kenjd

I have a Raptor 30 V2 and have been using a tower hobbies Digital Mini-Tach for airplanes. A local guy at the field said that would not work I needed a heli one. I just was wondering if it would work and if not what is a good tach to purchase. Rotor RPM seems to be very high but not sure. Any info would be helpful.

Thanks

Ken

loadthis

My Feedback: (3)

I dont see why it wouldn't work. Just take your measurements outboard of the flybar paddles.
Set it on two blade and measure the RPM on the main blades. I've never heard of a tachometer made just for helis.
I am still a newbie to helis but have used tachs for years on planes. Tachs measure the RPM by sensing the changes in light as the blade passes. If you hold your tach up to a flouescent light you will get a reading because flourescent lights flicker at a certain " flash per minute".
Take your readings outdoors without artificial light and you should be fine.



Happy holidays!

kenjd

That is what i thought but he was pretty positive about it. Where do you think is the best place to put the tach to get a good accurate reading. I was always checking at the tips.

Thanks

Ken

El_Guapo

The reason your plane tach may not work for helis is because you need to be within a few inches of the blade to measure the RPM. You're supposed to be checking the headspeed on the helicopter when it is in flight or in hover - Do you really want to be a few inches away from the rotor while the heli is in the air?
I guess you could try mounting the tach on the boom to get it close, but you still need a way to read the rpm.

There are special tachs just for helis - they have a viewport with a shutter. you look at the main rotor through the viewport and adjust the shutter speed until the blades appear to stop, then read the RPM off the LCD display. Here's an example of the Model Avionis Skytach, I have one and it is relatively inexpensive and works very well:

Go to http://www.modelavionics.com/ and click on "Optical Tach".

Hope this helps!
Jacek

fritzthecat

My Feedback: (4)

There are two ways you can tach a heli with a plane tach.
One is to mount the tach on the heli tailboom (rubberbands, tape etc) and have somebody else use binoculars to read the rpm.
Two is to mount the tach on a wooden stake and hover the helicopter over it. The other guy again uses binocs.
There are two popular models of heli tachs. The Model Avionics unit (see above) and the MinAir unit. Both work the same, the MinAir costs a little more. As with a plane tach, somebody else has to read the rpm while you fly.

Fritz

kenjd

Thanks for all that info. I have been getting the reading while the heli is still on the ground but light on the gear. I guess that is wrong. Next time i order parts i will have to add that to the list on parts.

Thanks again

Ken

tanasit

The thrid way:

I mounted my helicopter with several bungee cords to the cement bench at the park. The reading will be a little less than the actual in flight one which the helicopter can unload easier. I hover at around 1350 rpm and circuit at 1700 to 1800 rpm. I used to attend the rc heli world champion and noticed that the European flyer used a very low head speed for hovering but the Japanese use a high speed which they believe could cope with the wind better. Experience flyers can tell by just looking and listening only!

loadthis

My Feedback: (3)

Thanks for they eye opener. This forum is definitely an invaluable resource.

rusirius

Yeah, first things first... STOP USING THAT AIRPLANE TACH! It's not that it doesn't work, it's just that.... Well, for starters, you shouldn't be anywhere NEAR that heli when it's spooled up... ESPECIALLY sticking your hand inches from the blades with it light on it's skids! You also want the RPM to stay the same throughout the entire range of collective from just above 1/4 stick on up to full... I'd recommend around 1600 or 1650 in normal... (1850 or so for idle-up)... Get a tach made for a heli... I use the model avionics myself. Works great... Either have a friend read it while your in the air, or strap the heli down... You have to use some common sense if your going to strap it down though... Lock it down with a wood plank through the skids and bungee the frame down to the plank as well. Check the head and make sure everything is okay BEFORE trying this... Make sure it's locked down good, away from houses, cars, and anything else... And DON'T get ANYWHERE even CLOSE to it when it's spooled up.... This is perfectly safe IF you do it correctly... Don't worry about the heli, honestly the head has more stress put on it in some 3D manuevers than it does doing this.

kenjd

Thank's for that info i Hated doing it every time. Would a low rotor rpm cause to tail to wonder one direction slightly. I have a 401 with a 9253 servo. Just wondering because at first attempt to adjust rotor rpm the tail was wondering and then was better with more throttle. Thanks again for any info. this really helps because it cuts down on tuning time so i can fly. I am pretty new and i love it.

Ken

rusirius

yes, it could... The 401 tracks almost perfectly when it's set up right... Make sure it is in heading hold mode.... (gyro sensitivity greater than 50). I actually keep mine set for 100% sensitivity for heading hold mode... It won't hunt on you with the 9253... Make sure your delay is set for 0 and the 401 is set for "DS" (digital servo)...

Only other possibility I can think of is that you have "collective->rudder" mixing turned on... With a non-heading hold gyro, as you increase the collective the tail tends to rotate on you... So a lot of radios have the option to mix in some rudder to keep it straight... Make sure that's turned off, because if it's on, then when it tries to compensate for collective, it will actually give the gyro a command to change the heading...

kenjd

Thanks for that. I checked out every thing on the gyro and it seems to be setup right. I have it at 100% also and everything as you stated. So it must of been the rotor rpm. I am not sure how to even setup any of the mixes, but i know they are off. So i will work on the RPM.

Thanks again

Ken

i4c

One more option. An onboard tach that is esay to read in hover. Reads the rpm (0 to 2000rpm) of the main blades, stores the highest rotor rpm for recall on the ground. Accuracy of digital and "hall effect" sensor. Is a digital voltmeter any time it is not in the tach mode. Reads your battery pack to the 0.01vdc. Move transmitter sticks to work the servos which gives a loaded battery reading. Weighs 1 1/2 oz.

http://www.i4cproducts.com/v-tach.htm

Rod Johnson
i4c Products