Ralphius

Yeah I suppose with some software changes you could use it as a tracker, but at the moment it is most definitely a heliostat (it prompts for the target objects azimuth & elevation on startup and bisects the angle between sun and target to calculate the mirror angle) hence why it has to recalculate the mirror angle every minute. It's been running in the garden all morning today beaming sunlight through the north facing window of my house at a spot on the ceiling near the light bulbs. Works very well. I've put my Python code on github here if anyone wants to look but don't expect perfect code as I'm currently learning the language.

Haven't made anything with Lego Technic for a while so I built this working heliostat over the last few days. It's based round an old bathroom mirror (The only 3D printed parts in the model are 2x bathroom-mirror-to-lego-axle adaptors for the hinge) There are two NXT servomotors (one on the wheels for pan, one on the winch for tilt). These are controlled by a "BrickPi3" driver board attached to a Raspberry Pi Zero. The BrickPi3 HAT does the reading of the servo encoders and runs the PID loops, whereas the Raspberry Pi is running Python3 once a minute to calculate the sun position and send high level commands to the motors. There is also an NXT touch sensor that is used as a limit switch so that the Pi can automatically home the tilt axis when the model is powered up. The model turned out quite heavy so it is supported on 8x 43mm diameter wheels. The four at the outer edge are all driven and geared 1:1 to move in the same direction. The four inner wheels in the centre are idlers just to support the weight in the middle and reduce flex in the chassis. Questions or constructive criticism welcome :-) Ralphius

Yes it is at very early stages. The drive motors will be 2x technic PF large or medium, haven't decided yet. There will be one for the left side wheels and one for the right. I actually had a quick look at your youtube channel last night, had a look through your Arduino code on github as well :-)

@oracid Wow! Every time I come on this forum I am amazed by the skill and ingenuity of its members! Following your other thread with interest! I was playing with the idea of a 4x4 buggy with portal axles where each wheel is independently steered. Electronics not shown are an ESP8266 based Wemos D1 mini board with motor driver shield.

Gave up trying to mount them in pure technic (sorry purists) Found an excellent 3d printed design for an SG90 adaptor here: https://www.thingiverse.com/thing:4303585 Printed four of them and they work perfectly. Don't know who did the CAD but they've done a great job. Video below:

That jeep model is seriously impressive! I doubt I'll get anything that looks nearly as good as that! I do note that the builder states "can not drive or steer smoothly, so rather than a playable model, this turned out to be more of a proof of concept". I'm hoping that by using multiple motors I'll be able to reduce the mechanical complexity compared to that one and end up with something that not only drives but has a fair bit of torque behind it as well. Thanks for that, I'd never thought of using an idler instead of a universal joint like that! Not sure how it could be steered, maybe attach an L shaped beam to the green bracket perhaps? How would those size gears stand up under the weight of a heavy model? Bit worried they would skip or break? (My previous model suffered from repeatedly shattering the gears inside the diff when it came to an incline)

So the reason this chassis will be unusual is because instead of the wheels turning in parallel (ie linked by a track rod or rack\pinion), they will turn with diagonal opposed pairs together, ie. the front pair will both turn 45 degrees inwards towards each other, and the rear pair will turn 45 degrees inwards towards each other. This will allow zero radius turns on a 4WD chassis without the associated high torque requirements and required slip that is required of zero radius turns (contra-rotating) on a twin-tracked chassis. A pair of photos may help illustrate this concept better: Note this is NOT the model, it's simply to illustrate which way the wheels will turn. I'll probably re-use these wheels though. Actual model will be approx 25 studs square, all 4 wheels will drive, with the left two on one PF-M motor and the right two on another PF-M motor. Steering is probably going to be a PF servo motor although I might go with the mini linear actuator and motor instead. Suspension will not be required as there's probably enough flex in a studless chassis to accommodate a single wheel going over a 15mm obstacle. Also, yes I'm aware that with this design the vehicle can either drive in a straight line, or turn on the spot, but not at the same time, and not turn in a curve like standard steering. So my questions is, how on earth do I get the steering working while still having drive going through a UJ at each corner? I've had a quick look through the (massive) axle megathread but it all seems based on wheels turning in parallel or using special parts that I don't have. Ideas for mechanisms or info on similar models to mine greatly received! Regards, Ralph

After being thoroughly unimpressed with the PF servo motor, I've been trying to find a way to use cheap TowerPro SG90 nano servo's for part of my MOC that has a low torque requirement (steering rack). This would make it considerably easier to control the MOC from a raspberry pi which is also on my todo list. So has anybody found a good way of mounting an SG90 servo in a Lego Technic MOC? The servo seems 3.3ish studs long by almost exactly 1.5 studs wide, but that makes centering the output shaft difficult. I've found that drilling one end of a 2 stud long axle joiner out to 4.8mm makes it a really nice stiff push fit over the servo splines but I'd prefer to keep any damage to technic parts to a minimum if possible. I've attached pics of what I've got so far but I'm not completely satisfied with it so I would welcome any constructive criticism or alternatives. Apparently I'm not meant to link to imgur so I've inserted them as deeplinks: