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 :thumbsup:

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.

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?

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.

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.

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.

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.

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.

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.

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.

It seems not a lot of people have experience with the Robi Dyno :confused:

It seems not a lot of people have experience with the Robi Dyno :confused:

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 :thumbsup: .

Later, Bret

Now I have the ROBI DYNO, would like some people to give me their know-how about understanding this dyno's data ...

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.

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.



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.

Continued...



Flywheel Dynos




I hear all the time “my motor puts out XXX watts!”. What these people are refering to is the peak power output of a motor. (**please insert a picture of a dyno curve pointing to peak power**) Tuning your motor by peak power can be misleading. Peak power occurs only for a brief instant, so why limit your knowledge to just one instant? Most of the time you are racing you will be operating on the right hand side of the peak on the power curve, so it would stand to reason that this is where you want to add more power to your motor. (**show on picture of dyno curve**) I have seen motors with a high peak power but fall off in power so quickly that they were dogs on the track. Doing some track testing you can figure out roughly what the average amp draw of your motor is on the track. Using this amp draw you want to create a window around it that your motor is likely to be operating in. For example for stock offroad truck I try to look at the power from 20-25 amps.




How many times have you heard someone ask “How much RPM does that motor have?” I cringe every time I hear this question, because it really means nothing and usually the person asking it doesn’t want to hear my explanation. If you look at our sample dyno pull you will see that the max RPM is 23239 @3.00 seconds. I know this statement will ruffle a few feathers, but that number is worthless. Ok you ask “What is this guy smoking?” Well on the race track there are forces that hold your car back. These forces are in the equation that I gave you above; wind resistance, rolling resistance, inertial changes, and internal losses. A flywheel only has inertial changes, and a very small amount of wind resistance that can be considered zero for our purposes. This means that the flywheel on a flywheel dyno will accelerate until the motor has reached zero power. On the race track you will never even get close to this. I am guessing that the average RC car has at least 25 watts of power loss at its top speed. This means that your car will accelerate until the motor’s power drops to 25 watts then it will hold steady. This intern means that the motors maximum RPM on the race track will be just over 22,332 and not the 23,239 reported by the dyno.




Many dyno users also look at the spinup time of their motor. If you look at the dyno sheet you will see that the max RPM of 23,239 was reached in 3.0 seconds. But if you payed attention you would realize that your motor will never achieve this RPM on the track. So why worry about the spinup time to an RPM that your motor will never achieve on the racetrack? The time it takes the motor to accelerate to 22,332 RPM (the max the motor will probably do on the track) is only 1.7 seconds, so it makes a lot more sense to use this time to gage your motors performance by. Almost half of the spinup time reported by the dyno is to gain the last 907 RPM of the motor. A motor with the shorter spinup time to full RPM is not necessarly the motor with the shorter spinup time to the maximum RPM that the motor will see on the track, actually about 25% of the stock motors that go across my dyno are this way. If I went by the reported spinup time to choose my motors I would be slower than I would be with my back up motor.




Do you now understand why I stated that the dyno sheet included with motors tested on a flywheel dyno is useless. If the motor manufacture gave you all the info that would be great, but the info they give you doesn’t tell you much at all, except that the motor runs.




You want to test a motor at the voltage you will be racing with. Some dynos have adjustable test voltage and others have a fixed testing voltage. Not knowing any better I started dynoing my stock motors at 5 volts because it was much quieter. I found a stock motor that was probably the best stock motor that I had ever seen at 5V. I headed to the race track that week, put the motor in my car and it didn’t seem like my car had very much punch to it. I then took out the motor and dynoed it again, same results very fast. Then I decided to jack the voltage up because I was running a six cell class, the motor only gave average results this time. For a sanity check I then dynoed the motor at 5 volts again and it gave the same great results at 5 volts. Wow, what an eye opener that was. I learned the valuable lesson that a good motor at 5 volts is not necessarily a good motor at 7 volts. I began tuning my motors at 7 volts again and I was much faster at the track. So if your dyno has adjustable voltage test and tune the motor at the voltage that you are planning on it running at.




Amp draw is a method that many people use to tune stock motors without a dyno. The theory is that the more amps a free running stock motor pulls the faster it will be on the race track. There are some very fast racers that use this tuning technique so I decided to see if the theory held water. I dynoed some motors, recorded the results, and then I attempted to tune them by raising the amp draw. Then I dynoed the motors again and the results were somewhat shocking. I found a weak correlation at best between amp draw and dyno results. I guess that this method is slightly better than nothing, but you could end up de-tuning a motor thinking that you are making it faster, you definitely cannot compare two different motors by their amp draw alone.




Hopefully you now know what to look for and are getting your money’s worth out of your dyno. Now that you have blown a paycheck on a dyno and you understand what the results mean, there are no excuses for not running in the front of the pack. In all honesty owning a dyno won’t make you win races, driving and chassis tuning ability are much more important. There is no sense in being able to outrun anyone down the back straight and then loosing half a race track to them because they can keep up their cars speed through the turns and you can’t.