[Tim Harrigan]

Wow, glad we don’t see that very often.

[Tim Harrigan]

Mitchmaine, we have already seen instances earlier where the nylon rope buffer seemed to be more of an impedance than an asset, at least the average draft was higher in several instances. The key is that the spring constant and rate of response has to be right for the task at hand. That is why Andy is interested in an adjustable buffer. While the concept is interesting the tasks that most of us do are too variable in draft to make a single buffer a practical tool, other than perhaps for shock protection or if you are doing repetitive and predictable work.

Just because the nylon rope was an impedance in some cases we can not say the same about the compression spring until we can evaluate it and see how it is performing. The least we can do is learn something.:)

[Tim Harrigan]

Geoff, I appreciate your comments and observations in all the dicussions on this site so don’t think of yourself being on the fringe of the discussion. It seems to me we have all had experiences and abilities that add to the collective knowledge of this community of interest. It works well because so many folks contribute to the discussion. We could all keep to ourselves or have private discussions, but we make an effort to lay things out as clearly and completely as possible because we all have a role and responsibility in the education and advancement of those seeking to advance animal power as a reasonable choice for small farms and other sustainable enterprises. I have learned a lot from contributors to this site and I appreciate the effort from all.

[Tim Harrigan]

Well it certainly is a linear response. If you make inches the dependant variable (corrected 4/18, not independant) the predictive equation would be more useful for set up. I have been revisiting some of the work I did with starting forces, I think I will start a new thread.

[Tim Harrigan]

Countymouse;17566 wrote:

It is not a progressive spring, and is sold as a spring with a rate of 127 pounds per inch. I ought to calibrate it with known weights…. The reason I want to know is that I could try to optimize the system for minimizing head bobbing (if that seems attractive) OR to minimize max draft OR to maximize smoothness. These are probably not mutually exclusive goals, but it would help prioritize my designing if I knew which would probably give me the most “bang for my buck.”

If you have some front tractor weights they are nice to use because you can add in increments of about 100 lbs. It is nice to know for sure what the spring constant is and how it responds over the full length. As you become more familiar with the buffer will you be able to make it more compact? If we put a pull meter with it as it is the two things would be quite long and create a lower than necessary angle of draft.

The work I did was with a nylon tow rope, the response of your spring buffer might be similar but it might not. The response of the spring is likely more rapid than the nylon. The challenge is to link animal behavior to measureable things such as average draft, uniformity of pulling forces or other things that translate to improved performance.

Good observation and comments, Carl. That is what I was hoping for in my previous comment.

[Tim Harrigan]

That is interesting. How did you calibrate the pre-load on the springs? I am not sure it is linear across the range from fully compressed to released. It is nice to hang some known load on is just to be sure. I have learned not to be too assuming about whether draft is increasing or decreasing, I still am not sure what is better from the animals point of view, a more even pull or lower total draft, and to what extent you can have either one or both at the same time. Perhaps just observing the signals from the horse are best. I am going to be in Pittsburgfor a few days in June, if it works out maybe I could bring some equipment along and measure pull to compare with what you have.

I am most accustomed to observing oxen at work. Maybe some of the horse teamsters can comment on the head bobbing relative to high-draft work or any other observations.

[Tim Harrigan]

Looks good. For sure it will take some trial and error but with a little work it might work quite well. If your idea to trim the top 10% of draft forces can be achieved with careful observation it could be a useful task buffer. It would be a good learning tool also if you can calibrate the breakover forces for a range of compression settings. It will be interesting to see how well it works.

[Tim Harrigan]

Now I wish I had gathered more data when we were working with the arch. There is always another day.

I think we often underestimate or fail to recognize the subtle insight and application of mechanical advantage that so many of these farm tools and implements provide. The harness and ox yoke, eveners and single trees, there are so many examples of brilliance from those humble craftsmen.

[Tim Harrigan]

near horse;17482 wrote:

Is there anything we can say about the relationship on your graph between draft and speed? …. Were the animals allowed to move out at the speed of their choice or were they held to a certain range (like only walking)? ……I know the speed and draft measurements were taken very close together in time but were they actually simultaneous?….. It just seems that ground speed should end up being dependent on draft – higher draft we get a lower speed.

The animals were advanced at a normal ground speed for that work. I am not sure about the graph, generally higher speed means somewhat greater draft. Work is force times distance and greater speed gives greater distance. That would be more so with tillage tools than wagons. Tillage draft generally increases fairly rapidly with speed. The draft and speed measurements were simultaneous. I have not tried to line them up exactly to see how they lay out, there is probably a very slight lag in the draft measurement relative to the time stamp. I do not think the animals are that sensitive to draft regarding their speed in the normal range of drafts. They seem to have a comfort zone that they move in but they will get out of it with really big loads.

[Tim Harrigan]

mstacy;17471 wrote:

Tim,

I would love to see draft versus time graphs if you are using some sort of electronic data aquisition. The load buffering you refer suggest that periodic variation in ground speed is the root cause. I had not considered this but it makes perfect sense. You don’t happen to have any ground speed (vs time) data do you?

Here is a graph showing speed variations with the associated variations in draft. This is with oxen pulling a 1200 lb sled. There are other sources of variation in draft and pulsing, tillage is a good example with changes in soil, depth, moisture etc.

[Tim Harrigan]

Countymouse;17464 wrote:

At first pass, it seemed like the spring forces would be distruted efficiently through the singletree to a drawbar spring. Was the only benefit of the two spring set up to divide the load and possibly reduce the size of the spring?

I think so, but I am not sure. It seems like you are thinking it through pretty clearly. Overextension is my concern with the extension springs as well unless like you say the spring constants are very high. In that case it begins taking you back to shock load protection rather than task buffering.

[Tim Harrigan]

Yes, there is the potential for more efficient energy use if the buffer response matches the demands of the load, but based on some of the trials it looks like they could be a drag on the system as well. If they can give the energy back in a productive way. It would be good to be able to view a graph of the pulling forces in progress as work progressed but it happens too fast to visualize it. It is a series of pulsing that is hard to put in context. It looks like electronic noise. The advantage of the frequency graphs that I showed is that they accumulate the forces of interest so you can see where they are over time.

The singletree springs would have the advantage of dividing up the load into smaller segments so they could be smaller. I would like to know a little more about their design parameters to be able to predict when they might be of benefit.

The logging arch example is interesting, of course the log would have to be chained up short to get it off the ground. In addition to the lift, and the potential forward movement of the log, there is additional buffering in the start as the arch begins to move an instant before the log potentially creating an easier and smoother start.

[Tim Harrigan]

CM, sounds like a good plan. Do you have a set of tractor weights or something hang off the buffer to calibrate the pre-load? Seems like you could measure the threads and get a pretty good idea of where you are in short order.

[Tim Harrigan]

OldKat;17436 wrote:

motherearthnews; I had forgotten about motherearthnews. Glad you pointed this story out, it was a good read. I think everything they had to say was appropriate to that day, and probably more so to this day. If their coverage was timely then, it is “timeless” now.

As interesting as it was to read about our friend Jason, and it was interesting, I liked the little mini-profiles of other horsefarmers at the end of the story. Just tends to show how versatile and adaptable (and widespread) they really are.

Best of all I really enjoyed reading this;

Good find Joshua.

Yes, that’s it exactly.

[Tim Harrigan]

Countymouse;17447 wrote:

A spring that can store this amount of energy and release it gently is a pretty big spring, but the way, the one I will use is a coil spring of about 4 inches in diameter and 12 inches long.

Is this a compression spring or extension spring? I think the Pinney springs mentioned earlier by JAC were extension springs (4) that were attached to the single trees. It will be interesting to see what you come up with and how well they work.

[Author]

Posts