R/C Tech Forums

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

Reply
 
Thread Tools Search this Thread
Old 05-11-2011, 11:00 PM   #286
Tech Rookie
 
Join Date: Dec 2008
Posts: 5
Default

"What is an electric rpm sensor? "
Eagle tree sells a brushless rpm sensor that reads the pulses from the motor leads ( not the sensor wires ). Electronic would have been a better descriptor.

I'd post a link but I have too few posts, so if you google this :
Brushless Motor RPM Sensor V2 you can read the manual.
L8apxr is offline   Reply With Quote
Old 05-12-2011, 12:35 AM   #287
Tech Initiate
 
Join Date: May 2011
Posts: 31
Default

Quote:
Originally Posted by L8apxr View Post
"What is an electric rpm sensor? "
Eagle tree sells a brushless rpm sensor that reads the pulses from the motor leads ( not the sensor wires ). Electronic would have been a better descriptor.

I'd post a link but I have too few posts, so if you google this :
Brushless Motor RPM Sensor V2 you can read the manual.
not bad inf.
highhigh is offline   Reply With Quote
Old 05-17-2011, 01:42 PM   #288
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

This was not helpful. The motor stuttered and even stalled for a bit.
john


Quote:
Originally Posted by joeqsmith View Post

Could you try a simple step function? So maybe spin the motor up then start the logger but don't have the speed sensor hooked in. Then plug in the sensor. So the logger see's 0 then max speed in a step.
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com
John Stranahan is offline   Reply With Quote
Old 05-17-2011, 03:03 PM   #289
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

http://www.shopatron.com/products/ca....35115.0.0.0.0

The sentry seems to still be available. It goes into the shopping cart and shows availability for $70. See the link above.

I expected problems since my computer is newer than when I bought the sentry. I am running windows 7. It will not detect the USB device (unknown)

I have run the program in windows vista compatibility mode
I have run the setup program from the hard drive in a previous windows compatibility mode


I have dowloaded the beta 1.1 Sentry software and installed it.

Still no go.
The lack of a device driver seems to be the problem.

OK the problem seemed to be the 5 V power supply is bleeding into the system. I turned it off and then the device driver loaded up.
John

I am told by e-mail that the GTB works fine on 4.2 V. I disconnected the receiver pack and all worked fine. I had an earlier wiring problem that misled me.

Here is the first file. Motor off, motor run up to speed with a quick turn of the servo tester. It is a text file and not usefull to most of us.

The second file was with the RPM sensor disconnected, the motor at full speed, then the sensor lead connected to the Sentry (fortunately there was no smoke. There was audible stuttering.)

Scroll to the right to see the test data on these two files.
john
Attached Files
File Type: txt Copy of First Log.txt (9.7 KB, 100 views)
File Type: txt Copy of Second Log.txt (9.7 KB, 59 views)
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com

Last edited by John Stranahan; 05-17-2011 at 03:44 PM.
John Stranahan is offline   Reply With Quote
Old 05-17-2011, 04:58 PM   #290
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

OK then. Here is the first run at 4.2 volts with the Slave.

time,
Voltage Input V,
Current Draw Amps,
RPM rev./m

00:00:03.5
00:00:03.6
00:00:03.7
00:00:03.8

4.249
4.154
4.06
4.06

2.438
15.112
16.575
16.575


0
5249
6535
6535


I will see if the flywheel run is usable.

I have a couple suggestions now of running the output of the slave through a 3 pole Rectifier (AC to DC) device. We could measure output power electrically then, but the losses in the motor are apt to be large. This would allow the use of a single resistor or switchable load.

Addendum
I am having trouble with the flywheel data. Just not enough points. I will order up an Eagle Tree, but a steel flywheel may be in order on 1 cell. The attached file is a text file of the important measures on a flywheel run of a Speed Passion 13.5 on the McPappy Flywheel.

Addendum #2
I ordered the Eagle tree v4 150 A model from Amazon. I ordered the brushless V2 sensor from Eagle tree. I may get some usable data from some hot motors in the meantime.

john
Attached Files
File Type: txt Condensed 13.5 Flywheel.txt (1.9 KB, 78 views)
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com

Last edited by John Stranahan; 05-17-2011 at 09:51 PM.
John Stranahan is offline   Reply With Quote
Old 05-17-2011, 10:25 PM   #291
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

Addendum #2
I ordered the Eagle tree v4 150 A model from Amazon. I ordered the brushless V2 sensor from Eagle tree. I may get some usable data from some hot motors in the meantime.

john

First Flywheel Output

Speed Passion 13.5 on 4.2 V.

Note a couple of useful things. Power peaks at about 6000-7000 RPM. This coincides nicely with a slave motor test at 6500RPM max. When we get things going the motors in this range will be tested near peak Power. This is likely how they are run on 4.2 V.

I suggest wiring the slave this way. Put a .1 ohm shunt accross each pole.

A couple of glitches are evident. Efficiency creeps above 100. The motor is only pulling 1-2 amps so zero errors are magnified. I may need to recalibrate my 200 amp (user added) sensor.

The math craps out near the end. The reason is the flywheel is no longer accelerating smoothly but is topping out. I could not chop a couple of points from the file as then there is an insufficient number of data points. Hence the Eagle tree order. It has 5x the sample rate so I should collect 5 times as many points on this same run. Smoother fitting of the model will result.

Double click a second time on the graph for an enlarged view.
John
Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-speed-passion-13.5-4.20-v0001.jpg  
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com
John Stranahan is offline   Reply With Quote
Old 05-18-2011, 04:42 PM   #292
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

Test of the McPappy Dyno (on Slave Motor) Precision

What you want to differentiate two closely powered motors, is good precision. That means each time you test the motor you get very close to the same answer. Then when you test a second and it tests higher you can reliably say it has more power. Here are the results.

I set up a test of an LRP X12, 17.5 stock motor with a black motor shaft at 4.20 V driving an LRP X12 21.5 set up as pictured previously with .1 ohm resistors shorting each pole at 75F. I wanted to test the precision of the coupler tubing as well. I disconnected the tubing and slave motor between each run and started a new test only after 5 minutes had passed to allow for cooling. I ran a 5 second test. I discarded the first test without a look as the tubing had set for quite a while. I ran 7 tests. I collected test 2-6 without a look. I took 10 RPM readings from each test. Each set started on the fourth data point collected which usually had the dyno running stable at a set RPM. I averaged the 5 RPMs. I calculated the Relative Standard Deviation (RSD). This was only 6 RPM out of 5337 RPM average.

The RSD pecent is .12 %.

This is very low and gives you high confidence that if your motor pulls more RPM on the dyno then it is more powerful. If desired use a stop watch and make a test after 4 or 5 minutes run time as well to see if the motor fades.

Numerical results RPM
5347.1
5331
5338
5337.2
5331.9


26685.2 Total RPM for five test
5337.04 Average RPM for five tests
6.4 Relative Standard Deviation for five tests
0.12 Relative Standard Deviation Percent

Additional notes.
I used a thin 6 inch machinist ruler to align the two motors and make them coaxial. I was careful to set the slave motor, which was losened for each test to remove the tubing, square with the slots. About a 1/8 inch gap in the slot at the front of the motor could be seen. I prefer screwing the motor on and it worked very well.

This photo shows the wiring of the slave. I no longer use the battery (receiver pack).
John
Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-mcpappy-dyno-complete-002.jpg  
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com

Last edited by John Stranahan; 05-18-2011 at 08:10 PM.
John Stranahan is offline   Reply With Quote
Old 05-18-2011, 05:18 PM   #293
Tech Fanatic
 
Join Date: Apr 2004
Location: Baltimore, MD
Posts: 961
Trader Rating: 31 (100%+)
Default

If anyone is interested, I have one of the mcpappy dynos for sale. Never used it and am selling it with a slave motor and Sentry unit. I love this and had great plans for it. McPappy makes great items.
__________________
Former fast guy just trying to keep up......
Jamie Hanson is offline   Reply With Quote
Old 05-25-2011, 06:26 PM   #294
Tech Rookie
 
Join Date: Mar 2010
Posts: 5
Default

Jon,

Thanks for posting the info. The level of precision you report reflects well not only on the dyno, but on your power supply, servo tester and ESC.

Some questions.

What was the sd and rsd for the "within run" data points (for each run, points 4 to 10)?

How does the 5300 rpm compare to the average RPM the motor would be pulling in competition at these voltages.

Assuming you have power curve data for the motor you tested using this or another flywheel dyno, what is the power output for this motor at 5300 rpm. I am wondering how many watts the slave/resistor system is absorbing and the relationship between this and the power requirements (rolling resistance, drag etc) during a race.

In the interest of full disclosure, I ask these questions because I am wary of the slave system as being a good choice for determining which of two motors would be better to race with or for determining which motor is more powerful. Given the variable load the slave represents (little or no load at low rpm, steadily rising as rpm increase), this method of motor selection would only be useful if the power absorbed was closely related to race load conditions and would not account for subtleties such as the cars ability to accelerate from a start or out of corners etc.

Thoughts?

Thanks

DamoRC
DamoRC is offline   Reply With Quote
Old 05-25-2011, 06:27 PM   #295
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

I have the Eagle tree Data Logger installed now. I am having some difficulties. Amps read 180. Voltage reads OK at 4.20. Voltage does not seem to change much during a flywheel test. RPM readings contain spurious high RPM results with the flywheel stationary before a test is even started. I am using the V2 RPM sensor that is soldered on 2 motor leads. Poles are set to 3. It does go up and seem to read right during a flywheel test some times. Getting at the data seems to be a problem. It is supposed to be cut and paste into excell. Where do you cut from. And then when I turn a test off with the servo tester the power supply shuts down. How does it even know. The light is blinking normally on the Eagle tree while on. The GTB speed control seems to be working OK and is not overheated. I will tinker some more tomorrow but would appreciate any help with the beast.
john
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com

Last edited by John Stranahan; 05-25-2011 at 06:46 PM.
John Stranahan is offline   Reply With Quote
Old 05-25-2011, 06:43 PM   #296
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

Standard deviations on each set of the 10 data points ranged from 7 to 9 RPM and averaged 8 RPM. Again I say this is just outstanding for a motor dyno.

The average RPM of a run is not that important as it includes many off power sections. What is important is RPM at max power. My experience with four (NiMh) cell racing on the oval shows gearing the acceleration parts of the track very near maximum power. The 5300 RPM is near maximum power for the test motor. I suggested that this was a good load to use as a result. Max power readings are very reflective of power at lower RPM's at max throttle. The whole power curve will be higher if max power is higher. It is also reflective of power at higher voltage. Power will increase as a straight line with Voltage. Now its really up to a guy with the slave motor dyno and a track to really prove this out.

The actual power that the slave is absorbing is part of the present task at hand and why the thread was revived. Stay tuned. I only have one data point at present. Hopefully a simple formula will result that can be used on a calculator at the track and the Eagle Tree Digital display without need for a computer.


Quote:
Originally Posted by DamoRC View Post
Jon,

Thanks for posting the info. The level of precision you report reflects well not only on the dyno, but on your power supply, servo tester and ESC.

Some questions.

What was the sd and rsd for the "within run" data points (for each run, points 4 to 10)?

How does the 5300 rpm compare to the average RPM the motor would be pulling in competition at these voltages.

Assuming you have power curve data for the motor you tested using this or another flywheel dyno, what is the power output for this motor at 5300 rpm. I am wondering how many watts the slave/resistor system is absorbing and the relationship between this and the power requirements (rolling resistance, drag etc) during a race.

In the interest of full disclosure, I ask these questions because I am wary of the slave system as being a good choice for determining which of two motors would be better to race with or for determining which motor is more powerful. Given the variable load the slave represents (little or no load at low rpm, steadily rising as rpm increase), this method of motor selection would only be useful if the power absorbed was closely related to race load conditions and would not account for subtleties such as the cars ability to accelerate from a start or out of corners etc.

Thoughts?

Thanks

DamoRC
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com
John Stranahan is offline   Reply With Quote
Old 05-25-2011, 09:11 PM   #297
Tech Rookie
 
Join Date: Mar 2010
Posts: 5
Default

Thanks Jon. Look forward to seeing more data.
DamoRC is offline   Reply With Quote
Old 05-25-2011, 11:14 PM   #298
Tech Adept
 
Join Date: May 2003
Posts: 170
Default

John,
Curious if the brushless RPM sensor from the Sentry will plug into the Eagle Tree unit. I have a feeling that it might as the magnetic sensor (which I think are the same between the two units) uses the same port. It might be that picking up the RPM signal through the motor's sensor cable port might be more accurate.
calvin is offline   Reply With Quote
Old 05-25-2011, 11:29 PM   #299
SKJ
Tech Adept
 
Join Date: May 2002
Location: OC SoCal
Posts: 179
Trader Rating: 19 (100%+)
Default

John
If I remember correctly the Eagle tree won't work on less than 4.5 volts. You have to power the eagle tree with an external power supply. If voltage goes too low it will shut down and reset when voltage recovers.

Steve
SKJ is offline   Reply With Quote
Old 05-26-2011, 07:02 PM   #300
Tech Elite
 
Join Date: Aug 2002
Location: Houston, Texas
Posts: 3,777
Trader Rating: 27 (100%+)
Send a message via AIM to John Stranahan
Default

Eagle Tree Report
I have made progress with the eagle tree. The amp sensor saves amps times 100. It seems to graph it that way as well. That is the reason for the high number. I then calibrated The Eagle tree with an ammeter and the system running at full speed which was 1.35 Amps.

The data file which the Eagle tree saves is a space delimited data file. To open it in Excel choose tab delimited data file, then next, then on the next screen change from tab to space delimited by unchecking tab and checking space. It now opens into something readable. Resave it as a .xls file. Now you can cut and paste.

The system is operating at 4.20 Volts.

The Rpm sensor has limits that you can check in the software. I chose 0 to 6000 RPM as limits for a 5000 RPM test. A lot of the spurious data (mostly high RPM spikes) is now elimintaded. I have one test saved now and need to see if I have smooth RPM data.

The voltage needs to be recalibrated using your volt meter. It was off about .2 volts.

Things are looking better, but not rosy yet.
John
__________________
[email protected]
TeamCRC.com Mikes-HobbyShop.com
John Stranahan is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
KARZ Calgary xrayroooahhhh Canadian R/C Scene 19114 12-01-2017 01:26 PM
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks John Stranahan Electric On-Road 1776 03-01-2016 01:18 PM
Novak Sentry as Brushless Dyno mattnin Electric On-Road 132 01-29-2010 05:53 PM



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 12:31 AM.


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