RPM sensor

[MikeB]

Just came across this:
http://www.modelaccessories.co.uk/hobby ... ensor.html

anybody seen/done anything with one of these?

Mike.

[ShowMaster]

I was thinking of buying one at a hobby show in Jan but didn't.
I later on RCG I think posted that I saw a product that didn't require an optical signal to measure rpm on our motors. The topic never took off only some more discussions on how difficult the Frsky one was to use. I forgot all about it.
So maybe it's worth discussing it or at least how to make one that works with our Frsky interface. Good find Mike.
If you want to try one find a good source, a price, and send me your Paypal account and you can test it for me.

[ShowMaster]

I found this info on it

Function
- It detects the voltage changes at the wires of brushless motor, and then outputs the RPM signal. This RPM sensor can work with some speed control systems for helicopters. And one of its typical applications is to work as the RPM sensor for V-Bar system made by Mikado.
Specifications
- Size: 23mm(L)*10mm(w)*2mm(H)
- Weight: 6g (Input and output wires are included)
- Working voltage: 3.5V to 8.4V(1S to 2S Lipo)
- Current: 1 to 5mA
- Voltage range of the motor wires: 2 to 14S Lipo
- RPM range (for 2 poles brushless motor): 1000rpm to 300000rpm
- Working temperature: 0 to 50 Celsius degree or 32 to 122 Fahrenheit degree

[jhsa]

I would be interested in a RPM sensor, Hall effect, that would work together with the openXsensor..
Maybe my next project..

João

[thomas9x]

Haven't used Hobbywing's, but here is a brushless motor tach sensor that I created several years ago for an FPV OSD product. It connects to any two phase wires on the motor (or ESC). The Tach Signal output is electrically isolated from the motor (for protection).

Brushless Motor Tach.

- Thomas

.

[ShowMaster]

Looks good. So how does that relate to the 3 phase motor?
I'm used I the optical tach reading a 60Hz light as 3600 for a 2 bladed prop.
I have a Frsky optical sensor if I can find it. Maybe substitute this for the photo diode? I have no idea if the hub just sees highs and lows from the photo diode or has to see some other code from the Frsky sensor!
Scope time I'm thinking.

[rperkins]

I found this info on it

Function
- It detects the voltage changes at the wires of brushless motor, and then outputs the RPM signal.

I am wondering if the open source ESC firmware ,simonk, could be modified output this information. It can already do serial communications when updating the firmware, but it is not working as an ESC at that time. it does the serial COM through the PPM input, which is in use when working as an ESC. So a line would need to be added and the MCU , m8 usually, would need to have time to output the rpm without impacting the timing of the ESC routine. Just another crazy idea

[MikeB]

In searching for info on this unit, I did see that some Hobbywing ESCs seem to be outputting RPM data.

Mike.

[kaos]

I think this type of sensor works much better than optical or hall effect sensor. no moving parts needed. if we can add a function for gear reduction to display the real rpm for application that has gear reduction, ie heli.

[MikeB]

Er9x/ersky9x you can set a value for the number of blades. This is really the number of pulses for one revolution. Currently the maximum value is 50, so it depends on how many pulses you get from the motor for one revolution of the rotor head if this is enough. I think it could be increased to 250 if necessary.

Mike.

[kaos]

ha, I did not know that. I thought that needs to be used with an optical sensor from Frysky. thx.
if the function is already there, a simple voltage rpm sensor that can be connected to either D-rx and/or hub would be great.

for example, a typical/Align 450 heli main gear is 150T, the pinion is any where from 10-14T (11-13 most commonly) using 13T as example the gear reduction would be 150/13 = 11.538..
may be we need a number with decimals.
say using a 3S lipo with a 3500kv motor, theoretically, the rpm of rotor blades at full charge would be 12.6x3500x13/150=3822 rpm
would be nice if we have this 'voltage sensor' and be able to put some 'divider' to read actual rpm.
I know some planes also use a gear reduction prop too. To make it easier, just put pinion number and main gear number we can read flat out the rpm. for motor/prop without gear reduction just put 1 and 1 for pinion/main gear.
I think this can be used for simple prop, gear reduction prop, heli and edf as well. Now I am getting excited to see this being developed.

Tell me what I need to work on, I will glad to test this thing.

[MikeB]

A brushless motor may well have 12 or 14 poles. Monitoring the current on the 3-phase wires will likely give 6 or 7, or 12 or 14 pulses (blades) per revolution. Assuming 14 poles/14 pulses you would get 161.5 pulses per revolution of the rotor blades. This is the value needed so we probably don't need decimals, 161 or 162 would be good enough.

Mike.

[ShowMaster]

The one I saw at the hobby show had a digital readout in it so I guess it works. I wonder why it's not better known or advertised that there are tachs that can just connect to 2 motor leads?
The optical version is a pain but I guess it's easier that connecting to motor windings at the field.
I found 2 Frsky optical sensors in my hobby storage looking for my misplaced GPS. No GPS yet but I did find a V2 hub as well so I may mess with the tach idea.
I also found several different optical isolator ic's to use. No wonder my car won't fit in the garage anymore!

[kaos]

yep, I was thinking the decimals for application has gear reduction. so we may need a number for pulses per revolution, pinon number and main gear number?

[MikeB]

Or, as I did above, do the calculation and enter the result as a single number, saves flash and EEPROM space

Mike.

[kaos]

Dang, was trying to avoid pulling out my calculator in the field. I guess I still need my cell phone at the field.

How is the hobbywing sensor connected to Frysky hub/rx?

PS: just ordered 2 from helidirect.com for 3.49@

[jhsa]

I think this type of sensor works much better than optical or hall effect sensor. no moving parts needed.

Not everybody fly only electric.. Someof us also fly IC powered aircraft
So, an Hall effect sensor would be ideal for us

João

[ShowMaster]

Help me with the theory. For a 2 bladed prop.
The photo diode I'll call it, has the light interrupted 2x for every revolution by a 2 bladed prop. This results in the photo diode going from a conducting state to a non conducting state or probably a low to a high 2 times every revolution.
If replaced with a Hall Effect sensor and 2 magnets are placed on a prop backplate at 180 deg apparat and the hall is in close proximity, it will go from a high state to a low state when ever the magnets pass by.
Again 2 pulses per revolution.
This can be inverted if needed.
So the hall device can replace the photo diode in time frsky sensor?
For a brushless sensor using the posted circuit would cause the opto output to change level and could also replace the photo diode. Polarity inverting could be easily done if required.
The only real question I can't answer is how many pulses would come from 2 wires on most brushless motors? Maybe the tx FW RPM setting would need more setting values?

[MikeB]

I've just ordered one of the sensors I saw in the first post. While I could make something, I thought I would test a unit many can easily obtain.
With this I'm expecting either 7 or 14 pulses per revolution so I will just set the number of blades to 7 or 14 (I currently allow 1 to 50 blades!).

Mike.

[ShowMaster]

I found time to connect my Frsky RPM sensor to a hub and it does report 3600 RPM pointed at my florescent lights on the Taranis as expected.
Now to find a 120v AC to 6 or 12ac transformer in my junk box. I want to test the interface circuit on the bench then I'll try it on the brushless motor and monitor with my optical tach as a reference.

[kaos]

Not everybody fly only electric.. Someof us also fly IC powered aircraft
So, an Hall effect sensor would be ideal for us

João

IC power more power to do damage/hurt people, noise pollution, air pollution. should be banned from the planet earth!

[Tomkfly]

Is there anyway to use the tachometer output on a RCxell ECU?

Tom

[jhsa]

yeah, right..

Actually electric motors have more power than IC, and IC engines don't start spinning by themselves if you bump the throttle stick.. so, what is more dangerous? electric motors also spin faster and normally don't stop if they hit something
IC engines are a little dangerous when tunning them as the needle is very close to the prop on some of the engines, hence we should be a little careful and don't tune them from the front.
Electric motors are much more dangerous.. About the noise, I LOVE IT. Specially the big 4 stroke gas engines..

João

[ShowMaster]

I miss hand starting a IC engine in the cold and getting my fingers hit by the prop when flipping it.
It the manly thing to do! No chicken stick or glove.

[jhsa]

well, we shouldn't start our engine with bare hands

Still safer than an electric motor

[dvogonen]

I have stuck to smaller electrical planes lately and felt quite safe. Two weeks ago I was rudely awoken from that feeling when I picked up a small (but very fast) plane I had landed. I must have switched off the engine cut switch on the transmitter when I put it down to retrieve the plane. I didn't notice this since the ground was not perfectly flat and the signal got blocked by 20 meters or so of dirt. The receiver failsafe killed the engine anyway. When I raised the plane from the ground the receiver got signal again and the motor started at full throttle. The result was a really nasty cut about 5 cm long an half a centimeter wide. I was lucky to be hit on the outside of my wrist. 3 cm to the right and the cut would have severed the arteries to the hand.

Lesson learned: Never put the transmitter on the ground and never assume that the motor is safe until the power has been disconnected.

[ShowMaster]

well, we shouldn't start our engine with bare hands

Still safer than an electric motor

Meant as humor...

But then I'd be using an electric motor to start a IC engine that requires charging the starter battery. By going all electric it eliminates all the extra support items, gas, glow plug battery, pump, cleanup items, after run oil.
Wow, no wonder it takes so long to load my car to fly IC.
I do enjoy my IC engine stopping half way on the 100ft taxiway. To solve that I carry the nicad starter battery and the electric starter and it's battery along with me.
I've thought about installing wheels on my flight box so I can drag it with me. If I do use a neck strap I enjoy my tx swinging into the prop if I have to restart the engine and don't take the neck strap off.
Then there's the issue of just kneeling down to start it and actually being able to stand back up again. Even better if it on a cold day.
I also miss my engine quitting right after takeoff and the exciting dead sticks.
I solve that by adding an electric glow driver onboard powered by batteries.
My IC planes end up almost electric by the time they get into the air.

[MikeB]

I gave up on IC more than 11 years ago, just too fiddley and too messy. I too had an electric glowplug driver on board, and also a servo on the needle valve. The models do seem to last longer without the fuel/oil soaking in. The model in my avatar is over 11 years old, and I also fly a couple of other models that are over 9 years old.

I also treat "all" models as having a live motor/engine, and keep behind the prop.

Mike.

[jhsa]

Everybody obviously have their own preferences.. I love the sound of a good engine Don't mind the mess and the smell.. actually petrol IC engines are not that messy. A bit smelly, but they smell the same as the full size I used to fly, so I love'em. there's nothing like the petrol smell in a cockpit Still, IC powered models are safer
well, all that to say that I'd like a hall effect sensor even for electric models.. light weight, reliable, don't need big calculations with motor poles, just 2 little magnets glued to the prop holder. the sensor itself is normally very small, probably the size of a little transistor?
I think I will try to find a suitable one and ask/nag Rainer to support it on the openXsensor project

João

[ShowMaster]

Got the IC noise covered. The latest thing at the field is very loud sound machines in the electric planes. I think louder then an actual IC in the pit. Bomb drop sounds, machine gun sounds, you name it. So much for quiet electric flying.
I'm tempted to add a 10w amp to my Taranis so I can play some ACDC to drown out the noise. I need a speaker system in a backpack to compete.
What next? Maybe an atomizer to simulate burning castor oil or kerosene on them.
When I flew slope gliders years ago I used rubber bands stretched across a U yoke and in steep dives or high speed passed it really made a humming noise. I was kicked off the hill until I removed them. With the audio amps and mp3 players now think of the damage one can do to the quiet.
Humm technology.