Automatic Antenna Tracker

[H_Rocket]

Interesting, and a Contraves at that!

If I had the spare cash, I’d buy it just as a conversation piece. My late father worked on them at White Sands in the 70’s. Of course I’d also need a new house but if I could afford the EOTS, I could probably afford the new house.

 

[jqavins]

You can buy one...

https://www.ebay.com/itm/233673774321

Gee, at that price, I'll take two!

The drive pulley and a belt set (same as used on 3D printers) was purchased and bored out to suit the shaft, then screwed to the aluminium coupler. The standard grub-screw attachement for the pulley is not suitable for use on a CF axle.View attachment 541193

Would you explain that a bit more? Are there screws we can't see, coming up through the pulley into the bottom of the coupler? Wouldn't that restrict the flex of the coupler so that it doesn't tighten down on the shaft?

A second limit switch, for the other extreme of travel, was added to avoid the motor drive damaging any of the antennas or drive system. A simple snap-action switch was used this time, rather than an opto. A screw head on one of the collets activates the switch if the motion exceeds the expected range.
View attachment 541201

From this angle, it looks like the screw head that hits the switch lever would also, in the even of the software going mad and swinging past the switch, hit that other screw head as a hard stop. Assuming nothing breaks when that happens, it seems like a feature.

Wiring to the Processor plug was done, using very flexible silicone-insulated wires. These were dressed and run to assorted locations where needed.
View attachment 541202

Why are the processor and control box attached to the shaft? It seems like those are rotating mass that could be fixed lower, i.e. on the tilt section base plate if not the base of the whole unit. That'd mean longer cables and more complicated cable management, but nothing you can't handle.

 

[OverTheTop]

Would you explain that a bit more? Are there screws we can't see, coming up through the pulley into the bottom of the coupler? Wouldn't that restrict the flex of the coupler so that it doesn't tighten down on the shaft?

The holes cross-drilled through the collet are clearance. Those screws that hold the pulley are done up after the collet is clamped to the shaft.

From this angle, it looks like the screw head that hits the switch lever would also, in the even of the software going mad and swinging past the switch, hit that other screw head as a hard stop. Assuming nothing breaks when that happens, it seems like a feature.

There is clearance to the bearing retaining screws.

Why are the processor and control box attached to the shaft? It seems like those are rotating mass that could be fixed lower, i.e. on the tilt section base plate if not the base of the whole unit. That'd mean longer cables and more complicated cable management, but nothing you can't handle.

The Processor uses the GPS, accelerometers and magnetometer to measure where it is in space. That is how it senses the boom position and closes the loop. The sensors need to move with the antennas. I could have mounted the sensors only on the boom but that complicates wiring, requires more sensors and is not how it was designed. Not much mass in it anyway.

 

[OverTheTop]

Chain Wrangling​

Ok. Was thinking about how to get cables between the rotating upper section and stationary lower section. A rotation of nearly 360deg is needed, and there are limit switches to make sure those requirements are not exceeded. I figured there was a way of doing it using a cable chain and played with a few designs in my head. Using a cable chain obviates the need for things like hollow motor shafts or slip rings. Yes, it was doable. A quick search online then showed that there were commercial solutions available, but at ridiculous prices ($1400 for a set). So I sketched up something similar on Solidworks and threw the job at the 3D printer. I could have printed the chain also but it was easy enough to buy a short length.



Pen for scale. Outer diameter is just over 8".

The assembly works well! Even better than I thought it would. Rotation available is 450 degrees (1.25 turns), easily.

Note that there are some things that need to be done to give the mechanism a long working life. Cable strain-relief and guidance through the chain are both necessary for this.

Next up will be to make some adapters and standoffs to fit these parts to the base of the Automatic Antenna Tracker, and possibly a lid to keep the system somewhat clean. Also need to dodge the opto limit sensors, or perhaps move them.

 

[OverTheTop]

Could also be used to guide a video camera to keep it following the rocket, no?

No. I don't think it would accurately follow the rocket well enough, and particularly not smoothly. It might surprise me but I doubt it.

 

[jqavins]

Rotation available is 450 degrees (1.25 turns), easily.

That's metric, right? 1250 milirotation?

No. I don't think it would accurately follow the rocket well enough, and particularly not smoothly. It might surprise me but I doubt it.

How hard would it be to try? I'm with you in doubting, but being open to that surprise may be a good idea if it's as simple as strapping on a Go Pro.

 

[OverTheTop]

Base Assembly​

Time to describe the fixed base portion of this Automatic Antenna Tracker.

The base needs to be reasonably solid and stiff to avoid any resonances or movement as the turret is moving around. The main construction is formed with some 40x40mm aluminium extrusion that my work was throwing out. I repurposed it for this base, cutting pieces roughly to length with a metal saw and then machining the ends nice and square in the milling machine.


The main component in this base is the rather large, NEMA 42 size, stepper motor. That is quite a decent sized stepper, also retrieved from the bin at work. It weighs in at 4.7kg (10.3pound). A 6mm aluminium plate was machined to mount the stepper to the frame.



Power for this AAT will be 24V DC, provided by a 24V mains power supply capable of delivering a total of 6A. This was mounted on a plate, and a mains inlet (with fuses) and switch (also being thrown out from work) provided. I have mounted these on the inside of the frame to provide them with protection from being knocked or damaged. Seems to work well! Spare fuses are stored in the aluminium channel, under a press-fit trim strip. It is labeled so I remember there are fuses in there.



I have 240V power available in the field via a 1500W inverter on a second battery system in my car, so powering this via 240V mains is not a problem.

A plastic sled was 3D printed and cable-tied to the stepper. The TIC36v4 motion controller screws onto the sled.


Two limit switches (opto interrupters) were provided to enable home position to be found and to protect the turret assembly from excessive rotation. Connection between the base and turret will be via a cable chain and it will be capable of only just over 360deg rotation. Excessive rotation will damage the system and the limit switches protect against this. A collet on the shaft holds the pin which will break the light beams during rotation.


Cable Chain
Next up will be to add the cable chain system and some panels to keep the dust out of the base. It will work remarkably similar to how it is in this video.

I have started on this (see post #34) but it is not yet complete. Still some 3D prints to design and print.

 

[Hobie1dog]

Base Assembly​

Time to describe the fixed base portion of this Automatic Antenna Tracker.

The base needs to be reasonably solid and stiff to avoid any resonances or movement as the turret is moving around. The main construction is formed with some 40x40mm aluminium extrusion that my work was throwing out. I repurposed it for this base, cutting pieces roughly to length with a metal saw and then machining the ends nice and square in the milling ma


Power for this AAT will be 24V DC, provided by at 24V mains power supply capable of delivering a total of 6A. This was mounted on a plate, and a mains inlet (with fuses) and switch (also being thrown out from work) provided. I have mounted these on the inside of the frame to provide them with protection from being knocked or damaged. Seems to work well! Spare fuses are stored in the aluminium channel, under a press-fit trim strip. It is labeled so I remember there are fuses in there.


View attachment 542591
I have 240V power available in the field via a 1500W inverter on a second battery system in my car, so powering this via 240V mains is not a problem.

A plastic sled was 3D printed and cable-tied to the stepper. The TIC36v4 motion controller screws onto the sled.
View attachment 542592

That's the kind of fabrication work I love to see. Excellent work.

 

[manixFan]

Really fascinating project, watching with great interest. Thanks for taking the time and effort to document your work.

And don't be surprised if you suddenly get a lot of folks combing through the bins at your work looking for 'rocketable' goodies!


Tony

 

[OverTheTop]

POWER CHAIN ASSEMBLY​

Time to get back onto this. Christmas and work managed to get in the way, big time.

The power chain needs to be assembled properly to be reliable. It must wrangle the wires appropriately or reliability will be reduced. It is subject to quite a bit of motion so getting it right key to my sanity. I don't want to have this causing me grief on the launch range.

The wires must be strain relieved, preferably at each end. If this wasn't done then the wire could creep along with each movement, causing strain and stretching the cables. I sketched up a strain relief in SolidWorks and had it printed on our resin printer. They are quite small and the feature sizes are similarly fine. Didn't even bother to try on the FDM printer.
The three sections mate together and go inside the chain link. Notice that the holes are smaller in the middle and then bell out. This is to clamp the wires properly and also spread any movement over a longer distance. These pieces keep the ten wires nicely restrained at each end.




Next up were the spacers. These were printed on the FDM printer (0.4mm nozzle) in PLA.Every three links there is a spacer. These have through-holes that are clearance for the wires. Their purpose is to allow the link to control the wires and stop them crossing over or becoming tangled, which puts additional strain on them. These are glued in their links



Here is the resulting power chain, fully assembled, ready to mount on the mechanism.



I still need to put a plug on the end of this and a mating connector on the base unit. That will allow me to easily remove the rotor from the base.