Raspberry Pi Forums

Hello, I have a new project which I am researching at present and need some starter help from the experts.

I have a moving belt, 5 meters wide and 30 meters long. Under this belt, air is sucked through at 11 places. I have a sensor which should be moved in the x and y directions above the belt. The sensor measures wind speed and direction. At present I have a carriage which can be pulled along the y-axis via a rope. The carriage has a RPi connected to the sensor and streams the data to a tablet. This works great. This carriage runs on a 6 meter 4 x 8 cm aluminum rail. This is very heavy.

I want to build a new system whereby the carriage is on wheels (maybe) and the rails are smaller and lighter. It would be enough to cover a 5 x 5 meter area at once.

- No cables are allowed so power must come from a power pack (as I am doing now).
- The RPi + power pack + sensor + sensor holder = 2 kg (its heavy)!

I am looking for suggestions for motor / rail type etc. Any help welcome.
Thanks.

Sorry two further points:

- I don't need continuous movement. I will measure a matrix of points within the grid. The sensor is too sensitive to measure continuously.

- The movement does not need to be very quick (30cm / min would be okay, is this quick?).

- The accuracy of the position is not relevant, ± 1 cm is more than enough.

It sounds like a cool project. Just some questions to kick off discussion:

Firstly, which way is x and y? Is x the long axis (30 m) and y the short axis (5 m)?

Does the 6 m rail go perpendicular to the belt? (i.e. it lies along the y-axis)

Does the 5 x 5 m platform move along the entire length of the belt? Obviously it doesn't need to move in the short axis.

Or is the 5 x 5 m platform fixed over the belt and something else moves within the 5 x 5 m area?

Things to think of:

Aluminium extrusion can be used to make rails. Take a look at MakerSlide and Open Rail. You could also build something out of wood. The crossbars might be heavy if they have to span 5 metres.

What about hanging the assembly from the ceiling, or some kind of gantry?

For movement, stepper motors might work, but you might need something heavy-duty, which would need a lot of current, therefore a big (and heavy) power supply. The advantage of steppers is that assuming you don't have any slippage then your software can keep track of the number of steps that have been commanded, and therefore know the position of the platform.

Dc motors are another option. I don't know if you are building this commercially or a one-off, but you can rescue beefy motors from cars, such as wiper motors, seat motors, or power-steering pump motors. If you use a dc motor you need some sort of position detector. This could be some optical pattern on the side of the rails, or something like a slotted disk that is driven by the movement of the platform (not by the motor). An optical sensor detects the slots in the disk to know that the platform has moved.

If you can put the motors and drive linkages on the rails (i.e. not on the platform) then it doesn't matter how heavy they are. They can push and pull the platform with a rope, a toothed belt, a chain, or a 30 m long threaded rod (maybe not).

If you put the motors on the platform then can you have some sort of umbilical cable to feed power to the platform, instead of having the power supply (batteries?) on the platform. Ah, I just re-read your message. No cables allowed.

For batteries, take a look at radio-control model batteries. They have a good power density, so they might be light enough to go on the platform. For slow, heavy, ponderous machinery you could use lead-acid gel-cells. They are big and heavy, but they are easy to maintain and use, and they usually don't burst into flames

Can you draw a sketch and upload it here? The current system, and your new design goal?

This is exactly why I posted here. A great answer - thanks.

The x is across the band (5m) and the y is along the band (30m).

I have a problem giving out too many details due to company secrecy - sorry!

The main problem is that I must be at least one meter away, physically, from the band, as it is hot! Hence also, no cables.

I plan to take a 5 x 5m area and measure in the x and y axis, then move the apparatus along the y-axis and measure anew.

The option to hang above the belt deos not exist -sorry. There is a barrier left and rigth of the band which I cannot enter but I can put my rails onto it.

Hope this helps a little.