I have been sitting on the fence about Luke Isman’s pedicab.  I did not really want to become involved with the brew-ha-ha that was going on especially after I immersed myself in the Seattle accident that resulted in the death of Peter Dzioba.  I had blogged enough about pedicab controversies for a while.

I am just now getting around to looking at the engineering analysis that Luke produced to justify his pedicabs construction method.  Unfortunately he only looked at the strength of the materials, but did nothing to actually understand or explain the loads being applied to his contraption.

I do not think that this picture is up to date, as Luke claims to have welded many of the joints in the area around his trailer arm.  None the less, the configuration of the arm is basically the same.  And in this case welding may have made things worse, as it makes it harder to replace damaged members.

Luke has not consider modes of failure.  The most highly stressed, least supported area of his pedicab looks to be at the intersection of the upper horizontal boom and the vertical member that it bolts to.  The strength of this joint is dependent on the bolts that hold it together keeping all the members in compression.  Over time, the significant forces being applied to this joint by the 2 foot or longer lever arm are going to cause deformation of the overlapping tubes.  This will tend to cause the bolts to loosen and slop and play to be introduced into his hitch arm.  Slop and play in these joint areas will result in sudden peak forces being applied to the grade 5 bolts that he has chosen and the tubes that they hold together.  These sudden and jarring peak loads will further cause more sudden and rapid deformation of the tubes resulting in bending of the upper horizontal beam, crushing of the middle reinforcement tube, and deformation of the holes that the bolts pass through.  All of this is going to cause much greater stresses to be applied to the bolts holing this joint together.  Eventually some thing will give way.

When the hitch arm on his pedicab breaks, it is most likely to happen when it is under highest stress.  Typically this would be while carrying passengers.  Depending on whether his passengers weight is in front of or behind the trailer’s axles, the cab will flip backwards or drop forward.  In either case his customers are apt to hit the back of their head on concrete at a high rate of speed, or bust out some teeth as they are thrown forward  due to sudden deceleration.

One would expect that a diligent person operating a pedicab built in this way would notice this happening and take care to tighten the bolts, and if needed replaced the deformed tubes in this area.  Unfortunately history has shown us that not every pedicab operator is as diligent as they should be.  Not every pedicab driver will carry necessary tools with them at all times to be able to repair and maintain their cab.   I will save the details of my experience, but surprisingly few of the pedicab riders in Austin know how and when to properly maintain their machines.  Worst of all, Luke has spoken about building several of these machines to be sold and operated by people less familiar than he is with the limitations of grid beam construction.

While the materials that Luke chose may be plenty strong to build a pedicab, the industrial designer,  structural engineer, manufacturing engineer, product safety review team, not to mention the ergonomics and product liability consultants all fell down on the job.  In that this is a complete “DIY” job, those critical tasks are ones that Luke has left incomplete.  If I had a child I would be afraid for his or her safety on this thing.  Most obvious to me this is because of all of the sharp edges.  Sharp edges can make an otherwise normal bump in to an accident where blood is lost and people need stitches.

To quote from Lukes’s website: “I also don’t want to hear about liability.  Halliburton doesn’t worry about it, so why should we?”

Does Luke really want to be as bad as Halliburton?  What would Ralph Nader say to Luke?

I did not come to these conclusions by myself.  I have collected several of the comments that people have posted to Luke’s DIY Pedicab Saga and else where.

-Ken Cameron

_________________________________

Posted by: on September 1, 2008 at 1:14 PM

Death cab alright
I don’t know why you can’t get the point of that “Death Cab” joke. Your cab obviously looks dangerous to some people. As you pointed out they DON’T have a problem with home-made stuff, but the examples you showed all looked professional and yes, SAFE. Yours could be nicknamed “The Mangler”. I’d be worried to lose a limb in that thing if you went off a curb or something. Come on you’ve got tape covering the sharp edges, it looks like something made in Junkyard Wars in 30 minutes. You have the skills, why don’t you just weld something with nice smooth edges and try submitting that. I bet they’d approve it. The inspector obviously doesn’t want something scary looking going around town making other people doubt he’s doing his job. The last thing he wants is complaints from “concerned citizens”. Have a little pride in your work man.

Posted by: dan on September 1, 2008 at 1:15 PM

Have you looked into insurance for this thing? I can’t even imagine a reputable company insuring a vehicle like that for public transportation for many of the same reasons the city of Austin will not pass inspection on that thing (and probably more). Irregardless of how good of a job you personally feel you did assembling this thing, you need to prove that it is, in fact safe to carry passengers on. Pages of data sheets about the bolts you used and pictures of other odd DIY projects built with similar materials doesn’t really cut it…

Posted by: on September 1, 2008 at 1:31 PM

Dude, quit arguing and hire an engineer to look over your design. We may be budding engineers, but we aren’t experienced.

The design document lists the materials and their strengths, but does not account for multiplication of forces such as in simple machines like levers. Looking at your homebrew bicycle trailer, it appears you have bolts connected to the ends of the square tubing rods, thus you have levers.

There are many other things to consider that may become safety hazards, but only an experienced engineer could tell you what those are. This thing may be ready to ride around your backyard, but not for making a profit.

    Posted by: vivi on September 1, 2008 at 2:56 PM

I see several problems with your design.

First, the perforated tubing. These are designed to build static structures and not vehicles. No info is provided on impact resistance, and strength when bolted.

Second, the structure itself. everything is at square angles, which is dangerous (you seem to have covered the extremities with inner tubes fragments just to pass the regulations, not to actually protect the passengers and other road users), and weak structurally.

Third, the link between the bike and the seats is highly unstable. If you lean a little on the road, the weight of the trailer will pull you to the ground. Does it even qualify as a pedicab ? Looks like a simple trailer to me, but I’m not familiar with US regulations.

Fourth, do you really expect pad brakes on the bike (no brakes on the trailer form what I can see on the photos) to be able to stop your trailer with 2 people on it ? Think about braking while turning. Think about rain.

Fifth, the ¯| _ shaped structure. All the force is supported by a tiny surface of metal between the bolt and the inside of the perforations. It will fail quickly.

Sixth, your calculations are correct mathematically but do not make sense from an engineering point of view :
- Structural steel, page 7 : you assume yield strength is equal to joint strength. These are entirely different things. Surface of contact is not like continuous material.
- Bolts, page 8 : Each bolt is capable of 5580 lbs of shear strength. OK, but what does it say about the strength of the structure ? Nothing. From your photos it looks like the ¯| _ shaped structure is bolted about 10% from one end, which would create a x10 lever effect. Meaning only a 558 lbs-equivalent force on one end would break the bolt. And the tubing is probably weaker.
- Comparing the pure strength and thickness of steel used by other manufacturers does not make sense. The way steel is used is at least as important.
- On several instances you make a confusion between moment and movement, which illustrate your lack of knowledge in this matter.
- Etc.

In the current state, it is just normal for your design to be rejected.

Posted by: worn on September 1, 2008 at 3:23 PM

Yer contraption jes ain’t safe
Or - God forbid - he rear end a car, causing the ¯| _ arm to fail at the joints and causing the passenger section to ultimately flip forward in a pole-vault kind of motion when that strut digs into the pavement. Or worse, think 40’s cars and their ‘impaler’ steering columns: the possibility of sending a nice piece of perforated steel tubing plunging backwards at chest/throat of an unsuspecting rider.

Also: notice the bar before and slightly above the passenger foot rest on the commercial models? That to keep someone’s foot from inadvertently sliding forward off the rest and risk getting caught between the pavement and the pedicab frame. With your design such a thing could certainly result in a snapped ankle, which from a customer experience point of view, would tend to put a real damper on repeat business.

As a lot of other folks have already said, dude, you’re really gonna need a welded frame. I imagine it will be rather difficult to get permitted otherwise.

Best of luck.

Posted by: DrStrangegun on September 1, 2008 at 7:14 PM

I opened the PDF, and assuming your calculations are correct abut the shear on the bolts… you’re going to exceed it handily the first time you hit something with the bike. Everything looks ok except for the gooseneck, and that… you have bolts in shear at the end of VERY long levers, and even if the bolts don’t get sliced right in two they will slowly hog the holes out; and the offset mounting method you’ve uses adds a torsional load to boot, which square tube absolutely *sucks* at.

You may not think you’re wrong, but you need to step out of the ego cloud and take a very, *very* close look at what you’ve got here. Hell, test it even: Mount two spars of grid together the same way and length you have there, mount one end vertically, and stand (you probably won’t even need to jump) on the other end. Oh, and be prepared to catch yourself on somethign.

Posted by: stunmonkey on September 1, 2008 at 8:19 PM

Seriously, listen to what people are saying here.

As an engineer, I wouldn’t pass this thing either based on its massive number, scale, and obviousness of both structural and life/safety deficiencies and clear lack of its builders grasp of fundamental design theory. Just a few of the most basic problems have already been pointed out above quite well already by other engineers quite clearly, so I won’t bother to rehash them, only to second the analysis of the above posters.

More importantly, even were it to be perfectly structurally sound, I >still< wouldn’t pass it simply due to its appearance. Sad fact of life, if it LOOKS like a liability issue, its actually a real liability issue, reality be damned. Show a picture of that to a jury of Joe Normals, and all the expert testimony in the world isn’t going to sway them that the city was negligent (ie: liable) in allowing it on the road. The city, and any PE signing off on it both have very deep pockets so you know any attorney worth his beans would try to drag them into any suit related to this contraption, justified or not.
Image problems do have unfortunate real-life consequences even if they ideally shouldn’t.

That and no passenger would ride in it, So the business plan is a big fail as well. You obviously have drive, so put some craftsmanship into it. Make something BETTER, lighter, sexier, or in any other was quantifiably superior to the commercial crap out there. THAT is what DIY is all about. If you can;t be bothered to do that, just give up and get a commercial bike.

Posted by: on September 1, 2008 at 9:17 PM

I’m a mechanical design engineer, I’ve built bikes, I’ve taught welding; I think I’m qualified to comment on your project. I’ve built and ridden on things like your pedicab. They’re a lot of fun. I’ve never asked anyone to ride on them, they volunteered. I’ve never sought certification for them.

What you have is a crude prototype and a pdf. What you don’t have is a product on which you can build a company. You don’t have an analysis of the system, but a back of the envelope calculation of a couple parameters, nor do you have any testing that says that your pedicab is roadworthy. The discussion in your pdf displays a shocking degree of arrogance and little understanding of what an inspector would be looking for - it inspires no faith in the inspector that your project is safe and should be approved.

What you don’t have is an understanding of what you are doing. Are you trying to start a pedicab business, manufacture pedicabs, or design pedicabs? Those are three very different businesses.

(I also have to say, buying a welder without learning how to weld properly and safely is not a good idea. Galvanized steel is deadly to weld.)

How much have you tested this thing anyway? Riding it around is not testing. Strapping a couple hundred pounds in it and running into a wall at speed is testing. Hard corners on wet surfaces, dry surfaces, and wet-dry surfaces is testing it. How harsh should testing be? Look at it this way, if you run into the back of some car, and a passenger is impaled on a sawed off piece of strut, how is that going to play out? Frankly, if you haven’t broken it, you haven’t tested it.

Building good stuff is hard, really hard. But there’s not a maker who’s advancing the field who hasn’t put in their dues. You build it, you test it, you break it, you fix it, lather, rinse repeat. After a dozen iterations, you’ll start to see why experts are expert, why authorities deserve respect.

Posted by: No Name on September 1, 2008 at 11:00 PM

# DIYers much smarter than I are developing important products, and early versions won’t always look pretty.

Every company that develops through prototypes makes ugly early versions. The difference between you and them is that their early versions are prototypes that don’t get into production. They are tested, improved and scrapped before the final production version is ready.

That contraption you have built looks dangerous and uncomfortable to ride in. Do you have a 90 degree angle between seat and back rest? The bike will be unsafe to operate with two adults on the trailer. During a turn the trailer will push your bike over, because the hinge is located so high above the ground. Take a look at some commercial bike trailers (big and small) and copy the good features. Put the hinge near the rear axle of the bike and you will greatly increase stability. You will also be able to remove the two weak points from the shaft (the 90 degree angles).

Get a bike with disc brakes. Discs work better when wet and can handle higher loads than rim brakes. Rim brakes are notoriously lousy when wet.

What you’ve got now is a hack. With the help you’ve been given, you must turn it into a prototype and then into the final pedicab you are going to present to the city officials. You still have a long way to go. Scrapping this hack is not time wasted. It is time spent learning. If you go on pushing this hack to the city officials you will only waste time. Stop wasting time and go back to learning stuff.

Posted by: BobD on September 2, 2008 at 2:13 AM

stress and strain
How many strain gages have you bonded to that thing? Who did the vibrational analysis? How long before that structural steel street sign post material fatigues? Under normal dynamic loads and vibration levels, how long before those bolts come loose? How long before they wear through?

If you can’t answer these questions, you need to start thinking about why that is.

I reviewed your documents and they are far from an engineering analysis. An engineering analysis is generally done by a qualified engineer. I can see the amount of effort you’ve put into this, and I commend you for it, but you need to do it right. Use your whole ass, as they say (don’t do it half assed), and talk to an engineering services firm. You’ll pay out the nose for it, but you’ll get it done right.

Posted by: on September 2, 2008 at 6:08 AM

I hate to say this, but that is a prototype for an uncontrollable trailer, not a pedicab. When this story first started, I figured you had something that was a real pedi-cab (welded steel tube frame, common axle with a disk brake on the trailer, tail-lights & turn signals, “doubler” chain ring, etc.), not a lashed-up structural collapse accident looking for a place to happen.

Just from a general safety viewpoint, here’s some things that just jump to mind:
- No brakes on the trailer body.
- Static loading tube.
- Lash-up with bolts at 90 degree angles.
- Attaches to your seat post?
- Lights & Reflectors?

Make: You wasted how much bandwidth on this guy?

Posted by: Pete on September 2, 2008 at 5:22 PM

Correcting you’re “engineering” isn’t even worth my time. Your shear strength estimates are off for starters (yes that’s what efunda says but you’re using it wrong). When you know what you did wrong, go ahead and post again. But until then stay off the streets and stay off MAKE. I used to really love this site.

Posted by: meh on September 2, 2008 at 8:44 PM

After watching this guy wield a sawzall to make a “chicken tractor” I do hope that he gets some serious training before playing with serious tools. Make friends with the engineering dept at your local 4-year university and have a bunch of smart students come up with a design that they think is safe. They can give the design to 3rd world countries to fab up for their local use, and you can use the design to run your pedalcab business.

Get some good tools, good materials, and good training. Then start building. Otherwise, you might want to re-evaluate the reasons why all of the commercially available pedalcabs are so expensive.

Posted by: Nathan on September 3, 2008 at 8:56 AM

“this was meant to show I’d put at least a little thought into the strength of the cab.”

A little thought is not going to get it certified. The public and the government need indisputable proof to show that it is safe and strong and will not fail during normal use. A little thought is exactly the recipe for disaster that can get you, the city, and whoever else involved sued, particularly in such a litigation-happy world.

And please stop posting these until you get a design that is:

a) Safe
b) Professional
c) Certified

Posted by: Bob D on August 30, 2008 at 11:23 AM

uhm…
The inspector would be a complete and total fool to sign off on your designs if they were not stamped by an engineer. Get your designs professionally documented, put in front of a PE, and get the stamp. This will involve a good amount of work, solid modeling, stress analysis, fatigue testing, and so on. You aren’t special, (well, I think you are :)) so you need to conform to the same set of rigid standards that every other manufacturer has to, especially when people’s health, safety, and lives are at stake.

-Bob

    Posted by: Roadkill Pedicab on August 30, 2008 at 12:29 PM

From a pedicabber :
in my opinion, your cab is not safe and the city’s just doing their job.
I own a pedicab company here in town, Roadkill. I am not your competition - I am one of your pedicabbing peers, and I am in the same boat as you when it comes to having the responsibility to make this safe for customers. As I posted on the comments section of your youtube video, there is an increasing awareness on the part of this city as to the safety standards of pedicabs as their numbers grow and they become a larger part of the transportation equation for urban areas. This is in large part to due the recent fatal accident in Seattle, which generated huge debate in this industry because of the questionable streetworthiness of the vehicle involved, most specifically , were it’s brakes good enough ( no, they weren’t, is the popular opinion of most informed about the industry ) Your vehicle doesn’t even HAVE brakes, does it? As this industry (pedicabbing) evolves, safety standards will be reevaluated with an eye towards erring on the side of safety, and that’s something that I personally agree with. A DIY project may be fine for you, but when you invite the public to ride in your contraption, on the roads, in traffic, for profit, it does indeed become of interest to regulating authorities.
So while you may wish to inject this with a dramatic storyline of David Vs Goliath or the little man Vs the city, unfortunately for you that’s not the issue. The issue is safety. I’m not sure you could find an accredited engineer to “stamp” it. That means they stand behind it, in their professional opinion, it is safe, correct? Good luck with that.
And nobody likes having a camera sprung on them. It implies that you are trying to record them doing something wrong. Might work if they were wrong about your cab…but they’re not…

    Posted by: macetech.com on August 30, 2008 at 4:22 PM

Is the point of posting this here to stir up some kind of grassroots movement? I think the plans, or even just photos, of your vehicle should be available before anyone decides to jump on your human-powered bandwagon. The last few seconds of grainy video above is the first time I’ve seen this conveyance.

And it’s pretty frightening. Pedicabs I’ve seen not only appear to have stronger rear wheels, but they are built with a welded frame that would appear to be much lighter than your cab. Also, I’m not seeing the cable that leads from your bike, to the rear brakes. ARE there brakes on that trailer? Do you seriously expect normal road-bike caliper brakes and a tiny road-bike contact patch to reliably stop the vehicle when loaded with passengers? There’s also the fact that this is a trailer mounted on the back of a normal bike. Actual pedicabs are a large tricycle. They have a more stable three-point stance, while your vehicle is susceptible to jackknifing.

In any case, here’s one engineer who wouldn’t stamp this with approval. Maybe you’ve actually covered all of the above concerns, and in person the vehicle shows more thought for safety. I’d say to get the engineer inspection set up, but should have been after your first visit. Four times? You know what they say about trying the same thing repeatedly and expecting different results….

Posted by: deputydawg on September 15, 2008 at 10:39 AM

I hope everyone reads my input! I may be saving a life! Looking at the design from the standpoint of an engineer and certified welder this model fails miserably. No engineer or welder would put his stamp of approval on it. The industry standard for bikes as well as pedicabs has always been reenforced steel tubing with MIG/TIG welds since the beginning of time. Never seen a bike constructed of Telespar perforated tubing. Nor a trailer. Reason? It is used for sign posts because it “breaks away” on impact!

note these specifications: The reason is simple.

The Telespar system was engineered specifically
for sign-support use, then perfected with the help of traffic-control professionals.

B R E A K AWAY
A N C H O R
A two-piece breakaway system is easily created by
adding a 12 gauge outer sleeve of the next larger size tube to the original anchor base. This additional
sleeve, approximately 18″ long, provides a double wall thickness to accomplish the breakaway function.

SLIP BASE
BREAKAWAY SYSTEM
AASHTO standards for structural supports of highway signs require the “change of velocity standards for 1800 pound vehicles” be met. The Slip Base meets those requirements as put forth in the NCHRP-350 report as the post will break off.

Today most vehicles weigh more than 1800 lbs! So if you get hit from any direction your pedicab will shatter and just blow apart and more than likely someone will be seriously injured, if not killed. There is not any vehicle made using this material and to do so is, well just dumb! All manufacturers of pedicabs follow the standard use of steel tubing with their units as well as the hitch. The only nuts and bolts found on these are for the wheels and hitches. It’s common sense that bolts loosen, and crack or just break on force. And Telespar? Well read the specs as listed above . . .if it was safe would the industry not be using it???

your prototype itself is all wrong as far as design and balance as well as the safety aspect. Not to say it looks like a giant erector set! Expect to bottom out or flip. And just blow apart! This pedicab is an accident looking to happen, and it will over time. Best to use it at home or just park it and not risk injury to another!

I suggest maybe you take a class in design, engineering and welding and buy a welder and the proper materials. You would be wise to scrap this project and just start over or hire someone who knows what their doing. I feel pretty strong that your insurance company is not aware of the materials you used as they would never cover a vehicle used for public transportation made with Telespar. It’s cheap because its only used by highway departments in the erection of sign posts! You said you doubled it??? One peice inside the other??? That only makes the breakaway that much quicker.

It is my understanding that you have recently received your permit. I hope all the other pedicabbers read this and pass it on to their peers, friends, family and fares. I am sending a report in to the proper authorities whom I feel were badgered into giving you your license to kill.

Re: [pedicab] Re: video, blog by DIY pedicabber
Fri Sep 12, 2008 10:18 pm
Ohhh Gunn…….

Anyway, I do have one positive thing to say about this guy after
digging through everything he’s blogged or posted. That is- first, if
he put as much energy into building a decent trailer as he put into
building that crap and fighting for it, he’d probably have a nice cab!
Secondly, I wish I still had that youthfull exuberance!!!

Now to point out his flaw and throw a wrench in his spokes, pun
Intended!!!

If any of you dug into his report and saw the part where he qualifies
his design because of shear strength and surface contact etc. , vs.
welded joints and surface contact. Well read it, it’s good. Honestly
it took me a little bit, ok 5 min, to figure out why he was wrong. At
first it almost made sense!! Yikes!! I knew it couldn’t be but he did
a lot of math! And I respect numbers. However, knowing it couldn’t
possibly be, that his bolted together theory is stronger than a welded
4130 chro-mo joint, I figured out his flaw. Pretty simple actually.
Ashamed it took me more than 30 seconds to figure out. His connections
are not bonded by the entire surface are in which they connect and
overlap. Just go read it…. So one of the numbers in his equation are
false. His actual surface area for the equation should be the surface
area under the head of his nut and bolt. Which, BTW, are grade 5. Come
on. Grade 8 isn’t that much more. Regardless. His claim is that he’s
got about 2 square inches of connection of so. Where as he’s really
only got maybe 1/8″ of contact area in his connections.

Again, I’ve lost the exuberance that would allow me to do the math
here. But my limited knowledge of math and engineering tell me he’s
got somewhere around 3000lbs of shear strength. Multiply that by the
leverage and stress loads on a given joint and I’m honestly amazed
it’s able to hold itself together!

Sad thing is he rode my cabs for some time. So he knows the
difference. I’m just wondering if he’s not a little mentally unstable?
Not being rude here. Just seems like a logical conclusion. Someone
that puts that much energy into this, as he has, and comes up with
that, must have some “grade 5 bolts” loose???

Gary Geske
PedalTek LLC
602-348-9699
www.pedaltek.com