Newbie looking for diy rear rack build ideas.

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Chalo   100 GW

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Re: Newbie looking for diy rear rack build ideas.

Post by Chalo » Jan 31 2019 1:00pm

In days of yore, I used a 30-something pound SLA pack on a Jandd Expedition rack and a 50-something pound SLA pack on a Blackburn Expedition rack. The Jandd rack had a bigger platform and thicker stays; the Blackburn rack had more numerous stays and better lateral bracing. Both of the racks survived to do other duty on other bikes, and both were pretty shaky when carrying hard mounted batteries on top. Most racks are plenty strong enough to carry the weight of a big battery pack, but lack the lateral stiffness to do it without wiggling from side to side. They're intended to carry big loads in soft bags, which supply damping and shock attenuation.

If you can break up your pack into halves, mounting them on the sides in panniers will make the bike ride better. No matter where you put the batteries, having some suspension for them (fabric bags on the sides, closed cell foam pad on the rack top, etc) will dramatically reduce the beating your rack takes.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Newbie looking for diy rear rack build ideas.

Post by markz » Jan 31 2019 6:12pm

Cant do it in the triangle then there are bags that go over the top bar near the head tube, after that the only other option is rear rack. I have busted a few, the best one that held up, but still broke was the Electra. I would beef up any rear rack if a battery would be placed there. Them seat clamp racks, along with regular rack. I currently have a trailer clamp that I think goes on the seat post, and its real solid. I used it for a handle bar light mount, U lock stop, and 5S2P Makita hose clamped to it.

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Re: Newbie looking for diy rear rack build ideas.

Post by donn » Jan 31 2019 7:05pm

I've been idly considering a rack build. (Recumbent bicycle with rear suspension, so rack needs to cantilever from frame to benefit from suspension.) I believe I will be able to manage the brazing, but what's got me scratching my head is bending. I haven't settled on any specific design, and maybe I can get by without bending, but I'd sure like to have that option.

Anyone bend small steel tubes, like Tubus? Fill with lead or ice or something?

How about the aluminum rod that I suppose Blackburn racks are made of? Wouldn't that be the most cost effective material, without getting excessively heavy?

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Re: Newbie looking for diy rear rack build ideas.

Post by markz » Jan 31 2019 9:00pm

Just hit up your local metal store and take a look at what they have. I go to a place called Metal Supermarket because thats the only one I know, and that has scrap pieces, and will cut what you want. I found some aluminum square tubing that was able to fit snuggly inside each other, for your mounting points you need to get square stock that will fill up the empty space. Then maybe some aluminum angle peices, alum. flat stock. I basically did that at one point when my battery was on the rear rack, now its in the triangle. Too many full suspension bikes do not have space inside the triangle. I bet you could easily make a rack able to hold your body weight plus your twins weight.

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Re: Newbie looking for diy rear rack build ideas.

Post by wturber » Jan 31 2019 9:42pm

donn wrote:
Jan 31 2019 7:05pm
Anyone bend small steel tubes, like Tubus? Fill with lead or ice or something?
I think sand is often used. I haven't done it though. There are videos on YouTube showing guys doing this ... of course.
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Re: Looking for a chromoly rear rack, any suggestions?

Post by wturber » Jan 31 2019 9:49pm

alpharalpha wrote:
Jul 18 2018 2:54pm

Something to get by until I can upgrade the rear rack properly. Any ideas?
It is generally not a good idea to terminate a strut in the middle of a stressed member. That introduces bending loads. Some tubes are butted, and have thinner middle sections which makes doing that even worse. Though I'm guessing your chain-stays aren't butted.

Ideally you want to make triangles that have members that join at common apexes. So you should try to terminate as close to the rear dropout as possible.
"Commuter - DC Booster"
Iron Horse 3.0 hardtail - 48V / 1000W / 470rpm generic Chinese DD Hub motor (ebay)
8 x 36v 4.3ah 10s 2P battery packs - 1500W 30A DC Boost Converter delivers 54v and about 1000 watts peak
53T/42T Sakae Road cranks - 30mph+ on flats
viewtopic.php?f=2&t=90369

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Re: Newbie looking for diy rear rack build ideas.

Post by dustNbone » Jan 31 2019 10:03pm

I carried (and still occasionally do) a 16S A123 LiFoPo4 pack in an ammo box weighing about 23lbs on the Axiom Journey rack that was referenced above for a couple of years, along with large panniers that carry my groceries, camping gear, 30lb propane cylinder etc.

It's never shown any signs of fatigue, and the lateral movement even carrying near it's rated load is very minimal. I've hit a couple of wheel destroying potholes in that time, and the only part that seems to suffer is the lower mounting screws. I've never sheared one off, but have replaced them a couple of times to avoid it.

I'd say by far that is the weak link, the rack itself is extremely strong.

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Re: Newbie looking for diy rear rack build ideas.

Post by donn » Jan 31 2019 11:51pm

wturber wrote:
Jan 31 2019 9:42pm
I think sand is often used. I haven't done it though. There are videos on YouTube showing guys doing this ... of course.
Ah - I see there's a hand bender gimmick, and small dia. tubing seems to be OK to bend cold with no packing, as long as it's supported.]

But then I checked materials price ... no wonder tube racks are pricy. Aluminum rod for me - order of magnitude cheaper, and lighter, and also appears to be bendable with heat. Time to start practicing aluminum bending and brazing.

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Re: Newbie looking for diy rear rack build ideas.

Post by cooking monkey » Feb 01 2019 1:19am

markz wrote:
Jan 31 2019 9:00pm
Just hit up your local metal store and take a look at what they have. I go to a place called Metal Supermarket because thats the only one I know, and that has scrap pieces, and will cut what you want.
I will be there friday to check out what they have.

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Chalo   100 GW

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Re: Newbie looking for diy rear rack build ideas.

Post by Chalo » Feb 01 2019 2:32am

donn wrote:
Jan 31 2019 11:51pm
Aluminum rod for me - order of magnitude cheaper, and lighter, and also appears to be bendable with heat. Time to start practicing aluminum bending and brazing.
Keep in mind that heat treated aluminum is reduced in strength by up to 75% when you anneal or weld it. You have to grossly overbuild with aluminum if you aren't going to heat treat afterwards.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Newbie looking for diy rear rack build ideas.

Post by donn » Feb 01 2019 3:21am

That will be an interesting thing to look for. Maybe I can rig up some more or less repeatable dynamic load, and apply it to bent and "welded" parts that I've done for practice. Then try again after a few weeks - I understand there's an aging effect - and maybe try a few hours at 350°F or so in the oven or gas grill. I expect joins would really be more like brazing, with a aluminum-specific rod that melts at 600°F and is supposed to be pretty strong. Haven't tried it, though.

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Re: Newbie looking for diy rear rack build ideas.

Post by wturber » Feb 01 2019 3:16pm

My approach posted earlier in this thread has been simple tho probably not particularly elegant. But so far it has been very robust. I just use relatively hefty hardware store aluminum and tubing. I'm assuming it is 5000 series aluminum of some kind. My modified rack routinely carries 35+ lbs on a daily 32 mile round trip commute. It still seems solid and strong enough to sit or stand on.

https://endless-sphere.com/forums/viewt ... 5#p1393977
"Commuter - DC Booster"
Iron Horse 3.0 hardtail - 48V / 1000W / 470rpm generic Chinese DD Hub motor (ebay)
8 x 36v 4.3ah 10s 2P battery packs - 1500W 30A DC Boost Converter delivers 54v and about 1000 watts peak
53T/42T Sakae Road cranks - 30mph+ on flats
viewtopic.php?f=2&t=90369

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Re: Newbie looking for diy rear rack build ideas.

Post by donn » Feb 01 2019 3:50pm

That's something to think about. It looks like 1/2" OD, which I can get from a nearby source for a little over $5/ft, with an inside diameter that's about 1/2 mm larger than Blackburn rack diameter - so I could saw apart factory racks, sleeve the parts into the tubing and solder/braze. Maybe. Another thing to experiment with. 8mm rod is 70% of the weight, and 20% of the cost.

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Re: Newbie looking for diy rear rack build ideas.

Post by alpharalpha » Feb 10 2019 8:17am

dustNbone wrote:
Jan 31 2019 10:03pm
I carried (and still occasionally do) a 16S A123 LiFoPo4 pack in an ammo box weighing about 23lbs on the Axiom Journey rack that was referenced above for a couple of years, along with large panniers that carry my groceries, camping gear, 30lb propane cylinder etc.

It's never shown any signs of fatigue, and the lateral movement even carrying near it's rated load is very minimal. I've hit a couple of wheel destroying potholes in that time, and the only part that seems to suffer is the lower mounting screws. I've never sheared one off, but have replaced them a couple of times to avoid it.

I'd say by far that is the weak link, the rack itself is extremely strong.
That does seem like a good rack, and affordable as well. I've thought the lower mounting screws would be a weak point; DogmanDan told me about grade 8 bolts, much stronger; I also use 2 locking nuts facing outwards, might have to use a dremel to file down the bolt head on the rear cassette side to clear the smallest cog.

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Re: Newbie looking for diy rear rack build ideas.

Post by Chalo » Feb 11 2019 12:30am

alpharalpha wrote:
Feb 10 2019 8:17am
I've thought the lower mounting screws would be a weak point; DogmanDan told me about grade 8 bolts, much stronger; I also use 2 locking nuts facing outwards,
If your frame has threads in the rack eyelets, they'll be metric-- M5x0.8 or M6x1.0. The metric equivalent of Grade 8 is Class 10.9. It's stamped on the screw head with numerals rather than hash marks like inch sized fasteners.
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Re: Newbie looking for diy rear rack build ideas.

Post by alpharalpha » Feb 11 2019 11:20am

Chalo wrote:
Feb 11 2019 12:30am
alpharalpha wrote:
Feb 10 2019 8:17am
I've thought the lower mounting screws would be a weak point; DogmanDan told me about grade 8 bolts, much stronger; I also use 2 locking nuts facing outwards,
If your frame has threads in the rack eyelets, they'll be metric-- M5x0.8 or M6x1.0. The metric equivalent of Grade 8 is Class 10.9. It's stamped on the screw head with numerals rather than hash marks like inch sized fasteners.
Got them quite awhile back, was going on memory; actually I ended up purchasing class 12.9 bolts and the nylon insert lock nuts say grade 8 but also state metric; am thinking seller just didn't convert to metric. They also go from using class 8 to grade 8 in the description. Looking again on the site, wondering if I could use Button Head Socket Caps Screws instead?
s-l300.jpg
s-l300.jpg (10.7 KiB) Viewed 437 times
Might not have to grind down the head like with these ones?
71tVjGhjIzL._AC._SR360,460.jpg
71tVjGhjIzL._AC._SR360,460.jpg (13.12 KiB) Viewed 429 times

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Re: Newbie looking for diy rear rack build ideas.

Post by alpharalpha » Feb 15 2019 12:07pm

Chalo wrote:
Jan 31 2019 1:00pm
In days of yore, I used a 30-something pound SLA pack on a Jandd Expedition rack and a 50-something pound SLA pack on a Blackburn Expedition rack. The Jandd rack had a bigger platform and thicker stays; the Blackburn rack had more numerous stays and better lateral bracing. Both of the racks survived to do other duty on other bikes, and both were pretty shaky when carrying hard mounted batteries on top. Most racks are plenty strong enough to carry the weight of a big battery pack, but lack the lateral stiffness to do it without wiggling from side to side. They're intended to carry big loads in soft bags, which supply damping and shock attenuation.

If you can break up your pack into halves, mounting them on the sides in panniers will make the bike ride better. No matter where you put the batteries, having some suspension for them (fabric bags on the sides, closed cell foam pad on the rack top, etc) will dramatically reduce the beating your rack takes.
There's a significant price difference between the Jandd Expedition and the Blackburn, do you think one is better than the other? I'd get the Tubus cargo but my pack is going to measure around 7"Wx13"L.

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Re: Newbie looking for diy rear rack build ideas.

Post by Chalo » Feb 15 2019 12:58pm

alpharalpha wrote:
Feb 15 2019 12:07pm
There's a significant price difference between the Jandd Expedition and the Blackburn, do you think one is better than the other? I'd get the Tubus cargo but my pack is going to measure around 7"Wx13"L.
The version of Blackburn's Expedition rack that I used has been out of production for almost 20 years now. And it had a top platform no bigger than the one on the Tubus Cargo.

If I were you, I'd use the Tubus rack and make sure to support the bottom of your battery with a thin piece of plywood, Sintra, G10 or the like. No bike rack is so flat and smooth on top as to make a good surface for a brick battery.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Newbie looking for diy rear rack build ideas.

Post by alpharalpha » Feb 15 2019 8:40pm

The Tubus Cargo is the one I want. The larger platform of the Jandd Expedition would fit my battery pack better, each of those 30ah prismatic cells are 4"wide, 2.3"deep so if the 12"x4.5" Cargo platform could support that big a battery pack with some plywood etc over it then that'd be my #1 choice; if not the Expedition with it's 16"x 6.5" platform.

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Re: Newbie looking for diy rear rack build ideas.

Post by donn » Feb 15 2019 9:41pm

Chalo wrote:
Feb 15 2019 12:58pm
and make sure to support the bottom of your battery with a thin piece of plywood, Sintra, G10 or the like.
A couple layers of fluted polypropylene from a yard sign might serve pretty well there - fair support and a little resilience, weighs nothing.

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Re: Newbie looking for diy rear rack build ideas.

Post by alpharalpha » Feb 20 2019 2:18pm

There's also my pannier hooks. Right now I put a piece of eva foam between the platform and battery pack to raise it up level to the pannier hooks. Maybe do that with the new one too, gives it the resilience you mentioned. For extending the rack platform, I don't care about the weight, it could be steel plate etc; I think the design of the tubus cargo is excellent, would like it or ideally the logo with a larger platform. Contacted Jandd about my concerns and they replied "Not a lot, we replaced 3-4 in the last 2 years and we have been making these for 25 years"

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