Improved UTM seating - Improved connectivity after head change

[mvillion]

I have always been frustrated that after a head change, the FB would often not detect the new head. Additionally, I had issues with the soil moisture sensor coming off in the ground during the retraction phase of movement as the connection force was not strong enough to stay connected.

Using the magnets that came with FB tools, and purchasing some cheap magnets and screws from Temu, I have come up with a far better solution.

It solved the connection reliability issue AND the head connection strength issue.

NOTE: The magnets are already rusted prior to the experiments.

1 - Replace the magnets in the UTM with the Fat one from the strimmer head - Note the orientation of the magnets as they are upside down. Place two washers under the magnet to add a little bit of space. Do not use the cheesehead screw but make sure to use the flat head type. This increased the magnetic flux significantly by allowing the magnets to be really close.

2 - Ensure the screw used to secure the magnets to the tool are flat. They will get VERY close to the magnets in the UTM and cause a strong magnetic bond.

3 - Insert two washers under the B & C screws to ensure a good amount of pressure on the POGO pins.

This addresses the hardware aspects and I have also written software to support a ‘safe’ head loading as well. That can be found here. In the very rare event of the detection failing now, it will put the head back and try again 5 times to improve chances of getting a connection.

https://forum.farmbot.org/t/unreliable-head-detection/9781/12

The combination should solve the UTM tool head change reliability issue.

To be honest, we should move to an optical detection such as this kind of thing. I have ordered one to play with but it would remove the detection issue permanently.

DAOKAI 5PCS IR Infrared Slotted Optical Optocoupler Speed Measuring Sensor...

I know it is a bit messy at the moment and I intend to put together a better parts list and instructions but I just wanted to get it out there and see if anyone is interested.

[jan.janson]

I would be very interested to know how a) magnets, b) screws under pogo pins, c) pcb utm - especially header will look like after few months of use.

[mvillion]

As you can see, the magnets are already degraded from being exposed to the environment. These are magnets I took off the top of the tools, just swapping the order.

I would like to find a high quality source of magnets that meet the demand. I am going to experiment with FB sourced magnets.

a) The new arrangements do not expose any component to a higher environmental threat. It just puts the magnets into closer proximity to make the flux stronger.
b) The washers just raises the existing terminals so I am not expecting any additional wear.
c) No idea what the PCB has to do with the question. The PCB is not subjected to any change. What are you thinking here?

[jan.janson]

Hello,
The outdoor environment is very hostile—moisture, corrosion, dust, limescale, abrasion, and UV exposure are all major concerns.

Moisture, in particular, can cause galvanic corrosion. A good example of how to manage this can be seen in automotive-grade electronics: PCBs are typically protected by moisture-resistant coatings, and connectors are sealed to prevent moisture ingress to the pins. Here’s an example:
Using Moisture Protection Varnishes to Protect Electronics

Additionally, keep in mind that all materials used should be food-grade (non-toxic), especially if there’s any chance of contact with food.

These are some of my concerns with the UTM. I’m a DIYer, but corrosion, abrasion, moisture, toxicity, and other environmental challenges do matter—even for DIY projects.

[mvillion]

@jan.janson

These are some of my concerns with the UTM. I’m a DIYer, but corrosion, abrasion, moisture, toxicity, and other environmental challenges do matter—even for DIY projects.

Wow. You have great evidence of the problems faced. I see these as FB corrosion problems rather than my modification problems - but problems they are and they cannot be denied. You have seen my magnets suffering the same malaise as yours - which has always concerned me. The coating is a great idea and I think it has to become a must have. Your point about food safe is very important and the degrading agents will be dropping material into the soil which needs to be addressed as it seems to be the point of significant failure.

It does highlight the issue using pogo pins for a 5V pull down connection direct to the CPU GPIO port as any resistance on the connection there will just kill it. I think optical detection is the only way to go and there is 5V and GND in the head. It then comes to the actual fitting of the components into the UTM head. I have recently purchased 3 spare UTMs in the garage sale so I intend to play with this concept.

I would like to see optical sensor detection of head and an LED indicator when the head is in place. I know it might seem a little overboard but I want to get FB to be more than a glorified expensive hose. Without reliability at its core, I am resistant to changing the tools.

[jan.janson]

Hi, and thank you for your response.

Optical detection isn’t a foolproof solution — the channels can get dirty, or the sensors may be blinded by reflected light when the tool is off, and water can reflect light from the soil level. A magnetic relay might be a better option for detecting presence in this case.

Personally, I’d prefer a wireless power + radio communication setup (e.g., Arduino Pro Mini + nRF24L01):
https://www.aliexpress.com/item/1005005721893317.html

Magnets are useful, but mechanical locks are typically more reliable. The attachment between the tool and the carrier must remain secure even when the tool comes into impact with an obstacle (even in maximum weight load like 1kg tool). In such situations, the attachment mechanism must withstand the force of the impact without detaching. It’s crucial that the tool stays securely attached, no matter how strong the forces involved. Additionally, thinking about long-term durability (10+ years) is important.