RaceDroid -- free dynamometer runs, of a sort

[moto]

This is my report on DynaRoid Pro, the software dynamometer I have now given up on. I wonder if anyone on the site has had better experiences with it or a similar program. My intention was to get objective data on the change in performance I could feel when I added the OEM velocity stacks to my VHB30 carbs, on my T3.

To begin, since F = ma (force = mass times acceleration) and since we have accelerometers in our phones, it is no big step to suppose we could use them, along with information on the mass (or weight) of our motorcycles to calculate torque, a force, while accelerating. That would amount to a dynamometer of a sort. In practice, one would have to add corrections for wind resistance, at least, to get a useful torque curve.

RaceDroid is a free Android app that implements these ideas. (I have RaceDroid Pro, which may have cost me 3 or 4 dollars last year.) Here are examples of the two graphs the program provides for every run, in this case for a run last October to somewhere around 7000 rpm (this was before I got rid of my old tach with the bouncing needle). (You'll have to click to see enough detail, in another window.)





The graph on the right is the usual torque and horsepower display, by rpm. The one on the right shows the underlying acceleration values (meters per second squared), along with power, speed, and distance, this time showing seconds on the x axis instead of rpm. These are nice looking graphs, and people report good results using them.

There are some things to keep in mind, though. This program does not measure rpm at all; its only inputs are acceleration values and time (at least in the basic configuration I used for this run). The rpm scale is set by the user's input of a value for "rpm at maximum engine speed." The rest of the scale is set by the program's requirement that each run must start at 0 mph, which it enforces by requiring one to stop the engine and motorcycle before each run. The program also ignores any changes of gear during the run. This means that only the segment of graph corresponding to the highest gear that was used will be of interest. In these graphs that was 3rd gear, engaged somewhere over 3000 rpm, as can be seen by the big dip in the power curve during the shift.

The program does ask for more information, including the total mass of the vehicle and rider. I weighed my motorcycle (with half a tank of gas), my saddlebag contents, my own riding gear, and myself, all separately, using my digital bathroom scale. (I weighed the motorcycle separately at the front and back wheels.) This is an important measurement that has a proportional effect on the measured torque (and horsepower) since F = ma, and weight stands in for mass. If one gains, say, 5 pounds, one can find that out on the bathroom scale and adjust the total weight in the program to keep measurements comparable across time. Similarly, since gasoline weighs 6 pounds per U.S. gallon, and since my T3 holds something like 6.3 gallons, a full tank of gas weighs about 20 more pounds than a half tank, so the program should be informed of such a big difference.

Also required are the frontal area of the vehicle with rider, the coefficient of drag, and the percent power loss in the drive train. All these can be best guesses, but should be kept unchanged from session to session for comparability. Wind resistance corrections using the first two values are what account for the difference between the raw acceleration values (the blue curve) in the right-hand graph and the calculated torque values (the green curve) in the left-hand graph. Changing the declared power loss percentage makes obvious changes in the calculated torque values; the torque and horsepower curves are estimated values at the engine, obtained from rear wheel measurements.

Instead of relying on the phone's accelerometer, the program can be configured to use the phone's GPS, an external bluetooth GPS, or OBD2 via bluetooth.

Obviously, this is all subject to a good deal of error, especially with inappropriate values of the parameters just described. However, there are many reports by happy users.

I found however that I could not get satisfactory repetitions of the same curve measured under the same conditions. Here are two sets of three measurements in 2nd gear, to 6750 rpm, the first without the velocity stack and the second with it.




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I also tried using the phone's GPS as the input, instead of the accelerometer, but its values are only updated about once a second, so the graphs are worse than the ones based on the accelerometer. I purchased a Dual Electronics XGPS150A Multipurpose Portable Universal Bluetooth GPS Receiver with Wide Area Augmentation System device on a whim, hoping to get better graphs. This prompted a Wikipedia visit where I learned something new: the Wide Area Augmentation System is pretty cool. This unit can produce 4 readings per second, of much greater positional accuracy than the phone's GPS. However, while struggling with how to set it up to connect to my Android phone I came to a realization, namely, that I have spent way too much time on this project. Back it goes to Amazon.

The RaceDroid Pro program has a lousy user interface, which its developers proudly admit. They say they are engineers, not marketing experts. I think there is potential in this product for a rider who is interested in improving performance and is willing to take the time to learn the program and also how to control the testing conditions. It would be a good idea to get a more expensive, higher frequency, version of the GPS/WAAS unit, called the XGPS160, about $170. That one produces 10 readings per second, with a positional accuracy on the order of a meter, and should be able to produce much better curves.

However, I am not that rider. I was motivated more by curiosity, which I have pretty much satisfied. Another point came to mind: if you need a device to detect a performance change then it really wasn't much of a change in the first place. I can detect the difference made by the OEM velocity stack in the seat of my pants. That should be enough.

Has anyone else had good or bad experiences with programs like this?

Moto

[Huzo]

I love this stuff, just a couple of things…

Work done = force x distance
Power        = force x distance/time
Force         = mass x accelleration

If you put your bike over 400 metres and get a time, you can use S = a x t squared/2 and transpose for “a”
This reveals  a = 2 S/t squared

A 400 metre time of say 13 seconds would give you 800/169 = 4.7 m/sec squared

Now you have a figure for acceleration, you can go back and use force x distance/time

Since force = mass x acceleration
We can say
Power = mass x acceleration x distance/time

If your test mass (bike and rider) is say 80 kg + 220 kg = 300 kg  (for example)

We can say…
Power (Watts) = 300 x 4.7 x 400 / 13 = 43,385 watts = 43.3 kW

If you want horsepower, you divide by 0.746 which equals 58 hp

Now of course all this is very good if you need a number as your figure, but would you just be better to make your change then go for another thrash….?

[moto]

You are solving for a constant acceleration value, but gasoline engines have different rates of acceleration at different RPMs. That's what the torque and power curves show, and that's what's usually of interest. Your solution might be of more interest for an electric motor that produces constant torque.

You are also disregarding wind resistance, and making a calculation that might be suitable for a vacuum. The developers of RaceDroid did take wind resistance into account. You can tell this from the fact that the acceleration curve and the torque curve differ. Acceleration tapers off as the speed goes up because of wind resistance, in part. The formula used in the program back-calculates the implied torque after wind resistance is accounted for. The torque curve and the acceleration curve therefore increasingly differ as speed goes up.

All that said, your calculation is still very nice.

Moto

[Huzo]

You are solving for a constant acceleration value, but gasoline engines have different rates of acceleration at different RPMs. That's what the torque and power curves show, and that's what's usually of interest. Your solution might be of more interest for an electric motor that produces constant torque.

You are also disregarding wind resistance, and making a calculation that might be suitable for a vacuum. The developers of RaceDroid did take wind resistance into account. You can tell this from the fact that the acceleration curve and the torque curve differ. Acceleration tapers off as the speed goes up because of wind resistance, in part. The formula used in the program back-calculates the implied torque after wind resistance is accounted for. The torque curve and the acceleration curve therefore increasingly differ as speed goes up.

All that said, your calculation is still very nice.

Moto

Indeed and that had not eluded me, but the air density will not significantly alter, mechanical losses will remain constant and the relationship of drag with velocity squared will not disobey Newton.
Suffice to say.
When looking for a change in power, all will be revealed in how long it takes to do a SS 400 metres. Simply timing it will be ok, but working out the number is fun too.
You are of course correct in your assertion that the constant torque of the electric motor is more suitable for my calculations, but it’s a nice exercise.

[moto]

...
Suffice to say.
When looking for a change in power, all will be revealed in how long it takes to do a SS 400 metres. Simply timing it will be ok, but working out the number is fun too....

No, it won't. Some changes will increase power at low RPM and reduce it at higher RPM. In fact, that's the kind of thing I might go for. A single number like a quarter mile time can't reveal this sort of thing. But you're welcome to your opinion!

[Huzo]

No, it won't. Some changes will increase power at low RPM and reduce it at higher RPM. In fact, that's the kind of thing I might go for. A single number like a quarter mile time can't reveal this sort of thing. But you're welcome to your opinion!

Yes ok, agreed.
My point was/is, that having the torque x rpm (power) revealed in a print out as the revs rise, cannot be bettered.
You may indeed stack more torque into the lower range and take some from higher up or vice versa. But if you achieve the same SS400 metre time, then work done in a unit time is the same and therefore according to Isaac, so is the power figure.
You have moved a given mass, a given distance, in the same time.
If you can manipulate the characteristics somewhat to alter the delivery to your liking, then there is no disagreement.

[Tkelly]

I don’t understand any of this stuff but what did you find out about the t3 horsepower?Come to the Wonewoc rally Saturday morning and ride with us to see JoeBlocks motorcycle collection in Yuba.We leave at 10.Folks would like to see your bike.

[paul in rochester]

My favorite statement:
"Another point came to mind: if you need a device to detect a performance change then it really wasn't much of a change in the first place."

Wisdom.

[elrealistico]

Seems like the best use of the hp/torque to me, that's wat it's all for innit?

I don’t understand any of this stuff but what did you find out about the t3 horsepower?Come to the Wonewoc rally Saturday morning and ride with us to see JoeBlocks motorcycle collection in Yuba.We leave at 10.Folks would like to see your bike.

[guzzisteve]

You know what's going to happen? Some one will put their bike on a treadmill so it has drag. Coming soon on Utube.

[moto]

I don’t understand any of this stuff but what did you find out about the t3 horsepower?Come to the Wonewoc rally Saturday morning and ride with us to see JoeBlocks motorcycle collection in Yuba.We leave at 10.Folks would like to see your bike.

I plan to arrive Friday and may leave Saturday: The Wisconsin Moto Guzzi Riders already cashed my check! I will be avoiding crowded indoor settings, but would like at least to ride along to Yuba. Looking forward to meeting many and seeing their bikes!

As for what I learned about the T3's horsepower. I didn't find out the numerical value of its peak horsepower because the program depended on some imprecise guesses I made for certain settings (frontal area, coefficient of drag, percent drive line power loss) and because the results varied so much between runs.

The results from the program are hard to evaluate. One big problem is deciding where the peak rpm is on the graph. The program relies on the user to input a maximum rpm value, which can be adjusted after the run. So my choice affects the rpm labeling on the x axis. The developers say the graphs show an artificial drop off near peak rpm because of the moving average algorithm used to smooth the values. It is not really possible to detect the moment I cut the throttle (at a known rpm) by looking at the graph. Better internal processing of the recorded data could detect a sharp throttle cutoff and display that on the graph, allowing me to adjust the x axis scale fairly precisely.

In general, the graphs show my T3 has a dip in the torque curve between 4 and 5 thousand rpm, which accounts for my perception of a rush in power above 5 thousand. The bike pulls strongly up above 6500 rpm, but this does not always show up clearly in the graphs. Seat of the pants, having calibrated my tachometer, I can report the acceleration rush feels quite nice up to about 7000.

In short, the RaceDroid program tells me little I can't feel with my pants, but using it has made me more attentive to the torque curve in the higher rpms. My experiments in repeatedly running the bike up to near its redline have given me more appreciation of its nicely balanced performance in stock tune. (I even run the stock 120 main jets.) This is not a bike to short-shift.

I think RaceDroid is a pretty good effort that could have been better. But I don't think the developers are actively pursuing improvements now.

[moto]

Yes ok, agreed.
My point was/is, that having the torque x rpm (power) revealed in a print out as the revs rise, cannot be bettered.
You may indeed stack more torque into the lower range and take some from higher up or vice versa. But if you achieve the same SS400 metre time, then work done in a unit time is the same and therefore according to Isaac, so is the power figure.
You have moved a given mass, a given distance, in the same time.
If you can manipulate the characteristics somewhat to alter the delivery to your liking, then there is no disagreement.

I have trouble understanding your second sentence, in light of your previous emphasis on quarter-mile times. Or 400-meter times, if you will.

As for the rest, I don't understand why you are appealing to Newton. The mathematical definitions of work, and its derived quantity power, post-date Newton, I understand. I haven't read all of Principia myself, and never will, but leafing through my copy I see no reference to work or power. Work and power are applications of the Newtonian concepts of force, mass and acceleration, but your pal Isaac never mentioned them, I believe.

Your comments about the amount of work being done in the quarter mile are instead reminiscent of James Watt, who emphasized, just like you, that it didn't matter whether  a horse pulled with more or less force along the way, so long as it got a certain amount of work done during its shift. He was trying to motivate mill owners to buy his steam engines and sell off their horses. He also successfully standardized the unit of power work called one horsepower, by testing horses' ability to do work over a certain period.

Isaac, as an inventor of calculus, was all about instantaneous rates of change, like the term "a" in F = ma. That's the seat of the pants feel from moment to moment, not the amount of work that gets done. Isaac would be all about getting out on the highway looking for adventure, not selling engines to millers.

Moto

P.S. You continue to ignore the work being done in moving through the air, which is quite substantial at high speeds and eventually defeats the motorcycle's attempt to accelerate further. Watt didn't need to take this into account, of course.

[Tkelly]

All activities at the rally and lunch ride will be outdoors,look forward to meeting you,I am hoping to ride my t3 also..

[moto]

All activities at the rally and lunch ride will be outdoors,look forward to meeting you,I am hoping to ride my t3 also..

Thanks! I'm looking forward to meeting you. I believe I may have ridden what is now your T3, and look forward to seeing it again.

[Huzo]

I have trouble understanding your second sentence, in light of your previous emphasis on quarter-mile times. Or 400-meter times, if you will.

As for the rest, I don't understand why you are appealing to Newton. The mathematical definitions of work, and its derived quantity power, post-date Newton, I understand. I haven't read all of Principia myself, and never will, but leafing through my copy I see no reference to work or power. Work and power are applications of the Newtonian concepts of force, mass and acceleration, but your pal Isaac never mentioned them, I believe.

Your comments about the amount of work being done in the quarter mile are instead reminiscent of James Watt, who emphasized, just like you, that it didn't matter whether  a horse pulled with more or less force along the way, so long as it got a certain amount of work done during its shift. He was trying to motivate mill owners to buy his steam engines and sell off their horses. He also successfully standardized the unit of power work called one horsepower, by testing horses' ability to do work over a certain period.

Isaac, as an inventor of calculus, was all about instantaneous rates of change, like the term "a" in F = ma. That's the seat of the pants feel from moment to moment, not the amount of work that gets done. Isaac would be all about getting out on the highway looking for adventure, not selling engines to millers.

Moto

P.S. You continue to ignore the work being done in moving through the air, which is quite substantial at high speeds and eventually defeats the motorcycle's attempt to accelerate further. Watt didn't need to take this into account, of course.

Yes all very good.
Your comments regarding Watt are of course historically correct and I concur with most if not all of your assertions.
However, I was musing that if you make an alteration then re test the same machine at the same mass each time, then the issue of the drag being a function of the square of velocity, can be cancelled because we are looking for an overall improvement.
But I can see with you around, I will have to keep my statements nice and anomaly free….

[moto]

Yes all very good.
Your comments regarding Watt are of course historically correct and I concur with most if not all of your assertions.
However, I was musing that if you make an alteration then re test the same machine at the same mass each time, then the issue of the drag being a function of the square of velocity, can be cancelled because we are looking for an overall improvement.
But I can see with you around, I will have to keep my statements nice and anomaly free….

I can see you understand this stuff very well. Thanks for a fun discussion.

Moto

[Huzo]

I can see you understand this stuff very well. Thanks for a fun discussion.

Moto

Hope to cross swords in the future.
Touche’ to you Sir..!

[Huzo]

Oh BTW..
It’s true that the definition of power from work/time is Watt’s work, but the equations of motion are Newton.

[moto]

Oh BTW..
It’s true that the definition of power from work/time is Watt’s work, but the equations of motion are Newton.

As I said. I think we're wasting bandwidth here.