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  1. #11
    You haven't mentioned timescale.

    A few random thoughts.

    What you've described is achievable. I think some of the problems (for me, at least) are not the ones that you've identified, but more the physical manufacture, strength and weight.

    You mention a height of 20-25cm, and you're clearly concerned about space for the Arduino - perhaps rightly so. You've not mentioned a diameter, or otherwise defined the complete space envelope for the robot, but I'm taking a punt at around a diameter of a similar size of 20cm. Immediately I'd share your concern, and think particularly how you intend to power this robot - onboard battery or flying lead (I guess you're looking for the former). That's likely to present the highest space requirement in the system - be honest with yourself about how long you expect the robot to operate without recharging. You're likely looking at Lipo or lead-acid (cost vs weight). That's going to limit further the available space that you have to play with.

    Electronics - that's easy, once you've provisioned for it with adequate space and power :)

    In honesty, if I was looking at a system like this I'd probably go federated architecture - have a motor-control Arduino (using motor drivers like John mentioned), a joystick / I/O controller etc, and get them talking over serial interface. That way you're not as compromised by I/O lines on the Arduino, and you can develop and test each subsystem separately. As Andy says - you can pick up cheap knock-off Arduino for very little cost.

    Motors - find some cheap steppers, and stepper drivers - it gives you a reasonable degree of positional control without feedback systems. There are problems with keeping the motor coils energised - that impacts the longevity of the robot operation.

    In all honesty - get yourself some stiff card or balsa or similar and start making a very basic model of how you envisage the robot could be constructed - with the choices of components that you have available (or, if you can be bothered, use a CAD package to just place the component into 3d space). This will help to visualise the problem space of your build. In terms of build, itself, then if you have access to a 3D printer, it's probably one very good application for this type of work to build the skeleton of the robot to bolt bits to. Buy yourself a couple of cheap nano's, a couple of joysticks, motor controllers and steppers and start playing. Learn from this, grow your self-declared 1% understanding to some level where you can start to better understand the system behaviour that you want and how to implement.

    It's an interesting challenge - happy to chat further either here or PM.

  2. #12
    Hi Doddy.
    I build miniatures and film them, next to pets, as a hobby. The size of the pets forced me to go with 1:5 scale. That is why the smallest doorway has a width of 16-17cm and I need a robot body that can fit through that easily, and I would go with 12-14cm for that. The height of a door is 40cm, but in order to make the robot cute-ish, I would have him a bit more than half a door height. Click image for larger version. 

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    The structure/platform that will house all miniatures will take me until march to complete. It is designed with a thin floor and ceiling, and tested, that I can move a max 2kg object, with the help of neodynium magnets. As I film them, I need for the robot only the illusion of movement, and not necessary the actual robotics. This would be nice just to entertain the kid part of me, but it is optional, and I will easily dump it if there is not enough space.

    The tilt/pan option would be great to save me from reaching in the frame each time I need him to turn his head or look up.

    The most important part, which is not defined completely as design, but absolutely sure as a functioning principle, is the function3/stepper/4position thing. Even if the proportions of the robot will change very much, it will still include this in a form or other.

    I would go with on board batteries, and would like him to work for apx 30 minutes per charge, if it is possible. If I give up the stearing system, I guess I'll make room for the batteries.

    I said I would use steppers as the head enclosure is max 10 by 10 by 5-6 cm in heigh and I need two of them fitted in there, but 360 servos might work as well, I don't know yet. Surest way to go is to buy a few of each components I might need, as I live in a village and delivery costs quite a bit. So I would like to make one inclusive order, even if I will not use in the end some of the components. I'm talking the time so I can figure out all the possible components, the whole list and the smallest models of all things, drivers, motors etc.

    The structure of the robot is fairly simple, out of hard wood, finger jointed I think. I have only a cnc, and as soon as I will get my hand on those parts and be able to measure them, I'll design the whole thing in artcam and router it. (might need a few prototypes until I get it just right).

    I am not sure yet, what type of remote should I use, a play station controller or a arduino made one. From here I can start the list.

  3. #13
    Is the only reason you want stepper motors to position that head at 4 different places? Because if so it can be done with 360degree servos and a decent transmitter that sends a 0%, 25%, 50% etc signal. Granted, not as accurate as a stepper, but from what it sounds like you're doing more than accurate enough. I'd expect repeatability below 5 degrees. Removes any need for Arduino, and makes the electronics very very simple.

  4. #14
    Servos are more attractive as well from the point of view of avoiding the stepped-nature of the motor spindle rotation - put any mass away from the centre of rotation and it's going to be evident on camera that the head with be bouncing around each step position. Plus the built in gearing of the servo gives obvious benefit in loading. If the radio system removes the need for the Arduino - a good thing (you can, of course, use the ardi to drive the servo as well), but if the goal is simply to have a remote radio providing the drive and head motion, then a RC solution could work well

  5. #15
    AndyUK
    Yes, it is the only reason, and I inclined toward those as they seem smaller than servos in the photos. The enclosure is 4cm tall (interior of box head), and any motor which is less than that, is welcomed. No arduino then, but I still need an 8 button (in any format, individual or 4 way joystick) remote control only for this head movement. And a couple more for the tilt/pan.

    Doddy.
    The goal is to have the thing done the simplest way possible, for now. I will upgrade it in the futute, if required. The simplest idea for the mechanics of the thing, is like in the photo from the previous posts, one motor up and one down, back to back, in the centre. I have a couple of steppers from a broken printer, and they are like 1.5 cm tall, which is great for this. Servoes seem tall, but if they simplify the project, I'll figure out some gearing and position them off centre.

    Typing in google RC remote, I get lots of toy cars, and those classic remotes (front and back, left and right), and a few drone remotes which have lots of buttons (more like what I need). In the DIY section, there are also good ones, but to be honest I would rather buy one.

  6. #16
    This servo is £3 and 3cm tall. You could place them off-centre and use a gear to have two sharing the same space with one upside down to move the top and bottom of the head independently, or just one with a shaft to move both on sync.

    Not sure how to know what angular range they have though...

    https://hobbyking.com/en_us/hxt900-m...-12sec-9g.html

  7. #17
    They need to move independently. I'll pay happily more than that to get the metal gear ones. I guess I need at least 180 degree, so I can get 0, 90, 180 and -90. (I don't mind if it turns all the way back). Any ideea what remote control should I get?

  8. #18
    That would be at least 270 degrees. It seems most are 90 degree throws, you'll have to specifically look for one with enough range - you probably don't want continuous, because on those the signal is proportional to their rotational speed not their position.

    I would get an FrSky Xlite, but that's because I'd use it for other things too. It would unfortunately eat up a substantial amount of the budget :( but it is an awesome little TX.

    You'll need at least 6 channels, but the more the better. The Turnigy 9x has a decent reputation.

    https://hobbyking.com/en_us/turnigy-...-firmware.html

  9. #19
    The budget is amendable. It would be nice to stick to it, but if I'll not, that's life.
    The Turnigy 9x, 8 channels goes here for 60-70 pounds plus another 10-15 for the receiver. It does not say if the batteries need to be purchased separately, but I guess so.
    I found only a second hand FrSky. (I am not a fan of second hand electronics)

    On amazon.co.uk there are a lot of models, up to 16 channels, around 50 pounds, for sure of inferior quality than what you have mentioned, and I also checked drones and damn, they got a lot cheaper since I last checked. But never mind, around 100 quit for a durable remote sounds good to me.

    I'll wait a few days, to see if someone else has other model recommendations.
    So I got an RC transmitter, batteries and a receiver. 4 servos (2 in the head, 2 in the tilt/pan neck system), and I guess some batteries on board.
    What else do I need?
    Last edited by Radu_Andrei; 24-11-2019 at 12:44 AM.

  10. #20
    more details in next post. i have no ideea how to dele this one
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    Last edited by Radu_Andrei; 01-12-2019 at 06:33 PM.

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