Lego Spike Prime Weather Station with Raspberry Pi -- Episode 543

Great project.

( Now, can you make an input version that allows you to select the weather ?  )

One issue I find though is that these type of projects often tie-up what is often a very limited Lego resource. If you want to keep that weather station, you now have to go replenish your Lego box with the parts you have used, which I suspect could be quite expensive as motors were never the cheapest of Lego parts. Alternatively you view this as the prototype version and then you recreate it with a final build using cheaper components along with 3D printing and then return the Lego parts from the prototype version back to Lego stock for the next project.

With this build, you have hidden most of the Lego look behind the printed cover sheet. Perhaps for true 'LegoLand' style you could use some of the flat shiny tiles (yup the ones that are a nightmare to remove) mosaic stile with stick-on numbers where required.

Yes, I think this fits the prototyping model really well, quick to build up a working model and test the theory and code before buying specific hardware.

As a bonus, I do lots of school sessions as a stem ambassador, and taking this in to the schools has sparked alot of attention from the children.

If only I could use it as a weather input, that would be bliss!

"...I do lots of school sessions as a stem ambassador..."

That sounds like a pretty cool role.

Did you see shabaz's recent comment when asked about the potential of his current project for use in teaching scenarios ?

/products/raspberry-pi/raspberrypi_projects/b/blog/posts/xr-1000-pico-based-robotic-motion-subsystem?CommentId=b8269e42-1107-42fd-a248-e580c635d788

Nice project! Very cool using the motors to make an electronic display. I'd not heard of Lego Spike before.

I wonder how similar the UART communication is between the Raspberry Pi build HAT, and the motor control board I worked on.. probably I have a less flexible API that only operates one motor at a time (using commands like 'm2 100 cw' sent over UART, to indicate that motor 2 should turn 100 units clockwise, except for motors assigned into pairs, in which case both are controlled simultaneously using commands like 'fwd 100' etc. I figured it's good enough for some basic projects, but more advanced ones would need code changes there.

From Katie's video I could see that from the Pi side, there is a Python library to abstract away the UART commands, whereas currently my project doesn't have that, and the connected board (e.g. the keypad project) would use Python code like this to move a pair of motors forward:

uart.write(("fwd 1000\n\r")

or, a bit cleaner using a simple function::

command_send_uart(command.index("fwd"), "1000")

Also, I've pre-assigned two connectors to be a pair of motors, and the other two connectors to be controlled as separate motors, since at the time I figured that may meet 80% of needs (a weather station would be in the 20% however! : ) although that's easy to modify, it currently entails modifying the code on the motor control board.

The lego integration with the Pi Build HAT is nice, I can see it being attractive to schools as a result, I guess my motor control board is needs a bit more work to integrate with Lego/Fischertechnik, although it could be possible.. maybe with 3D printed adapters for the motors I used. I'm no good with 3D CAD and don't have a 3D printer however!

FYI Fischertechnik are continuing to embrace Arduino, R-Pi, micro:bit platforms as alternatives to their own controllers via various 3rd party adapters and controllers

https://www.fischertechnik.de/en/teaching/arduino-microbit-u-co

A new range of kits as well, some which now include mechanum wheels.

"...maybe with 3D printed adapters for the motors I used. I'm no good with 3D CAD and don't have a 3D printer however!..."

Shouldn't be too difficult to come up with something. Your BOM on Github only appears to list the white gearbox motors. There appears to be engineering drawings (with about half the dimensions required). May need to give those callipers some exercise.

The trouble with Lego I suspect is that their tolerances will be pretty darned fine in order to allow the bricks to be a good friction fit without being too tight or too loose. One workaround though might be to glue the 3D printed adapter in-between two thin Lego plates.

Hi Dave,

That makes sense, better to incorporate a cheap brick or plate into the adapter, rather than try to make something from scratch to snap onto Lego.

I found an AliExpress page with reasonable diagrams with dimensions, and have added them, colorized to make them easier to follow, into the blog. I've quickly checked, and it seems consistent with what I'm measuring them to be too.

Incidentally, they are really nice motors : ) The mounting holes are nicely spaced with round numbers for easy prototyping, and M2 screws fit. There are wheels on AliExpress with 3mm D shaft, so they can fit on directly too. And they come in several gearbox settings, and with a normal connector already attached. Perfect : ) 

It also gets around a few printing issues if using FDM printing, like gravity and printing on air.

I saw that drawing but it is missing most of the dimensions on the mounting flange.
(btw looks like you have miscoloured the left end of the shaft in the lower drawing ? where the D flat ends and becomes round)

Overall height of the flange is missing, assuming 15 +/- 0.20 as is same as diameter of gearbox
Overall width of the flange is missing, just the hole centres.
No curve radius from the mounting hole to the outer edge of the flange.
(No centres for the screws through the flange into the gearbox or detail.)

Also there are no dimensions for the PCB attached to the motor.

Main missing measurement I think though is the overall width of the flange.
From that can calculate outer radius by subtracting mounting centres then finally draw line tangents between that and the motor diameter to get the flange straight edges.

If going for a full enclosed motor brick, then the next question might be how the motor flange should align with the end face of the new motor brick. Three main options here:
Flange completely on the outside of the brick with a 15mm dia hole in the brick face for the gearbox.
Flange completely on the inside of the brick with a 6mm dia hole in the brick face for the boss protrusion from the flange face.
Flange set into the brick face with a flange profile shape cut out of the brick face.

If going for a more skeletal design, then perhaps could look at basically attaching a 2x4 Lego plate top and bottom, with a little bit of additional 3D extrusion to fit it neatly to the cylinder of the gearbox and the mounting flange. The rest of the motor would be exposed (handy if it tends to run warm). 

The last question (for the time being) would be the alignment of the output shaft in relation to the Lego co-ordinate system. This may be important if you want to be able to directly mesh with existing Lego Technic gears. Or it could simply be "don't really care, we will work with what we have got".

They are pretty small as well so looks like they could be used for all sorts of smaller projects which used to be an issue at one time with the larger motors - everything had to be scaled up to suit the size of the motor unit. Although SLA resin printing may be better at this size. 

I've added some manually-measured dimensions onto the diagram in the motors section on the blog page, it's still not fully dimensioned but hopefully usable now. Personally I think it would be best with the third style you mention (shape of flange cut out of the brick face), so that the white surface is flush with the outside of the brick, because the shaft length is short (unless as you say there was some adaptation of the shaft to suit existing Lego shafts/gears - but the 'don't care' option might be good enough : ). That's a good point, the normal Lego motors look quite large.

I've added some manually-measured dimensions onto the diagram in the motors section on the blog page, it's still not fully dimensioned but hopefully usable now. Personally I think it would be best with the third style you mention (shape of flange cut out of the brick face), so that the white surface is flush with the outside of the brick, because the shaft length is short (unless as you say there was some adaptation of the shaft to suit existing Lego shafts/gears - but the 'don't care' option might be good enough : ). That's a good point, the normal Lego motors look quite large.

Some napkin sketch type calculations would suggest that the overall motor brick would likely end up being 4x4 Lego units square by three bricks high. 31.8 x 31.8 x 28.8mm (WxDxH) to keep it nice with standard Lego geometry and yet be large enough to accommodate the motor plus room for a 4x4 Lego unit plate glued on top and bottom.

Hi Dave,

Wow - that's really neat! It looks better than real Lego motors : ) Very nice compact design. I take it just the green bit is 3D printed and the plates would be normal Lego as you mentioned earlier.

I think I might bit the bullet and get a 3D printer at some point this year (and just rely on 3D files created by others for now, since I'm still a beginner).

If you don't mind, can I add that image into the motor controller blog post? Just so it doesn't get lost in the comments, that this is how people could use such motors. 

I can't edit the comments : (

I was thinking, perhaps an iteration of it could also have holes on the rear (maybe the other sides too) to accommodate studs for both old and new style technic beams as shown here in yellow and blue. But that may result in a bigger cube if the plastic doesn't have the thickness internally for the studs to fit in, so perhaps it's not worth the effort, since the small cube design is nice and useful as-is.

Yes, the green bit is the 3D printed bit and the red and blue are the standard 4 x 4 plates used to cap it off.

Could potentially get it a bit smaller but at the risk of ending up with non-standard spacings.

Currently it matches the height of 3 normal bricks (or 9 plates).

By rotating the flange by 45 degrees it may be possible to fit it into 3 units wide but not sure if you can get a 4 x 3 plate to cap it with. Could also reduce the height to 2 bricks plus 2 plates, but thought it was easier to start off like this as a proof of concept.

Feel free. I'm already feeling guilty about filling up Katie's project thread here... 

Lots of holes like that can be tricky with FDM 3D printing. What might be easier is to build three sides out of the motor block out of Technic beams and then just 3D print the faceplate for the motor on the fourth side and then trap it between the top and bottom plates. A few dabs of glue if you want to make it a permanent motor block. 

Done, thanks.

This is a really affordable alternative to Lego motors if a 3D printer is available (which probably a lot of schools have by now).

A small laser cutter could be used as an alternative to make it as well. Could cut a load of end panels out of a single sheet to mount the motors on, using castellation top and bottom to knit with the lego bumps for additional strength.