Inertial Navigation System?

[Speakerguy]

I was watching a History channel documentary on Nazi technology, and they talked about the V1 flying bomb being the first weapon to use INS based on gyroscopes, and how amazingly accurate they were for something of their time being able to fly to Britain from Germany and hit cities with some decent accuracy.

Anyway, with todays MEMS products, would it be possible to make an INS for an RC helicopter, RC airplane, or model rocket (I imagine that would be most difficult)? I know that GPS would be a much more modern and accurate method for accomplishing the same thing, but I have something of an interest in just doing things 'the old way' for personal edification.

Any recommendations on where to start? I won't be loading these with warheads or anything, though I might try and target a friend's farm or something to test my accuracy.

 

[dknguyen]

It is possible I guess. It is difficult, however, to use gyros and accelerometers (and anything realy that requires mathematical integration) for absolute navigation. So acceleration to determine absolute distance travelled is almost completely out the window since you need double integration (almost regardless of how well you can calibrate them). With gyros you might be able to pull it off with calibration. It's difficult though. If you want to see the accuracy of an affordable calibrated unit from Microstrain, check out these videos:

The Journey Robot - David P. Anderson

They don't exactly give you a sense of the accuracy of the gyros though since it is a ground vehicle that is also fusing double integrated acceleration with odometry. But you get the idea of the accuracy.

Analog Devices also now has calibrated 6-axis gyro+accelerometer units for about $700.
ADIS16350
ADIS16354
ADIS16355

For all intents and purposes the 54 and 55 are your better bets since the 50 is onyl calibrated at room temperature while the others are calibrated across temperature ranges.

THe best gyros I have found are those from Silicon SEnsing which run about $150 each per axis. They aren't calibrated but have very good uncalibrated specs that you might get away with certain absolute positioning applications with some creativity. By far, the easier applications are those where there is a periodic "resetting" of the integrated values to correct the bias offset that will occur for the gyros- like a compass for the heading and infrared horizon sensors for the roll and yaw (Melexis MLX90614 is the best one I've found with the digital interface. It's also calibrated. I don't know how well raw analog thermopiles are matched since they must work in pairs, but I couldn't figure it out so decided on these digital ones instead).

http://www.uavs.net/horizon_sensing_autopilot.pdf

From my research, I've drawn my own conclusion that it isn't possible to do dead reckoning with accelerometers without some kind of external absolute positioning like GPS to make the unbounded error bounded. Orientation (with gyros) is much easier to deal with, but in "absolute orientation" schemes you would still need IR horizon sensors and compasses. Two of the biggest problems with acceleration odometry are the double integration and how the distance vector is dependent on the gyro readings. So the acceleration odometry is built on top of the gyros (and all their errors).

 

[ericgibbs]

I was watching a History channel documentary on Nazi technology, and they talked about the V1 flying bomb being the first weapon to use INS based on gyroscopes, and how amazingly accurate they were for something of their time being able to fly to Britain from Germany and hit cities with some decent accuracy.

Anyway, with todays MEMS products, would it be possible to make an INS for an RC helicopter, RC airplane, or model rocket (I imagine that would be most difficult)? I know that GPS would be a much more modern and accurate method for accomplishing the same thing, but I have something of an interest in just doing things 'the old way' for personal edification.

Any recommendations on where to start? I won't be loading these with warheads or anything, though I might try and target a friend's farm or something to test my accuracy.

hi spkrguy,
Im afraid that program misinformed you, the V1 flying bomb 'buzz bomb' had no INS navigation.

It was launched from ramps pointed towards London from France and Holland, it hadnt got the range to fly from Germany.
It had onboard a propeller driven veeder counter which measured the distance flown, the fuel line was cut at a predetermined count and the engine cut.

The INS system was first used in the V2 in 1944, again it was launched from France and Holland, not Germany.

I was only 12 years old at the time, but I do remember, when the engine stopped on a V1 you got under cover. No such luxury with V2, no whooshing sound until after the bang.

Regards

EDIT:

**broken link removed**

**broken link removed**

 

[dknguyen]

I'll quickly outline the the various layers of an IMU and how each one is built on the other, and how far you have to go for particular applications.

Layer 1: 3-axis Gyro + integration for each independent axis
Application: Dampening and stabilization of the vehicle response, in the presence of a pilot, it can be used to lock the vehicle in it's current orientation when the controls are released for short times. Over time drift will occur, but the pilot is there to correct for that and usually controls aren't released for a very long time either so drift is not a big problem.

Layer 2: 3-axis Gyro + integration foe each independent axis + integration of the collective angular readings
Application: Allows you to keep track of where the ground is. Without high quality gyros, external absolute reference sensors such as horizon sensors and compassesm or a pilot unbounded error will occur flipping the vehicle over time. The math starts to get tricky as you need to convert the pitch/roll/yaw angular readings on the plane to a coordinate system relative to the ground (which itself is built up on previous successive math operations of the same kind) in order to keep track of where the ground is.

Layer 3: 3-axis Gyro + integration foe each independent axis + integration of the collective angular readings + acceleration
Application: Dead Reckoning. Now you also need to use the acceleration readings double integrated built on top of the results of the tricky math from Layer 2 to figure out the distance and direction travelled between samples. Unbounded errors run abound! Best to have some kind of reference system to bound the error just like the gyros. GPS is about the only one I can think of for bounding positional errors short of terrain mapping + radar scanning.

In my projects I've all but abandoned Layer 3. Layer 1 and 2 are quite possible though.

 

[3v0]

I was only 12 years old at the time, but I do remember, when the engine stopped on a V1 you got under cover. No such luxury with V2, no whooshing sound until after the bang.

I recall a documentary saying the V1 was such a terrifying weapon because it could not be aimed accurately. You could not avoid it by staying away from "high value targets". It was just as likely to land on a house as an airplane factory.

 

[ericgibbs]

I recall a documentary saying the V1 was such a terrifying weapon because it could not be aimed accurately. You could not avoid it by staying away from "high value targets". It was just as likely to land on a house as an airplane factory.

We mislead the Germans by reporting they were falling outside the London area, IIRC too far North, so they reset their ramps, so in fact they started falling South of London.

When the allies pushed the Germans back after 'D day' they started aiming for targets in Belgium and Holland.

 

[Speakerguy]

Perhaps I got the V1 and V2 confused. It has been a while since I saw the documentary, but the project has been in the back of my mind since.

 

[ericgibbs]

Perhaps I got the V1 and V2 confused. It has been a while since I saw the documentary, but the project has been in the back of my mind since.

hi,
The gyro in the V1 was used to keep the wings level in flight.

Allied pilots used to fly wing tip to wing tip with the V1 in order to distrupt the air flow over the wing, made it tilt the V1 so that the gyro went unstable and the V1 flipped over and went down.

Some pilots actually pushed the damned things over with their wing tip.!

 

[dknguyen]

hi,
The gyro in the V1 was used to keep the wings level in flight.

Allied pilots used to fly wing tip to wing tip with the V1 in order to distrupt the air flow over the wing, made it tilt the V1 so that the gyro went unstable and the V1 flipped over and went down.

Some pilots actually pushed the damned things over with their wing tip.!

Why couldnt they be shot down again?

 

[ericgibbs]

Why couldnt they be shot down again?

hi,
Do you mean shoot down instead of tipping.?

Have you seen the newsreels of what happens when the V1 blows up in mid air.

The prop driven planes were only fast enough to intercept the V1 if the plane was head on
or made a diving approach in order to match the V1's speed.
The later Meteor jets could match their speed.

Triple A or ack ack did shoot down a lot of V1's

IIRC about 5 or 6000 were launched against the UK.

 

[Boncuk]

The INS system was first used in the V2 in 1944, again it was launched from France and Holland, not Germany.

Sorry, I didn't know that "Peenemünde" is located in France or Holland.

 

[Nigel Goodwin]

Sorry, I didn't know that "Peenemünde" is located in France or Holland.

Google will soon tell you where it is (Germany).

Peenemünde - Wikipedia, the free encyclopedia

But V1's weren't launched from there, they didn't have the range.

 

[Boncuk]

Google will soon tell you where it is (Germany).

Peenemünde - Wikipedia, the free encyclopedia

But V1's weren't launched from there, they didn't have the range.

I don't have to google that since I know where Peenemünde is locacted. I happen to be German.

BTW, the V1 never had a fuel shut off valve. The fuel was calculated for a certain range and when the engine quit that thing descended unaimed.

Hans

 

[Boncuk]

Why couldnt they be shot down again?

Would you fire a cannon on a flying bomb, knowing that you get in the radius of destruction? At that time there were no air to air missiles.

 

[ericgibbs]

Sorry, I didn't know that "Peenemünde" is located in France or Holland.

hi,
When I say launched against the UK, I dont mean tested at "Peenemünde", which is of course on the Baltic coast.

One of my best friends was in the Luftwaffe during the war.
I have been to Germany on business many times.

Regards.

PS: I dont agree regarding the fuel cut off, but I will re-examine my data.

 

[3v0]

I think Hans has it right unless the documentary producers got it wrong.
EDIT: About the fuel running out on the VI.

 

[Sceadwian]

All peizo/physical/mems gyros have drift, it is impossible to dead reckon with them. They're great for increasing stability though, and if you have some other method to calibrate for drift, gyros work well if you need very high update rates, so they're generally good to supplement GPS. GPS itself doesn't update fast enough to stabilize something on an RC scale very well, at least if you're in anything but stead controlled flight already.

 

[Diver300]

Why couldnt they be shot down again?

One of the teachers at my junior school had been a pilot in WWII. He flew Hurricanes in north Africa.

He told us that he only had about 30 seconds of ammunition. Depending on what guns were fitted, they would shoot up to about 15 kg of ammunition in a 3 second burst, so that would be about 150 kg in total. There wasn't room for any more, and they couldn't handle more weight, while keeping enough performance and fuel.

Tipping the V1s was the only option once the ammunition had gone. The V1s didn't shoot back so there was no particular danger in getting close.

 

[Mikebits]

hi,
The gyro in the V1 was used to keep the wings level in flight.

Allied pilots used to fly wing tip to wing tip with the V1 in order to distrupt the air flow over the wing, made it tilt the V1 so that the gyro went unstable and the V1 flipped over and went down.

Some pilots actually pushed the damned things over with their wing tip.!

I found this, kinda cool.

YouTube - Spitfire vs V1 flying bomb

 

[Boncuk]

Tipping the V1s was the only option once the ammunition had gone. The V1s didn't shoot back so there was no particular danger in getting close.

... and a minor correction: A 500lbs bomb has a destruction radius of 1000feet. To get into close gun range to destroy an airborne target the distance must be 800feet or less. Any more questions about "no particular danger in getting close" to a flying bomb?