Part Failure: 3D Printed Titanium Handlebar at the Tokyo Olympics

Lot of power generated by some of these guys, this is pretty cool: https://youtu.be/S4O5voOCqAQ

tomjelly said:

Lot of power generated by some of these guys, this is pretty cool: https://youtu.be/S4O5voOCqAQ

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Bad setup - no fan to cool the rider? Sub-optimal bike layout (he looked somewhat constricted, should of had clipless pedals for more efficient stroke). And no idea of the efficiency of the generator/converter to toaster?

I bet with a more optimized setup he would have annihilated that bread...

Milland said:

Bad setup - no fan to cool the rider? Sub-optimal bike layout (he looked somewhat constricted, should of had clipless pedals for more efficient stroke). And no idea of the efficiency of the generator/converter to toaster?

I bet with a more optimized setup he would have annihilated that bread...

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Meh, only thing wrong with toe clips was comfort. He had dual straps so his feet were well connected.

Likely the design had a lot to do with it. Much easier to fabricate a design with high stress points using printing whereas handlebars made from drawn tubing or billet would be more consistent.

The failed component shown in the photo was paper thin.

Light = faster and in bicycle racing many components are designed to the point where they are much closer to failure points.

john.k said:

It looks like pumice,and has tensile strength equal to blackboard chalk.

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John surely you jest a bit. Like blackboard chalk?//-you may be exaggerating again. It is ok. John you are killing us with your outlook! I like you OZ fellows though a lot and your women even more! Not that they like me that much in return of which you guys can relate! They seem kinder than y’all deserve actually. Their accent is endearing and attractive when they flee to America. Who would expect such a exodus to this terrible place according to some leftists we read from here from OZ?

Not you as you just seem to be playing devils advocate a lot with the US. I have not heard you opposing us setting up the manufacture of the Nuclear submarines though. Does that make y’all good money? Will you not give away any intellectual property in the process?

You guys are living in a strange world. Denying how y’all really are how much can y’all actually mess up over there? Seriously? Like the titanium being like blackboard caulk a exaggeration . There are so many things printed which are just fine and including titanium.

Stop teasing us again John. You waiver back and forth on most things which makes many of us like you. Please be agreeable as it is workable with our shared values.

Milland said:

Bad setup - no fan to cool the rider? Sub-optimal bike layout (he looked somewhat constricted, should of had clipless pedals for more efficient stroke). And no idea of the efficiency of the generator/converter to toaster?

I bet with a more optimized setup he would have annihilated that bread...

Click to expand...

That particular machine was a common trainer for velodrome racing at the time when that demonstration was done (2015) . It was NOT the most sophisticated, but it was one of the few that was both adjustable (notice the stem height and extension are adjustable) and robust enough to withstand the arm reactions.

The cylist is pursuit sprinter Robert Förstemann, and the pictures are not wrong- he was a beast.

Clipless pedals, however, would NEVER have been able to withstand that loading. They're fine for touring and road race loading, but not secure enough for fixed-gear velodrome racing. If you have a foot come disengaged in a velodrome race, you are going down, and getting hurt... because it comes disengaged at a high speed, and high load, flying out-of-control either into your front wheel, back wheel, or your knee hits you in the chin. Watch olympic velodrome racing setup, you'll see that once the riders mount, two assistants support them, while the coach installs thick straps locking their feet down. Back when I rode, guys my size were set with TWO straps on each foot, just like Robert is in this video.

The one part that would have been more appropriate with loading, is the drive ratio. In a velo race, his pedal cadence would have been well above 180rpm. At the speed they've slowed him to on this trainer, he was pulled way out of his powerband. A modern electronic trainer would demonstrate better... because the velodrome cyclist's load increase is a function of wind resistance... higher physical output occurs because the aerodynamic drag of higher speed, is climbing- the only time a velodrome sprinter sees a high torque load at low speed, is when he's coming off a track-stand (stationary balance position) and accellerating to pace velocity. Every sprinter's power comes from going from 85rpm to 220rpm or so, and holding it just long enough to clear the finish marker. If they geared that 750w load for a 200rpm pedal cadence, he WOULD have had that bread on fire, as his peak power is up around 2200, with a 3 minute run over 1200w.

I had no doubt the cyclist was legit, you don't get thighs like that doing skateboarding. I do think the demonstration was pure BS, not just for the gearing reasons you point out, but for the fact that Mr. Förstemann didn't show the least bit of sweat dripping off during the "ride". I'm sure if he'd been given a proper chance and his choice of setup, some proper toast would have been made.

Going by the video, the time of exertion is roughly a minute. Going by this page, top sprinters can do about a kW for 30 seconds:

"If you fancy yourself as more of a sprinter than a climber, then German powerhouse André Greipel has been recorded to peak at more than 1,900W during a sprint and can hold an average in excess of 1,000W for 30 seconds."

How much better are pro cyclists? - watts per kg & power output | Cyclist

I bet with proper fitting/gearing and a fan that 700W could have been sustained for two minutes or more.

[I never had the lungs for any sort of racing, but when I was commuting by bike in the 80's and 90's I kept up a pretty high cadence for casual road use (80-100), thankfully showers were available at both ends]

It may not have been just material failure. The writer of the linked article speculates that the failure could be due to overtightening a fastener.

Yeah, the video as posted, has been shortened a bit... and it doesn't include the rest of the environment in that 'room'... IIRC they did that at a national sports medical / performance assessment location in Europe. I think his total run time on that dyno was about 2 minutes, and they DID have airflow in there, but he wasn't running long enough to get into a heavy perspiration state. Notice the walls- that's sound suppression to keep a dyno run from carrying into the adjoining rooms. The dynos I was one, all same scenario, and until the platforms (Frame, seat, handlebars, etc) were designed by actual riders, they were lousy. Some they put ME on, were nothing more than high-priced gym exercise bikes with a modified car-alternator as the variable load... they were basically 'brainless' in their ability to simulate a 'realistic' cycling load (meaning, a load profile that has rolling resistance, climbing incline load, and aerodynamic drag calculated and applied). Nowdays, a guy can do all of that with the same car alternator, an Arduino, and an old furnace blower.

I totally agree that if his gearing was better, he WOULD have had a much more successful 'pull', but one thing is certain- sprinters go WAY beyond their VO2 max... they HAVE to. In this demo, Robert never got there... he wasn't matched properly to the load... they bogged him down too low to give him a proper cardio-vascular load.

Fastener failure is certainly a possiblity... insufficient, or excess torque, a stress riser in just the right spot... too much loading... not enough meat in the design. There's a picture on the wall of a local pub here, of a dirt-track motorcyclist throttle-on in a curve, inside foot sliding, that says: "If you're in control... you're not trying hard enough"...

That pretty much sums it up. I'm glad the kid is okay.