Draft buffers

[Tim Harrigan]

Ground skidding a log will create more friction than the same total weight on a sled, scoot or stoneboat. It depends on the surface and lift on the log but it could be 50-60% of the weight of the log rather than 40%. This shows the practical difficulty of matching a buffer which should be fairly predictable with loads that are unpredictable. Of course it is also be difficult to quantify the impact of a buffer just by watching it.

[jac]

Just looking at Carls fotos there…Is there any reason why the leaf spring has to be mounted in angle iron ?. Could the smaller helper spring not be put on the inside of the curve and the spring turned so its curve is around the horse so to speak with a shackle on each eye to take the heel chains and the pulling hook round the other way.. no friction that way and lighter ?….
John

[Carl Russell]

Countymouse;19192 wrote:

….. When you say the spring never recovered, do you mean it never decompressed at all or just never decompressed completely? A partial decompression while moving also indicates stored energy being returned to the system. With heavier loads, I never saw the spring completely decompress, it just fluctuated between different degrees on compression. This is still a good thing from a design point of view. Compressing and not moving, though, is pretty bad.

The spring partially compressed then fluctuated slightly, but never decompressed until the horse stopped. I also agree that there is some beneficial effect, but I am idealizing that an effective buffer would recover more completely. But maybe it is more the storing of the energy, or trapping of the energy, in the compressed spring, rather than the release that really creates the increased in efficiency.

Carl

[Andy Carson]

@jac 19196 wrote:

Just looking at Carls fotos there…Is there any reason why the leaf spring has to be mounted in angle iron ?. Could the smaller helper spring not be put on the inside of the curve and the spring turned so its curve is around the horse so to speak with a shackle on each eye to take the heel chains and the pulling hook round the other way.. no friction that way and lighter ?….
John

John, that is a good idea. I had origionally looked into the design you are describing, but decided against it because I was worried about what might happen if the single tree was overloaded. In the design I made, the spring would decompress completely if overloaded and “bottom out” on the angle iron. At this point, the buffer would act like a standard singletree. Having something for the spring to “bottom out” on prevents overbending of the spring and the angle iron acts as a safety feature in that if the sprign breaks entirely, the singletree is still intact. Now that you bring the advantages of this system again, however, I think there is probably a way to incorporate this design aspect without compromising safety, perhaps by making a reinforced “bottom out bar.” I will play with some drawings. Thanks for the thought.

[Carl Russell]

So I just spent two days at an event showing people some of the stuff I do with my horses, including skidding logs. I took the buffer singletree to demonstrate it as well. There were quite a few comments by folks who seemed to know a little bit about working horses. There was general appreciation for the concept.

Also, I was skidding logs on a level grassy surface so I had more time to observe the action. As I see it now, the spring compresses to the point where it can suspend the weight, or sustain the draft, then as the animal moves forward it fluctuates just slightly with draft spikes. In this case it did work as I had envisioned, returning the stored energy, but in much smaller fluctuations than I had expected, so they had escaped my observations in the woods.

Kinda cool.

Carl

[mitchmaine]

another field observation for you guys. i have a peice of fallow ground to rotate to buckwheat so i thought i might scratch it up a little last night. my spring harrows still have that spring on from earlier use in this thread, i think. anyway, in spite of our rains, the ground is pretty hard down bottom, and the harrow got going pretty hard and it started to sing. the load and the give of the harrow springs and the load spring all started vibrating and giving off this sound something like the horns at the world cup soccer games. very strange. what do ya make of that?

field agent mitch

[Andy Carson]

Mitch, I would guess that is a harmonic oscillation. I wouldn’t have thought you could hit a combination of pull speed, drag force, and spring constants that could produce a sound though. Very interesting. When I see harmonic oscilaltions, I get kinda nervous about what might happen next. Harmonics can amplify peak forces and cause behaviors that are strange and unexpected. I always think to the video I saw of a bridge that would swing wildly in response to a very specific wind speed (I can’t remember the name of this bridge)… At any rate, as a matter of practice I would try to avoid any combination of drag, speed, and spring constant that gets you into a harmonic. This was one of the reasons I liked the friction on draft buffer II. I have to say though, the friction seems to dampen the responsiveness enough that I think it’s better off with a shackle.

Carl, I am glad you had a chance to see the buffer in action. It probably would work best with a more predictable load such as a log on smooth grass. That’s not to say it wouldn’t do anything on less predictable surfaces, but it might be really hard to see the action. One of the things that I found fascinating was watching the action of the spring while also watching the action of the horse. This way, you could really see which magnitude and duration of the forces generated during different parts of the stride. I am very curious what types of things were said about the buffer when you showed it. This may help me design a presentation that answers common questions and (especially) to design a better “buffer III.”

[mitchmaine]

andy, the spring harrow was set to walk on its points, and scratch at the bottom of the pan. so it was at its greatest load probably. it seems that the harrow itself might be a buffer when it works like this. the two springs might be working and giving to the same resistance at the same time, one giving before the other. creating the noise. i think it was the buffer spring making the racket by compressing and slamming back against itself many times per second. just a guess. later.

[Andy Carson]

Draft buffer III. I guess I like this one because I felt like painting it… These changes address the following concerns:

1. Much beefier design (two inch 3/16 wall square tube in front, spring shackles are 1.5 inch x 3/16, overall design loosely based on traditional chain and spreader)
2. Friction reduced (with spring shackles)
3. Hitching length “normalized” (moved spring behind bar and added connectors for heal chains)
4. Gradual overload protection (instead of a harsh solid stop, the geometry of this set-up progressively increases the spring rate to cushion and protect the singletree from very large overloads. This increase in spring rate ought to be especially dramatic if the springs starts to “bend the wrong way.”

Report to follow soon… Thanks everyone for the constructive criticism and ideas.

[Andy Carson]

Ha! I forgot the picture… Here it is.

[Carl Russell]

Oh man Andy, I really like that one.

It makes so much sense once I see it, but I just haven’t been able to picture that type of modification. It appears to address many of the functionality issues. I am still interested in how these will hold up in situations where there is rapidly changing angles of draft, or abrupt shocks. I worry about them rolling and twisting out alignment if jarred just right. But that may be a slim risk.

Nice job, Carl

[Gabe Ayers]

maybe a centering pin like a spring stack on an axle will keep it all in place?

[Andy Carson]

I tried the buffer on the disc this morning. The action is good, and the buffering effect seems to be more effective without the friction. I have to say it’s much harder to feel the effect on something like a disc where the draft forces change quite a bit from second to second. The effect is by far easiest to feel on a sled, but I wanted to see if there was any twisting of other adverse events with a jerky action. No twisting, but the system of “clamping” the hitch point in place around the spring stack is not sufficient to keep it from slowly “walking” over to one side of the spring stack. I think it’s kinda cool that Jason predicted this would happen just by looking at it. You’ve been doing this a while, huh? I am going to put in a center bolt.

[Andy Carson]

I put the bolt in and that solved the “walking” problem. Everything looks really quite stable. The only problem is that this buffer is so heavy it changes the balance point on the disc. Not really a big problem, I just had to shift weight around to balance it out.

[Tim Harrigan]

OK, it has taken longer then expected to get a new draft measurement system together to do some testing with Andy’s draft buffer but now I am ready to roll. Here is a graph of the pulling forces for a 600 lb stone boat drawn with my ox team last evening in a trial run. Read the pulling force (pounds) from the left vertical axis, time in seconds on the horizontal axis and travel speed in mph from the right vertical axis. The pulling force is shown with the orange diamonds, the speed with the green circles. I pulled this 8 second piece at random out of a much longer pull.

The sled with weights was 600 lbs, the average pulling force was 253 lbs but you can see the tension in the chain bounced rapidly between about 175 and 500 lbs. If you look closely you can see the spikes in the pulling force track the spikes in travel speed. This is one place we are curious to see if Andy’s draft buffer can have an effect on the pull. We would like to see the buffer spring store some of the energy exerted in the high-pull peaks and give it back in the low end troughs. We will see.

These forces were measured 5 time per second. I can measure up to 10 times per second. I did a series of starting pulls with my team last night at 10 measurement per second, have not looked at it yet, if it is interesting I will post it.

Andy, you may have to mud those crops in and send me that buffer.

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