Heading hold gyro

[wardbob]

Does anyone know how sensitive these devices (used in RC helicopters, etc.) are? That is, if put in a small car, how close to a straight line can they hold it? A PICaxe would provide a starting reference signal to the servo.

Here are several of many available.

http://www.hobby-lobby.com/gyros.htm
http://www.rcmodels.org/csm/csm_hlg200_heading_lock_gyro.htm
http://www.deeteeenterprises.com/NS.Futaba.GY-401.Gyro.php
http://www.maxxprod.com/pdf/PG2033.pdf

Some cheaper ones can be had for less than $50 US. None seem to give the info I need.

Thanks.

 

[BeanieBots]

I don't think it would work in a car
I don't have much experience of heading lock type gyros but the one I do have, integrates the tail rotor demand with respect to time. Hence, any gradual build up of error gets cancelled. In a car, any directional error is not only a function of steering error, but also of velocity due to the way the dynamics work. That is not the case in a helicopter which can turn on the spot with no forward motion.
On many units, it is possible to adjust gain and rate, so it might be possible.
For what it's worth, the 'Robot Wars' boys use rate gyros rather than heading lock to help with steering.

In a helicopter, heading lock really does lock the heading solid but that is with respect to gusts of wind. Over time, the heading can/does drift slightly. It works by integrating rotational acceleration rather than a compass bearing, so drift is enevitable. Well, at least, the one I have does.

 

[leftyretro]

Does anyone know how sensitive these devices (used in RC helicopters, etc.) are? That is, if put in a small car, how close to a straight line can they hold it? A PICaxe would provide a starting reference signal to the servo.

Here are several of many available.

http://www.hobby-lobby.com/gyros.htm
http://www.rcmodels.org/csm/csm_hlg200_heading_lock_gyro.htm
http://www.deeteeenterprises.com/NS.Futaba.GY-401.Gyro.php
http://www.maxxprod.com/pdf/PG2033.pdf

Some cheaper ones can be had for less than $50 US. None seem to give the info I need.

Thanks.

Well from your attached PDF link:

"This compact lightweight gyro is suitable to use with all size helicopters, airplanes, cars and boats. Please read the instruction manual completely before oper-"

So I see no reason that it could not be made to work, just a matter of proper installation orientation and gain adjustment. Looks like a neat device, having 3 of them would be cool to experimate with a 3 axis platform of some kind. Maybe in time the price will come down some.

Lefty

 

[MPep]

My impression is that the RC type gyros are generally a Rate sensor, meaning that they detect small variations of movement which then gets processed and an appropriate signal sent to the tail rotor/rudder, etc.

Therefore they are only good for short-term corrections.

A fluxgate sensor is used on boats (as part of their autopilot system) for the heading, and the rate sensor is used for small corrections caused (usually) by wave motion, but can also be because of strong cross winds, etc.

If my notion of a heading-lock gyro is incorrect, then please advise me accordingly.

 

[leftyretro]

My impression is that the RC type gyros are generally a Rate sensor, meaning that they detect small variations of movement which then gets processed and an appropriate signal sent to the tail rotor/rudder, etc.

Therefore they are only good for short-term corrections.

A fluxgate sensor is used on boats (as part of their autopilot system) for the heading, and the rate sensor is used for small corrections caused (usually) by wave motion, but can also be because of strong cross winds, etc.

If my notion of a heading-lock gyro is incorrect, then please advise me accordingly.

Well their application as a heading-lock gyro for tail rotor correction in helicopters is one of their most common applications. However they are in fact very general purpose in nature.

They normally are constructed using a single axis accelerometer and typically a proportional type control algorithm. The input (control setpoint) is the normal servo signal from a R/C receiver, but could just as easily come from a Picaxe. The output error term is sent to the controlled servo to correct any 'angle error' felt by the gyro.

By adjusted the gain control one can give the gyro as much control as desired to the controlled servo, up to the stability limit of the system. Too much gain and it will oscillate around the setpoint value.

Cool device but for many Picaxe type applications, just the fundamental accelerometer sensor could be programmed to perform the same function at a somewhat lower cost.

Lefty

 

[BeanieBots]

Don't get "Heading lock" and "Rate Gyro" mixed up.
They are very different devices.
Both used in helicopters to make flying easier but VERY different functions.

Rate gyro sends a signal to appose any rotation. (makes it stiff to turn but will not return to original heading)
Heading lock will "correct" any rotation back to the original heading.

Some (eg the one I have on my PICO) can be switched between the two modes. Flight controls are very different between the two modes.

For example:-
Imagine you are holding the helicopter.
With rate gyro, if you turn it slightly, the tail rotor will increase torque. Turn it a bit more and the torque will increase a bit more.
With heading lock, turn it slightly and the tail rotor will keep increasing in torque until either it can't increase any more or the turn is cancelled out.

 

[krypton_john]

Does anyone know how sensitive these devices (used in RC helicopters, etc.) are? That is, if put in a small car, how close to a straight line can they hold it? A PICaxe would provide a starting reference signal to the servo.

Here are several of many available.

http://www.hobby-lobby.com/gyros.htm
http://www.rcmodels.org/csm/csm_hlg200_heading_lock_gyro.htm
http://www.deeteeenterprises.com/NS.Futaba.GY-401.Gyro.php
http://www.maxxprod.com/pdf/PG2033.pdf

Some cheaper ones can be had for less than $50 US. None seem to give the info I need.

Thanks.

You could get an i2c fluxgate compass from mindsensors.com for under $40 bucks and use magnetic heading.

 

[wardbob]

Thanks to everyone for their input.

I missed the part in the pdf that mentioned car use.

I have a school project to give some kids, so I think I will try one. I'll let you all know what I learn.