Servo for controlling a rocking horse

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Servo for controlling a rocking horse

Post by mandarin » Fri Nov 13, 2009 4:32 pm

Post by mandarin
Fri Nov 13, 2009 4:32 pm

Hello!

I have been asked to setup the necessary components to make a computer control the rocking of a rocking horse, and am wondering about a thing or two that you robot building guys :) may have the answer to.

I have attached a drawing to show you how I picture the setup. Since the rocking horse is quite old I cannot modify it in any way, so the obvious choice is to tie a wire around one of the legs to control the motion.

If you take a look at the setup you'll see that it's quite simple. The rocking horse is placed on top of a box, and on the inside there's a servo pulling the wire attached to the rocking horse. The servo doesn't need to rotate more than maybe a quarter of a rotation and will rotate back and forth to create the rocking motion.

The issue I though of was that at a certain speed the rocking horse will sway past the point where the wire stays tight. The wire gets slack, and when the rocking horse starts to sway backwards it will be "free" until the wire tightens again. I am afraid that when the wire thightens the strain will over time be too much for the servo.

If I could've used a metal rod instead of the wire I would have absolute control over the motion, and the rocking horse would have the same tempo as the servo. And there would be no strain on the servo.

Am I mistaking? Will this ever become an issue? And if so, does Robosavvy have a servo that could handle such a strain?

Image

Best regards,
Thomas Viktil
Hello!

I have been asked to setup the necessary components to make a computer control the rocking of a rocking horse, and am wondering about a thing or two that you robot building guys :) may have the answer to.

I have attached a drawing to show you how I picture the setup. Since the rocking horse is quite old I cannot modify it in any way, so the obvious choice is to tie a wire around one of the legs to control the motion.

If you take a look at the setup you'll see that it's quite simple. The rocking horse is placed on top of a box, and on the inside there's a servo pulling the wire attached to the rocking horse. The servo doesn't need to rotate more than maybe a quarter of a rotation and will rotate back and forth to create the rocking motion.

The issue I though of was that at a certain speed the rocking horse will sway past the point where the wire stays tight. The wire gets slack, and when the rocking horse starts to sway backwards it will be "free" until the wire tightens again. I am afraid that when the wire thightens the strain will over time be too much for the servo.

If I could've used a metal rod instead of the wire I would have absolute control over the motion, and the rocking horse would have the same tempo as the servo. And there would be no strain on the servo.

Am I mistaking? Will this ever become an issue? And if so, does Robosavvy have a servo that could handle such a strain?

Image

Best regards,
Thomas Viktil
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Post by limor » Sat Nov 14, 2009 2:08 pm

Post by limor
Sat Nov 14, 2009 2:08 pm

I would put the servo in full rotation and finetune the rotation speed manually.

kids do tend to go crazy on these horses and so fixing the servo in one place and using a string of given length may not work as you would want.

another idea is to attach the servo on the horse's behind or its chest and attach a pendulum to the servo (pendulum can be at 45deg). when the servo/pendulum goes back and forth it will create a swaying effect (finetune the tempo manually). the advantage is that if the kid inserts her own movements, there is no risk in things breaking.

at RoboSavvy.com/store :
- servo controller board
- 8kg servo

You can power the board with a standard 6V 1Amp DC power supply
I would put the servo in full rotation and finetune the rotation speed manually.

kids do tend to go crazy on these horses and so fixing the servo in one place and using a string of given length may not work as you would want.

another idea is to attach the servo on the horse's behind or its chest and attach a pendulum to the servo (pendulum can be at 45deg). when the servo/pendulum goes back and forth it will create a swaying effect (finetune the tempo manually). the advantage is that if the kid inserts her own movements, there is no risk in things breaking.

at RoboSavvy.com/store :
- servo controller board
- 8kg servo

You can power the board with a standard 6V 1Amp DC power supply
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Post by mandarin » Mon Nov 16, 2009 10:46 am

Post by mandarin
Mon Nov 16, 2009 10:46 am

Thanks for the reply!

I've been thinking about this during the weekend and have come to the same conclusion as you; to put the servo in full rotation and finetune the rotation speed.

I might not have made myself clear on that point, but no one's going to ride the horse. It's a part of an exhibition.

The idea of using a pendulum is pretty good idea! I've made a note of that for possible future cases.

Thank you for the links. I'll do some research to find out how I can mount the servo to the stand where the rocking horse will be. I guess I can find some info on how to use an Arduino to communicate with the servo controller board.
Thanks for the reply!

I've been thinking about this during the weekend and have come to the same conclusion as you; to put the servo in full rotation and finetune the rotation speed.

I might not have made myself clear on that point, but no one's going to ride the horse. It's a part of an exhibition.

The idea of using a pendulum is pretty good idea! I've made a note of that for possible future cases.

Thank you for the links. I'll do some research to find out how I can mount the servo to the stand where the rocking horse will be. I guess I can find some info on how to use an Arduino to communicate with the servo controller board.
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Post by limor » Mon Nov 16, 2009 1:33 pm

Post by limor
Mon Nov 16, 2009 1:33 pm

why do you need the arduino in this case ?
why do you need the arduino in this case ?
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Post by mandarin » Mon Nov 16, 2009 1:46 pm

Post by mandarin
Mon Nov 16, 2009 1:46 pm

I am going to use a couple of sensors to control other parts of the exhibition, and they're all connected to an Arduino. So I thought it would be convenient to connect the servo to the Arduino so that I could start and stop it from the software that controls the sensors.

But after a bit mor research I found out that I didn't need anything else than power on/off. So I might just go for a simple power switch and skip the Arduino part.
I am going to use a couple of sensors to control other parts of the exhibition, and they're all connected to an Arduino. So I thought it would be convenient to connect the servo to the Arduino so that I could start and stop it from the software that controls the sensors.

But after a bit mor research I found out that I didn't need anything else than power on/off. So I might just go for a simple power switch and skip the Arduino part.
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