Adjust rear parking sensors

[Big_Jim1967]

Afternoon all

Having just fitted a bike carrier bracket to the towbar on my 66 plate Tepee, the rear parking sensors can now "see" the tow hook all the time, making the sensors trigger when I select reverse gear. The tow hook on it's own must be close enough to the back bumper that they are out of "vision", so it works fine on its own.

Its the old fashioned two bolt flange type of towbar, so I know I could just unbolt the hook, but that'll be a faff when if/when I need to use the trailer.

Has anyone found a way of adjusting the angle of the sensors, so the angle is changed just a little, to miss the hook?

Thanks

Jim

[Sol]

No way of adjusting them mate. To work, they need to be at the angle they are at. Otherwise you see road, or sky. Think about the angle as it radiates out, if you don't have them at 90 degrees to the body. Not much use if you tilted them. Did you do vanishing point perspective or geometry at school? Flip that round, it's the same. Anything more than 90 causes an arc tangent swing that increases the error with distance. It would become huge after a few feet, detecting virtually nothing. Less than 90 means your sensors pick up the road surface constantly, rendering them useless.

[Pedronicus]

As Zion says, no way of adjusting them. If it was me I would put up with the faff of taking the ball off depending on how often I would be using the carrier or trailer. Also remember that the sensors detect from the bumper surface so the extended projection of the tow ball needs to be taken into account even with no bike carrier fitted.

[Big_Jim1967]

No way of adjusting them mate. To work, they need to be at the angle they are at. Otherwise you see road, or sky. Think about the angle as it radiates out, if you don't have them at 90 degrees to the body. Not much use if you tilted them. Did you do vanishing point perspective or geometry at school? Flip that round, it's the same. Anything more than 90 causes an arc tangent swing that increases the error with distance. It would become huge after a few feet, detecting virtually nothing. Less than 90 means your sensors pick up the road surface constantly, rendering them useless.

Hi Zion
I think they "see" or "scan" (whatever the word is) an arc of about 140° horizontally, so my thought was I could skew them outwards by about 10° (or maybe even less) then the tow ball would then be in the blind spot. They obviously don't scan 70° vertically downwards, or it would "see" the tarmac all the time. 
I was thinking of a circular plastic ring between the bumper and the sensor that is thicker on one side than the other. It might only need to be a couple of mm thick (if that) to achieve this.
One of the DIY kits on the bay has something similar so you can adjust for a range of vehicles, but I didn't want to shell out for the whole kit.
Ah well
Jim

[cancunia]

If there are 4 on the back, can you disable the inner 2?

[Sol]

If there are 4 on the back, can you disable the inner 2?

In most systems that would generate a fault, and the rest would stop working I guess. The BMW was that way, when one stopped working it disabled the whole system.

[Sol]

No way of adjusting them mate. To work, they need to be at the angle they are at. Otherwise you see road, or sky. Think about the angle as it radiates out, if you don't have them at 90 degrees to the body. Not much use if you tilted them. Did you do vanishing point perspective or geometry at school? Flip that round, it's the same. Anything more than 90 causes an arc tangent swing that increases the error with distance. It would become huge after a few feet, detecting virtually nothing. Less than 90 means your sensors pick up the road surface constantly, rendering them useless.

Hi Zion
I think they "see" or "scan" (whatever the word is) an arc of about 140° horizontally, so my thought was I could skew them outwards by about 10° (or maybe even less) then the tow ball would then be in the blind spot. They obviously don't scan 70° vertically downwards, or it would "see" the tarmac all the time. 
I was thinking of a circular plastic ring between the bumper and the sensor that is thicker on one side than the other. It might only need to be a couple of mm thick (if that) to achieve this.
One of the DIY kits on the bay has something similar so you can adjust for a range of vehicles, but I didn't want to shell out for the whole kit.
Ah well
Jim

Hi Jim, thats a good point and a possible solution that you could at least try. I notice when I reverse into our parking spaces at home, where there is a kerb at the inner end of the space, (think car park bays at 90 degrees to the pavement) the van picks up the kerb for a bit when the bumper is about 6-8 feet away from it, then stops seeing it so I guess it must not just be a horizontal scan, as ultrasonics just bounce waves off a target and any returning waves show that something is there, then the doppler shift tells the control unit how far away it is. Sound waves in air are like expanding bubbles within expanding bubbles which is why it's very difficult to draw a real sound wave - it behaves differently to a water wave as that operates on a flat plane.

Anyway you can try it and if you manage to avoid the tow bar, then an assistant can be used to test detection by moving about, closer and farther away form the sensors - to the side etc. Now I think about it, skewing the two inner sensors away from each other by a slight amount will project the dead spot (cos there will be one before the waves overlap) further out from the towbar. Even spacing the heads out from the bumper surface but keeping them level, may achieve the same result - if you can keep the dead spot still close to the bumper that should work. I think you are getting what is represented in the red lines, and the green lines would be the answer - or all sensors would need to be a good bit out to miss the towbar.

Is there not an alternative close coupled towbar available>? The kind that just appears from underneath, looks kind of like an excited appendage.... if you get my drift.

[Pedronicus]

Perhaps the OP could post up a link to the make and model of carrier that he has fitted and maybe even a picture of the rack fitted on his vehicle.

[Big_Jim1967]

Hi Zion
Yes the sketch you added is exactly what i was trying to achieve. 

In my haste (and the dark and rain) I hadn't spotted that the towbar has four holes not just two I expected. The "fix" was to undo the (incredibly) tight bolts and refix both the bike rack bracket and the tow hook on to the lower holes.

The reversing camera can now see it, but the parking sensors can't. Result. 
No more constant bleeps of an object being too close. I'll just have to live with the bike rack being a couple on inches lower than it might have been. Its not a worry as it still seems about the same height as it was on my old car (VW Touran)

Thanks for all the help, I guess i should have looked at the towbar in the daylight before asking for help.

Ta

Jim

[Brixmis7]

No way of adjusting them mate. To work, they need to be at the angle they are at. Otherwise you see road, or sky. Think about the angle as it radiates out, if you don't have them at 90 degrees to the body. Not much use if you tilted them. Did you do vanishing point perspective or geometry at school? Flip that round, it's the same. Anything more than 90 causes an arc tangent swing that increases the error with distance. It would become huge after a few feet, detecting virtually nothing. Less than 90 means your sensors pick up the road surface constantly, rendering them useless.

Opps thats above my pay grade