How to: compute Watts and Calories for for a bicycle, up a hill

In summary, the conversation discusses the difficulties the speaker is facing in trying to compute Watts and Calories while riding at any measured angle, using a BS2p basic stamp with various sensors and a math coprocessor. The equations being used involve factors such as mass, pedal speed, gear ratio, pedal crank length, front tire circumference, and rolling resistance. The speaker also mentions the lack of a direct conversion between Watts and Calories and suggests using potential energy as a rough estimate for Calories burned while going up a hill.
  • #1
wmazz
14
0
At 6'5", 300 lbs. and old as dirt, I am a walking and rolling testimate to F=ma. This part of my project is difficult for me, because I have never taken a physics class. All the examples I have in books and PF, deal mostly with force moving down a hill. I am trying to compute Watts and Calories, while riding at any measured angle.

I am using a BS2p basic stamp reading an 2 axis accelerometer, 2 hall sensors and a gear tooth sensor. A math coprocessor handles the math. With my current set-up the BS2p determines what gear I am in, at any time, or if I am coasting. Every calculation is started after the front wheel completes a rotation, but I have no idea if it is accurate.

Watts = ma*gr*pcl*s*sin(theta) + Rr (so long as theta is never zero) If theta = 0, then Watts = ma*gr*pcl + Rr

Calories = watts*0.2388459


m = Mass = 145kg
a = Pedal Speed = 22pi/9 rad/sec
gr = Gear Ratio = 44 : 18 (2.44 to 1) (This is gear ratio I use the most)
pcl = Pedal Crank Length = .175m
s = Front tire circumference = 2.2m
Rr = Rolling Resistance ??

I left gravity out, because I felt it would be part of Rolling resistance. Once the initial equation is working I figured on gathering Rr by comparing computed and measured data

thanks

Bill M.
 
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  • #2
There isn't a conversion between Calories and watts. Watts is power, Calories are energy. You want to know a rough estimate of how many Calories you burn going up a hill? Just find the potential energy from the change in height: m*g*h. This will be in joules though so you will have to convert to Calories which is 4184 J/Cal. So:

145 kg * 9.806 m/s^2 * h (m) / 4184 J/Cal = 0.34 Cal/m * h (m)

This value is going to be less than your actual work done due to the losses in the system, but it could be used as a sanity check for the equations that you have been trying to work with.
 
  • #3


I would first commend you on your determination and ingenuity in creating a setup to measure your power output while riding a bicycle. It is important to note that your equation for Watts and Calories is correct, but it is missing a few key components that will affect its accuracy.

Firstly, as you mentioned, gravity should not be left out of the equation. It is a crucial factor in calculating the power required to ride up a hill. The term "ma" in your equation should be replaced with "mg", where g is the acceleration due to gravity (approximately 9.8 m/s^2). This will give you the force required to overcome gravity while riding up the hill.

Secondly, your equation for Watts also needs to consider the efficiency of your body and the bicycle in converting energy into motion. This is represented by the term "eff" and is typically around 20-25% for cycling. So your final equation for Watts would be:

Watts = mg*gr*pcl*s*sin(theta)*eff + Rr

As for the term Rr, it represents the rolling resistance of the bicycle and is affected by various factors such as tire pressure, road surface, and bearing friction. It can be difficult to accurately measure, so it is common to use an average value for Rr based on the type of surface you are riding on. A rough estimate for Rr on a paved road would be around 0.01-0.02.

Once you have all the correct components in your equation, you can then use it to calculate the power output (in Watts) required for riding up a hill at a given angle. To convert this to Calories, you can use the conversion factor of 0.2388459 as you mentioned.

I would also recommend gathering data from your setup and comparing it with the calculated values to ensure accuracy. You can also make adjustments to your efficiency factor if needed to better reflect your own body's efficiency.

Overall, your approach to calculating Watts and Calories for riding up a hill is sound, but it is important to consider all the factors involved to ensure accuracy. Good luck with your project!
 

1. How do I calculate the watts needed to ride a bicycle up a hill?

To calculate the watts needed to ride a bicycle up a hill, you will need to know the grade of the hill (in percentage), your body weight, and the weight of the bicycle. Then, you can use the following formula: Watts = (body weight + bike weight) x (grade/100) x speed (meters per second). This will give you the minimum watts needed to maintain a constant speed up the hill.

2. What is the difference between watts and calories when riding a bicycle?

Watts and calories are two different units of measurement. Watts measure power, which is the rate at which energy is being expended. Calories measure energy, which is the amount of work that can be done by a certain amount of energy. In cycling, watts are used to measure the power output, while calories are used to measure the energy expended.

3. How do I convert watts to calories when cycling?

To convert watts to calories, you can use the following formula: Calories = watts x time (in hours) x 3.6. This formula assumes that the cyclist has a 100% efficiency rating. If you want a more accurate conversion, you can use a power meter that takes into account your individual efficiency rating.

4. How can I increase my watts and calorie burn when cycling up a hill?

To increase your watts and calorie burn when cycling up a hill, you can try interval training. This involves alternating between high-intensity efforts and recovery periods. You can also try incorporating strength training into your routine to improve your power output. Additionally, make sure you are using proper gear ratios and maintaining a good cadence (around 80-100 revolutions per minute) to optimize your efficiency.

5. Is there a maximum number of watts or calories that can be achieved when cycling up a hill?

There is no specific maximum number of watts or calories that can be achieved when cycling up a hill. It depends on the individual's physical abilities and the difficulty of the hill. However, it is important to listen to your body and not push yourself beyond your limits to avoid injury or exhaustion.

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