greetings fellow gearheads!
I've built the beginnings of a ticker but am stumped.
A good working example of a scimitar has the last stage oscillating in both counter and counterclockwise rotations.
So...I can get mine to oscillate by putting a heavier weight on one leg of the three-armed wheel much like a traditional clock. Still, when I balance it best I can It gets nudged by the escapement gear and sent spinning but eventually loses momentum and comes to a stop.
I'm not sure what I'm missing here. It almost seems like there must be something that is going to force the three-armed wheel to hit a spring or something to make it go back in its opposite direction.
I've studied the videos but am still perplexed.
any help is most greatly appreciated!
https://youtu.be/ZJGBntqxvoQ
problem with scimitar???
Re: problem with scimitar???
Hi:
Looks to me like the weight is such that the vanes dont spin enough, If you watch carefully, you'll see that the vanes can only spin one way in reality, so the spring hits it, it spins and spins in one direction until its momentum stops it, this will happen just as the weighted part gets to top of stroke.. almost .. that's just the physics of it, it will always end it motion near the high point for the weight, then it rotates backwards due to the weight being almost at the top, it must then rotate backwards, and it will but that will make it retrigger, which makes it go forward again at high speed.
Yours seems to almost work, it just needs to spin a lot more on trigger. Yours never makes the weight go over the top, which would make it spin more.
Consider the vanes as a pendulum, the initial kick sends the pendulum up, as your does, but the momentum isn't enough in your case to make it go over the top. It must go past the top at least once to be proper, mine ( at the stage your at) will rotate a few times 4 or 5, and then resets when it rotates backwards to retrigger. Once the vanes are added, its kind of an optical illusion that it rotates both ways, in truth it rotates many tomes one way, then half a rotation backwards after stopping with the weight high, and retriggers to repeat many clockwise rotations before that 1/2 rotation backwards to trigger.
Add more spring power and/or balance the wheel so that it is only very slightly out of perfect balance. When the things stops rotating the heavy part will always end just a few degrees from the top on its last rotation. The weight offset should be just enough to trigger it, no more. It doesn't take much, yours seems too heavy on its return. Try adding pennies or other weight to the other arms so the heavy part, when held at 1:00 will rotate CCW with just enough power to trigger when released by hand, no more.
That should get you going. Once the vanes are added, you'll need to fine tune a bit, but always aim for the offset in weight to be just enough to trigger, no more. this will allow for more than 1 , and up to 10 rotations from a single kick. Typical is 4-5 rotations CCW before it starts to go CW to retrigger. Its all a game of mass, momentum, and balance. It should be near perfect balance, spin it by hand and it should rotate several times before stopping, the heavy part will always be near top of stroke and then it will reverse only 1/2 turn.
The vanes, however, once added, may rotate in their own directions based on their balance, ( which should be near perfect balance as you can get to instill chaos in their spinning).
Keep going, your very close...
Regards,
Art
Looks to me like the weight is such that the vanes dont spin enough, If you watch carefully, you'll see that the vanes can only spin one way in reality, so the spring hits it, it spins and spins in one direction until its momentum stops it, this will happen just as the weighted part gets to top of stroke.. almost .. that's just the physics of it, it will always end it motion near the high point for the weight, then it rotates backwards due to the weight being almost at the top, it must then rotate backwards, and it will but that will make it retrigger, which makes it go forward again at high speed.
Yours seems to almost work, it just needs to spin a lot more on trigger. Yours never makes the weight go over the top, which would make it spin more.
Consider the vanes as a pendulum, the initial kick sends the pendulum up, as your does, but the momentum isn't enough in your case to make it go over the top. It must go past the top at least once to be proper, mine ( at the stage your at) will rotate a few times 4 or 5, and then resets when it rotates backwards to retrigger. Once the vanes are added, its kind of an optical illusion that it rotates both ways, in truth it rotates many tomes one way, then half a rotation backwards after stopping with the weight high, and retriggers to repeat many clockwise rotations before that 1/2 rotation backwards to trigger.
Add more spring power and/or balance the wheel so that it is only very slightly out of perfect balance. When the things stops rotating the heavy part will always end just a few degrees from the top on its last rotation. The weight offset should be just enough to trigger it, no more. It doesn't take much, yours seems too heavy on its return. Try adding pennies or other weight to the other arms so the heavy part, when held at 1:00 will rotate CCW with just enough power to trigger when released by hand, no more.
That should get you going. Once the vanes are added, you'll need to fine tune a bit, but always aim for the offset in weight to be just enough to trigger, no more. this will allow for more than 1 , and up to 10 rotations from a single kick. Typical is 4-5 rotations CCW before it starts to go CW to retrigger. Its all a game of mass, momentum, and balance. It should be near perfect balance, spin it by hand and it should rotate several times before stopping, the heavy part will always be near top of stroke and then it will reverse only 1/2 turn.
The vanes, however, once added, may rotate in their own directions based on their balance, ( which should be near perfect balance as you can get to instill chaos in their spinning).
Keep going, your very close...
Regards,
Art
-
Tristar500
- Newbie
- Posts: 9
- Joined: Sun Feb 16, 2025 2:22 pm
Re: problem with scimitar???
ArtF wrote: ↑Mon Feb 17, 2025 4:17 am
in reality, so the spring hits it, it spins"
I'm not sure I'm understand about the spring?
Also, are you saying that the vanes have one heavier side making it naturally want to rest with the heavy side down? Or are the vanes in perfect balance?
Where I get confused is why when the vanes (referring to the 3 arm spinning thing) is kicked by the escapement and sends it spinning , what causes it to reverse direction? (is it that the vane assembly is asymmetrically balanced or am I again missing something?
Hi:
Looks to me like the weight is such that the vanes dont spin enough, If you watch carefully, you'll see that the vanes can only spin one way in reality, so the spring hits it, it spins and spins in one direction until its momentum stops it, this will happen just as the weighted part gets to top of stroke.. almost .. that's just the physics of it, it will always end it motion near the high point for the weight, then it rotates backwards due to the weight being almost at the top, it must then rotate backwards, and it will but that will make it retrigger, which makes it go forward again at high speed.
Yours seems to almost work, it just needs to spin a lot more on trigger. Yours never makes the weight go over the top, which would make it spin more.
Consider the vanes as a pendulum, the initial kick sends the pendulum up, as your does, but the momentum isn't enough in your case to make it go over the top. It must go past the top at least once to be proper, mine ( at the stage your at) will rotate a few times 4 or 5, and then resets when it rotates backwards to retrigger. Once the vanes are added, its kind of an optical illusion that it rotates both ways, in truth it rotates many tomes one way, then half a rotation backwards after stopping with the weight high, and retriggers to repeat many clockwise rotations before that 1/2 rotation backwards to trigger.
Add more spring power and/or balance the wheel so that it is only very slightly out of perfect balance. When the things stops rotating the heavy part will always end just a few degrees from the top on its last rotation. The weight offset should be just enough to trigger it, no more. It doesn't take much, yours seems too heavy on its return. Try adding pennies or other weight to the other arms so the heavy part, when held at 1:00 will rotate CCW with just enough power to trigger when released by hand, no more.
That should get you going. Once the vanes are added, you'll need to fine tune a bit, but always aim for the offset in weight to be just enough to trigger, no more. this will allow for more than 1 , and up to 10 rotations from a single kick. Typical is 4-5 rotations CCW before it starts to go CW to retrigger. Its all a game of mass, momentum, and balance. It should be near perfect balance, spin it by hand and it should rotate several times before stopping, the heavy part will always be near top of stroke and then it will reverse only 1/2 turn.
The vanes, however, once added, may rotate in their own directions based on their balance, ( which should be near perfect balance as you can get to instill chaos in their spinning).
Keep going, your very close...
Regards,
Art
Re: problem with scimitar???
>>is kicked by the escapement and sends it spinning , what causes it to reverse direction? (is it that the vane assembly is asymmetrically balanced
Yes. But not by much. Imagine your vanes have just 1/4 of a gram extra on one arm. You spin the vanes by hand with some amount of thrust , the vanes will spin and spin and spin.. but, in the end when it stops spinning, that 1/4 gram weighted arm will be near 12:00 so long as the asymmetric weight is more than the friction of the bearings that oppose the rotation. This is because in an asymmetric system , the weight is removing rotational energy more than any other thing in the system, and it removes energy only on the upswing of the weight, once over the top it adds energy to the rotation, so it wont stop after 12:00 but only just before 12:00. This means that gravity, after it stops, must make it rotate backwards to pull that weight by gravity to the bottom.
The trigger is arranged so that it triggers when the weight gets to 6:00. You are ensured by gravity and physics that you will have almost 1/2 rotation backwards. So imagine the initial kick makes it spin 5 times, or 10, or 100, doesn't matter, the heavy arm will always be near 1:00 ( if spinning CCW ). and so , after any number of rotations the arm is between 12:00 and 2:00, this means it WILL now spin in reverse until the weight hits the bottom at 6:00 ( and momentum will carry it past 6:00 to about 8 or 9:00. ), The device re-kicks when it hits the trigger at 6:00. And so, the cycle continues.
SO the best scimitar 3 arm vanes revolve really easy and multiple times if you kick it. The offset of weight on one arm is just enough to push the trigger as it rotates backwards. If you dont have enough weight, it will hit the trigger and bounce back. The secret is to set the trigger sensitivity to be as hair trigger as you can make it, and the mass of the entire vane system is enough to press that trigger. This means the vanes are "almost" balanced.
Consider any pendulum, you pull it 25 degrees to one side and let it go, it will swing to "almost" 25 degrees the other way, its the same with the vanes, once the weight goes over the top during rotation, its a pendulum, and will swing to "almost" 12:00 as it goes around. If it has enough momentum it will go over the top again and slow a bit, this repeats until not enough energy is there to go over the top, and that's the point where it will reverse direction and try to go to "almost" 12:00 in the other direction, but it will trigger when it hits 6:00 because scimitar only triggers in that direction, and only at 6:00.
I can see on yours the offset is way too much weight, make it much more balanced, it will seem to you as it it isn't unbalanced at all as it rotates, and will not show its unbalanced nature until it stops, ( at which point that heavy vane will be at 1:00 or so.. as long as the weight is more than frictional energy.
Try this:
Mark one arm, remove the trigger and simply spin it with your hand, note the thing always ends that direction of spin with the heavy arm upwards near 1:00. If it doesn't, say it stops at 4 - 5:00, lower the weight. The perfect asymmetric weight is when one arm is just overweight enough to end at 12:01. It can then swing backwards to the trigger at which point the mass of the vanes trigger it from momentum, its not the weight per say that triggers it. Its the angular momentum. If it doesn't trigger, add weight to all three arms to keep it still just off balanced, but adds mass to the entire vane system.
If I spin mine by hand without triggers, it will spin 10 times, but always ends at 1:00 no matter how many times it rotates. It has enough mass to always trigger when it hits 6:00. Remember, the laws of physics says that , after stopping at 1:00, it will always try to rotate backwards to 11:00, but gets kicked at 6:00.
Adjust your weighting to "near" perfect balance. You'll find it starts to spin many times. Its all a matter of balance.
Regards
Art
(Sorry for the verbosity)
Yes. But not by much. Imagine your vanes have just 1/4 of a gram extra on one arm. You spin the vanes by hand with some amount of thrust , the vanes will spin and spin and spin.. but, in the end when it stops spinning, that 1/4 gram weighted arm will be near 12:00 so long as the asymmetric weight is more than the friction of the bearings that oppose the rotation. This is because in an asymmetric system , the weight is removing rotational energy more than any other thing in the system, and it removes energy only on the upswing of the weight, once over the top it adds energy to the rotation, so it wont stop after 12:00 but only just before 12:00. This means that gravity, after it stops, must make it rotate backwards to pull that weight by gravity to the bottom.
The trigger is arranged so that it triggers when the weight gets to 6:00. You are ensured by gravity and physics that you will have almost 1/2 rotation backwards. So imagine the initial kick makes it spin 5 times, or 10, or 100, doesn't matter, the heavy arm will always be near 1:00 ( if spinning CCW ). and so , after any number of rotations the arm is between 12:00 and 2:00, this means it WILL now spin in reverse until the weight hits the bottom at 6:00 ( and momentum will carry it past 6:00 to about 8 or 9:00. ), The device re-kicks when it hits the trigger at 6:00. And so, the cycle continues.
SO the best scimitar 3 arm vanes revolve really easy and multiple times if you kick it. The offset of weight on one arm is just enough to push the trigger as it rotates backwards. If you dont have enough weight, it will hit the trigger and bounce back. The secret is to set the trigger sensitivity to be as hair trigger as you can make it, and the mass of the entire vane system is enough to press that trigger. This means the vanes are "almost" balanced.
Consider any pendulum, you pull it 25 degrees to one side and let it go, it will swing to "almost" 25 degrees the other way, its the same with the vanes, once the weight goes over the top during rotation, its a pendulum, and will swing to "almost" 12:00 as it goes around. If it has enough momentum it will go over the top again and slow a bit, this repeats until not enough energy is there to go over the top, and that's the point where it will reverse direction and try to go to "almost" 12:00 in the other direction, but it will trigger when it hits 6:00 because scimitar only triggers in that direction, and only at 6:00.
I can see on yours the offset is way too much weight, make it much more balanced, it will seem to you as it it isn't unbalanced at all as it rotates, and will not show its unbalanced nature until it stops, ( at which point that heavy vane will be at 1:00 or so.. as long as the weight is more than frictional energy.
Try this:
Mark one arm, remove the trigger and simply spin it with your hand, note the thing always ends that direction of spin with the heavy arm upwards near 1:00. If it doesn't, say it stops at 4 - 5:00, lower the weight. The perfect asymmetric weight is when one arm is just overweight enough to end at 12:01. It can then swing backwards to the trigger at which point the mass of the vanes trigger it from momentum, its not the weight per say that triggers it. Its the angular momentum. If it doesn't trigger, add weight to all three arms to keep it still just off balanced, but adds mass to the entire vane system.
If I spin mine by hand without triggers, it will spin 10 times, but always ends at 1:00 no matter how many times it rotates. It has enough mass to always trigger when it hits 6:00. Remember, the laws of physics says that , after stopping at 1:00, it will always try to rotate backwards to 11:00, but gets kicked at 6:00.
Adjust your weighting to "near" perfect balance. You'll find it starts to spin many times. Its all a matter of balance.
Regards
Art
(Sorry for the verbosity)
-
Tristar500
- Newbie
- Posts: 9
- Joined: Sun Feb 16, 2025 2:22 pm
Re: problem with scimitar???
Thanks for the clarity Art.
The shaft for the vanes was not spinning well and the problem was both poor bearings and some misalignment. I'm remaking the frame of the scimitar to make it more rigid (laser cut acylic is a beautiful thing but large sheets are prone to warping under load.) I also turned and machined an aluminum bearing hub for both the vane bearings and the bearings supporting the weight that drives the apparatus.
I should have something to show later tonight or tomorrow. Your explanation was most helpful, thank you!
One last question. What is the purpose of the spring you describe as a "clothespin" type? I've got a spring on the ratchet for winding but unclear what the other one does.
I'm curious if this mechanism would suit a much larger scale. My work as an artist is mostly public art, mostly kinetic wind sculptures some in excess of 26 feet tall.
I'll get scimitar working and then I'll have a much more comprehensive understanding of its inner workings and limitations.
The shaft for the vanes was not spinning well and the problem was both poor bearings and some misalignment. I'm remaking the frame of the scimitar to make it more rigid (laser cut acylic is a beautiful thing but large sheets are prone to warping under load.) I also turned and machined an aluminum bearing hub for both the vane bearings and the bearings supporting the weight that drives the apparatus.
I should have something to show later tonight or tomorrow. Your explanation was most helpful, thank you!
One last question. What is the purpose of the spring you describe as a "clothespin" type? I've got a spring on the ratchet for winding but unclear what the other one does.
I'm curious if this mechanism would suit a much larger scale. My work as an artist is mostly public art, mostly kinetic wind sculptures some in excess of 26 feet tall.
I'll get scimitar working and then I'll have a much more comprehensive understanding of its inner workings and limitations.
Re: problem with scimitar???
>>What is the purpose of the spring you describe as a "clothespin" type? I've got a spring on the ratchet for winding but unclear what the other one does.
That spring makes the arm fall back to rest position after being pushed out on a trigger point. Depending on orientation and weight of the arm, it may be omitted if the arm naturally falls back due to gravity.
Regards
Art
That spring makes the arm fall back to rest position after being pushed out on a trigger point. Depending on orientation and weight of the arm, it may be omitted if the arm naturally falls back due to gravity.
Regards
Art
-
Tristar500
- Newbie
- Posts: 9
- Joined: Sun Feb 16, 2025 2:22 pm
Re: problem with scimitar???
Ah, ok, that's what I was thinking. Good old dependable gravity seemed to be working the way I have it oriented. A light spring might make things more reliable for the long term.ArtF wrote: ↑Tue Feb 18, 2025 8:18 am >>What is the purpose of the spring you describe as a "clothespin" type? I've got a spring on the ratchet for winding but unclear what the other one does.
That spring makes the arm fall back to rest position after being pushed out on a trigger point. Depending on the orientation and weight of the arm, it may be omitted if the arm naturally falls back due to gravity.
Regards
Art
I've got it working!
https://youtu.be/N5rUoOb9PtQ
Re: problem with scimitar???
Awesome.. That spins perfectly.
Its always a thrill when it starts to work, congrats.!
Regards
Art
Its always a thrill when it starts to work, congrats.!
Regards
Art
-
Tristar500
- Newbie
- Posts: 9
- Joined: Sun Feb 16, 2025 2:22 pm
Re: problem with scimitar???
Thanks Art!
I'm refining parts of it as I work out the bugs.
I'd be intrigued to design a double Scimitar where the vanes ran in opposite directions.
I've seen mentions of plans for the "Bat". Is that available anytime soon?
This gets fun once you get enough insight into how these things work, and develop the patience to tweak and re-tweak.
I'm refining parts of it as I work out the bugs.
I'd be intrigued to design a double Scimitar where the vanes ran in opposite directions.
I've seen mentions of plans for the "Bat". Is that available anytime soon?
This gets fun once you get enough insight into how these things work, and develop the patience to tweak and re-tweak.
Re: problem with scimitar???
The "Bat" was seen on one of my videos once, it hangs in my garage because its too large for my house.
I've never cared for its trigger, was going to redesign it, but the thing is large enough I've never gotten back
to it. I may take it down one day and photo it for a video.. you never know... :)
I've never cared for its trigger, was going to redesign it, but the thing is large enough I've never gotten back
to it. I may take it down one day and photo it for a video.. you never know... :)
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