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Old 01-01-2006, 06:48 AM   #1
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Default Robi Dyno, How do you choose your best motor

Using a Dyno is only useful when you know how to interpret the data, My favorite dyno is the CE dyno but its rather hard to get hold of one these days so I have to do with the Robitronic Dyno. The problem I have is this.

Is the information from this dyno accurate and which information should I consider more important when choosing a good stock motor.

In theory If the power is there speed should just be a matter of gearing the motor right… right? However is the Data from a flywheel dyno accurate enough at the relevant amp and torque readings? Also how do the numbers from the Robi compare to those from the CE Dyno

Now if I were to follow what everyone is saying it should be a matter of choosing the motor with the higher power numbers and then gear it right, but what if motor 1 has better numbers between 18 and 25 amps and motor 2 has better numbers between 25 amps and 33 amps.

Which motor would you prefer? Motor 2 is up on power but down on RPM.

Motor 1 . Peaks at 34500 rpm/7volt/75%eff/126.7 watts
Current RPM Power
18 26000 82
20 24500 92
22 23300 101
28 20000 117
33 17700 124

Motor 2 Peaks at 29500 rpm/7volt/78%eff/123 watts
18 21500 90
20 20500 100
22 19500 106
28 17000 117
33 15300 123
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Old 01-01-2006, 06:56 AM   #2
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hey if yuor motor have alot og torque (Nmm) you will have great accelleration but you cant gear to have a hight speed because then it will overheat. If you have a motor with alot of speed (rpm) you cant gear it down to have alot og power because i dosn have the power to pull it. so you gotta look at the combination of power and torque.

Like if you are driving a very small indoor carpet track you gotta pick a motor with high torque.
but if you are out site on a big track you gotta pick one with high rpm.
and then just combinate the two of them to pick the right motor for your track

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Old 01-01-2006, 07:40 AM   #3
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Well consider this, if you have motor that delivers 100watts of power, and spools up quickly you can gear it low for quick out of the corner acceleration but it will not have a high top speed, or alternatively you can gear it higher to get a higher top speed but it will have no punch. However if you find the right gear you can have a good mix of acceleration and top speed.

The trick to any motor is finding the right gear for such a motor, under gearing a motor would make it run out of revs too soon, over gearing a motor would make it work too hard. Each of these options will cause the motor to over heat and ultimately die.

I see a Dyno as a means of choosing the best motor for the application. Having a look at the information I posted of the motors, which motor will give me the broadest range of gearing options without over/under gearing the motor? Which information to guys with the Robi dyno usually look at, maybe someone here can post there best numbers for a stock motor, and tell us why the consider those numbers good.
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Old 01-01-2006, 07:46 AM   #4
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when i am testin i look at the rpm the torque ant the amps that the motor pulls. you are right you gotta find the best gearing for the motor but you also gotta find the best motor for the track i have a motor with a torque on 93 rpm 33500 and 7 amps and i cant use it for my track because it as a high speed but no power my other motor has a torque 109 31000 rpm and 7.5 amps and thats is just crasy its just to wild mann but very good for indoor racing but would probently not do the trick outdoor
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Old 01-01-2006, 08:04 AM   #5
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you my also want to play with the springs on the motor. even though the tuners choose the springs to get the most out of a motor on the dyno, a very revvy motor can be awesome on small, indoor tracks when adjusted properly to the track
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Old 01-01-2006, 08:06 AM   #6
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yes sorry the springs and the brushes are very importent to
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Old 01-01-2006, 03:03 PM   #7
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watts are the key, and if you are looking at a robi then also look at the spool up time, that is the time it takes to get to full rpm. those are usually the best motors, you want lots of watts and quick spool up time
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Old 01-01-2006, 03:05 PM   #8
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i think you gotta ,make your own experiences and your own way to pick the motors using the data that you have available
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Old 01-01-2006, 10:03 PM   #9
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oh yea, u also want a nice curve. i look at robi dyno sheets all day long, lots of info on the sheets.
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Old 01-04-2006, 09:03 AM   #10
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Here is another way that I look at Robi data. I use the partial average power feature that is built into the dyno. Its on the bottom left corner of the computer output. A sample graph is found in the link below. You need to inspect the power graphs and insure that they are free of power spikes (sharp upward spikes in the curve from some kind of noise) for them to work well. This post is on the CE dyno thread. There is a lot of other useful info on this thread.

http://www.rctech.net/forum/showthre...no#post1986718
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Old 01-04-2006, 03:19 PM   #11
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Does anyone have accurate dimensions and weight of the Robi Flywheel?
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Old 01-04-2006, 04:08 PM   #12
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I have used the robi dyno for about 5 years now and the biggest tool that me and my buddy found (who also has the dyno) is set the amp steps in the options menu to whatever you feel your car is pulling.
For instance for oval stock racing I used 18-26 amps. If a motor hit 100 watts at that average watt range it was a missile on the track.

Another good feature is the gear calculator---once you find the right rollout for a stout motor was use that motor as a benchmark motor.

First you save that motor's dyno run and then put in the fast rollout for that motor in the gear calculator.

Then spin up another motor (note this only works if the motor is the same type for instance a Monster.. do not try and compare a Monster to an Epic )

Then it will show you where to gear the motor.

We use this for 19T motors right now and it's spot on.
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Old 01-05-2006, 12:44 AM   #13
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Thanks John and Erok, there is some realy usefull information in both your posts, What range would you be looking at for normal stock racing?

I currnetly look mostly at what my moters are producing on the 20/22 amp marks and tune according to that, it also seems to work quite well but I have heard other people looking more at peak power and peak RPM. I have never used the average limit feature but it does make sense. I also use the table feature quite extensively.

As for the gear calculator. I ave used it as a baseline and have found that it used the RPM value calculated at 30Nmm Torque. this value seems Fine for longer tracks but on shorter tracks I Use the value at 50Nmm or sometimes even 60Nmm. I have a rolout sheet that I compiled using my Benchmark motor and this seems to work rather well.

The following is one of my favourite motors, I recon this would be a screamer accoring to your standards Erok . I will apreciate your thoughts on this motor and perhaps you can also post some pics of a motor that you have found to be good in Stock.
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Robi Dyno, How do you choose your best motor-motor-robi.jpg   Robi Dyno, How do you choose your best motor-motor-table.jpg  
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Old 01-05-2006, 05:03 AM   #14
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hey guys I tried to get the software from Rob from Robi but no reply. Anyone know whereelse i can get it? The free version cannot save data.
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Old 01-05-2006, 05:11 AM   #15
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Unfortunately the windows version is linked to the Dyno Serial no so you have to buy a licnese for your Dyno, you can use the dos version without any restrictions though
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