FYI

By accident this morning I left the voltage sensing leads disconnected on my Robitronic Dyno as I was testing a 19 turn Chameleon motor. This dyno run was at the 5 volt setting. Peak power was 77.4 watts, after I hooked up the voltage sensing leads, I ran the same motor again and it peaked at 89 watts. That is about 13% loss in power essentialy due to the voltage drop of the power leads that go from the dyno to the motor. On the Robi these are about 18 or 20 inches long.

Next topic...

I beleive much of what Fred is saying is true. With todays batterys, run time is kind of a non issue. However pack voltage is also important, and at some level, reducing battery consumption by having a more effcient motor will keep your battery voltage up at higher levels during the time you are running. How much of a factor this is would depend on how much voltage your packs are loosing while you keep discharging them. So... effciency can't be completely ignored, but it is much less important then it used to be. Almost to the point of being a non issue. Unless of course your running spec batterys... then it is just as important as it was 10 years ago...


Mainly what I mean is this... if you have a motor that puts out 60 watts peak, and the peak occurs at 30 amps, yet you have another motor also with 60 watts peak, but it achives this peak at 26 amps, then the second motor would be the better choice in my opion.

If the peak power isn't exactly the same, it gets a bit more complex... but you should see my point.

I believe Trinity said on their site they switched over because supportability of the Robi was a bit of a problem.

Trinity rarely does something because its a better way to do it, they do stuff because they can sell more of something, make a buck etc etc.

It is also faster to mount the motor in the fantom that it is the robi for a place that churns out 1000's of motors saving 10 seconds each would save time which would save money....

Here is one for all the fantom Guru's.... I own and understand the Fantom dyno quite well but was debating one number with another owner. The number in question is "efficiency amps" shown as EAMPS and relates to the power and efficiency numbers at a particular point in the run. This is separate and not to be confused with overall, max, or average efficiency. While comparing two motors numbers on the screen and "E" or "p" is pushed this number is shown. Any takers? Thanks in advance.

Could be the amperage at which peak efficiency occurs. At 7 volts on the CE dyno, stock motors have peak efficiency around 16 amperes. What numbers are returned?

Dont think so, there is a separate screen for that, I'll pull up a run and check to see if its the same though.....returns seem to be in the 14 - 18 range though for 19 turns. best i can figure is that it attempts to tell how many amps in relation to overall amps are being wasted maybe as heat???Thanks for the input.

There really isnt such a thing as wasting current, you waste power not current.

This might seem kind of simple but is it efficiency multiplied by amp draw at a certian point?

Wow... this topic is starting to get about four differnt discussion threads going at the same time, all related to one another... it is getting harder and harder to respond to them...

I went back and read Tfram's comments about the TurboDyno and if it was inherently causeing a bias toward effciency in motors. I still don't understand his logic that brought him to the question, but I think I understand the basic question he's asking... It seems to apply directly to what Fred and Rich were saying... (probably no cooincdence since they were replying to his post)... Basicly I don't think the TD itself causes the bias towards effciecny, I think it's the way we interpet the data.

I think it boils down to how you look at the numbers. I started to look at some of my data in relation to Torque, at first glance it seemed to make sense to me... then I looked at a motors that have drasticly differnt max RPM... then it get's really confusing for me. Since we have fixed gearing in our RC cars, you have to compensate for the gear selection if you view by either RPM or by Torque.

At this point I still like to look at data in relation to Amp input... However I'm looking at graphs that show the data from min to max amp input, and it's easy to see where the motors peak at and in my head I am able to force the power curves to shift to the right or left simulating what would happen if I geared the motor differntly... The Robitronic actualy has a screen that even solves this mental gear shifting issue pretty well.

On the Robitronic dyno they have a option that lets you view the data in relation to percentage of maximum RPM. This view is really quite interesting, and from what I can see it pretty much eliminates alot of the issues with viewing

I think I'll have to write up a litttle discription of what I'm talking about including some graphs that illustrate it...

DynoMoHum,

In reading through your last post I'm noticing that you're fucusing alot on peak numbers. Be very careful about looking at only peak numbers because the overall powerband is very important. Just as an example, back in the "turbo era" in F1, BMW made some of the most powerful engines in history. The problem was that the powerband was very narrow and they needed alot of differant gear ratios to make the car perform (5-6 speed gearboxes). On the flip side would be the trusty old American V8's used in drag racing. By design the V8's have a huge powerband and are more suited to using less gear ratios (3-4 speeds back in the day). In RC we only have one ratio to work with and need a wide powerband. The entire curve needs to be considered.

When looking at graphs based on RPM, it is very easy to see how far you have to shift your gear ratio in order to hit the same area of the powerband of two differant motors. Each motor will have it's own sweet spot and needs to be geared accordinglly.

One thing for us to remember is that when all is said and done, it's a combination of torque and RPM (POWER) that sends our cars around the track. How much current that is used is just a product of efficiency; it needs to be considered and improved but is not what moves the car.

If you control the input power like the turbo dyno does, and power increases, then efficiency also increases. I still just look at the power number for stock motors.

A reason to use ampdraw (rather than torque) as a basis to compare motors is that we have a handle on amp draw. We can easily measure the average ampdraw in a race and tune our motors to maximize power near this amp range. If you plot your power curves vs ampdraw it is a lot easier to see differences in motors.

I believe that in many fullzize car races,long distance LMP or Lemans cars (where fuel is limited), Nascar where an extra pit stop will cost you the race, that engine makers may indeed be looking at how much power is produced for a given fuel consumption.

Originally posted by John Stranahan


A reason to use ampdraw (rather than torque) as a basis to compare motors is that we have a handle on amp draw. We can easily measure the average ampdraw in a race and tune our motors to maximize power near this amp range. If you plot your power curves vs ampdraw it is a lot easier to see differences in motors.



You got it John!!!!!! If your best motor is drawing 30 amps average for 4 minutes, tune the rest to draw the same amps.

I NEVER used to pay ANY attention to peak numbers... However I recently have decided that it may be the single biggest factor in electric RC racing. Not the only factor howerver... width of the power curve would be one of the next items I would consider along with the location of the peak in relation to amp draw(bringing effciency back into the picture).

I have what I beleive are very sound reasons for my new approach. At the heart of my new approach is that a stock motor of today, typicaly achives peak power between 30 and 40 amps when operating around 7.2 volts. Average is around 35 amps for the motors I've dynoed on my Robitronic (we could debate the accuracy of this till the cows come home... but anyway that's what I'm going by for now). So... with a 3300 pack, you could average up to about 39.6 amps during a five minute race and then dump... In 4 minute racing, you could average 49.5 amps and dump... My point is that with todays batterys you could aproach 40 amps average during a race and still make time.

At around 4.8 volts a stock motor typicaly peaks between 25 and 30 amps.... and this makes my new theroy even more appealing...


You can never get more power from a electric RC motor then it puts out at it's peak. If you pull 40 amps from the motor and it peaks at 29 amps, your wasting power by operating in a extreemly ineffcienct area of the motor's operating range. Idealy if you could constantly operate the motor at exactly the peak location you would make most use of the motors power. However with having to slow down and speed up at various points in the track this is impossible... Still... at it's most simple form my theroy says never gear a motor so that it averages more amp consumption then then the motor draws when it's achiving peak power...

If you follow this logic peak power is the most important number on a motor. The next two most important charactoristics would be the width of the power curve around it's peak, and the effciency of the motor around it's peak.

Furthermore... if you follow my theroy then it becomes very interesting to ponder the idea that we should be gearing our cars to produce as much power as possible, and this would seem to occur where the motor achives peak power.


Trying to take the theroy a step further I am forced to question if we really should make every attempt to avoid exceeding a amp load, that would exceed the current consumption at the motor's peak power point... Obviously you can not do this ALL the time... if you slow too much you will have to operate in that area where effciency is really bad and you have not achived peak power yet... (So driving becomes a huge issue in achiving the second part of my therortical goal)...


Anyway... do you see what I'm talking about?

By the way... for those of you have not followed my other threads on current consumption... I'm am 99% convinced that in todays racing, amp draws of 25 to 30 amps are happening every day by many of the top level drivers. This is what first got me thinking much more about peak power...

Clearly width of the power band is very important, as is effcinecy... but only if you've got power first.

Average ampdraw only works in oval racing (sometimes not even then).

I know that in sedan we're seeing amp draws between 20 and 50+ amps several times a lap. It's important to have good torque out of the corners and good horsepower on the straights.

If using amp draw seems to make sense then use it. I'm just saying that sometimes it will be misleading and it's not the best way to compare motors with the turbodyno's because the amp draw is related to efficiency. If you test by torque, a motor with more RPM makes more power regardless of how efficient it is.

Yes, efficiency is important in some forms of racing. And it used to be in stock RC racing. Now, we see sedans coming off the track with 100 seconds of runtime left so there isn't an issue with ampdraw. Also, with the new cells, the voltage doesn't drop much at the higher currents. Tuning to amp draw is like all the Nascar engine builders that are living in the stoneage taking notes down in "the book" instead of using computers. Yes, it works for them but it could be better.

One of the reasons I've started to break away from the average amp draw as the basis of all my tuning and choosing needs... If you always tune based on previous amp draw use, then your pretty much eliminating the possibity that you could actualy go faster if you tried something else... like maybe you could go faster if you had a motor with higher peak power, and geared up just enough to start using it...


For now I'm sticking to the idea that you should avoid gearing in a way that forced you to operate in a condtion that leads to averge amp draw that exceeds the amount of current used by the motor when it achives peak power. This is not to say I don't beleive that you will never operate above that point... but it does mean that I beleive that if you operate at average amp rates higher then the location of the peak, your probably over geared... or your not keeping your speed up enough in the corners and need to work on setup and/or driving skill...


Of course this is all just a starting point... and you still have to use lap times for your ultimate dyno.

A motor that makes more power will show more power on the dyno sheet. No need to even look at RPM until you are ready to adjust the gearing.

Fred-I see that you have a handle on the amp draw as well. A stock truck on an indoor clay track will pull 75 amps coming out of the corners. I would tune the motor for this truck to have more power higher in the amp range than a touring car that draws fewer amps coming out of the corner due to the higher corner speeds. I don't see you quoting how much torque the motors put out coming out of the corners. The reason for that is the only way to know would be to use the ampdraw that we know the motor is pulling and then use dyno data to find out what torque it puts out. Torque increases linearly with ampdraw. Not much difference between using one or the other. No need to use insults.

When you tune near the average ampdraw you should bias your power higher than this value because when the car is accelerating it pulls more than the average. The average just gives a starting point.

Ok... ok... lets all just calm down... I know that discussing dynos is alot like discussing religion or politics, but I think were doing pretty good here. I don't see anyone insulting anyone else myself...

Now if your refering to Fred's comments about the NASCAR guy useing a notepad insted of a computer... I wasn't aware that any of us here are NASCAR engine builder.... so it shouldn't be insulting to anyone...

I could say that anyone useing a CE TurboDyno is alot like a NASCAR engine builder using a notepad insted of a computer... and that might be insulting to some... But hey... that's actualy a reasonable analagy... One of the main reasons I don't use a TurboDyno is there is no interface to the computer on them... :)


But seriously... I don' think anyone has been insulting here... lets keep it that way.

I don't mean to be insulting. Like I said, if using amp draw works for you or anyone else, then use it.

I would figure torque based on logged RPM, voltage, and motor temperature. You could do the same with amp draw and temp for a given motor, that's not the point that I'm trying to make. My point is that it makes more senst to compare multiple motors based on a fixed torque rather than current draw.

Once you find out how the car is performing on the track it makes more sense to compare motors based on that torque rather than current draw. If the motor has more rpm at a given torque it will go faster on the track. If you compare two motors based on Current and power, it becomes harder to make that assumption because two motors rarely make the same torque or RPM at a given amp draw even though the overall power might be the same.

Fred B,thats something I always did when I had a turbo dyno(test motors by torque settings}But as you said you must first know what works on the track.Back when I had a Turbo six cell oval was still going strong and I used 4,6,8,10,12 for settings on the dyno,on short tracks I tuned for more rpm at 10 and 12 and for large outdoor tracks more in the 4to8 range.Always worked for me,and it was easier to relate track performance to the dyno.
With the Fantom I mostly look at specific amp loads simply because I dont think any flywheel dyno gives an accurate torque measurment.
On a CE dyno if you have one motor that makes 16,500 rpm at a 10 torque setting on one motor and 17,500 on another motor the latter will be faster as long as the amp draw isnt considerably higher.
This is just my opinion that I base on what I have seen and done,your mileage may vary:wave:

Sorry, but I don't "get" the torque steps. I see a huge fault in it. What if one motor puts out considerably less Torque and considerably more RPM than another motor?

What I'm getting at is that we always gear different motors differently, and some are even geared 8 pinion teeth different. If these two motors produce the exact same power curves, then they will perform exactly the same on the track (this is independant of amp draw, which may vary). Now if we looked at these two motors with torque steps, then one will look MUCH better than the other.

Mike,

Huh, 4:51PM ? How come you aren't writing code?

Jep

Jeff,

Um, 4:53... Still at work?

Tom, Pat, John and Dyno,

I've got one for you!

John mentioned about a truck pulling 75A when accalerating out of a corner.
How did you measure this, John?

Now one for the group.
I'm thinking about using some kind of data logger to see what kind of amp numbers are really used per track/motor combo, etc...
Suppose it says; average Amps are about 39.
What would I be able to do with that number, if (what I understand from all of you) all dyno's are differently.

I mean this info would still be meaningless/useless.
Because if I would tune my motor using a Robi, instead of f.i. a Fantom or so I would be tuning it differently.

Guys is this right?
What is your point of view on this one.


BTW love to see so many enthousiasts making there points, and supporting those by very interesting theories.
Keep it up you all.


Regards,
Pizza

One will look much better than the other......yes and it will perform much better also as long as the amp draw is within reason.

When you compare motors using torque, the torque values are the same. If motor A makes more RPM than motor B at the same torque then it will be faster on the track at that torque given the same gear.

If you need to change the gearing you'll have to figure out what the new torque is just the same as you would have to figure out what the new amp draw was. A motor with a completely different powerband will typically draw a different current. If you're tuning mod motors this is more of a problem. Also, figuring the torque is much easier on an oval than on a roadcourse because on an oval you have less turns/current spikes.

The biggest advantage of tuning by torque is when you're tuning a single motor with the same gear. If the RPM goes up at a given torque it's faster. If you tune by current the power might go up on the dyno but if there is a change in efficiency, you might not see the same result on the track.

I've been using a datalogger to take my measurements on the track. I try to sample at about every foot on the fastest part of the track.

Track data is only useful if your dyno can run at the same voltage you see on the track. Some dyno's can and some can't but in general all of the dyno's on the market do a fairly good job of showing improvement over a baseline.

Fred,

what kind of data logger do you use?

Pizza

I've spent too much time looking around to let everyone know what I'm using...There's alot out there from cheap ONSET units to more expensive systems like the Valitec system. The one I'm using is similar to the Valitec system without digital channels. Look around you'll need about 10Hz sample and enough memory for an entire run. The smallest I found was from Siliconsoft but it's too slow. Whatever you get, you'll have to strip it out of it's case to get the weight down.

There's a few ways to get the current, most use a current shunt. I found a neat little module that slips over the power wire.

For the oval types, the ONSET "HOBO" is probably good enough to get some average and peak data for a run but it's too slow for roadcourse stuff.

FB

I believe the new keyence zero extreme performs some of these functions i've heard?

If you guys would like to take the time to look at a series of web pages I've made that show pretty much all of the ways you can view dyno data... There are four pages total, with a couple images on each page with some questions and comments. It's really not very long winded like I can be... but I think it would be interesting to have some discussion on these methods of viewing motor data...

Start here

http://www.wiltse.net/torque.htm

follow the links at the bottom of each page, and come back and discuss these if you like....

Personaly I can't make heads or tails of data in relation to time, RPM, or torque... Amp input and Percent of max RPM make perfect sense to me however... All these images show the same two motors by the way...

I used to race on a high grip indoor clay track. We used to set the slipper quite tight due to the good traction. You could hear it slip on the slow corners. I just hooked up an analog amp meter in series with the motor. With the truck stalled and full throttle applied the meter read 75 amps max and then 58 amps continuous while the slipper slipped. In separate test on two speed controls I reduced the amp limiter in steps until I noticed a slight reduction in punch out of the corners. At about 65 A there was a noticeable reduction. Fast laps on this track were achieved if I optimized the motor at 40 A on the CE dyno. Really simple. Took fairly stiff springs. In the touring car I optimize it to give the best average power from 15-30 amps. A bit lighter springs are required. You optimize the range that gives you the best track performance.

Anyone,
Ever tried using the Victor Hi-IQ data logger?

Fred B
Do you have a link for such a unit?

Regards,
Pizza

Victor engeneering is out of bussines. Stormer hobbies still has units available in their closeout section.

Try a search engine...the sites should come up if you use the company names. There's alot out there so do some digging.

Ok Dyno, I'll reply to your web pages...

I'm going to comment on your last graph. You said that both motors will perform the same on the track if geared to make the following graph.

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

I believe that Motor 1 will out perform Motor 2 any day at the track. Here's why...
After we apply gear ratios to motors and installing them in our cars, all power numbers can be thrown out and we only need to look at the Torque that is being produced at the rear wheels of our cars. Torque is the acceleration of our car, because the weight of our cars is constant. The formula is F=MA or Force = Mass times Acceleration, but I really should put it A=F/M or Acceleration = Force over Mass. Force here is the Torque of our motors.

Now with that being said, Motor 1 has more Torque in the initial RPM range. In a drag race, Motor 1 will always beat Motor 2, as long as they are geared the same as in the above graph. This is because Motor 1 will always put out more Torque at a given wheel RPM than Motor 2. If we change gear ratios, it changes everything.

The reason we compare 2 motors by looking at power numbers, is because we don't know what the gear ratio will be yet, so the power numbers take that into consideration by using both RPM and Torque. When we apply a gear ratio, we can make the motor have a Ton of Torque, by gearing it really low, or we can have a motor with a Ton of Speed (wheel RPM) by gearing the motor really tall. Now what every racer wants is both of these, great acceleration and great top speed. Both are trade offs and the motor with the most Power will have both, because it can be geared taller than another motor and still have the same acceleration.

Mike, I think one or both of us misunderstand each other... and/or this graph... This graph is in relation to percentage of maximum RPM for each motor. If you select the gears correctly Motor 2 will have to have a lower gear (higher ratio?) then Motor 1. Based on info that I beleive you and others told me previously, it's my beleif that with optimal gearing for each of these, the torque and RPM at the wheels will be identical for both of these motors when you choose the correct gear... I'll put the same data into your dyno viewer and adjust for something like 20 amps, and I think you'll see what I'm saying is true. Either that or I'll find out that I'm wrong... :)

Dyno Guru's;

Correct me if I'm wrong on this. Motor #1 produces more torque throughout it's power-band than M2. Motor #2 has less overall torque but a considerable higher max rpm.
Therefore;
M1: gear lower numerically to take advantage of its superior torque characteristics and make up for its lack of rpm over M2.
M2: gear higher numerically to provide more acceleration while the higher rpm will provide an equal top speed to M1.

Question;
With any motor, how critical is having the exact gear ratio. Say an EXPERT motor tuner KNOWS his car needs a 7.00 final drive for motor XYZ. BUT can only get within +/- 2% because of Gear availability or chassis limitations.

Thanks, Popsracer

Well... I learned something I think... But my intial idea is still valid... I just didn't understand how the efficiency differnance of these two motors would change the picture... It turns out that if you make your gear selection based on 20 amps, you will in effect over gear Motor 1... or undergear motor 2... However if you use RPM at 35 amps (peak power, equal effciency) you get the desired effect...

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

I'll add this to my book of tricks... and my web page... In my opion this reinforces my idea that peak power is King, and I also beleive it pretty much backs up Fred's idea that effciency is not all that important... but you have to twist your mind like mine to see this... :)


I'm confused about image attachments to posts... they seem to go away eventualy... that's why I've been avoiding them lately. As well as to spare people who don't want to view them.

Pops... in my opion gear selection is absolutely crititcal... too high and you get a mushy feel, two low and get great acceleration but poor top end.

In terms of actual gear ratios and how far off you can be... I don't have that answer. I'm still working on figureing out how to gear correctly. I mean I know how to do it on the track, but it's trial and error for me now, I want to figure it out much better using dyno data and/or comparison to notes I have from another motor that I also have dyno data for...

To all;

I finally received a reply from Fantom on having a Facts Dyno converted to 7 volts.
$50 + shipping and you must use the special software they designed for Trinity (which they don't use). The software is downloadable from DecCosoft.

Popsracer.

BTW; I have ordered a Robitronics.

Any chance of a version that would allow entering CE Turbo Dyno data?

DynoMoHum;

Were my assertions of M1 & M2 correct, or am I way off base.

I probably be asking LOTS more questions once my Robi Arrives.

Thanks, Popsracer
R-C Tech Forum (http://rctech.com)

If when you are saying that by gearing lower you mean use a lower pinion, then I am pretty sure it is the opposite (at least I do it the opposite). :)

If a motor has more torque then I would use a larger pinion since it has enough 'rip' but not enough top end (RPM). If a motor has less torque, then I would use a smaller pinion since it has more RPM but less 'rip.'

-Rich


Originally posted by popsracer
Dyno Guru's;

Correct me if I'm wrong on this. Motor #1 produces more torque throughout it's power-band than M2. Motor #2 has less overall torque but a considerable higher max rpm.
Therefore;
M1: gear lower numerically to take advantage of its superior torque characteristics and make up for its lack of rpm over M2.
M2: gear higher numerically to provide more acceleration while the higher rpm will provide an equal top speed to M1.

Question;
With any motor, how critical is having the exact gear ratio. Say an EXPERT motor tuner KNOWS his car needs a 7.00 final drive for motor XYZ. BUT can only get within +/- 2% because of Gear availability or chassis limitations.

Thanks, Popsracer

Opps... Mike... gear selection based on some specific power number (not amp input) is what I want from a viewer like yours... This would make the effciency issue a non-issue... (I think)

I'm quite certian that if you took these two motors and geared them based on their RPM at some perticular output power number you would get a graph just as the one I have shown above when I used 35 amps as the gearing point.


By the way... Motor 2 in this data is owned by Hobbytalk's own Jake from, Mt Pleasant, Michigan... that's a motor I dynoed for him at a race a couple weeks ago... Motor 1 is one of my motors... I choose them specficly because they were so equal in terms of over all power output, yet the RPM and Torque are SOOOOOO much differnt. This RPM/Torque differnace is what makes them so confusing when you start looking at data in relation to RPM or Torque.

I still maintain with firm commitment that both of these motors are witin about 1% of each other with the exception of Effciency... that is once you gear them properly.

I have also just a hour or so ago figured out why looking at at electric motor data in relation to amp input can be misleading... (back to Tfram's comments of a day or so ago)... In my humble opion if you have not found the peak of the power curve, you haven't got the whole picture yet... More on this later...

If you look at the view of Dynomohum's two motors as power vs ampdraw a couple of things are apparent. Motor 1 has more torque and less RPM. It is going to have to be geared taller than motor two (more pinion teeth). When geared correctly the power from 60 amp to 25 amps is very similar, so the two motors will accelerate a touring car on a high grip track about the same. At an amp draw of less than 25 amps motor one has the edge. It has more power. It is going to be faster on the straight where the motor does not pull as many amps due to high motor speed.

Gearing-in a touring car on indoor asphalt a .05 difference in the cars overall ratio is easily felt on the track. Keep tinkering with the gearing. Often a single tooth change on 64 pitch gears is way too much. Have a selection of spurs and pinions so that you can split the gears finely. Work out the ratios on a calculator for the different spurs that are available.

Power vs Amp Draw (http://www.wiltse.net/amps.html)

Gearing gets so confusing, espeicaly when some people talk about high gear, they really mean lower ratio, etc....

I find it much less confusing to speak in terms of pinion size... When I say lower gear, I mean smaller pinion size. Higher gear, refers to larger pion..

Motor 2 needs a lower gear, becuse it has more RPM and less torque. Motor 1 has more torqu and less RPM so it needs a higher gear...

If I'm not mistaken... when I say lower gear, I really mean a higher gear ratio... Just like a 4.11 rear end is a lower gear then a 3.83... so now if your not confused... then you follow me. :)

DynoMoHum;

OK, I got it right then. I meant Numericly higher/lower 7.00 vs 6.80 FDR. 7.00 would be HIGHER ratio numerically but a but a LOWER ratio in relative terms to the 6.80 ratio.
That's why I like to use Final drive ratios when comparing one car to another.If someone says he's got a 87~27 spur and pinion. That doesn't really tell me much unless I'm running the Exact same car. BUT Final ratio can be applied no matter what brand of vehicle you are driving.
I don't believe a rollout calculation is nesessary for touring cars as most all rubber TC tires assemblies are VERY close to the same O.D. with few exceptions.

Popsracer

DynoMoHum;

I used to Drag/Street race my 1968 Plymouth RoadRunner back in the late 70's and 80's, so I understand how gearing works. Yes it can be confusing when two people are not on the same page when disscussing gear ratios.

Popsracer

Actually pops, I think a large number of racers go by 'roll out'... that is how many inches does the car move with one revolution of the motor. This really is the best way to do it. Tire size plays a significant role in the final gearing.

THis goes back to what you orginaly asked about... lets say your missing a pinion size and you can't get the perfect gear as a result... well you could use differnt size tires... :)

Also many racers use the largest spurgears and finner teeth gears, this allows a higher resolution of final roll out... but then your motor needs to be able to slide in and out far enough to work with the bigger spur gear, etc...

But like I say I'm still somewhat of a gearing novice...

Judging by the chart you provided, Motor 2 will be faster given the same gear ratio as long as you never see a load over peak power on the track. At least that would be the case provided the less efficient motor doesn't heat up and lose power. Motor 2 will also consume more power in order to go faster.

Motor 2 looks a little sick judging by the graph because of how abruptly it falls off. I'd see if it was in need of a turn or if the brushes needed more breakin.

Looks like it's another one of those trade off deals. Motor 1 is good under a heavy load and motor 2 is better under a lighter load.

I can see were all starting to go in differnt directions here... John was refering to my graph in relation to amp input, and I'm not sure what graph Fred is refering too...

I really think my graph made with Mike Golden's dyno viewer tells the real story. This graph takes into account gearing, and the graph pretty much tells us what will be seen at the wheels of the car when you gear these two motors based on the RPM location of Peak power. However for some reason I can't see the dotted lines in this graph, so I can't tell you for sure which lines are which... I can tell you that the amount of power, torque, and RPM differance when geared this way is not significant. If you do the math as Mike did to make the graphs, this is clear.

Now if Mike could tell us actual spur, pion, and tire sizes needed to get this gearing acomplished we'd be all set.


All other graphs I have shown can easly be misinturpeted one way or another...

DynoMoHum;

I believe that mostly it's Oval Racers that use the rollout calculation. That 1/10 % in gearing can really make a difference in the cars ability to maximize a motors power and rpm, that could be .05 mph difference over the others cars on the track.
On the club level in T/C that I race in. I have yet to see anyone take tire diameter into account. With Foams in T/C class, it's all about compensating for uneven tire wear.

Popsracer