Robitronic Dyno Data - HobbyTalk
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post #1 of 16 (permalink) Old 07-19-2005, 09:16 AM Thread Starter
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Robitronic Dyno Data - Modified 7 or 8 Turn Motors

I have a Robitronic Dyno and will like to master the art of interpreting its data. I managed to find few threads already here about dyno data, however not specifically about the Robitronic system only or not related to my subject.

So, I need to know how to set it up (i.e. preferences) and what are the most important things to look for and fine-tune for low wind motors especially such as 7 or 8 turn motors for On-Road Racing with 6 Cell batteries. Thanks a lot

Last edited by dhiracing; 07-19-2005 at 09:59 AM.
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post #2 of 16 (permalink) Old 07-19-2005, 10:46 AM
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Definately run the input voltage at 7.5v

I felt the biggest feature was you could adjust the Average limit.
For example for stock motors I would set it to 18 - 26 amps
If we got a Monster or Epic Stock to pull around 100 average watts, you had a good motor. You have to set this up in the Setup/options screen.
Then it calculates it and puts the average watts on the main screen after a dyno pull.
Look in the left hand bottom corner for this number.

Also the bottom table on the Graph/Table screen is very important.
It shows you RPM, Torque, and Wattage at the various amp steps.
You can adust those amp steps as well.
For example you might wanna look at higher levels for mod motors like 35+
For stock we looked at 18-26 A, for 19 25-35, etc

Find a motor that runs good on the track and use the dyno to see the numbers.
Then use that motor as a benchmark.
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post #3 of 16 (permalink) Old 07-19-2005, 11:25 AM Thread Starter
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Thanks for the feedback, including suggestions. I only hoped someone had already tested and tuned low wind motors on the Robitronic Dyno.

For example ...
M1 @ 35 amps: revs 39,400 - power 162 - eff 78 - torque 40 - voltage 6.0
M2 @ 35 amps: revs 40,300 - power 150 - eff 72 - torque 36 - voltage 6.0

- Why is the voltage 6.0, if I made simulation for 7.5V?
- During racing I think we reach 35 amps with 7.2V+ or am I mistaken?
- What can you see from the data above of Motor 1 and 2?

Just need a clear explanation at what figures to look when using the Dyno and where to improve?

For example ...
- Is the value of FRICTION important to decide what springs to use?
- Is POWER the most important thing to look at?
- What CURRENT steps are important for low wind modifieds?
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post #4 of 16 (permalink) Old 07-19-2005, 09:43 PM
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Not to get off the topic but does anyone know who fixes Robi's. I've got one thats broken and would love to get it back up and running. Thanks in advance.
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post #5 of 16 (permalink) Old 07-19-2005, 11:05 PM
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What happened to your dyno?? I blew the F.E.T.s in mine and a local electronics shop did mine. Not the cheapest way I guess but its up and running and had it back in two days with no trouble.
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post #6 of 16 (permalink) Old 07-20-2005, 04:49 AM Thread Starter
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Quote:
Originally Posted by erock1331
I felt the biggest feature was you could adjust the Average limit. For example for stock motors I would set it to 18 - 26 amps
Besides my questions as per my last post ...

For example if I change average current limit, how will it effect the results shown on the table? I think by default for Modified motors it is set up between 40 and 80 amps.
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post #7 of 16 (permalink) Old 07-20-2005, 07:53 AM
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The ave current limit, only effects the front page average watt caclualation.

To change the results on the table you need to change the amp steps there.
If you are running the windows version I beleive you just bring up the table and then click on amp step numbers, the cursor comes up and I think you just type in the steps you wanna view.
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post #8 of 16 (permalink) Old 07-20-2005, 07:55 AM
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Quote:
Originally Posted by ekid138
Not to get off the topic but does anyone know who fixes Robi's. I've got one thats broken and would love to get it back up and running. Thanks in advance.
Most just send em back to Robi

But expect a long wait from what I heard.
My buddy contacted them about getting the updated EPROM chip for his unit to be able to run 7-19T motors and they took their good old time, I think over 2-3 months to get the chip to him. One nice thing is there was no charge for it.

Last edited by erock1331; 07-20-2005 at 07:57 AM.
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post #9 of 16 (permalink) Old 07-20-2005, 11:03 AM
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the sensor on the motor stand went bad. It doesn't pick up the flywheel anymore. I was actually hoping to find someone Stateside that could fix it.
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post #10 of 16 (permalink) Old 07-20-2005, 02:48 PM
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If you know it's the sensor on the motor stand, perhaps you could contact Robitronic and get just a replacment circuit board... ( I think all that stuff on the stand is on a single small circut board) Shouldn't bee much of a problem fixing something that simple.
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post #11 of 16 (permalink) Old 07-22-2005, 03:14 PM Thread Starter
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It seems not a lot of people have experience with the Robi Dyno
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post #12 of 16 (permalink) Old 07-22-2005, 04:03 PM
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Quote:
Originally Posted by dhiracing
It seems not a lot of people have experience with the Robi Dyno
Yea, I got rid of mine because I don't like throwing an instant 6 or 7 volts to the motor, it seems to just blow the brushes off the com and arc. Just not the ideal thing for me.
I found that the "friction" thing was a real boner. Too many variables to really work.
Trust your motor builder, and rebuild your motors as he had them .

Later, Bret
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post #13 of 16 (permalink) Old 08-01-2005, 08:25 AM Thread Starter
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Now I have the ROBI DYNO, would like some people to give me their know-how about understanding this dyno's data ...
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post #14 of 16 (permalink) Old 08-01-2005, 12:13 PM
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FYI

I've owned both the CE TurboDyno and the Robitronic... I personaly feel that the TurboDyno is harder on motors then is the Robitronic... but then it depends on what settings your useing and/or how much of a load your trying to read on the CE TD, etc...

Dyno Data in general is very hard to fully understand. Not easy to give you a simple answer as to what to look for.

In general when looking at stock/fixed timing motors, peak power is just about as good a indication as any ohter single data point. However no single point alone is worth much.

I personaly feel spin up time is something that the typical user should not even be concerned with, the Robi itself calculates torque based on the change in RPM (accleration) over a period of time, but if your not a physics geek, I'd ignore spinup time...

Don't ignore RPM completely, but don't set your hart on it either. If you have two motors with the same Peak power, the one with the higher RPM is almost certianly going to be a faster motor on the track, if you get the gearing correct...

Well those are about my only quick and dirty words of wisdom... I really don't have time to go into a lengthy explination of it all... If you have some specific questions, I'll try to address them when I get a chance.
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post #15 of 16 (permalink) Old 08-01-2005, 04:28 PM
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I wrote this a few years back when I wrote for Xtreme RC Cars Magazine and they chose not to print it so I figure its fair game to put on here.


Quote:
Dynos are without a doubt the holy grail of RC support equipment among electric racers. Their cost is often prohibitive to many. A dyno is next to useless to anyone that doesn’t understand how to properly interpret the data or run a representative test on their motor. In the pits I often see people brag about how well their motor dynoed, when many of these people have no idea what they are talking about. I work in the world of data collection and find that many test engineers get lost in the data collection and the interpretation of the data from their $100,000+ data acquisition system, so don’t feel bad.




What a dyno does.




A dyno is simply a piece of test equipment that runs your motor and measures the power output of the motor. Dynos can accomplish this task in several different ways. Since power is a product of torque and angular velocity both of these can be directly measured and power can be calculated. An example this type of dyno would be the Competition Electronics Turbodyno. A dyno can also accomplish its job by accelerating a flywheel. Examples of this type of dyno include the Robotronics Pro Master and the Fantom Facts Machine. A flywheel dyno measures angular velocity and the time from the beginning of the dyno run. It then uses the change in angular velocity over a set amount of time (angular acceleration), and since the inertia of the flywheel is known, torque can be calculated from this. Then power is obtained from the product of torque and angular velocity. Each type of dyno accomplishes its job quite well. It is only a matter of personal preference as to which one is better. The dyno user is much more important than the type of dyno used. The flywheel dynos, however give so much data that it is easy for the user to be overwhelmed and make mistakes interpreting the data. Because Competition Electronics no longer manufactures the TurboDyno we will concentrate on the flywheel style dynos.




What makes my car go?




Your car is accelerated by power, not RPM or torque. Upon doing the analysis on an accelerating car you will find that the acceleration of your car is governed by the simple equation below.




Acceleration = Power from Motor – Inertial Changes – RollingResistance – WindResistance – InternalLosses




Inertial changes come from Newton’s Law force is equal to the product of mass and acceleration. The greater the mass or acceleration the greater the inertial changes of the car. Rolling resistance is the energy lost from the tires contact with the ground, increasing the speed or weight of your car will increase the rolling resistance. Wind resistance is caused by your car having to cut through the air, the faster it is travelling the more wind resistance your car will be subject to. Internal losses are any loss of energy internal to the car, such as transmission, bearing, and friction losses.




With some basic algebra knowledge you will see that once the losses are equal to the power from the motor your car will quit accelerating. The equation will also tell you that the less power your motor is putting out the slower your car will accelerate. You can compensate for low RPM or low torque if you motor has the power it is only a matter of gearing it correctly.




How do I tell if I have a good motor?




OK, interpreting the data is where most mistakes are made. If you look at the dyno sheet included with some motors you will see only a few numbers on some such as a peak power number, a peak RPM number, and efficiency number and sometimes a spinup time if a flywheel dyno was used. If you get a dyno sheet that looks like this do yourself a favor and just throw it away, I will explain in a bit. If your motor came with a dyno sheet that has 5 or 6 data points on it (from a TurboDyno), these are actually somewhat useful, and again you will see why in a bit. I have noticed that some motors that I bought included a dyno sheet but the brushes didn’t even have wear marks on them, so I wonder how that particular motor was ever dynoed.




TurboDyno




Looking at the example dyno sheet from the TurboDyno you will see data at a certain amp load. The TurboDyno has the easiest to understand data output and is a lot less prone to mistakes made in analyzing the data than the flywheel dynos (not necessarly better, just more idiot proof). The downfalls of this type of dyno is you can not get any data points from a dead stop and you are limited to the number of data steps. To determine what you need to look at to go fast is often just trial and error and once you find a good spot to look at from a combination of dyno and track testing you can use that range from then on. For 6 cell stock racing 20-25 amps is a good range to look at to see if you have a good motor. If you want a bit more power at top end you should lower the amp number that you look at, for example 19-23 amps. If you want a fancy graph like the flywheel dynos give you just input your data into a spreadsheet and graph the data.



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