[Closed] Robotics stuff - motor for winding string/cord

Throw more voltz at the motor? It'll burn the brushes up in short order but you're not looking for 100000 cycles...

As NW says, more volts.

With DC motors, speed is directly proportional to voltage. As it'll only be getting intermittent use, it should be fine.
Just don't go daft with the voltage, and make sure it's not near anything too flammable, just in case you do overheat the motor.

Lego motor + technic gearing?

What would be good is a motor that just continuously, and slowly winds the spider up, and then when it's up, the spider suddenly drops down again!

"gearmotor" is what you need to google for, generally, low voltage dc brushed motors with a reduction gearbox on the end. I'm trying to think of a simple way to make a winding drum that winds on the string, then allows it to suddenly spool off when the spider gets to the top, so that you can just power the motor and leave it turning in the same direction without having to control / reverse it etc

Alternatively, if the spider is light (low mass) you could use an big RC servo, and extend the lever arm to get more travel. This would have to be controlled by an arduino or similar because it needs a pulse coded control signal to tell it where to drive too.

If you need to drive and reverse the DC motor, then you need an H bridge to do that, and you probably also will need to know where the motor has got to, ie how much string is on the drum. you can get gear motors with encoders built into them, so you can pulse count to work out the position of the spider

ie

[url= http://howtomechatronics.com/tutorials/arduino/arduino-dc-motor-control-tutorial-l298n-pwm-h-bridge/ ]arduino-dc-motor-control-tutorial-l298n-pwm-h-bridge[/url]

The advantage of this approach is the spiders path can be more random and it's speed can vary during it's climb and drop, which would look more realistic!

The diameter of the drum and the speed of the motor will set the max velocity of the spider. Your winding drum may want to have a separate tamping roller, ie a sprung loaded, un-driven roller than keeps the string on the drum from coming loose and bunching/knotting up, especially if you want to drive your spider very dynamically!

This could be easily achieved using siemens g120c and a torque matched three phase motor. [/singletrackworld overkill answer]

A simple way to speed up the rate at which the string is wound / unwound is to use a larger diameter winder. i.e attach a sowing thread bobin on the shaft. Anything large diameter but still light weight to minimise torque.

To get the spider to drop quicker still make it heavy! Use the motor to only really wind it up but let the weight of the spider pull its self down.

You could get round knowing where the spider is by just using a timer. For super low tech you could just use a RC circuit.

Start with the spider unwound turn on motor for n seconds, when n is a number that will mean the spider is lifted up at much as you need but not so much that it is too much and wound up wound the motor!

Then turn off motor allowing spider to drop.

RC timer turning on transistor powering motor. Maybe a diode (reversed) over transistor to cope with voltage spikes cause by the motor being wound "backwards". Prob less than £3 from Maplins in parts

https://startingelectronics.org/beginners/start-electronics-now/tut2-transistor-timer/

[url= http://www.technologystudent.com/cams/camq2.htm ]Slooooooow motor and snail cam????[/url]

Use a pot in place of R2 to vary the timing. Also the transistor may need to be different but you get the idea

I like timbs idea more than my own actually.

Thanks for all the suggestions.

[quote=maxtorque ]What would be good is a motor that just continuously, and slowly winds the spider up, and then when it's up, the spider suddenly drops down again!

Yeah - that's exactly what I'm after, I'd like to be able to drop the spider on somebody. The cam suggestion looks interesting, I wonder if I can scale it (I'm trying to drop the spider about a metre).

Thanks also for the comments about how to control it, all interesting and useful stuff, but I probably should have mentioned that I've already mostly got that sorted and mainly after suggestions for the mechanical side of things. I had the crane motor controlled from a RPi last year via an H-bridge (I think the one I have will happily drive any motor I'm likely to get, it's way over-rated for the one I'm currently using) - though last year I had a bat, have a nice big spider ordered for this year. The RPi is kind of overkill for this, but it makes for easy control over Wifi - and I could also easily control a servo from that. I had wondered about a servo, but I think I'm going to need a very big (ie expensive) servo for the amount of torque I'd need given a 50cm long lever arm - I could try the biggest one I have and see what it will do.

As for how it was controlled - I did think about using an optical sensor with something on the cord running through that to stop it at the top, but as the motor has a built in overload clutch I found just timing it worked well enough to turn it off shortly after it reached the top. At the bottom, the winder simply starts to wind the cord back in as soon as it has wound it all out. So all done just using timing which seemed to work well enough. I may need to rethink this a bit if using a more powerful winder motor. The RPi connected to the motor was running as a slave - running pigpio daemon http://abyz.me.uk/rpi/pigpio/pigpiod.html which allows control of GPIO pins (and hence H bridge and motor) via IP socket interface. Main control software running on the RPi in my skull with the bat/spider controlled directly from that over wifi - it's triggered by a PIR sensor in the nose http://singletrackmag.com/forum/topic/raspberry-pi-6/page/2#post-8049209 for video of the skull. It was all fully automatic, but I'll probably tweak it a bit this year and maybe add a web interface as son wants to sit in the house and frighten little kids by dropping a spider on them rather than going out trick or treating.

I wonder if I can scale it