Here's an idea

[colbyweb]

I have an idea for all the electronic gurus out there. I have just enough electronic knowledge to know that this should be easy, but not enough to build it. Here it is; a tachometer that would go between the ESC and motor leads (preferably for a brushless motor). It seems to me that there should be a pulse going through the leads for each revolution and it would be easy to run that through a counting IC with LCD readout. It would be even better if it had an inductive pickup. I've often wondered why none of the watt meters have this feature. Or does the hyperion emeter have this feature? Maybe there is a reason why it won't work, but it seems feasable to me.
-Rick

[Chippie]

but...Won't the insertion of anything in one phase lead to problems for the esc in sensing the back emf from that phase ? just worth a consideration at the design stage? :)

[Mr.RC-CAM]

Using the brushless ESC's output seems to work fine as a motor tach sense lead. The user would need to know what divisor to set for each motor design to get the correct reading though.

I use this method to display motor RPM on my video overlay project. The basic ESC tach sensing concept is discussed here: http://www.rc-cam.com/forum/index.php?showtopic=748

RC-CAM

[Brad B.]

RC-Cam,

I checked you your above link and have previously "discussed" video overlay "stuff" with Bill (yb2Normal) with blackwidowav.com. He mentioned trying icircuits.com. Do you know of any other sources, including any DIY'ers for video overlay electronics?

Thanks,
Brad

[Mr.RC-CAM]

Brad, regarding OSD projects, there are a small handful to choose from. Besides Intuitive Circuits:
Decade Engr Bob-3: www.decadenet.com
Sx Video OSD: www.parallax.com/detail.asp?product_id=30015
Alti-OSD: www.kapelec.com/altiose1.htm
SimStick: www.hobbyengineering.com
STVPro: www.blackboxcamera.com

There are a random assortment of others out there too; just Google "OSD video Module" and see what you find. BTW, I'm working on a very sophisticated OSD design for A/P'ers. It is flexible enough to work in other R/C video applications too. If all goes well I may offer it commercially. Bloggy details to the ongoing project are found here: http://www.rc-cam.com/forum/index.php?showtopic=757. And, another nifty OSD project from a couple years ago is the MAHI Artificial Horizon: http://www.rc-cam.com/forum/index.php?showtopic=294

Since this discussion on OSD's is a bit OT, it would be best to start a new thread to see what sort of advice other ezoners can offer.

[colbyweb]

Am I the only one interested in a tachometer?
-Rick

[Mr.RC-CAM]

Am I the only one interested in a tachometer? I doubt that. :) Do you have an application that does not work with the traditional handheld tach?

As mentioned, a brushless ESC can be used for tach sensing. I can confirm that because it works for me. However, for most R/C hobbyists, the simple optically sensed tachs are very convenient. They are very reliable outdoors and do not require connecting a cable to the model. On the other hand, for onboard telemetry and other instrumentation, hacking into the brushless ESC is useful. However, the folks that are into this sort of application are not mainstream hobbyists.

If you are interested in using your brushless ESC to supply tach pulses then you could hack a standard optical tach. In a nutshell, you would just replace its photo transistor with a optoisolator. Then connect the optoisolator across two phases of the ESC/motor leads. There are a couple of resistors needed in there too, but I think you get the basic idea. The reading from the modified tach would need to be scaled for the particular motor/ESC you are using (Y vs. Delta and/or Pole count seems to be involved).

[mike50]

I doubt that. :) Do you have an application that does not work with the traditional handheld tach?

As mentioned, a brushless ESC can be used for tach sensing. I can confirm that because it works for me. However, for most R/C hobbyists, the simple optically sensed tachs are very convenient. They are very reliable outdoors and do not require connecting a cable to the model. On the other hand, for onboard telemetry and other instrumentation, hacking into the brushless ESC is useful. However, the folks that are into this sort of application are not mainstream hobbyists.

If you are interested in using your brushless ESC to supply tach pulses then you could hack a standard optical tach. In a nutshell, you would just replace its photo transistor with a optoisolator. Then connect the optoisolator across two phases of the ESC/motor leads. There are a couple of resistors needed in there too, but I think you get the basic idea. The reading from the modified tach would need to be scaled for the particular motor/ESC you are using (Y vs. Delta and/or Pole count seems to be involved).
I was interested in using this method (optoisolator across two of the three motor leads), but I haven't because of a perceived problem (maybe I'm thinking incorrectly though).

I understand how the commutation provides an appropriate signal for a tachometer, but doesn't the superimposed PWM signal, based on throttle setting, cause problems?

I was also worried about the back EMF, when the pair of wires is not powered exceeding the maximum reverse voltage for the LED. Or, perhaps the applied reverse voltage if you use the brake exceeding the LED reverse voltage. Is that a problem?

Mike

[Mr.RC-CAM]

I understand how the commutation provides an appropriate signal for a tachometer, but doesn't the superimposed PWM signal, based on throttle setting, cause problems?I have not seen any problems due to throttle settings. I am using a CC25 brushless controller. The opto wires that are connected to the brushless ESC will be subject to EMI/RFI, so I keep them very short. A simple low pass filter on the output of the opto may be needed on some ESC/motor combos to combat false counts due to ringing.

I was also worried about the back EMF, when the pair of wires is not powered exceeding the maximum reverse voltage for the LED.Yes, LED reverse breakdown can be an issue with some Opto's. I have a 1N4002 diode on my opto's input for protection.

[minifly]

I took my fluke multimeter (now gone, was in a stolen car :( ) and put it on 'volts dc' across two of the motor leads on my mega 16/15/4.

I set it to detect Hz, and compared it to the readout i got on my optical tach. It was exactly half.

[CRT_PJ]

This is exactly how some of the jet guys do it.

http://www.edfinfo.com/howtorpm.html

Good luck.

[kfong]

I've seen someone put an led and a 1k resistor across 2 of the motor leads and used a tach to determine the rpm, you would still have to do some calculations. On an edf it would make things easier. You could then have the led routed to a convenient location to take occasional readings.

Kin

http://www.embeddedtronics.com/

[Brad B.]

Brad, regarding OSD projects, there are a small handful to choose from. Besides Intuitive Circuits:
Decade Engr Bob-3: www.decadenet.com
Sx Video OSD: www.parallax.com/detail.asp?product_id=30015
Alti-OSD: www.kapelec.com/altiose1.htm
SimStick: www.hobbyengineering.com
STVPro: www.blackboxcamera.com

There are a random assortment of others out there too; just Google "OSD video Module" and see what you find. BTW, I'm working on a very sophisticated OSD design for A/P'ers. It is flexible enough to work in other R/C video applications too. If all goes well I may offer it commercially. Bloggy details to the ongoing project are found here: http://www.rc-cam.com/forum/index.php?showtopic=757. And, another nifty OSD project from a couple years ago is the MAHI Artificial Horizon: http://www.rc-cam.com/forum/index.php?showtopic=294

Since this discussion on OSD's is a bit OT, it would be best to start a new thread to see what sort of advice other ezoners can offer.

RC Cam, I have been reviewing your work per the "bloggy details" above. It is terrific! Great job. If I understand all of this correctly, this custom programmable GPS overlay can be purchased at:

http://www.dpcav.com/inspire/inspire.htm

(I wish I could've played with one during beta testing.)

So, assuming I am able (financially) at some point to purchase this and a camera system, say from http://www.blackwidowav.com, I can connect the inspire system and have all this overlay data transmitted to the receiver / monitor, correct?

Again, nice work. I admire your initiative and persistence.

Thanks,
Brad

[Mr.RC-CAM]

So, assuming I am able (financially) at some point to purchase this and a camera system, say from http://www.blackwidowav.com, I can connect the inspire system and have all this overlay data transmitted to the receiver / monitor, correct?
That is correct. In case it helps, there is a forum discussion dedicated to Inspire Q&A's here: http://www.rc-cam.com/forum/index.php?showtopic=1114

[Brad B.]

That is correct. In case it helps, there is a forum discussion dedicated to Inspire Q&A's here: http://www.rc-cam.com/forum/index.php?showtopic=1114

Yep, I have already seen it. Thanks.
Brad