New High Resolution Sonar Line from MaxBotix: HRLV

Our friends at MaxBotix have updated their offering of ultrasound sonar sensors by adding the new High Resolution LV line. The defining characteristic of this new line of sonars is the 1mm resolution. Yes. 1mm. Well, more correctly, "the HRLV-MaxSonar-EZ Sensors offer calibrated 1 mm accuracy of 0.1% at 1 meter," so at greater distances, the ranging might be off by a millimeter or more. Up to 5 millimeters at 5 meters, if the accuracy were linear. I can live with that. *grin*

The new sensors offer a similar near end range, a minimum of 30cm, and the data sheet describes a 5 meter maximum range. This is slightly shorter than the 6.4 meter maximum range of the LV line or the 7-10 meter range of the XL, but my thinking is beyond 15 feet off the deck, you might not notice if your multicopter switches to using the barometer for alt_hold. Like the other product lines, the specifics of range are most likely subject to the beam pattern. As with the LV line, it is available in a variety of beam patterns off the shelf, and they offer custom solutions for customers who require it.

This new sensor line offers the same interface as existing sonar products, including analog, serial/TTL, and pulse width, comes in the same form-factor we to which are accustom, but the manufacturer provides details on additional distinguishing characteristics of this new line over the LV line, including:

Higher resolution output
Automatic calibration of, noise, humidity, and voltage for consistent, long term, operation.
Automatical compensate for speed of sound changes due to the effects temperature changes
Advanced firmware to handle a variety of noise sources
Simultaneous multiple sensor operation
Noise filtering is even better than previous MaxSonar products
Automatic target size compensation

With this level of resolution, I expect there are new technical challenges related to air temperature changes in near-real time, and this suspicion is somewhat supported by two features of this sensor. First, there is it's onboard support for compensation of "self heating" through an onboard temperature sensor. Second, there is support for an external temperature sensor, also available from MaxBotix, which when combined with the onboard temperature sensor, can eliminate a potential "drift of ... up to 3%."

The product page also reports that the HRLV are designed to support simultaneous sensor operation, but it is not clear from the initial information if this is handled through time triggered operation, as with the other sonar lines, or if this sensor discriminates between its pulse and those of other nearby sonar units in some new fashion.

Here are the beam patterns available off the shelf.

There are a range of other features worth discussing, but let me not distract you from the important questions. Or rather, the important question. With this type of high resolution, I would expect this sonar to come at matching high price. Like the LV and XL lines, different sensors are priced differently, but t The lineup is advertised at MSRP $28.95 - $34.95 for a single sensor, with volume discounts available.

I should mention right now that I have no ties to MaxBotix, except as a fellow customer. I don't get any discounts by bringing this news to you, and at these prices, I don't really need any (but I'd gladly go in on volume purchases if anyone wants to organize some, hint-hint 3DR team.) I was notified by email about the new line in a product announcement email. And that is important to this audience because it also informed me of another useful bit of information. These sonars are begin offered at a 25% discount until 7/15/2012 if you use the discount code en4v en4V [the code is case sensitive.]

A quote included with the product announcement (not attributed):

“1-mm resolution is so stable, that when measuring typical objects at a distance of one meter, the readings do not change by more than 1-mm.”

See the linked data sheet or the product Web page for more information.

Robert you certainly have more challenges on the tradional heli as you mention but here are some addtional tips. You mentioned using shielded cable and this in itself can increase the interference if the sheild acts as an aerial. So check on how you ground the sheild. Maxbotics have some good information on there FAQ page. I am sure you know about these things but just mention it just in case. Another thing I have found is it is really important to use a twisted pair version of the cable to cancel any near end crosstalk. Similar in fact to the principal used in Network cabling. I have also found temperature can be a factor so some insultation around the outside to the sonar helps. You can alone use a cone around the sensor to help elminate side noise but I have not tested this. I noticed Maxbotics have these adaptors with might be worth looking at. Ultimately I looked at the MB 1240 becuase it has similar range (7m) and beam shape to the MB1200 but looks to reduce the external noise impact. i.e is less sensitive Looking at your heli by the way promted me to get my Trex 500e setup so I can do some similar testing. If you have a look at the link in my last post there is a pointer to the main sonar discussion. I mention this becuase there is a lot of collective testing information and one alternative which is using a separate Arduino processor and using I2c signaling of the range finding. Still lots of work to do but we are getting there :-)

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Comments

Peter McCulloch November 29, 2013 at 3:36am

Hello,everyone.I am fairly new to Quadcopters but i have just bought a HRLV maxsonar and cant seem to find how to connect to my ardupilot 2.5.
MaxBotix Inc June 20, 2012 at 3:01pm

This is Scott from MaxBotix. Sorry I missed your post earlier Mike, but here is the information you requested on the scaling of our HRLV-MaxSonar-EZ sensors.

The pulse width scaling on the HRLV-MaxSonar-EZ sensors is very simplistic for our end users, 1uS is 1mm. So if you have a pulse width of 400uS the target is 400mm away.

The analog voltage scaling for the new HRLV-MaxSonar-EZ sensors is Vcc/5120 per mm. The analog voltage, however, has a 5-mm resolution. This allows a person using a 10bit ADC to connect to a our sensors and multiply the ADC's output by 5 so the range is known. For example, 60 bits corresponds to 300-mm (where 60 * 5 = 300), and 1000 bits corresponds to 5000-mm (where 1000 * 5 = 5000-mm).
Greg June 18, 2012 at 1:17pm

Mike thats a good point about the i2C bus. Is there scope then in APM2 to use the digital side of the sonar? It is something I have not looked into yet?
Moderator

Michael Pursifull June 18, 2012 at 10:41am

Because APM1 did not have any spare TTLs, and PWM is a blocking IO call. But some people have injected an ardiuno mini pro as a controller, then used i2c between them. Several dev's have cautioned against overloading the i2c bus as it is shared. Over use will degrade critical attitude sensors.
Rob_Lefebvre June 18, 2012 at 10:31am

Greg, I do have the shield connected to ground only at the APM side, thanks though.

This is why I think I'm up against the accoustic noise limit.

I was interested in the whole I2C signalling idea. Honestly I'm not sure why we're not already using one of the built-in digital methods the Maxbotix includes.
Greg June 15, 2012 at 4:01pm

Robert you certainly have more challenges on the tradional heli as you mention but here are some addtional tips. You mentioned using shielded cable and this in itself can increase the interference if the sheild acts as an aerial. So check on how you ground the sheild. Maxbotics have some good information on there FAQ page. I am sure you know about these things but just mention it just in case. Another thing I have found is it is really important to use a twisted pair version of the cable to cancel any near end crosstalk. Similar in fact to the principal used in Network cabling. I have also found temperature can be a factor so some insultation around the outside to the sonar helps. You can alone use a cone around the sensor to help elminate side noise but I have not tested this. I noticed Maxbotics have these adaptors with might be worth looking at. Ultimately I looked at the MB 1240 becuase it has similar range (7m) and beam shape to the MB1200 but looks to reduce the external noise impact. i.e is less sensitive Looking at your heli by the way promted me to get my Trex 500e setup so I can do some similar testing. If you have a look at the link in my last post there is a pointer to the main sonar discussion. I mention this becuase there is a lot of collective testing information and one alternative which is using a separate Arduino processor and using I2c signaling of the range finding. Still lots of work to do but we are getting there :-)
Greg June 15, 2012 at 3:43pm

Good to hear from you Scott. I have been looking at different sensors for a while now and Chris will remember my visit around December in the US when I talked about the MB1240 and MB1200 comparision. In my research the MB1200 is one of the most sensitive sonars and unfortunately is susceptible to the acoustic and electrical interference from a multicopters electronics including the vibrational / noise harmonics from the motors. The MB 1240 looks to be a good alternative. I have also recently posted my modification to the Maxbotics sonar to incoporate the passive filter Scott mentions on a quick connector. I did this to test multiple sonars and to avoid the occasional issues with have to solder the filter into the end of the wiring harness. I suspose a nice evolution of this would be a surface mount alternative and a more compact connector. For me this system works really well. I am well overdue to update my sonar page but meanwhile here is the link to my recent article. http://www.diydrones.com/profiles/blogs/sonar-quick-connector-and-p...
Rob_Lefebvre June 15, 2012 at 11:54am

Scott, I have the electrical filters and shielded wire, and it is on the softest mount imaginable. It's angularly stable due to wide-set vibration mounts, but the mounts are very very very soft. I even bolted it to a mass of aluminum to help soak up vibes. I've done everything short of strapping my smart phone to the heli to actually measure the sound level. ;)

I'm going to try one thing before ordering an MB1240: Currently the sensor is mounted near the motor/geartrain. I'm going to move it out onto the tail. It will be in the quietest location on the heli. A bit further away from the gear noise, but still very exposed to the rotor blade noise.

Does the frequency of the vibration make a difference? The gear noise is a very high pitched whine. I wonder if it can punch through low pitched noise more than high pitched noise?

You can get some sense of it here:
MaxBotix Inc June 15, 2012 at 9:42am

Lefebvre, you may also need to consider vibration noise being introduced to the sensor as well before switching sensors. If it is possible, mount the sensor on a softer mount so the vibration is absorbed before it contacts the sensor.
Moderator

Michael Pursifull June 15, 2012 at 9:26am

Scott, can you tell us something about the scaling used in the HRLV units?

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