Sunday, February 16, 2014

Making It Easier For Heavy People To Pedal Up Hills

In bicycle racing, big guys win the sprints on the flat because they have more power and the slight increase in rolling resistance from the extra weight doesn't use much power. The climbers however, are always tiny because human power output doesn't increase proportionally with weight even when the extra weight is all muscle. For many non racers that extra weight is mainly fat which is always a hindrance. They may be able stay with their colleagues on the flat but on a hill they'll be dropped. The usual (and best) strategy is to lose the fat but another solution is to use some assist to carry the extra load up the hill. People sometimes spend thousands of dollars to carry just one or two kilos less bicycle weight up hills and a little assist would be a cheaper alternative.

The goal is to make hills as easy to climb for heavy people as light people or alternatively to make hills less steep even to the point of requiring the same effort as riding on the flat. Say you weigh 90 kg but your riding colleagues way 70 kg and have expensive bikes that are 3 kg lighter. You want enough extra power to carry 23 kg up the hill so you can keep up with them. If you add enough power to carry your weight plus the bike weight, perhaps 12 kg, equating to 102 kg in the example case, then riding up a hill will feel the same as riding on the flat.

The extra power to achieve this is supplied by a motor and to know how much power to request from the motor requires knowing the weight of the rider, the weight of the bike, the speed of the bike and the grade of the hill. Three of these parameters are easily determined but the grade is more difficult.

Barometers can measure height change without calibration using the hypsometric equation. Constant temperature can be assumed to remove the need for a temperature sensor. This increases error but eliminates error due to inaccurate temperature sensing. Air temperature sensing is difficult because the sun can heat the sensor housing. A change in sunlight levels from cloud or sun direction as the bike changes direction can cause the housing to change temperature while external air temperature remains the same.

Measuring grade requires the change in pressure to measure the height change plus the distance travelled between pressure measurements to get the grade. This is how the IpBike app estimates grade. Normally distance is measured using wheel revolutions but I think it will use GPS distance in the absence of wheel sensors. So a barometer would do the job except that you need a reasonable height change which takes a while on a grade. This would mean no help from the motor at the start of the hill and extra motor power after the hill had already passed.

Alternatively an accelerometer can measure the grade with a fast response. This overcomes the problems of the barometer but introduces more. An accelerometer will respond to changes in speed as well as grade. Braking will look like descending and reduce assist and accelerating will increase assist which is  good because the motor will also compensate for the heavier rider during acceleration. Longitudinal vibration will be sensed and may require a little low pass filtering. A single axis accelerometer has to be aligned with the direction of motion and be perpendicular to gravity but this is not practical to do. The readings from a three axis accelerometer can be rotated to match this alignment:-

$$$$Acceleration_T = a(A_x- K_a)+b(A_y- K_b)+c(A_z- K_z)$$$$ where $$$$\text{Acceleration_T}\\$$$$ is acceleration in the direction of travel, $$$$\text{K_a, K_b and K_z}\\$$$$are accelerations due to gravity in the particular axis direction, $$$$\text{A_x, A_y and A_z}\\$$$$ are measured accelerations and $$$$\text{a, b and c}\\$$$$ are the components of a unit vector in the direction of travel in the coordinate system of the accelerometer.
$$$$\text{K_a, K_b and K_z}\\$$$$ are calculated as the average of a three axis accelerometer over a long enough period while riding. They can be calculated as a moving average over a period of minutes while travelling faster than 10 km/h but will gradually rotate when climbing a hill to match the grade.

Lifting the front of the bike while stationary so that it rotates through about 30-45 degrees and sampling the accelerometers will give a second vector. Taking the cross product of this and the gravity vector defines an axis about which the bicycle rotates when it climbs a hill. This measurement and calculation should only need to be done once as a slight change in sensor rotation about the bike's vertical axis will produce only a small error in the final result. Taking the cross product of the rotation axis with the gravitational vector gives a third vector normal to the other two and therefore in the direction of travel. The scaler components of this vector after normalising provides the values $$$$\text{a, b and c.}\\$$$$ Using Newtons second law, the force required to counteract this acceleration along the grade produced by gravity is:-
$$$$F= m \times Acceleration_T$$$$ where $$$$\text{m}\\$$$$ is the mass we wish the motor to carry up the hill and the power required to do it is calculated as $$$$Power = F \times Speed$$$$ Motor power controlled with this sensor would give immediate help at the start of a grade but in a long hill the power would fade over time.

The barometer is slow to respond but more accurate over time and the accelerometer that self calibrates is responsive but inaccurate over time. Fusing the two sensor outputs gives the best result and this can be done with a simple complementary filter or kalman filter . The assumption that the measurements are corrupted by stationary white noise produces a stationary kalman filter that is identical in form to the complementary filter according to a comparison of complementary and kalman filtering for combining measurements of vertical acceleration and barometric vertical velocity to obtain an estimate of vertical velocity.

In inertial measurement units gyroscopes are often used for sensing rotation but for this case do not add useful grade information.

Tuesday, February 11, 2014

What Killed Noelene and Yvana Bischoff?

Surely not food poisoning.

Following reports that an Australian woman Noelene Bischoff and her 14 year old daughter Yvana died in Bali after falling ill only hours after checking in to room 7 at the Padang Bai Resort, I was curious.

Food poisoning was suspected but I've frequently been ill after eating in Bali and couldn't imagine, not just one, but two people dying  from food poisoning within seven hours of becoming unwell? So I visited the Padang Bai Resort.

After first seeming to know nothing of the incident, as she'd been off that day, the lady on reception advised she was unaware which room they had become sick in. When asked specifically for room 7 she advised it was unavailable but we could have room 6. I'd already seen 7 was unoccupied but she said it was booked.

Padang Bai is a small harbour in Bali from which boats leave to neighbouring Lombok and which features diving, snorkeling and a modest coral reef.

Traders along the waterfront were confident that nothing bad had occurred in Padang Bai, suggesting the  Bischoffs had become ill elsewhere and merely arrived in Padang Bai before the effects became severe. They were also sure the fish served in Padang Bai was healthy as it was caught locally. In press reports the resort manager Mr Bareato had also said the resort buys fresh fish from local fishermen each day. The enthusiasm of locals to maintain the reputation of their community I've found common in Bali, as well as a tendency to blame Javanese when there is trouble. This attitude minimises robbery and violence, as mostly people are looking out for visitors which may in part, stem from recollections of economic devastation in the wake of the bombings. A terrible time for locals, but a period of heavily discounted abundance for visitors that weren't discouraged.

Twelve hours before their deaths, Sunshine Coast mum and daughter Noelene and Yvana Bischoff laughed and joked with waitstaff over a seafood lunch in Ubud and this meal was thought unlikely to have been related to their demise.

Just metres from room 7 is the Buddha Restaurant which the lady on reception had advised was a separate business to the hotel. It was here they ate dinner around 7 pm. So we tried it for lunch.

We asked the waiter about the Bischoffs but he knew nothing about the incident. The press reported the Bischoff's had ordered mahi mahi fish, chicken curry and vegetarian pizza. Just six and a half hours after the meal, Noelene was dead. It was the mahi mahi fish which doctors say is the main suspect.

A day later another Australian, Heath Barclay, fell ill five hours after eating a ham pizza. A Facebook friend mentioned the Bischoffs, "I then check the net and to my horror I had eaten at the same place and had fallen violently ill," Mr Barclay said. "With the police [crime scene] tape in full view of my room at the hotel it was a living hell – I thought I could be next." The 34-year-old plasterer rushed himself to a Denpasar hospital where he was put on an intravenous drip for nine hours. "I was blood tested and told I had severe dehydration and a bacterial infection from food," he said. "I don't really know what would have happened if I didn't go to hospital. If it was the same thing, I can't imagine how terrible it would have been for a 14-year-old girl." However, I can imagine his colleagues on the building site having fun comparing his reaction to that of a 14-year-old girl. Of course it wasn't "the same thing", just the usual unpleasantness of food poisoning combined with the uncertainty of where it originated when he, as I usually have done, ate in more than one place over the previous couple of days. However, it raised suspicions of the pizza and the cleanliness of the kitchen. I glanced in the kitchen and it looked spotless and better equipped than most Bali restaurants. I asked the chef about the Bischoffs but she said she knew nothing and had been rostered off that night. Most staff in Bali work punishing 10 - 12 hour shifts, six days a week so you can be pretty confident of meeting someone that works in a business by turning up at any random time. Padang Bai Resort seems far more generous with leave provisions than most or perhaps we were unlucky. Like Heath Barclay, so far we'd learned nothing more than what had been in the papers.

At lunch Jarrod, in the foreground, couldn't be persuaded from his perennial favourite, sweet and sour pork. Jenny, on the right ordered the vegetarian pizza, but it was only available after 6 pm. Not desiring chicken curry, she settled on leek and potato soup. I requested the mahi mahi (pictured below).

Jenny reported the soup tasted as good as it looked.

The mahi mahi was served with chips and a side salad. It too was lovely. Following a pleasant lunch we went snorkelling and sightseeing. There were no ill effects.

The sudden and mysterious death of two family members was undoubtedly distressing. ‘‘We want the truth,’’ the family spokesperson said. ‘‘We want to know if it was an accident, or if it wasn't an accident. Were they poisoned, or was it something else? ... "We’re worried that there will be a cover-up if the autopsy is done in Bali." Indonesian authorities respected the Bischoff family's request and allowed the bodies to be returned home for autopsy.

A colleague suggested it was probably medication administered in response to initial symptoms that was the culprit but we'd left Bali, none the wiser. Eventually the preliminary autopsy finding was that they died from a combination of food poisoning and existing medical conditions after they ate fish". It was reported that "Malcolm Bischoff, Noelene's brother, said it appeared they both suffered from scombroid food poisoning that, coupled with their asthma and, in Noelene's case, migraine medication had formed a fatal cocktail." My colleague hadn't got it quite right but it was a prescient observation.

Malcolm Bischoff stated "I'm sure we wouldn't have got that answer if the autopsies had been held over there [in Bali]" I'm not so sure, but the Indonesian authorities were wise because Malcolm would likely have been sceptical of the same findings from them. Having accepted the results, Malcolm said "scombroid food poisoning can result from eating spoiled fish, meaning the restaurant's preparation could have made no difference". This defence of the restaurant might be helpful as there was only one other patron having lunch when we were there. He hadn't heard of the Bischoffs and, better informed, some of my party would have preferred to eat elsewhere.

According to the Courier Mail, "scombroid food poisoning occurs when fish like tuna, mackerel, sardines and mahi mahi, is left in temperatures over 5 degrees. After the fish has died, naturally-occurring bacteria can then convert the amino acid histidine into the toxic histamine which can cause severe, allergy-like symptoms." Histamine is not destroyed by normal cooking temperatures, so even properly cooked fish can be affected.

While the autopsy is not yet finalised it seems that the Bischoffs were unlucky. The other people that ate the same fish included the resort manager Giovanni Bareato. They probably didn't have the complicating factors and scombroid concentration varies in different parts of the flesh.  None reported ill effect.

Despite the confidence of the traders that no one from Padang Bai was involved, it does implicate the fisherman who supplied the fish. Had the fish been refrigerated there would not have been scombroid and I'm surprised I've not seen this angle pursued. I don't know the practises in Padang Bai but I've seen fisherman elsewhere in Indonesia selling their daily catch straight from the boat without ice or refrigeration. Convincing fishermen of a need to change this practice is probably a difficult task but, as with Heath Barclay and the Bali bombings, human reaction to tragedy is rarely nuanced, tending to indifference or panic. I'm sure the traders of Padang Bai want to avoid the latter and another scombroid death might provoke it, even though motorbikes is the more common source of tragedy.

Thursday, February 6, 2014

Well it would be a secret if not for Google maps suggesting it as a route from Queanbeyan to Araluen.

Not far from Canberra in NSW, Australia is an intersection of Gumms road and Vernelli road. Gumms road is a through road but from Vernelli road it is disguised as a gated farm entrance. It is a region where it seems easy to imagine that intergenerational incest could remain hidden among the "smaller farms, used increasingly as hobby farms or boltholes for those on the fringes of society".

View Larger Map

Coming from Gumms road, turning right on Vernelli road takes you to Harold's Cross road but turning left is more interesting, the route of a songline. A songline is a path across the land originating from the dreamtime known only to insiders, usually Indigenous Australians of past generations. To outsiders they are invisible and in my youth I'd found the concept difficult to grasp. What I couldn't see, didn't seem real but nowadays I find it fascinating that what people see is hugely influenced by their frame of reference. Traditional songlines are recorded in song and markings, noticeable only by the group, but modern day songlines, also  known only by insiders are recorded in apps like Strava and Google maps. They exist only within a context, can be overlapping and may have no physical indicators.

A GPS track along the almost secret 7 km section of Vernelli road. There are two wadable water crossings, numerous gates and some steep sections.

Turning left, the dirt road with many gates services only three houses. Vernelli road becomes impassable to normal vehicles as it approaches the  third house, 1.1 km from Gumms road. It is a lovely house, off the grid and secluded by trees just above Bourkes creek. It's as hidden as it is possible for a house to be and was only visible looking backward from the creek. Beyond the creek there is only some wheel ruts and after a while they fade as well. I was here on a bicycle, fortunately mountain style, because Google maps had suggested it as a route from Queanbeyan to Araluen.

However, without the GPS tracking live on a map as I rode I wouldn't have believed it was a road or been able to follow it. On the ground there is sometimes no indication which way to travel, though in places there is cuttings and grade smoothing, indicating it has been a substantial road in the past and in others there is a few metres of  trees separating the road from surrounding paddocks. These are the physical evidence confirming this songline, recorded in cyberspace.

A view down Vernelli road which passes between the trees in the centre of the image. It is taken from the location indicated in the GPS track image above. Grass growing in the wheel tracks indicates the absence of regular traffic.

There are two Strava sections labelled Vernelli (Road/Rd) Climb. The most popular with 20 riders starts in Gumms road, turns right into Vernelli Road and provides a route to Cooma road that is more substantial but longer than the route I followed which Strava records just 3 riders traversing. Without any physical evidence, an observer without Strava  would have no idea this songline exists, yet the creator (not me) and a few insiders know I'm the king of this mountain, probably the only one I'll ever rule.  These insiders can form a whole community that is invisible to non members. Another cyclist is recorded  coming this way, travelling from Wollongong to Melbourne in another instantiation of modern songlines; cycling routes. Perhaps Vernelli road also follows an Aboriginal songline as; being a short route meandering along ridge lines to the Shoalhaven river, it fits many of the criteria.

If you're passing through then Vernelli road, down to Cooma road, is an interesting path which you would never find without becoming an insider but for those on their own, don't get injured as it might be weeks before another insider comes by.