R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 01-26-2003, 11:10 PM   #1
Tech Elite
 
Neil Rabara's Avatar
 
Join Date: Jul 2002
Location: Lone Star
Posts: 4,821
Default What Dyno's really do

For all to appreciate,

posted by darnold:

"Dyno's- Good subject that i would like to share a few thoughts on but by no means would say is definative or most accurate.

I personally try to keep in mind that a dyno is a diagnostic tool and as such the ability to understand the information that it provides and apply that to the appropriate type of racing.

Two general types of dyno's, load and flywheel. The Facts dyno Appears to be more reliant upon rpm and software programming but does a very good job none the less. The old CE gave actual load and rpm information but left much to be extrapulated regarding applicable data when compared to the Facts. The Robi while being flywheel seems less dependent upon rpm and I personally like the CS. In the case of the CS and possibly the Robi the torque info may be more voltage dependent instead of rpm dependent thus giving more accurate torque info than the Fantom.

Regarding info reading the one thing i think the CE did was focus peoples interpretations along the line of "area under the curve" by having to view the amp stages. This info is available in the old Fantom software as well but it seems to get missed a lot. The whole issue with area under the curve is that this is the determining factor regarding horsepower. More area under the curve the more Potential horsepower. I say Potential because it's one thing to have "x" amount of h.p. and another to access it.

Accessing h.p. is the biggest issue that makes dyno's Seem inaccurate. IE. Motor "A" has a peak of 210watts vs. Motor "B" with a peak of 245w. Yet the racer experiences the 210w motor as being faster on the track and thus thinks the dyno (flywheel or load) is inaccurate. What the racer didn't realize is that the dyno told them this but they missed it because it's "buried" in the info.

Basically, the rpm range that the racer operates within on a particular race course is of course linked with amp draw(in electric motors). Thus rpm and torque in an electric motor always occurs at a given amp draw so you can look at h.p. based upon "amp stages" or rates or you can view h.p. based upon "rpm stages" or rates (or even torque stages). H.P. is torque x rpm over time and of course some source of "fuel" is used and thus this "fuel rate" is linked with the torque vs. rpm over time. This is what gives us the nice "curves" seen in the flywheel dyno's software. The area under the H.P. or Watts curve with its corresponding amp and torque lines tell us the same info as the CE with its "amp stages".

The result of all of this as it applies to our our racer example is that the racer missed the fact that they can only access a certain amount of amps or more accurately they operate within a certain amp range. Thus the h.p. developed within that range is what needs to be compared. Often the max h.p. or watts that a motor can generate can not be accessed by the racer so comparing max h.p. can be irrelevent. Therefore t doesn't seem to be important whether the dyno info is from a flywheel or load sensor, dead stop or already spinning state.

So what is it that is applicable? Well it seems that at the least knowing your rpm or amp operating range for a given track or class/type of racing can tell you Where to compare h.p. figures of various motors. A personal idea that i have been toying with is a simple algorithm that may give a "relative" efficiency type number. The formula is to simply divide the max h.p. by the amp draw that it occurs at. So if you had a 210w motor that made it's h.p. at 40amps vs. a 254w motor that made it's h.p. at 68amps guess which motor probably allows you access more of it's h.p.?


The 210w motor would be the answer with the key being whether or not your batteries allow you to operate within a higher amp range which could allow you to get at more than the 210watts of motor "a" that motor "b" has available.

It is this missed info that i think makes some motors look like "dyno queens" and others look like nerds. However, all of the dyno's out are good at giving us the neccessary info to compare motors Before we run them, what good are they if we are only going to judge motor based upon what they do on the track? We might as well ditch the dyno's.

Hope this helps..."
Neil Rabara is offline   Reply With Quote
Old 01-27-2003, 07:38 AM   #2
Tech Adept
 
pkranger63's Avatar
 
Join Date: Jan 2003
Posts: 162
Default

Great post!! I have been toying with the idea of getting a dyno. I love tunning a car as much as driving it. You post answered many questions I had concerning the what all those figures it spits out means

Thanks
pkranger63 is offline   Reply With Quote
Old 01-28-2003, 04:50 AM   #3
Tech Master
 
johnbull's Avatar
 
Join Date: Aug 2001
Location: Malta. G.C.
Posts: 1,762
Default

Hi guys. Greetings from Malta.

RC INFINITY. Great starter post. Well done.

I have a CS dyno, which I have had for 3 or 4 years now.

I find it very good with stock motors - above 17 turns, because they don't draw so much current, but not so good with hot mod motors.

The only problem I find with the CS is the fact that it relies on cells for powering the motor. We all know that no two packs give identical performance, and we all know how quickly they discharge in mod applications, especially when being given the sort of treatment a dyno test does.

Nowadays I use 2 packs of 3000 cells in parallel. It reduces the problem somewhat, but it is not satisfactory.

Now a question about the figures the CS gives. Assuming we are talking about say a 21 turn sealed stock motor, which figures would you go for if you were choosing one of six identical motors, as the best of the lot. Would it be RPM. Would it be power, efficiency, current draw, or torque. I know that some figures are relative to others, for example a high revving motor will give more power than a similar low revving one.

I could ask the same question for say 9 to 12 turn modifieds.

Basically I find that with so many parameters shown, they tend to confuse people more than help.

I also have an Orion motor tester but I consider it a total waste of money and time, except to use it as a power source to run in motors.

Your comments would be appreciated.

regards

Joe from sunny Malta.
johnbull is offline   Reply With Quote
Old 01-28-2003, 07:08 AM   #4
Tech Adept
 
Join Date: Aug 2001
Location: Grimsby, UK
Posts: 212
Default

rcinfinity, that is a really good post.

I realised the inaccuracies of motor dynos a while ago so i devised new tests for measuring the output of motors, what it consists of is how efficiently the motor brakes and accelerates.
which is what the driver sees on the track. Think about it, when you think "wow - good motor" its based on how fast you get out of the corners.


just a correction but

Power (Kw) = Torque (Nm) * Angular Speed (rad/s)

sanj
schumacher is offline   Reply With Quote
Old 01-29-2003, 10:27 AM   #5
Tech Elite
 
Neil Rabara's Avatar
 
Join Date: Jul 2002
Location: Lone Star
Posts: 4,821
Default

Thanks, the person who wrote it (darnold) should be commended.
Neil Rabara is offline   Reply With Quote
Old 01-29-2003, 04:42 PM   #6
Tech Elite
 
Brian McGreevy's Avatar
R/C Tech Charter Subscriber
 
Join Date: Jan 2003
Location: Illinois
Posts: 4,081
Trader Rating: 10 (100%+)
Send a message via AIM to Brian McGreevy Send a message via Yahoo to Brian McGreevy
Default

schumacher,

yes we generally decide which motors are best by how much rip they have. If the motor has low top-end then its not that good of a motor now is it? I judge how good a motor is on teh track by how much mid-range power and top-end it has. The low-end torque on a motor is only used one time during a race for the most part. That is why when you look at dyno readings, the back half (first part) of the curve is insignificant because you only use that part of the powerband once during a race. Dave Arnold's explanation about "area under the curve is very accurate in determining which are your best motors.
__________________
USVTA Member #211

Support Formula SAE - get kids into engineering!
http://motorsports.illinois.edu/
Brian McGreevy is offline   Reply With Quote
Old 01-29-2003, 04:43 PM   #7
Tech Elite
 
Brian McGreevy's Avatar
R/C Tech Charter Subscriber
 
Join Date: Jan 2003
Location: Illinois
Posts: 4,081
Trader Rating: 10 (100%+)
Send a message via AIM to Brian McGreevy Send a message via Yahoo to Brian McGreevy
Default

Mr. Arnold has also taught me a lot of what i know about interpreting dyno results. Kudos to Dave
__________________
USVTA Member #211

Support Formula SAE - get kids into engineering!
http://motorsports.illinois.edu/
Brian McGreevy is offline   Reply With Quote
Old 01-30-2003, 06:09 AM   #8
Tech Master
 
johnbull's Avatar
 
Join Date: Aug 2001
Location: Malta. G.C.
Posts: 1,762
Default

Please Mr. Arnold!!!!!!1

Can you tell me what figures to look out for on the CS dyno.

Regards

Joe from sunny Malta.
johnbull is offline   Reply With Quote
Old 01-30-2003, 09:44 AM   #9
Tech Elite
 
Neil Rabara's Avatar
 
Join Date: Jul 2002
Location: Lone Star
Posts: 4,821
Default

Try emailing him, you'll have better luck.
Neil Rabara is offline   Reply With Quote
Old 01-30-2003, 02:38 PM   #10
Tech Elite
 
Brian McGreevy's Avatar
R/C Tech Charter Subscriber
 
Join Date: Jan 2003
Location: Illinois
Posts: 4,081
Trader Rating: 10 (100%+)
Send a message via AIM to Brian McGreevy Send a message via Yahoo to Brian McGreevy
Default

I can tell you. You want to look at max power, power at max effic., low and high end torque, and the amp draw at all those point. What you are going for (mainly for mod) is the most powerful motor with the least amount of amp draw. Dave's theory which actually is quite true is, that when you divide the power by the amp draw, you get a certain #, that number is your "Track Power" number. So lets say you have a 250 watt motor and a 240 watt motor. Lets say the 250 watt motor draws 69 amps and the 240 watt draws 64 amps. Your track power # for the 250 watt is 3.623. Your track power # for the 240 watt is 3.75. The higher the number, the better. This works with stock motors as well. On the CS dyno w/o a laptop, look at all the #'s the readout gives you, with a laptop, look at the power curve, and also at those same #'s that it gives you. Once you use the dyno more and more, you'll be able to understand which numbers are important, which ones are not, and what good numbers really are and how to use those #'s to tell what it'll be like on the track.
__________________
USVTA Member #211

Support Formula SAE - get kids into engineering!
http://motorsports.illinois.edu/
Brian McGreevy is offline   Reply With Quote
Old 01-30-2003, 03:28 PM   #11
Tech Adept
 
Join Date: Aug 2001
Location: Grimsby, UK
Posts: 212
Default

axiom,

if you divide the power by the amp draw you get voltage

power = current x voltage

so the "track number" is in actual fact the voltage. what your/he implying is that the torque generated by the motor is greater

have a nice day

sanj
schumacher is offline   Reply With Quote
Old 01-30-2003, 09:06 PM   #12
Tech Apprentice
 
michael b's Avatar
 
Join Date: Nov 2001
Location: bartlett, tn
Posts: 38
Default

Dynos are just tools we use to compare motors. What one should do is find a motor that works well on your track, then dyno it to see why itís better then your other motors. It should be better somewhere. Then work with that and other motors to enhance those qualities that separate your best motors from the mediocre ones.
michael b is offline   Reply With Quote
Old 01-31-2003, 09:13 AM   #13
Tech Elite
 
Neil Rabara's Avatar
 
Join Date: Jul 2002
Location: Lone Star
Posts: 4,821
Default

I use my Facts Machine dyno as a comparison tool, utilizing a bench mark, then subsequent tinkering, putting it on the dyno, then on the track will give me an idea about the performance of the motor. I really only use it when I get a new motor.
Neil Rabara is offline   Reply With Quote
Old 02-01-2003, 03:51 PM   #14
Tech Elite
 
Neil Rabara's Avatar
 
Join Date: Jul 2002
Location: Lone Star
Posts: 4,821
Default

Does anyone know if there is a dyno for nitro engines?
Neil Rabara is offline   Reply With Quote
Old 02-02-2003, 01:41 AM   #15
Tech Fanatic
 
darnold's Avatar
 
Join Date: Feb 2002
Location: Bolingbrook, IL
Posts: 940
Trader Rating: 2 (100%+)
Default

Business has kept me busy along with some recent testing.

Schumacher great call. My rumenations regarding that potential formula was to look at a possible "relative" efficiency number. In other words i wanted to get some idea of "how much" h.p. i might be able to access due to the amp draw restrictions for a given class like my 12th mod but be able to compare various motors with it.

Maybe you guys can help with this since I'm not brushed up on this stuff, so if it's off kill me mercifully, LOL! It seems to me that since we are solving for v having "equalized" the other variables then we see which one has the greatest "percentage" of power (which I think in electric motors can also be resolved as efficiency).

IE: power = v x i so to solve for v we have done power / i = v so where v is greatest it would seem to = <efficiency since efficiency is input/output. Greater efficiency should = a greater percentage of h.p. that one Might be able to access. If this is correct then we may have a "relative" formula for figuring out efficiency in a comparative analysis between motors.

Normally it seems that the efficiency number of a motor is more of a static or isolated component within our dyno readings to the particular motor itself and not indicative of which may be faster on the track. In other words it doesn't seem like we can normally take a motor that has 80% efficiency vs. one with 70% efficiency and say the 80% will be faster on the track. I wanted to take into account the amount of power being developed to help determine that.

Is this stuff correct? Remember engineers, physicsist and electricians if i'm wrong just fix it please and save the flames. LOL!!

(oh boy i've opened a can of worms on this one and gone over my allotted one paragraph so i might have to buy lunch for a lot of people, LOL!)


JohnBull- I look at max watts and the amp that it occurs at as the amount of power out of the corners and the lower watts reading as the power for the straight. The amount of amps that the power occurs at dictates how much of it may be accessed. The higher the amps the less of that power can be had due to the "fuel economy" issue of finishing the race. Hope this helps.

RC Infinity- As far as i know they DO make a dyno for nitro engines as i remember an article in RC Nitro(?) that talked about one but i don't know who makes it or the name of it.
darnold is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
How do dyno's work? Doyle Cole Electric On-Road 1 10-21-2006 10:11 AM
dyno's Scott Loewensti Oval, Larger Scales and More 0 02-09-2006 03:30 AM
Speedo's-Dyno's 1fastdude R/C Items: For Sale/Trade 0 02-06-2006 08:37 AM
Dyno's, Com cutter's and... Where in Aus? MDL Australian Racing 5 01-18-2005 02:26 PM
Dyno's for sale. II Fast R/C Items: For Sale/Trade 16 12-07-2004 01:13 AM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 07:04 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net