Building a compact cargo bike

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Building a compact cargo bike

Postby IdleMind » Wed Jan 27, 2016 10:52 am

I recently started seriously thinking about building a small cargo bike, mostly because of what I've seen on this forum. So I've been working on a design for a few weeks and thought before I get far into building I would post and see if anyone finds any major flaws. Here is a 3D CAD image and a 2D CAD drawing with some dimensions. I will be building soon and will post my slow progress.

I have built bikes before, but I am far from an expert at knowing the intricacies of bicycle design. This will have 20 inch wheels and a low powered front hub with top speed around 18 mph.

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Re: Building a compact cargo bike

Postby Drunkskunk » Wed Jan 27, 2016 11:36 am

Nice design!
You'll have a much smoother ride if you move the pivot points. On the rear, you can move that pivot point all the way up near the crank. Long arm suspensions ride much smoother since the angle of the motor changes much less through the same amount of suspension travel. Same idea in the front, if you move the pivot point back, you can get a much smoother ride.

I'm curious about why you chose a dual shock setup front and rear?
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Re: Building a compact cargo bike

Postby cwah » Wed Jan 27, 2016 2:30 pm

Needs more space for batteries and accept proper suspension
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Re: Building a compact cargo bike

Postby IdleMind » Wed Jan 27, 2016 4:12 pm

Those are good suggestions. I make the swing arm stays from 3/4 tubes. I weld plugs in the pivot end and then drill & tap them on an old lathe. The lathe can take up to 3/4 dia thru the spindle so that limits the tube size. If I made the swing arm longer then it woul reduce it's torsional stifness, so that is why I don't want to make it longer. Also I ride roads and paved bike trails so I don't need long suspension travel. There will be stops to limit wheel travel to 2.0 inch and it will have a fairly stiff springs so it seldom bottoms out.

I would prefer longer swing arm length on the front. I made compromises to get the spring leverage to wheel leverage so I could use springs that I have and get the spring rates that I wanted.

The battery box shown is 5.6" wide by 4.1" high by 15.3" long and can be built up with 10s15p 18650 cells

I have a similar leading link front suspension on my recumbent and it works great. Conventional is not always superior.
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Re: Building a compact cargo bike

Postby Lurkin » Wed Jan 27, 2016 4:16 pm

cwah wrote:Needs more space for batteries and accept proper suspension


The entire front triangle is begging to be used for battery capacity.

What exactly do you mean by "proper" suspension? The fork setup seems an odd choice given the price and availability of off the shelf fork suspension. I suspect this design has been used for strength rather than travel.

Whats the plan with the carry capacity? it it to have a bucket on top of the rear rack, or are you planning to use panniers off it?
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Re: Building a compact cargo bike

Postby Drunkskunk » Wed Jan 27, 2016 4:33 pm

I really like the front fork. For a front hub motor, that's a great idea. I think it solves the weakness of the Monarch Springer design with that lower hoop. If it works out, you might have a marketable front suspension for hub motors.
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Re: Building a compact cargo bike

Postby Jonathan in Hiram » Wed Jan 27, 2016 5:28 pm

The cargo rack is a little higher than it strictly needs to be, lower would be a bit better.

With that high top tube getting on and off with the rack loaded where you can't swing your leg over it is going to be a bit awkward depending on how old/agile you are. A mixte type of frame in the front would give you a lower top tube.

Like your front suspension design and the frame generally looks pretty stiff for predictable handling.
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Re: Building a compact cargo bike

Postby Deafcat » Wed Jan 27, 2016 5:28 pm

roads and paved trails... why any suspension at all? at least settle for hard tail.... i dunno... maybe my opinion is irrelevant as I only build rigid frame bikes :P

(but I wouldn't use any suspension unless the terrain requires it)
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Re: Building a compact cargo bike

Postby IdleMind » Wed Jan 27, 2016 6:46 pm

Thanks for the comments, they are helpful. I originally planned on just having a carrying rack with the option of setting a box on it, that's why it's so wide. But maybe paniers would would be a good idea, I will consider making the rack as narrow as the battery. And maybe the top tube is a bit too high, I will look into that.

The cargo rack is 26" from gound, I need room for suspension travel and a fender, I will take another look at that too.

The drawing shows the trail being 2.92", I thought I might get a comment or recommendation on trail. It seems too much to me, but that's about what I use on recumbents with good results.
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Re: Building a compact cargo bike

Postby Jonathan in Hiram » Wed Jan 27, 2016 11:53 pm

Long with a lot of trail and not too much steering axis inclination will make it stable which is a good thing for a cargo bike particularly when you are loaded.

What I've noticed playing around with different bikes and motorcycles over the years is that the inclination of the steering axis tends to affect low speed stability the most and the trail is more about high speed stability.
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Re: Building a compact cargo bike

Postby Lurkin » Thu Jan 28, 2016 12:30 am

Deafcat wrote:roads and paved trails... why any suspension at all? at least settle for hard tail.... i dunno... maybe my opinion is irrelevant as I only build rigid frame bikes :P

(but I wouldn't use any suspension unless the terrain requires it)


there are plenty of rigid cargo bikes for sale. suspension makes this one unusual and of interest. The main issue I have with using a trailer is that there is no suspension softening bumps to the load or me.
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Re: Building a compact cargo bike

Postby amberwolf » Thu Jan 28, 2016 3:00 am

Deafcat wrote:roads and paved trails... why any suspension at all? at least settle for hard tail.... i dunno... maybe my opinion is irrelevant as I only build rigid frame bikes :P

(but I wouldn't use any suspension unless the terrain requires it)

Heavy load, one pothole you can't avoid (or can't see under the puddle in the rain) and byebye wheel.

A good enough wheel might not actually break, but it can certainly be damaged, and enough of those kind of hits could break it. I haven't broken the one on CrazyBIke2 *yet* but I've dented it in the latter instance with no real load, and if I had had a heavy load on it, I don't know exactly how bad it could've been.

I've also dented the same good rim type on a different wheel on SB Cruiser, hitting a curb edge.

It's possible that if I had had enough suspension travel neither would've been damaged. It's also possible it wouldn't've made much or any difference. ;)
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Re: Building a compact cargo bike

Postby cwah » Thu Jan 28, 2016 3:06 am

Lurkin wrote:What exactly do you mean by "proper" suspension? The fork setup seems an odd choice given the price and availability of off the shelf fork suspension. I suspect this design has been used for strength rather than travel.

Whats the plan with the carry capacity? it it to have a bucket on top of the rear rack, or are you planning to use panniers off it?


Suspensions that are commonly used like the mountain bike ones!

Battery should be on the frame so that rear can maximize carrrying capacity.

And side loader like the xtracycle would be good too
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Re: Building a compact cargo bike

Postby dogman dan » Thu Jan 28, 2016 6:46 am

I think in general, it's a really good design. I might mount the rear shocks a tad more vertically, but other wise it mostly looks real good.

since I greatly prefer a rear motor now, I'd make it rear motor drive. And then use a regular front shock. I'd shorten the headset tube to the same 5" or so length common on MTB's to allow more shock choices. This will also lower the top bar some in the process.

Carry the first battery in the triangle, still plenty of room for a nice triangle bag or box. Then the second battery if needed in the rear trunk.

My last two longtails have been no rear shocks. One has no shocks at all. This works fine with a long enough bike. The shorter the bike, the more it will need that rear shock. Similarly, the heavier you load it, the more it needs that rear shock.
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Re: Building a compact cargo bike

Postby Jonathan in Hiram » Thu Jan 28, 2016 8:46 am

I get the impression the OP is designing around parts he already has, has the front shocks but no suspension fork, he might already have the front motor. Tubing is pretty cheap, building the fork if you already have the shocks would be cheaper than buying.

Thanks to fairly severe financial limitations from medical debt that's the way I have to do things, scrounge the parts as cheaply as possible and then design around what I have on hand.

Not to mention I can't tell you how many times over the years I have gone into making something, plan it around a certain set of parts and then find out one or more of them is unobtainium for some reason. For instance Grin had the Phaserunner controller listed as being available at the beginning of the year for about three months and I held off buying anything else because that's what I wanted.. Now I think it's listed as coming in March or later, if I had known that I wouldn't have bothered waiting.
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Re: Building a compact cargo bike

Postby IdleMind » Thu Jan 28, 2016 9:39 am

The bike in my avatar has the same type of front suspension as this and I like it a lot, and it works good with a small front hub motor. The rear springs are positioned to be in a direct load path to the top tube and the leverage to the pivot point is about right for some springs that I have.

I will be decommisioning a trike and my Walmart bike to use some of the parts. One of those parts being a 3 spd coaster brake hub which has perfect gear spacing when set up for 18 mph top speed. The front motor allows more options for a rear hub.

I should have called this a utility bike because I don't expect to be carrying a lot weight on a regular basis. I will be using it as a winter bike because I don't like riding a recumbent in the winter. And for making trips to stores.

I built the rear swing arm a few days ago and will post photos soon. But still working on design changes so it will be a few days before I can start the frame.
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Re: Building a compact cargo bike

Postby IdleMind » Thu Jan 28, 2016 7:24 pm

A few days ago I started making the rear swing arm. That comes first because I need the pivot hub before I can make the frame. I have also started making parts for the spring assemblies. But most of my time is spent making design chamges to the frame. Your comments are making me reconsider and it will take some time to get things worked out. Here's some photos of how I make a swing arm.

First I make a hub with bosses with 3/8 tapped holes in each end.
Image
Them make chain stays with 3/8 tapped hole in one end and fit the tubes using a board to help with allignment for welding.
Image
Then I make 3/16 thick drop outs and weld into notched tubes.
Image
Kind of crude, but it works and its a start
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Re: Building a compact cargo bike

Postby macribs » Thu Jan 28, 2016 10:52 pm

Looking forward to watching your project evolve. Like the drawings a lot. Full suspension, neat!
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Re: Building a compact cargo bike

Postby dogman dan » Fri Jan 29, 2016 7:36 am

Looking a lot better than I could do. Explain about how your pivot works. It almost looks to me like just some eyebolts pivoting on a bolt screwed into the center piece. Is it just that simple?

How does that get lubed? Is there a bushing in there or something I don't see? Cheap walmart bikes just pivot on a plastic bushing, no lube.
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Re: Building a compact cargo bike

Postby Jonathan in Hiram » Fri Jan 29, 2016 8:03 am

Dan, you might be interested in how I made a swingarm pivot out of two old bike steering tubes and head bearings. The pinch clamps are made from tubing and 1/4-20 coupling nuts for threaded rod, they will be brazed to the frame when I get the rest of it made. I'm way too focused to take pictures while I'm working so I don't have any "during" pics..

This is for a project I'm working on now, I still have to add the shock mount but that will be part of the final fitting so I get everything lined up just right. Mostly I don't jig stuff up but tack it together and then bend/twist it to alignment, put a few more tacks, check for straightness again and adjust if necessary and then do the final fillet braze.

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Re: Building a compact cargo bike

Postby LI-ghtcycle » Fri Jan 29, 2016 9:26 am

*** edit *** working now.. Windows 10 glitch maybe ...
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Re: Building a compact cargo bike

Postby IdleMind » Fri Jan 29, 2016 10:32 am

Dogman, those are called Heim Joints, some guys call them rod end bearings, I bet you've seen them before. It's like a small ball joint, these are cheap ones but they work well for this. You can get better ones that have grease fittings, but I just put a few drops of oil on them once or twice a year.

I am sorry for any problems with the pictures, anyone know anything about why this might be.
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Re: Building a compact cargo bike

Postby dogman dan » Sat Jan 30, 2016 6:58 am

Oh right, tie rods. Thought it had to be something better than a simple eye bolt. Thanks for the explanation. Looks great!

Jonathan, that looks like a good idea too. One I have thought about also, is converting a square taper bottom bracket to a pivot.

What I really wish, is that the motorcycle junkyard still existed. It was a great resource back in the 80's. Buying a cheap pit bike frame just for the pivot has crossed my mind.
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Re: Building a compact cargo bike

Postby IdleMind » Sat Jan 30, 2016 9:23 am

You guys had some good sugestions, here's a revised side view.
--I shortened the head tube and lowered the top tube, it improves the structure and looks better
--You don't see it in the side view, but the carrying rack is narrower for better use of paniers
--I decided to use the same battery as for my recumbent, it's a different shape so it loads from the side instead of the back
--I lengthed the wheelbase 1" in the back to make just enough space for the battery

The changes in the back have had a bad affect on frame strength. The original version had a straight line load path from the axle to intersect of seat and top tubes. Now the battery is right where there ought te be a strucural member. At some point I may add an additional strengthening tube.

Anyway, I will be starting on the frame today.
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Re: Building a compact cargo bike

Postby craiggor » Sat Jan 30, 2016 10:29 am

Some people say motorcycles have telescopic forks because they look good.Earls forks are proper suspension.
uploadfromtaptalk1454167529174.jpg
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found these on bent rider-can any one identify this recumbent thread.sorry for bad pic.it won't load on to my tablet.Rubber Moulton style suspension could be changed for mountain bike shocks.
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