[TC13] Pentagon Clock - Wind-up Pendulum Clock

[mocbuild101]

10 hours ago, Didumos69 said:

I decided to not synchronize this clock with real time, even though two clicks almost correspond to a second. I like challenges like the escapement, the wind-up mechanism, the optimal gear ratio and multiple concentric hands and I don't like being tied to specific RPM ratios for the hands.

I think that's the right decision, it keeps things a lot simpler.

[aminnich]

Well, I better just stop building now, We have a winner! 

This is a fantastic build!

[Didumos69]

On 12/30/2017 at 4:42 AM, aminnich said:

Well, I better just stop building now, We have a winner!

Thanks, but I think there will be more competition over the next two weeks.

On 12/29/2017 at 12:49 PM, Didumos69 said:

The next step will be to add hands. I decided to allow my self to come up with a fictitious LEGO time system (e.g. a LEGO day might have 3 6 LEGO hours and a LEGO hour might have 9 minutes), as the main challenge for me is to have a model that shows how a clock works rather than having a clock that tells the exact time. I'm aiming for 3 hands, each with a different speed.

I managed to make a setup with 3 hands. I think this means the fictitious LEGO time system I had in mind will have 4 hours in a day (2 in a clock cycle) and 5 minutes in an hour . All hands perfectly aline every 2 hours and every single hour the minute hand aligns with the second hand.

Btw, I also managed to extend the autonomy to 16 minutes by gearing down from 20:1 to 18:1, but this will all change when I install the hands.

Edited December 31, 2017 by Didumos69

[Boulderer]

Really like the use of the differential. 

[mocbuild101]

Interesting design, I never thought of putting parts inside the differential like that...

[Didumos69]

This is how it should be going to work. I had to remove the pendulum temporarily, because I need to route the axle to which the hands are attached through the pendulum. I already have an idea to achieve this. Because the pendulum has been removed it does not have constant speed now. And it runs much faster now. Eventually it will be running about 10 times slower.

Edited December 31, 2017 by Didumos69

[Didumos69]

I installed the hands and that meant I had to fine-tune pendulum length / weight and gear ratios all over again. Even though I suspect my pullback motor to be damaged I'm actually quite content with the result. I will be buying a new motor, but I don't expect big improvements on the current setup. The fictitious LEGO time system of this clock has 4 LEGO hours in a LEGO day (2 in a clock cycle), 5 LEGO minutes in a LEGO hour and 30 LEGO seconds in a LEGO minute, with every tick being a LEGO second .

Below you see the gearing setup I found to be optimal. The output of the pullback motor is geared up 10:1 for the escapement (it was 18:1 in my optimal setup without hands). To maintain an acceptable autonomy interval, I had to extend the pendulum to slow things down to compensate for the reduced gear ratio. The 10:1 escapement axle is geared down 1:6 towards the hands, which gives an overall pullback-hands ratio of 5:3. I tried extending the dark tan axle coming from underneath the pullback motor for the hands, because it has the same gear ratio as the yellow axle. However, I ran into two problems: 1). The hands would rotate counterclockwise during wind-up and 2). I couldn't route the axle through the pendulum. So I decided to us a 8t-48t gear combination in front of the pendulum instead. The hands axle still extends through the pendulum, but one stud higher and only to support it properly.

Some observations to illustrate how sensitive the whole system is:

• With my original pullback-escapement ratio of 18:1 and an overall pullback-hands ratio of 3:1, the system slows down severely when the second hand and minute hand are both moving upwards.
• With a slightly different escapement which would reduce the pendulum amplitude by roughly 50%, the pendulum turns into a vibrating string and looses it's function as pendulum.
• With a pendulum that is 8 studs shorter, the autonomy decreases from 9 minutes to 6 minutes.

Here's a video of the current state. Sorry for the bad quality, it was a little too dark. Next step will be to add some sort of housing. With the longer pendulum I diverted from the idea of having a standing clock. It will be hanging on a wall instead.

Edited January 2, 2018 by Didumos69

[Davidz90]

Great job! 

 

7 hours ago, Didumos69 said:

Some observations to illustrate how sensitive the whole system is:

• With my original pullback-escapement ratio of 18:1 and an overall pullback-hands ratio of 3:1, the system slows down severely when the second hand and minute hand are both moving upwards.
• With a slightly different escapement which would reduce the pendulum amplitude by roughly 50%, the pendulum turns into a vibrating string and looses it's function as pendulum.
• With a pendulum that is 8 studs shorter, the autonomy decreases from 9 minutes to 6 minutes.

Indeed, lego clocks are very sensitive mechanisms.

• You may consider counterweighting the hands, so that there is no difference in moving up and down.
•  Reduced pendulum amplitude needs reduced torque to work - 1/2 amplitude means 1/4 of power, so that probably pullback-escapement ratio would need to be increased 4x, for 4x autonomy. Of course, it would work only with light clock hands.
• Shorter pendulum = faster clock. If You want to make lego seconds equal to real seconds, some means to precisely control the pendulum length would be needed 

[Didumos69]

3 hours ago, Davidz90 said:

Indeed, lego clocks are very sensitive mechanisms.

• You may consider counterweighting the hands, so that there is no difference in moving up and down.
•  Reduced pendulum amplitude needs reduced torque to work - 1/2 amplitude means 1/4 of power, so that probably pullback-escapement ratio would need to be increased 4x, for 4x autonomy. Of course, it would work only with light clock hands.
• Shorter pendulum = faster clock. If You want to make lego seconds equal to real seconds, some means to precisely control the pendulum length would be needed 

Thanks @Davidz90! I will retry the smaller amplitude with less torque.

[Didumos69]

6 hours ago, Davidz90 said:

Reduced pendulum amplitude needs reduced torque to work - 1/2 amplitude means 1/4 of power, so that probably pullback-escapement ratio would need to be increased 4x, for 4x autonomy. Of course, it would work only with light clock hands.

I tried this, but the whole system gets to sensitive to the variation in torque and small variations in friction. It does not give a nice constant ticking and it halts every now and then. It was worth the effort though, at least now I know.

[lcvisser]

You made some great progress! The 3 hands are ingenious and the overall looks are clean and robust. Very curious to see the final entry 

I see the new pull-back motor works a lot more steady than the old one I have. Mine shows quite a bit of slowing-down: I had about 10 minutes of autonomy, but during that time it slowed down by >10% (measured by counting seconds/turn of the output). I ended up ditching the whole clock idea because of this.

With respect to the wind-up mechanism: I put the lock/ratchet on the differential housing, instead of on the axle as you have. In this way, you can wind-up without interfering with the hand motion. This can perhaps simplify your setup? You can see it in my (crappy) video: 

 

[Didumos69]

Thanks @Ludo Visser, too bad you had to cancel. Also with the new pullback motor the power slowly declines. With low torque pendulum and high torque pendulum this led to declining clock speed as well. Only with medium torque it runs steady untill it stops.

About the ratchet, I use the diff housing as input, one output for the ratchet and one output for the escapement. Also in my case winding up does not effect the hands, only torque to keep the clock going, drops temporarily. I used the diff this way so it actually gears up the input with a 2:1 ratio when the ratchet locks. My escapement only works one way, so during wind-up the ratchet engages.

Edited January 4, 2018 by Didumos69

[Didumos69]

In the process of designing the clocks bodywork I was troubled by the length of the whole thing. I like symmetry, which is why the pullback motor was sitting in the tail of the clock, but I figured I could also use two pullback motors along the sides of the main structure. That would make the whole thing more boxy and give me more power at the same time. So I bought two small pullback sets and rebuild the whole thing once again, and it turns out to be the best decision of this build! Using two motors allowed me to revert to the 18:1 gearing and I now have an autonomy of 15 minutes!!! In the process of revising I also made sure the pendulum has even less friction; it no longer rubs against the frame supporting it.

Here's a short video showing the setup with two pullback motors.

Edited January 5, 2018 by Didumos69

[Didumos69]

Here's a longer video. They say watching a clock tick can be very meditative , so sit down and relax...

Edited January 5, 2018 by Didumos69

[Aventador2004]

Great work, I think you have a solid chance of winning.

[ThatOneBuilder]

This build is amazing! Lego clocks always fascinate me :-D

Also I think it would be better if the hour hand was changed to an axle instead of a liftarm :)

[Didumos69]

3 hours ago, Aventador2004 said:

Great work, I think you have a solid chance of winning.

Thanks! Of course I hope I will do fine in the competition, but I don't count on anything.

3 hours ago, ThatOneBuilder said:

This build is amazing! Lego clocks always fascinate me :-D

Also I think it would be better if the hour hand was changed to an axle instead of a liftarm :)

Thanks!

I could do the hour hand like this using the newpart. If I also replace the dbg 5l liftarm in the hands section with 2 thin ones, I can have one on each side of the 24t gears. That will secure things better.

Edited January 5, 2018 by Didumos69

[agrof]

Great idea and engineering, my favorite so far.  

I would only change the pendulum arm to something more sleek, and elegant.

[mocbuild101]

Nice progress! I haven't looked at this topic for a while, and it's great to see how much you've got done!

[Victor Imaginator]

Wonderful video, very relaxing to watch)

I noticed that arrows movement isn't regular. And looks like arrows weight cause it. Maybe shortening arrows or adding counterweights will make this construction even better.

[Boulderer]

Great. I love it. 

With the laptop holding the build like that, I got the impression of the clock looking like a prop plane 

[Didumos69]

18 hours ago, agrof said:

Great idea and engineering, my favorite so far.  

I would only change the pendulum arm to something more sleek, and elegant.

Thanks! The pendulum is more stiff this way, but I will make the pendulum weight and the clock itself more elegant.

9 hours ago, mocbuild101 said:

Nice progress! I haven't looked at this topic for a while, and it's great to see how much you've got done!

Thanks!

7 hours ago, Victor Imaginator said:

Wonderful video, very relaxing to watch)

I noticed that arrows movement isn't regular. And looks like arrows weight cause it. Maybe shortening arrows or adding counterweights will make this construction even better.

Thanks! I added counter weights for the minute and second hands, which was also suggested by @Davidz90. It works better now.

3 hours ago, Boulderer said:

Great. I love it. 

With the laptop holding the build like that, I got the impression of the clock looking like a prop plane 

Thanks! Yeah I have the association with a prop plane too. I hope the clock house will eventually take us away from that impression.

Update I balanced the minute and second hands completely and I made the hour hand an axle too (as was suggested by @ThatOneBuilder). The autonomy now extends to over 15 minutes. I have to admit though that the last 3 minutes seem like a real struggle.

Edited January 6, 2018 by Didumos69

[Didumos69]

19 hours ago, agrof said:

I would only change the pendulum arm to something more sleek, and elegant.

1 hour ago, Didumos69 said:

Thanks! The pendulum is more stiff this way, but I will make the pendulum weight and the clock itself more elegant.

I was thinking of doing something like this for the clock house and something similar, but smaller, for the pendulum weight.

[Aventador2004]

Love the clockhouse, make a special place for it.

[Didumos69]

2 hours ago, Aventador2004 said:

Love the clockhouse, make a special place for it.

hanks! Here's the whole concept: