I recently purchased a Fantom dyno and am not clear on what it's actually telling me.

I've read through many of the threads dealing with motors and motor tuning and have Big Jims motor black book.

I was hoping I could get some help understanding the information that is presented by not only my dyno but other models also.

Snuffy...

I'm not sure I can help you much... I have very limited experiance with Fantom dynos...

I've got lots of experiance with the Robitronic Dyno, and a fair amount with the Competition Electronics dyno.

I'd love to understand the Fantom dyno better. Right now I'm quite confused by some of the numbers that people give from the Fantom. To me, they often seem to disagree significantly with both the CE TurboDyno and the Robitronic. I mean this in a very general way, because there is almost no way to directly compare the numbers from one dyno to another, perticularly when the dynos are differnt manufactures. In a general way I basicly always see the same thing when I compare dyno data on my Robi to the data I get from the CE TD. The numbers are a differnt, but the slope of the curves at least consistantly go in the same directions when you make changes to the motors being tested.

If somone with a Fantom dyno could post some actual data that some of us non Fantom users could view, maybe we could get a better handle on what the differances are, and possibly figure out why they occur. If anyone does have Fantom data they'd like to share, I would be willing to put it up on one of my web pages... (basicly I have almost unlimited space, and bandwidth... at a low monthly fee that I pay out of my own pocket, it's a non comercial site, no banners or advertising) So... I'm offering a place to put it, all you'd have to do is get it to me... Hank is probably also willing to put up some data, but I can't speak for him...

I have some data. I try to save my pulls but don't allways. What are you looking for? The time based sheet? I don't really know what to send.

Also, I and possibly others would like to gain an understanding of what the CE and Robi numbers mean. They all spit out data, if you don't understand what the data means it's a useless tool. It was not my intention to limit this discussion to only the fantom dyno.

The single most common view I use is when showing the data in relation to AMP input. If the Fantom can display data in this format, I would like to see it for a few motors, with some explination of what type of springs and brushes are in the motor, etc...

What I was really thinking about is the actual data files that the Fantom surely must save. The Robitronic dyno saves two files, one is some sort of propritary data, and only the Robitronic dyno can read it (as far as I know). The Robi also saves a text file that can easly be read by almost any program such as Excel, Word, or any simple text editor. If the Fantom has some files simmilar to this, they could be posted somwere where others could download them, and then use some Fantom demo software to view them. (Assuming Fantom has demo software that allows people to view files).


As for dyno data in general... I feel peak numbers in general are not all that helpfull. At least not unless you have the surrounding data to put it all into perspective. Peak RPM in perticular is almost worthless, unless it has some indication of power/effciency that is being produced at that point. Even then, it's not of much value, except possibly to help choose gearing.

Somewhere Pat Collins (I think that's the name) has a pretty good general description of how to use a dyno. It's mainly focused on the Robitonic Dyno, but I beleive the principles he sites are pretty much universal. I'll see if I can find a refferance to it... it really is good reading.

Here's the data file from my Dyno. It's only readable by the Dyno software. It can be downloaded from http://www.deccosoftware.com/software/FactsII/Facts2-0199-CD.exe

Most of the motors should have comments assigned to them listing com size, brushes and springs but some of them don't.

There is a search facility here at Hobbytalk...

if you search for 'dyno data' there are quite a few topics simmilar to this one... one of them I starte contains the text that Pat Collins wrote that I spoke of earlier... it's about half way down on the following page...

http://www.hobbytalk.com/bbs1/showthread.php?s=&threadid=2424


I have never seen a whole lot of discussion about the Fantom. I think partly because Big Jim never really liked Fantom dynos, and I think some people may have felt intimidated and/or uncomfortable trying to discuss the Fantom here as a result. I for one really would like to understand the Fantom, because there are so many others that have them... At least I could have a reasonable chance of talking with Fantom users about motors if I understood their dyno data... So I'll take a look at the Fantom stuff you posted...

rcavenger also just posted some stuff on the Monster Motor topic... so data is starting to apear now...

is there anyway to export data from the Fantom into a text file that Exel could read?

I'm going to have to do some house cleaning on my lap top if I hope to install the decosoft program... it may be a while before I can acomplish this... :(

Ok... I downloaded and installed The Fantom Facts Machine software... I also downloaded and unziped a file called allData.abc, however when I attempt to open a file with the Facts Machine software, it doesn't see the file I unzipped...

WHat am I doing wrong?

Never mind... I think I figured it out...


So if I understand this correctly... all fantoms dyno data gets stored in this one file? Is there a way to create smaller files? like say you had 6 dyno runs that were all related and wanted to save them seperately so you could send them to someoene else to look at?

Anyway... I'm starting to look at the data now...

Thanks.

The windows version of the software doesn't allow that or I haven't found where it is in the program. I'm not sure about the dos version. I'll check on it.

Actually I think it is there... but it doesn't work in my demo mode...


The data sure does look a whole lot differnt then the data on the Robitronic dyno... I'm still trying to make heads or tails of it.

TMFU,
You can save individual motors with the "File Transfer" button in the "Files" tab under "Individual Motor Test Maintenance & Viewer" button. It seems that the File Transfer saves the Files in the "Old" format. Then under "File" -> "File Converter", you can add the motor into the big list. With this info, you could export the motors you wanted to save separately, then rename your "allData.abc" to something else, and import the files you wanted into a new "allData.abc". That would allow you to send only the files you wanted to someone else. I know its a little convoluted, but it would work.

I compared all of Snuffy's motors to the Monster, and The monster does show to be better than any other motor that he has run, except for "RM". What does RM stand for?

Now I'd really like to see the exact same motors run through a Robi and a Fantom. That would be interesting.

BTW, Snuffy, Thanks a Ton. I've been waiting a long time to view data from a Fantom.

Seperate issue/thing...

I've been trying to use the 'option' menu item 'post time based data to clipboard' so that I could transfer some of the data into excel... so far it keeps all I get is the same data over and over. That is, I can't seem to be able to get it to save the data I'm looking at to the clipboard, it just the only thing in the clipboard is for "2K2-08 1-1-02"... never seems to change... Is this because the demo version is cripled? or is it user error on my part? Which ever it is... can someone tell me how to do it, if it's possible from the demo version?

My ultimate goal is to view data in relation to amp draw... since that's what I'm most used to looking at...

Now I did something, and I no longer have anything in my clipboard... how do you get a perticular motor's data into the clipboard?

Mike,
RM stands for Revenge of the Monster.

Here it is, sorry I lost the spread sheet described at the bottom, I will work on making it again (computer virus hit me last year).

The Robitronics dyno is a very nice piece of equipment and can be very useful to a knowledgeable user. The problem is that most people that I see using the Robitronics or any flywheel dyno for that matter just don’t know what to look for. Even the most experienced motor men can find themselves just staring blankly at a screen with tons of data not knowing what to do with it. Big Jim Greenemeyer prefers the Competition electronics dyno because it tells him the information he needs without the clutter of too much information.

Many neophytes come on bulletin boards asking about the RPM of a motor, thinking this is what they need to know. Experienced racers try to tell them that is not really what to look for but they can relate to RPM the easiest. A semi-experienced racer knows it is power and not RPM that makes the car go, but many just look at the peak power produced which is only slightly better than asking what the RPM of a motor is. Most racers with the Robitronics dyno will tune their motor for the peak RPM, the maximum power, and the maximum torque numbers and total spin up time but do yourself a favor and don’t even look at these. They are next to useless believe it or not, more on this later.

If you are new to the Robitronics dyno I recommend using the view data screen on the menu to look at your data. Its fairly hard to relate the graphs to actual performance, even for the most experienced motor tuner.

I am going to limit the scope of this work to stock motors because they are what I have the most experience with. The most important thing about tuning a motor to perform on the track is actually knowing what you need the motor to do. Simply saying “I need a faster motor” can mean many different things. Often this statement doesn’t even have anything to do with RPM. By knowing what you need a motor to do you will have to approximate the amp draw of your motor in the situations that you feel that you need more power. If you constructed some type of speedometer you could work backwards and find the RPM range of the motor you also need more power, but I find that a good guesstimate will get the job done nicely.

Here are my guesstimates for 6-cell stock touring car and offroad racing. If you feel that you need some more out of the corner punch try to increase the power at 25 amps. For more of a top end feel shoot for maximum power at 15 amps. For overall “goodness” of a motor look at the power at 20 amps. And also the average power between 15-25 amps is a good indicator of the motors performance on track. If you tune to these parameters and feel the motor is a little soft coming out of the corners bump them up a few amps and try again. I stress again the importance of tuning a motor for the range that you are going to run it.

Now that I discussed what to look for when tuning a stock motor I am going to discuss the downfalls, shortcomings and quirks of the Robitronic dyno and its results. First lets discuss the peak power number and why it is not very important. Peak power is the power at one specific point in the power curve. When you are racing your motor is constantly changing RPM, even when going down a very long straight away. So you are probably lucky if you operate at one specific point 1/100th of the time it takes to make a lap. Secondly look at where peak power occurs, in stock motors running off 6 cells it is almost always at 35 amps give or take an amp. Just about the only time your stock motor draws this much current is when you peg the throttle coming off the line. In my experience in offroad and stock sedan a 20 amp average amp draw is fairly typical.

Although I find the peak power number fairly useless, using it is not all that bad the next mistake is far worse. Tuning for the peak RPM is just about the worst mistake that a motor tuner can make. The flywheel dynos load is provided by the acceleration of the flywheel. When the flywheel has reached maximum RPM the load is very small because the acceleration is very small. The power required to keep a flywheel spinning at 30k RPM is only a few watts. However when a car reaches maximum speed there is rolling resistance between the tires and ground, wind resistance and mechanical resistance in the drive train holding the car back. One day I may design a flywheel dyno that also has some sort of braking resistance so it provides the best of both worlds.

Spinup time can be somewhat useful in determining how quickly the motor can pass through its entire power band but it can also be quite misleading and I recommend that most people avoid using this number because its redundant if you use the power numbers to your fullest advantage. I say spin up time can be confusing because you can have two motors with virtually identical power bands where motor 1 takes 8.13 seconds total spin up time and motor 2 takes 5.84 seconds spin up time. (See the picture) You will notice that on motor 2 all of the extra time it took to spin up was at the very end of the power curve. Remember from before that it is impossible to get a motor in a car to operate in this range anyway, so this tells us that this extra spin up time reported by the dyno doesn’t mean a thing! You can check the elapsed time that it takes a motor to accelerate from a 30 amp draw to a 20 amp draw and use this number, but that is a fair amount of work and again it is redundant.

To figure out how much total drag is on a car find out its speed and you can work backwards to get the RPM of the motor at this point. Then you can find out the wattage the motor puts out at this RPM and viola, that is the drag of your car at maximum speed. I have created a spreadsheet to calculate the rollout, the tire RPM and motor RPM using your car’s speed, tire diameter and gear ratio. (attached).

TMFU,

I think posting Time based data to the clipboard only works when you actually dyno a motor.

I would really like to see this spreadsheet if you can find a copy. I was working on something similar... stymied for lack of data on drivetrain and rolling resistance. Drag is actually pretty easy, just pick Cd of 0.5 and area of 30 inches and it's pretty close.

TMFU,
I stand corrected.

With the Save Time Based Data to the clipboard option checked, Open a motor test and go into the time based data. It is automaticly coppied to the clipboard. Just paste it into the program of choice.

Somehow I have 'un-selected' the save to clipboard option... and now I can't get it selected again... I even removed the program and instaled it again, and I can not get that menu item selected again...

Man... this really frustrates me... I got one set of data copied over and I can't get anymore...

I have one question about the AMP curve... why is it not reasonably smooth? I would think that it should be smoother... On the Robi, the amp pull and all the other curves are much smoother. I can not think of a good reason for the amp input to have such pronounced changes. Does anyone know what causes this?

TMFU

THe dyno not measuring fast enough would cause more pronounced steps in the curve, as well as a motor that arcs alot. I noticed on my Robi that if the motor isnt in the best of shape the curves were wiggly.

Dan

Here is an excel spreadsheet that I just made relating car speed to motor RPM, I threw a rollout and total gear ratio calculations in it for utility purposes too. Enjoy

PS had to zip it because this website dont allow xls files

Pat

Dan some stuff I forgot

If you measure your cars topspeed you can then find the motors RPM using the spreadsheet. Now using your dyno (if its a Robitronics) you can find this RPM and the power associated with it and this power number will equal your losses. Its sort of the back door quick and dirty way of doing it but its much more accurate than guessing at some values.

TMFU,

What's your email address? I want to send you something that may help.

iggy@merit.edu

As for your dyno data... I sure wish I could view power, RPM, torque, and effciency all in relation to amp input...

However I must say... if the Fantom is correct about your Monster, it sure does have some massive peak power...

I must say I am a bit skeptical... but that's my general nature I guess... I know my Monster doesn't show any kind of power like yours... at least not when I compare it to any other good motor I have... Your monster is has like 10% better peak power by the looks of it... I sure don't see that on my dyno... (neither one)

I have 3 monsters. The data I recorded was for the two lower motors.

OK... Tire dia is usually more like 65mm, isn't it? ROAR rulebook says 63 min, Proline sells a 61.

Is that a typical rollout for a stock motor? Where would you gear a GM3?

Oh I just stuffed numbers in it to make sure it worked, didnt pay any attention to what the numbers would be for.

The first thing I would do if I owned and Fantom and the Decosoft Fantom II software, is to demand that they add a view simmilar to this...

http://www.wiltse.net/images/Fantom_PvsM.gif


These are just the first two motors I compared like this... If the Fantom numbers are to be believed clearly there is a huge differance in where this power comes and at how efficently it's generated...

TMFU, here is how to turn it back on...

I hope you like hacking...

Disclaimer:
To anyone reading this: "If you don't feel that your computer skills are up to doing this, don't do it. You could really mess your computer up if you change or delete the wrong thing."

Press your Start button and go to "Run...". Type in "regedit". This will open the Registry Editor. Open the tree "HKEY_CURRENT_USER" -> "Software" -> "decCo SoftWare" -> "The Facts Machine II". If you click on the folder "The Facts Machine II", you will see a list of all the settings that are stored for the Application. Double click on the "Post Excel" and change its value to "1". It doesn't matter if that is 1 hex or 1 decimal (they are the same).

Now my app copies all the time based data to the clipboard in Excel format.

Thanks for the tip Mike...

Let me comment a little about the graph I just posted. If you look at this, you can clearly see that bellow 26 amps(well it's not clear that 26 is the point... but trust me it is) but bellow that point the P2K2 motor shown hear is doing a much better job of putting out power then does the Monster(RM) shown. However above 26 amps, the Monster is kicking out the power at a much geater level.

Based on this this data, the P2K2 motor would be a much better choice if you were racing in a Spec class or some other class where you were averaging less then 26 amps.

Conversly... if you were competing in a type of racing forced you to average greater then 26 amps to compete at a high level, then this Monster motor would be for you...

Now if you averaged exactly 26 amps during your race... it would be pretty much a matter of personal preferance as to wich motor you'd choose... The track would likely also dictate to you wether you'd gain most by having peak power(low RPM) or lite load power(high RPM).

Either way... gearing becomes critical in getting the most out of the motor you'd choose.

Now... these are not my motors, and not my data... and quite frankly I have not seen the same kind of awesome peak power from my Monster... and/or my P2Ks and P2K2s do a much better job at producing peak power then this one does, if I tune them for it. That is... My own data doesn't back up this large skew in power output between these two types of motors.

I'm just trying to show how I would interpet Fantom data if I owned one... Your millage may vary...

Ok, here is Snuffy's Fantom data for two Revenge of the Monster motors, I've aranged it so that the data is all shown in relation to AMP input for both motors. I've used Excel to do this...

I'm pretty sure we are comparing apples to apples here since both motors have very simmilar RPM.

Based on this data, I personaly would be willing to say with out reservation that the motor labled here as RM-02 is by far the better motor of the two. If these were my motors and my dyno, I'd deffintlly go back to the drawing board on RM-03 and try to figure out just what is going on with it, and why it is so bad near it's peak RPM. Something really is causeing RM-03 to suffer badly bellow 32 amps.

My guess is that both RM-2 and RM-3 would acclerate form 0 to 50% max RPM virtualy the same, but that RM-3 would lack all top end speed.

I have no clue at this point what would cause this type of behavior... perhaps a out of round commutator, or springs that were too soft??? I don't know.

I personaly have a very hard time seeing this obvious differance when I look at either of the two graphs that Fantom II software gives. I can kinda see the same thing on the Fantom's power graph if I look really closely and make my brain jump through hoops. But it gets kinda obscured by fact that the data in the Fantom graph is in relation to RPM. I basicly never use the RPM based graph on my Robitronic dyno for this reason.


http://www.wiltse.net/images/RM2vsRM3.gif

Other interesting things about RM-02 and RM-03 from Snuffy's Fantom II...

If you look at the Peak numbers for these two motors these two motors, the are very simmilar. It's basicly impossible to see any significant differances in the peak numbers given for these two motors. This in my opion is a very good example of why PEAK numbers are worthless...

ALso... the Low Medium and High Power factors are quite simmilar, and I really don't understand these numbers and what they mean. Since I have not seen any documentation yet on how they come up with these numbers, I pretty much find them to be of dubious value.

Input Power Factor, Output Power Factor, and Average Effciency... Does anyone know how they come up with these numbers or what they mean? At least with these numbers there are some significant differances between these two motors and that's a good sign.

One could assume that average effciency of 18% that is given for RM-03 is worse then the 25% figure given for RM-02 and with that assumption my assement of these two motors agrees with these two Fantom numbers.

What about Output Power Factor???? The Fantom is giving RM-03 a value of 102, and RM-02 a value of 93... Is lower better? or how can one interpet this???

Input Power Factor? I'm not sure I can even begin to guess how this number is used or caclulated.

Can anyone point me to documentation for these nubmers? Obviously IPF and OPF are used to calculate Average Efficency... but how do they come up with IPF and OPF? Do they just calculate the sum of all the input and output power nubmers collected during the dyno run or what?

How come the Low, Medium, and High Power factors don't seem to add up that way?

I'm confused by Fantom's numbers to say the least... Espeicaly when I view them as they relate to these two Monster motors that Snuffy has dynoed.

The power factor numbers are calculated numbers that consider the input versus output at specific intervals.
I never look at the graphs as I think they are all worthless.
I have both software versions but I dont really like the windows stuff
The DOS version tells me everything I need to know,why make it complicated.
I find the user specified amp values to be the best way to sort out motors using the Fantom.

Is there somewhere to obtain the DOS software for the Fantom? I mean for download on the net? Or could someone send me a copy if that's ok?

I can send you my copy as long as I get it back,send me your shipping address.

Here is some more data for those interested.

TMFU,

The graphs are very nice. I have one question. You said that you believe that RM02 is the better motor and I think I understand why but could you explain how you came to that conclusion?

Ultimately I'd like to be able to look at the data that my dyno spits out and be able to tell how the motor will perform on the track and what I may be able to do to tweak the motor to what I use it for. Right now I really have no clue as to what I should look at or what what I'm looking at means. The graphs do help. I'm going to try to make the graphs myself.

I found something in the software that's quite interesting today. If you graph more than one motor to compare in the software and right click in the graph area a window opens up displaying the peak values and the vlaues at the amp point you set in the options menu for each motor you are comparing. I think this will be very usfull when I understand just what everything means and how to use the info.

I almost forgot the motor data is an excel file.

Snuffy,

The reason I said that RM-02 was better then RM-03, is based on the fact that they both have nearly identical peak power, yet RM-02 maintains it's power out towards it's highes RPM output. RM-03 basicly falls off really badly as it's RPM reaches Maximum. The more I have looked at the RM-03, the more I feel it has some serious problems, I'm not sure exactly what is causing it to fall off (loos power) so badly as it aproachs max RPM.

I don't remember which one it is no, but it's either the Monster motor or the MOTOR TEST, but I bleive both of those are as good or better then RM-02, and One of them looks alot differnt then RM-02.


I'll try and describe better what I'm looking at and put it all in a web page... with the graph above and another graph or two.

Aside from all that....


I have observed something I find odd about the Fantom data that Snuffy has provided. If you look at the initial data for each of the motors, more offten then not, the motor with the highest inital RPM reading, also has the lowest initial Torque reading.... and of course the oposit is also true.. that is... more often then not the motor with the lowest initial RPM reading also has the highest initial torque reading..

That may seem to make some sense, if your thinking about the fact that High RPM motors ussualy do have low torque. However I don't beleive that really applys too the early RPM.

Based on my basic knowlege of physics and torque, it would seem to me that a motor with high initial Torque would acclerate the flywheel much faster, and therefor achive higher RPM early on as the dyno does it's thing. Think of it like this... the torque is directly responsible for the accleration, so higher torque should mean higher RPM when checking the first reading. This would produce results that are pretty much just the oposit of what the Fantom seems to be showing in most of Snuffy's data.

I've looked at some of my Robitronic files, and the motors with high torque do indeed have higher RPM for the initial readings... this is what I would expect. It is also just the oposit of what appears in the Fantom data. I beleive this is very odd to say the least.

Further more... if your still thiniking I'm mistaken in my way of thinking... it seems that in Snuffys data, the motors with the highes maximum RPM also have very high Maximum Torque. This is really just the oposit of what I have seen in pretty much all of my motor testing...

TMFU,

I think your assesment of the Fantom dyno is right on target. I'm not sure if the software actually uses spool up time to caculate touque. Many times, I've seen it tell me motor A has more tourque than motor B, when motor B spools up faster.

I'm beginning to think that that may be part of the reason I'm so confused about what it's telling me.

Well.... Total spool up time can be misleading, even if everything is being done correctly. Initial readings and final readings can change dramaticly over time, this is a direct result of how the power is distributed on a motor, and this will change significantly with normal tunning techniques such as spring changes, hood alignment, brushes, etc...

However... if a motor constantly has higher torque then the one it's being compared to, then it had better reach any given RPM before the other motor... if it doesn't then in my opion something is wrong. When I say constantly, I mean from 0 to X RPM torque exceeds the other at every step along the way.

back to the idea that spoolup time is difficult at best to understand motor proformance... From my experiance Torque is rarely so straight forward that any given motor has the exact same shaped torque curve. One motor may start out with more torque then the other, and may very well finish with less toque. These same to motors may very well have the the same output power, but at any given moment the time to reach X RPM will be different... So it takes a person with a better mind then mine to figure it all out when you look at the numbers in realtion to time...

Looking at data in relation to RPM is much the same and I think it is also the same for the same types of reasons.... This is why I rarely look at spool up time or data in relation to RPM.

Snuffy read my post again

The only way to get torque on a flywheel dyno is by using the change in RPM between two measurements and the amount of time that it took and you get the angular acceleration. Torque is then a product of the angular acceleration and inertia of the flywheel. Then once you have RPM cause it is measured directly, and torque you get power.

Like I said in my original post spool up time can be misleading because the last 100 RPM can take over half of the spoolup time and on the track your motor will never be able to achieve this last 100 RPM anyway.

Oh and there were some questions of efficiency

efficiency is simply equal to power out divided by power in then multiplied by 100%

Power in = voltage*amps
Power out = angular velocity*angular torque

Pat, or anyone else for that matter... What is the actual formula for calculating torque from a flywheel?

At the following site...

http://www.land-and-sea.com/public/articles/kart_racer_dynamometer_article.htm

I found the following formula

Torque = JM * rpm per second / 9.551

where JM represents the Polar Moment of Inertia of our inertia dyno's flywheel.

Based on my knowlege of math, this is basicly a linere function .

If my algerbra is correct, I could come up with the following formula to calculate 'JM' , when we know RPM per second and Torque.


JM = Torque * 9.551 / rpm per second

I used Delta RPM / .1 to come up with RPM per second from one Fantom data point to the next.

IF you use that formula and plug in the numbers that the Fantom has given for Snuffy's motors, the calculated value for 'JM' changes from one data point to the next. By my calculations sometimes the value I come up with changes by 10% or more from the average number. I think that it should remain constant...

Can anyone confirm that these formulas are correct and/or double check what I have found with regard to the data that Snuffy's Fantom gave?

Doesn't the torque change depending on the RPM of a dc electric motor?
Wouldn't that change the value of JM from point to point? Or am I missing the point?

JM is a physical property like weight and doesnt change unless your flywheel is falling apart while its being turned.

Torque can be expressed in any number of units, mostly depending on what your JM is given in. It is easiest to use units of grams, meters...basic metric units without the prefixes.

For angular acceleration you want to express it in units of radians per second. One revolution is equal to pi radians, where of course pi is 3.141592....... and for dimensional analysis radians per second is just expressed as 1/seconds.

The equation for angular torque is expressed in most books by all greek letters so I will spell them out.

Tau=alpha*Iota
Tau is torque, alpha is angular acceleration, and Iota is inertia.

This is exactly equilivant to Newtons Law Force=mass * acceleration

Well.... near as I can tell the Fantom has some significant error in it. THe variation I speak of does not follow any easly seen pattern. I don't have any easy way to show you my data right now, or I'd post it. My best guess is that the erorr is somehow related to and error in sensing RPM and/or the time interval... Either that or the time intervals they post are not exact,... even so of the few dyno results I've looked at so far, some of the variation is in exsess of 15%. It really seems too large to be easily explainable.

To be fair... I currently have no ablity to check this same type of thing with my Robitronic data. This is because it is not easy to get the interval between data points. The data the Robi spits out is given every 100 RPM, and there is no time interval assoicated with it. It might be possible to kind see if the change in Torque is consistant with the power and RPM given... I don't know any easy way to figure it out. IF anyone else has ideas on how to check the Robi's data I'd give it a shot. Given that the Robi data is always so consistant , very smooth, and makes no sudden changes in direction I don't really expect any problems with it... but it would be good to double check it.

TMFU,

How are you making theese graphs? I've been trying to do it without much sucess. Could you post one of the Excel files that I can disect?

TMFU time is recorded somewhere because there is a chart available that uses time as the X Axis. It doesnt necessarly need to be even time intervals, Im sure it is recorded in even time intervals somwhere and then the data is reduced and put into the format of points evey 100 RPM.

The data needs to be taken much faster than it takes to complete one revolution at the highest RPM that the dyno will see for it to be accurate. If I were designing a dyno I would make sure that it sampled atleast 5 times in each of the flywheels quadrants (the sticker is 4 seperate sections) so lets say the fastest motor on the dyno would lay down 50,000 RPM that would be over 16,000 samples per second. So the information has to be "somewhere".

I sold my RObi a while back because I just dont get to race enough to justify having a dyno but I have been thinking about buying a fantom or a CE just to play with and since they have good resale value I probably wouldnt loose anything.

Yeah, I'm sure internaly there is some record of the time interval. What I really meant is that the text file that the Robi produces dosen't include the time interval... so I can't use my formula too come up with 'JM' from the Robi data and verify any of the numbers the Robi is giving. I could get the numbers from the Robi by looking at some of the data screens the Robi is capable of, but this would be very tedious and prone to typos if I tried to do it on a big scale.

I've spent most of the weekend looking at this matter with the Fantom, I still haven't fully resolved it all, but at this point I have found no glaring errors as far as the Fantom is concerned.

I do think that fantom is doing some data smoothign or something however. Especialy with regards to the initial RPM and torque figures they give. I don't beleive these initial figures are accurate. When I calculate the initial torque with a constant 'JM' I always find the motor with the highest initial RPM also has the highsest initial torque. This is in stark contrast to what the Fantom reports for Torque at that point. However that should not be much of a problem in the grand scheem of things, but it is odd that Fantom seems to be fudging this data point.

The other large errors I appeared to be seeing, I think are related to realtively small errors in time and/or rpm measurmenet, and the largest errors occur at the highest RPMs, and at that point Torque is so low that the error becomes more or less insignificant. I'm still looking at this matter but it doesn't seem all that serious to me now.

I have also basicly come to the conclusion that the Fantom is not useing 'average RPM' to calculate power output. Either that or the figures they give are already averaged... I have yet to determin just how much of a issue this could be. The only thing I have to go by is the web page given previously that explains how dynos work. In that document it indicated that 'average RPM' should be used. I've only looked at this part of the puzle for a short time. At this point it does make some pretty serious diffreances in the reported power output, but it also seems rather consistant and at first glance it doesn't seem to make that much differance as long as you always caluclate it the same way.

I do see what appears to be a small bias toward higher RPM motors, but at this point the most I have seen is less then 1%. I have always figured that any dyno is going to easly have at least 1% error... so I'm not sure this is a big issue just yet. I'm still looking at it.

Does anyone know the actual figure that is used for 'JM' with the typical flywheel used on the fantom? Changing the 'JM' figure does effect the power curves rather significanty. I have yet to be able to reverse engineer this number with any degree of confidence. I have made an educated guess and started using a 'constant' number in my calculations. However I'd like to use the actual number if I could find it.