Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Time Bandit on July 15, 2014, 06:45:18 pm

Title: Micro Radar Drive (maybe the smallest worldwide?)
Post by: Time Bandit on July 15, 2014, 06:45:18 pm
After loosing my hobby room in an old industrial building in the beginning of this year, I had to move to "smaller projects".
My appartment has no real hobby room and my neighbours are a little clairaudient to use my machines within the appartment. I can tell you, it really sucks to use a fret saw again, if you are used to a CNC mill  :}

Now this issue and my spinal disc problems since summer last year led to something else. I learned to program AVR mikrocontrollers and design PCBs.

One of my first own projects Im going to show you now, a really tiny radar drive.

In the past I always used a bigger geared motor and a small wire to drive my radars, but was never really happy with it, since you always see the wire. The reason for this was, that I always found the small geared motors (with 4-6mm diameter) too expensive and not steady enough. I used those once and changed the motor at least once a year since something broke him.
In addition to this, these motors with planetary gears are just 6mm in Diameter but at least 25mm long, so they would never fit within a 1/48 scale radar housing and pretty loud at running.

Motivated by a thread in a german forum where somebody used tiny stepper motors to drive a all-round light, I thought okay Im building this, but much smaller.
I found some very small stepper motors (6mm diameter and 7mm length) on the net, bought them and started to test with an old ULN driver.
Unfortunately those small motors have a step size of 18.
So in "full step mode" at the low rpm of a radar drive you see the single steps since its running just with 10 Hz.

So I had to find something else and remembered the "micro stepping" feature of my CNC mill.
So I again searched the net and found this
A tiny stepper driver which is capable of 1/16 microstepping and current limiting and is normally used for 3D printer stepper motors, so should be big enough to drive a 6mm stepper motor  ok2
1/16 means I could run the driver with > 100Hz so the single steps cant be seen with bare eye (same effect your TV uses to make moving pictures).

After the delivery of the driver I built up the control on a breadboard, which you can see in the following pictures.
And it really worked  :} at 12V motor voltage and around 200mA current.

Title: Re: Micro Radar Drive (maybe the smallest worldwide?)
Post by: Time Bandit on July 15, 2014, 07:14:12 pm
Mhh is there a chance here to embed the youtube video in a post?

So I started testing.
The problem is, the motors are rated only 150mA in full step mode, so the motor went really hot, like 60C.
Another thing is, at 12V and 200mA the motor has nearly no torque. It is capable to drive a radar beam like in the movie and also twice the size, but if I moved to real 1/25 sized beam it started to loose some steps.
Maybe because the beam was not perfectly "running round" but I didnt like it.
The motor should have a lot more torque if powered with higher voltage. I remembered those really cheap chinese voltage converter modules (which I normally use as BEC in my models) and found a step-up converter module which would make 35V out of my 12V battery voltage.

So i decided to do a endurance test with the small beam and design a real PCB. It ran for 4 weeks at those 60C and is still running. It seems the motor is not bothered by the temperature.

Yesterday I recieved the PCBs, some 10mm stepper motors to use in my 1/25 model and some step-up power modules as you can see in the picture.
My "control" prototype with the green PCB just consists of the mentioned A4988 driver, a Atmel Attiny45, a variable resistor to change the rotation speed and direction and some capacitors.
It is switched on and off with a normal multiswitch module (on if the signal wire is tied to ground).

Unfortunately my back disables me completely since saturday (I did not imagine to stay in bed during my holidays... :(( ) and the cable box to finish the prototype stands in the highest shelf, so I stopped for today and wait for my missis to help me with it.

I come up with some more results tomorrow and hope for better torque with the small 6mm motors at 35V.
If this does not help I can easily switch to the bigger sized motors, 10mmx11mm will still fit in the radar housings.

Title: Re: Micro Radar Drive (maybe the smallest worldwide?)
Post by: hama on July 15, 2014, 09:59:29 pm
Very interesting! I'd really want a system like this as it would be so much easier to install in any model.
Good luck!
Title: Re: Micro Radar Drive (maybe the smallest worldwide?)
Post by: david48 on July 16, 2014, 09:35:53 am
Iam also interested in this for my build of Fairmount Alpine. I would have space in the superstructure . Please keep us posted on your R&D
Title: Re: Micro Radar Drive (maybe the smallest worldwide?)
Post by: rsm on July 16, 2014, 12:23:32 pm
My electronics abilities aren't up to this so I have used tiny geared motors from Precision Microdrives for my small radar installations. They work pretty well.