Guni 36er Riders (and anyone else): Maneuver Analysis Request

General
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Since I’ve never ridden with brakes and I don’t have time to keep my finger on the pulse of everything happening in the world of unicycling, I was quite surprised and excited to see the braking maneuvers in this video:

When Martin enters the frame of the video (see first photo below or refer to the video at 4:48), he’s already braking significantly and he has got his unicycle frame pretty far back. Also note that his pedals are about even, with the right pedal in front.

Looking at the last visible frame of Martin’s first extreme braking maneuver, you can see that his unicycle frame is now further back still and his pedals are about halfway between even and vertical. Just during the visible portion of this braking maneuver, it looks like Martin completed about one and a quarter revolutions and traveled nearly 11.8 feet in distance.

Given that Martin started braking before he entered the frame of the video, what’s your best estimate/guess as to the total distance of his first braking maneuver shown in the video?

How fast would you estimate/guess he was travelling when he initiated braking?

I think there is a possibility that Martin may have fallen off his unicycle as he approached or reached zero km/h since he edited to the next scene before showing a return to an upright position. If I pulled off such a maneuver, I would want to capture it in its entirety. It is still quite impressive, nonetheless.

How many riders would you estimate/guess are capable of this level of aggressive braking?

Martin CHARRIER - RIDE EVERYWHERE-1
Martin CHARRIER - RIDE EVERYWHERE-11455×818 167 KB

Martin CHARRIER - RIDE EVERYWHERE-2
Martin CHARRIER - RIDE EVERYWHERE-21454×819 213 KB

WARNING: I AM ABOUT TO START BABBLING ABOUT AVIATION – STOP HERE IF YOU’RE NOT INTERESTED.

Some of you may have read about previous aviation analogies I have made with unicycling. Well, here comes another one! :astonished_face:

What really fascinates me about this type of aggressive braking maneuver is that it reminds me of a quick stop maneuver in a helicopter. It seem both maneuvers could potentially be used if and when finding oneself in a dire situation where there are few good options IF you recognize your predicament in time. Also, in a helicopter, the perfect timing of inputs for several coupled controls (collective, cyclic, pedals and throttle) is required in order to pull off the maneuver properly. On a unicycle, it seems a similar dynamic is at play.

If you have any interest in seeing a helicopter pilot performing quick stop maneuvers, you can check out these videos:

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That is some mighty braking! :collision: I can’t say for sure how fast he was going when he started braking; what I’m interested in is the g’s he experienced when stopping :distorted_face:

I like to think I can lean back quite a bit when I’m braking hard, though I don’t think I lean back nearly as much as him in the video

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You’d feel that the next morning :sad_but_relieved_face:

I think he stayed on but the punched in shot was too tight hence the change to another stop. He probably started braking after he’s entered as he’s not back far enough to stay on at that point.

This is something I’d love to learn but self preservation prevents me from trying…

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I think many road and muni riders can do this kind of braking, maybe not all with this kind of amplitude though.

I used to play quite a lot with that, but I have stopped during last unicons after bending one of the arms of my brand new flansberrium muni… It was not that much, but, after removing the wheel, it could not be put back in place (and since then, @jaco_flans does thermal treatments on all his aluminium frames to reduce the risks).

It is actually fairly easy once you know how to do a “break coast” stop. You just have to start braking, lean backwards, and brake harder and harder until you reach full stop. The harder part is getting back up and keeping on riding.

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Hello guys,

I was told about this chat on my video haha. To give my own answer, I would say I was going at around 30 kph, and the total braking distance was about 8 m, with effective hard braking over about 3–4 m, the rest being just rolling or applying slight pressure on the pads.

I can confirm that it can be learned naturally with practice, including keeping the right amount of energy to get back to vertical at the zero-speed point. This is similar to what we do when running and stopping, although it looks more natural and stable on legs, and at lower speed.

The g-forces are fine for any part of the body, even the next morning :wink:

I like the comparison with the helicopter. Personally, I’ve always thought that their cousins, autogyros, look like flying unicycles because of their maneuverability.

Wow sorry for your frame Aurelien… :confused:

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It went back to Canada with Jakob, and I’ve got it a few weeks later, fixed and with heat treatment, so no big deal.

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OK, for anyone interested in g forces when stopping, a bit of high school physics…

Acceleration can be calculated from initial speed and distance.

Assume constant acceleration a m/s^2, for s meters distance, from a speed of v m/s.

a = -v^2 / 2s

v = 30kph / 3.6 = 8.33 m/s approximately and s = 8m

so, a = -8.33^2 / 16 = -4.34 m/s^2 approximately (assuming constant over 8m)

but if speed was almost zero after 3.5m, deceleration would be just more than 1g

and at 1g, the reverse “lean-back” angle would be 45 degrees

I know, completely pointless math drivel, but very nicely controlled braking, and a very nice and inspiring video overall!

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Great to see you back here and thanks for answering my questions! I very much appreciate it.

Gyroplanes were the first type of powered aircraft I ever flew! I have a passion for both helicopters and gyroplanes… and hang gliders (which are the first type of unpowered aircraft I flew, at the age of 12), but I think helicopters have the most in common with unicycles. While gyroplanes are quite maneuverable, they cannot hover (which would be analogous to idling on a unicycle), though they can remain still over a fixed point on the ground when pointed into a sufficient headwind. Also, helicopters can move in forward, backward, and side to side directions, while autogyros are limited to forward flight (other than drifting backwards due to a strong wind). Of course, conventional unicycles can only roll forward and backward. Crab unicycles, on the other hand, can roll sideways, but can’t roll forward or backward.

I had assumed that saving enough energy to get back to vertical would be a vital component to this kind of braking. This is yet another aspect of the maneuver that has many similarities to both hang gliding (especially flare timing when landing) and flying helicopters (specifically energy management during autorotations). Really cool stuff!

By the way, your video was incredible! Amazing riding, incredible scenery, phenomenal editing, and a fantastic score. It felt like a real cinematic experience!

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In the Ride the Lobster era, Chuck Edwall, then the fastest unicyclist in the world, had a video where he demonstrated a quick stop from full speed in one wheel revolution. I can’t find it now but it was a similar technique.

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Wow, that sounds incredible! I would really enjoy seeing that video. Was Chuck’s one revolution stop from full speed on a guni 36er or a standard 36er?

If you ever come across a link you can share or are able to somehow facilitate getting that video uploaded, it would be most appreciated.

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OK, let’s have a look at Chuck’s possible speed:

v = sqrt (2 * s * k * g), v being the speed before braking in m/s.
s is 36in wheel rolling circumference = 2.8m;
k is coefficient of friction of tire on asphalt = 0.9 (at best);
g is acceleration due to gravity = 9.8m/s^2.
So v = sqrt (2*2.8*0.9*9.8) = 7.03m/s^2 = 25.3kph.

It looks like Chuck was not at his top speed when performing his one revolution stop, unless he had some magic tire or did some strange pre-stop-jumping force multiplying trick.

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I’d be very interested to know where you’re getting this number from.

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If you type “road friction coefficient data” into Bing or Google, you get:
“.. Typical Values - Dry asphalt: μ ≈ 0.7–0.9, Wet asphalt: μ ≈ 0.4–0.6 ..” from Bing
and " Road friction coefficients Define tire-road grip, ranging from approximately 0.8–0.9 for dry asphalt to below 0.2 for ice .." from Google search.
If you look for a research paper in Google Scholar with that search you get a huge number of results, but they are typically trying to estimate the friction (often on wet roads) for anti-lock braking systems and autonomous vehicles.
Bicycle tires are not going to be as good as hot racing car tires which may have a friction coefficient of just a little bit more that 1.0.
Sadly, it looks to be hard to find actual authenticated data for real world bicycle tires.

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Surely the contact area plays a massive part here (which will increase under heavy braking), and that appears to be not being considered at all?

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It actually has basically no effect (when there is no gravel).

A surface in contact with another one can hold a horizontal force equal to the horizontal pressure it can hold multiplied by its surface. The horizontal pressure holdable is equal to the vertical pressure multiplied by a coefficient (here 0.9). And the vertical pressure is equal to the vertical force applied divided by the surface.

If you factor everything, you get Fv = Pv x S x k = Fv / S x S x k = Fv x k

Since the vertical force is always the weight of the rider multiplied by g, the acceleration is the weight of the rider multiplied by g and by k (the factor of adherence). So, with k = 0.9, it is impossible to decelerate faster than 0.9 g, and the tire surface has no effect.

That is NOT true when there is gravel involved, because you don’t get only slippage anymore, but also “surface sheering” I have no idea if it is the right word when the gravel on surface starts moving. It is also true when there are really high forces applied (such as with racing cars).

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Well, the surface area matters because it affects k. Surface area for a unicycle tire is more or less weight / tire pressure, so say, 180 pounds / 30 psi = 6 square inches. At 60psi the contact patch would be half the size. The relationship to k isn’t linear, but that’s why you get better traction with lower pressure (probably due to tire deformation to fit surface imperfections).

(It would hurt my brain to do that calc in metric units, sorry).

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Im not into all this math stuff, but the reason to hang back with a chopper is because the propellers are then in backward position, kinda like pulling the helicopter backwards which is a great braking maneuver, but a unicycle doesnt have such a component. There the reason to hang back is because otherwise the frame will fly forward at heavy braking, so you hang back to compensate for that.
Though the braking seems similar, Id say the reasoning behind it is very different.
I do wish Id be able to brake like that on my uni’s but I dont ride that fast and I just as easily hop off the front. My main 36” speed is only 17-18 kph. Im just a leisure rider.

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What you are referring to as “propellers” are called rotors on a helicopter. Helicopters don’t have propellers, but gyroplanes do (they have a rotor for lift and a propeller for thrust). Helicopters utilize their rotors for both lift and thrust.

When I said “it reminds me of a quick stop maneuver in a helicopter,” I did not intend to imply that the reason the aggressive braking maneuver on a unicycle reminds me of a quick stop maneuver in a helicopter is because of the physics related to how they slow down. Unicycles and helicopters clearly have very different dynamics when it comes to the types of forces used for braking and deceleration/stopping. The reason I made the comparison is because of:

(1) the visual similarity.

(2) the requirement to carefully modulate precise control inputs in order to successfully pull off the maneuver and (on a unicycle) ride out of it or (in a helicopter) fly out of it (without losing or gaining altitude). Both maneuvers also require energy management.

However, in a helicopter, things are a lot more complicated due to cross-coupled controls. When you gently pull aft on the cyclic to initiate the flare, you also need to lower the collective and reduce power by just the right amount to prevent the helicopter from ballooning up or dropping down. When you reduce power, you are reducing torque, so you also need to simultaneously add just the right amount of right pedal input (on American helicopters because their rotors spin counterclockwise) in order to prevent the helicopter from yawing to the left. On a European helicopter, it would be a left pedal input (because their rotors spin clockwise) in order to prevent the helicopter from yawing to the right. If you end the maneuver in a hover (rather than flying away), you then have to raise the collective (which increases the pitch angle of the rotor blades) and increase throttle (because hovering requires far more power than flying), as well as initiating a corresponding left pedal input to counteract the torque reaction.

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oh boy why did I have to start that discussion. Yeah rotors, I hadn’t thought of the right term. I have never flown either helicopter or airplane. But thanks for your explanation.

Now I wonder how it would be if I could tie a rotor to my back and occasionally lift off the ground while riding my 36". :slight_smile:

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Haha, starting such a discussion with an aviation guy is like opening Pandora’s Box!

Actually, there have been pilots who have flown foot-launched (unpowered) gyrogliders, which look like a rotor connected to a simple frame. That would probably be the closest thing to tying a rotor to your back. To launch you’re going to need a relative wind of about 20mph. Thus, if you could hold the frame of your gyroglider while riding down a slope on your 36er on a day with a decent headwind, you could surely lift of the ground and fly away. Landing your 36er gyroglider will be a bit tricky, but not necessarily impossible.

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