[Tim Harrigan]

This is good stuff, Ethan. Thanks for posting it.

[Tim Harrigan]

I think an important consideration is how fast do they have access to how many apples. If the trees are in the pasture they would have access to just a few apples that dropped initially, more later as they matured and dropped from the trees. So the stock would have time to adjust. If you just turned them in for the first time later in the season and the gorged themselves on apples with no adjustment period, now you have a problem.

[Tim Harrigan]

[Tim Harrigan]

Nice, Carl. That is very cool.

[Tim Harrigan]

@Countymouse 28363 wrote:

3. A “bucket” that could scoop manure up about 3-4 feet and dump it would be awesome. No need for telescoping on anythign “fancy.” I will be curious to see what you come up with (if you pick up this concept). I have sketched something like this out before, but it always got too far-fetched looking. At least a few people who use draft animals almost exclusively keep a tractor just for the bucket. It’s definately a need that hasn’t been filled.

Andy, how about a ramp and a bucket on a frame with a wheel on the front and two handles in back? 🙂

[Tim Harrigan]

Carl, how do you stack the logs next to the trail? If you are walking those logs up those rails with a peavey I am more than impressed.

[Tim Harrigan]

Good stuff, Carl. Thanks.

[Tim Harrigan]

@dominiquer60 28165 wrote:

It may be Andy’s fault, but you are an enabler Tim:)

Maybe, but he makes it so easy.:cool: He has two farm dogs, Pythagorus and Isosceles. 😉

[Tim Harrigan]

Andy, I have come to the same conclusion, the front of the runners compress and firm the soil as the implement moves across it so the back of the sled is running on firmer and smoother soil and thus a somewhat lower friction coefficient. It is like a wagon on soft ground, the front tires firm the ground and reduce the rolling resistance for the rear tires running in the wheel track. The simplified approach to predicting draft based on a load and the surface has the advantage of being straight forward but it lacks precision if you really want to understand the details. In fact, the approach does not account for the surface area of the sled or boat so in theory you could take the load off the boat, turn it on edge and reload and the draft would be the same. That is the incompressible assumption that we know does not hold, but it is pretty close in some cases.

I compared a stoneboat with a sled with 4 inch runners traveling across firm hay ground, soybean stubble in the spring and then a recently planted oat field. The sled and boat were identical on the firm hay ground, sled draft was somewhat higher than the boat draft on the soy stubble, and considerably higher on the oat ground. So that was a clear demonstration of the compression and compaction of the soil where the reduced flotation from the reduced runner surface area increased sinkage and increased draft.

I have thought about changing the surface material but not the shape of the runners. You rockered the runners, but you also seemed to describe a natural process of wear whereby the runners took on a rockered profile. So do the runners naturally develop a low-draft profile? Are you suggesting we need to be more attentive to mimic the shape of worn runners when we replace them with new runners? That makes sense to me.

I have wanted to test an implement pulling a load over the same surface but with increasingly greater loads. I suspect that under the same conditions, a pulling contest for instance, when the sled is loaded to a % of the team weight, the bigger team pulls a greater portion of their weight e.g. experiences a higher friction coefficient than the smaller team. Because of the compressibility of the soil and the work needed to compress the soil. It is not something you can see, but I suspect it could be measured.

[Tim Harrigan]

@dominiquer60 28153 wrote:

This is the nerdiest thread yet…:)

You can blame that on Andy. :rolleyes:

[Tim Harrigan]

Andy, check out post #26 in the draft buffer thread of the working with draft animals section. Look at the graph comparing pulling forces for a sled at various hitch angles and with the center of the load shifted from front to center to back. I think you will find it interesting.

[Tim Harrigan]

@Countymouse 28145 wrote:

“…I like an analysis that treats the front of the log differently than the back of the log because the front can dive into the ground and till while the rear cannot. Because of this fundamental and important difference, I think the friction coefficient for the front of the log will be different from the rear. Also, I don’t think that a lift to one side of a log will necessarily shift that same weight to the rear…”

I agree that the friction from the front and back are different, I just have trouble picking the functioning system apart in that way. It is interesting to do an ‘what-if’ analysis but I prefer to start from the measured values and go from there. When you re-integrate your front and rear-of-log solutions do the actual measurements validate your approach with the tongs or choker? I agree that the weight transfer itself is not significant, after all the rear end of the log will not carry 1050 lbs until it is standing on end. But small shifts are likely to cause considerable increases in drag on the end of the log.

“….Sled: …what really jumps out at me in this plot is just how flat it is. All resulting draft forces from an angle of 7 degrees to 29 degrees are within 2% of the minimum. So, for all practical purposes, the angle of draft doesn’t matter for a sled…”

Yes, I agree, so much so that one would be justified to ask ‘Who cares?” It always comes back to point that we want to harness the animals in a way that allows them to apply their power comfortably and efficiently. There is a lot of room available to do that.

“…Tongs: the resulting (front) friction coefficient is 0.78. Wow, can the front dig in!…”

Yes, possibly, but you will notice that I angled off the front of the log to prevent that from happening. So I doubt that this is realistic in this case. Again, do the measured values verify the results for your reintegration of the front/rear components?

“..The graph illustrates how much more sensitive this setup is to draft angle, with a 2% increase over minimum draft at 27 degrees, a 5% increase over minimum draft at 20 degrees…”

“…Chain: …the resulting friction coefficient is 0.89 for the front end of the log (which is similar to the friction of a car tire on pavement). Wow again!…”

These coefficients seem quite high and would indicate considerable ground disturbance or plowing of snow if in the winter.

Again, I think the physics of hitching is interesting and instructive, but the bottom line is it has to allow the animal to apply their body mass and strength in a way that is comfortable and efficient. We know that it means a low hitch point for heavy resistance. Also, because of variations in terrain, etc., I think an actual optimal hitch angle would probably be a few degrees greater than a calculated optimum. So observation and teamster skill in adjusting to the situation are key components.

[Tim Harrigan]

Andy, let me point out a few things about these skidding methods that complicate the analysis. The stoneboat is 8 feet long and weights 175 lbs so the weight of the load was 1225 lbs rather than 1050. The log was 12 feet long so it extended about 4 feet past the back end of the boat, but the log was carried off the ground in back so your front/rear assumption about the friction caused by the rear of the log is problematic. I have a little bit of a problem separating the front/rear contribution to the friction of the log. There would be some lift on the front that would reduce friction as you mentioned but with the tongs and choker chain there would also be load transfer from the front to the rear of the log that would tend to increase friction at the rear. An advantage of the tongs is that they provide a fairly constant hitch point even as the log rolls. The choker chain is a quick and sure hitch, but the chain wrapped perpendicular to the direction of travel acts as a brake, similar to bridle chains on a sled. Also, and what annoys me most about a choker is that the logs tends to roll so the hitch point is near the top of the log, nosing the leading bottom edge into the ground, and reducing the hitch angle by raising the hitch point. These are the things that I think account for the higher average draft and the higher maximum draft for the choker compared to the tongs.

At any rate, your analysis is pretty close but your approach is a little different than mine. First of all, I want to calculate the kinetic friction coefficient without the effect of the lift at the front of the log or boat. Because I measured tension in the chain or the resultant force Fr, at perhaps a 15 degree hitch angle (I will check that this evening) I estimate the horizontal component Fh as Fr/cos(theta) where theta is the hitch angle. With that the Fh becomes 406 lbf for the stone boat, 549 for the tongs and 565 for the choker chain. Then, based on the load weights the observed friction coefficient is 0.33 for the boat, 0.52 for the tongs and 0.54 for the choker chain. Then, and I will take a leap here to keep from killing anyone other than you who reads this, to find the optimal hitch angle one has to find the angle theta which provides a minimum pull. This occurs when the first derivative of the pulling force, P, with respect to theta, equals 0. This occurs when the value of the kinetic friction coefficient = tan(theta).

So an optimal hitch angle for the stone boat is 18 deg., 27 deg. for the tongs and 28 deg for the choker chain. Those are close to your estimates and you are right that an optimal hitch angle is different for different hitching methods. And you are correct that in most cases we cannot hitch at an optimal angle because of physical constraints so the recommendation is to hitch as close as possible. I think it is cool that an optimal hitch angle for a wagon for instance with low motion resistance is quite low because it is low anyway with the high hitch point. An optimal hitch angle for tongs with greater resistance is greater which works out nice because the hitch point is lower. It is nice when the theory and practice are consistent, gives you reason to think that there are opportunities for real and acceptable changes with good ideas.

Rock on, draft animal nerd. 😀

[Tim Harrigan]

Elke, I don’t know, but if you could find some horns that are no longer attached to their owners you could try it out and practice a bit. I am sure long, thin horns would bend easier than shorter, thicker horns. Good luck with that.

[Tim Harrigan]

Anne, thanks, that is a great offer. I will let you know.

[Author]

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