I'm not too keen on. It makes the centre of gravity high and I don't feel comfortable have 1kw off homemade battery on my back. I reckon a combination of a sleeve and some rubber insulation (eg shower pan liner) might just do the job.

 

[flat tire]

The problem's not the battery boxes it's the batteries inside the box. Also that setup looks fine and you have nothing to worry about IF you do a decent job of mounting it. And one more thing, conductive battery boxes can be quite a bad idea so I hope you have plenty of shielding. In any case, you are one step away from having a cool looking bike if you fix that ghetto mount.

 

[MarkLeeds]

The problem's not the battery boxes it's the batteries inside the box. Also that setup looks fine and you have nothing to worry about IF you do a decent job of mounting it. And one more thing, conductive battery boxes can be quite a bad idea so I hope you have plenty of shielding. In any case, you are one step away from having a cool looking bike if you fix that ghetto mount.

I've wrapped the batteries in loads of capton tape and heatshrinked. I'm going spray the cases black inside and out as well.

I really hope it 'll work well - I've spent so much time on it. I'll post a full build thread when I've got it going. Thank you to you and everyone else for all your help.