[Tim Harrigan]

Carl Russell;17433 wrote:

By comparing the two hitches to the zero of the stationary load, the spikes are not off-set by the reaction forces… or are they, and I can’t see that either?

Can we see these numbers showing high and low spikes above and below the average as zero? (like the wagon on the hay ground chart). That would show me more accurately how the buffer softens the line relating to draft.

Carl

Can you elaborate on this? I am not sure exactly what you are asking.

[Tim Harrigan]

Carl Russell;17433 wrote:

The unbuffered must surge forward and reduces the draft more than the buffered one. Somehow it seems there must be a balancing there somewhere.

It seems like loads that are surging forward are going to be light loads so maybe it is not quite so important. With heavier loads it would be most helpful to buffer the high end loads which is what the nylon did with the rubber tires and horse harness.

I think the balance is the real challenge when considering a draft buffer. Generally they are going to be effective over a small range of pulls and you work your team over a wide range of pulls. That is why I come back to shock load protection for most situations.

[Tim Harrigan]

Carl Russell;17433 wrote:

……… but it still brings me back to where does the energy go that is required to do the work?

There is energy wasted in every mechanical system as friction, heat, etc. It seems like the spiked forces that are in excess of what is needed to move the wagon is wasted energy. The goal of a buffer is to capture that excess energy and return it as useful work. So it is an attempt to improve the mechanical efficiency of the system and on the high end minimize the soft tissue buffering. The forces that the animals buffer could be seen as wasted energy as well.

[Tim Harrigan]

near horse;17428 wrote:

One other question regarding one of your graphs Tim. Why did using nylon harness on the steel wheeled units result in higher average horizontal draft for both oxen and horses? Didn’t the nylon harness give lower values for the rubber-tired wagons?

The nylon did give lower values for the rubber-tired wagon when pulled by the horses. There was not much difference with the ox drawn rubber tired wagon, perhaps because all the pull was through a single rope rather than 4 traces and the applied pull did not match the elastic coefficient of the nylon rope.

I think with the higher draft of the steel-tired wagons it seems like the elastic connections pre-loaded a certain level of pull in the traces and the recovery speed of the nylon was too slow to return many of the pull forces and allow an accumulation of low draft pulls.

[Tim Harrigan]

near horse;17378 wrote:

Do you think the pulsing is actually accentuated at “the extremes” of resistance – both high and low? I’ve noticed the pulsing when using a light sled that tends to glide forward after the initial pull leaving the team with almost no load, then they “catch up” or take up the slack and it’s another spike (albeit not an overall big load).

Yes, it seems like it. When there is little resistance the load tends to catch up and put slack in the line then snap taught.

[Tim Harrigan]

Carl Russell;17417 wrote:

I appreciate all the work that Tim put into these studies, but I am trying to point out how these numbers do not support a concept that buffers reduce draft requirement. ……….My point about the differences between how horses and oxen move is that I think this has more to do with the differences in numbers than the different harnessing systems. There are still too many variables between these experiments then I can accept as definitive………………… I would like to see comparisons of the same pair of horses, or oxen, with different harnesses on doing the same work.
Carl

I appreciate Carl’s observation that there are many variables to consider and I agree. We could use more information but we are trying to work through it with the information that we have.

Based on what I have seen I do think draft buffers can reduce draft if we think of draft as the pulling force transmitted to the team. There is a question of draft compared to what? If we compare horses to oxen are we assuming horses are 100% efficient? We can see that the bounce or pulsing in the load from the striding delivery is not much different between horses and oxen. The question is how much pulling force does it take to move a load, and after that, how much force does it take a team of horses or oxen to move the load? Maybe the standard would be a steady pull with a tractor to remove the pulsing of the stride and at a 0 degree hitch angle to remove the lift component. But that takes us again to another system were we do not have the soft tissue animal mass buffering and other things that are going on.

I do not see the pulsing as a negative regarding draft forces. If you look at the stoneboat draft graph with different hitch angles and load shifts you can see that the pulsing pull of Will and Abe at an 18 degree hitch angle was equal to the measured draft with the steady pull of tractor at 30 degrees with a balanced load and much less than a 30 degree tractor hitch with a front load! So is there some draft buffering going on there? Seems like it. The pulsing is not like a full stop and start because you have inertia and momentum with a moving load.

My hypothesis is that the multi-component horse harness with evener and single trees is a more efficient buffer than the ox yoke. I am not seeing much difference in the load pulse from the stride between horses and cattle. The soft body tissue effect is conjecture but it certainly is a good argument for well fitting harness and neck bows. The hitch angle I can deal with by resolving the vertical and horizontal draft components based on the hitch angle. You can do that fairly easily by dividing the measured pull in the chain by the cosine of the hitch angle to compare the horizontal pull of each system. I attached a new graph that shows the horizontal draft components. It looks a lot like the graph of the tension in the chain graph but somewhat lower values because the lift component has been removed. Basically, a greater hitch angle reduces the resulting horizontal value more than a lower hitch angle. The horse hitch was 16 degrees (not 18 degrees, my mistake earlier), the ox hitch was 10 degrees. You still see a lower measured draft with the horse hitch than with the ox hitch.

The horse hitch has multiple components to distribute the load and a relatively soft collar to help absorb the spikes in pull before they are transmitted to the horse. The ox hitch has a rigid beam and a chain with no give. How well the forces in the ox hitch are buffered depends on how the animals move together. If the animals are stepping out of phase with each other meaning one is in the acceleration phase of the pull while the other is in the deceleration phase the yoke beam acts like a class 2 lever where the yoke on the neck of the decelerating ox acts as the fulcrum for the power applied by the accelerating ox with the load in the middle of the beam. That seems like the ideal situation.

Sometimes the animals are in phase where they are stepping forward together and they lose the lever effect. They both push forward and they spike the pulling force because there is no give in the chain and no mechanical advantage from the levering effect. All the buffering is soft tissue and that is not an ideal situation. Soft tissue does not have an infinite ability to buffer forces. That is why buffers for shock loading are important. So in some ways it is just in the numbers like Carl suggests, but the pulling forces are real and perceived by the team. It is true that if you look only at the wagon it should not take more pulling force for the ox than the horse, but the efficiency of the applied pull is different for the horse than the ox. My guess is perception is reality for the teams. If I had to drag one of two loads by myself and I knew one required 100 lbs avg pull and the other required 120 lbs average pull, I am pretty sure which one I would chose.

Carl, you will have to explain your comment about the same pair of animals with the same harnesses for a valid comparison. We used the same team with the same harness, but switched out the traces and they both pulled the rubber and steel tired wagons. Same with the oxen, pulled the same wagons as the horses. Are you suggesting we put the ox yoke on the horses?

Here are the graphs again for convenience, hitch angle/load balance and wagon draft resolved to horizontal forces.

[Tim Harrigan]

OldKat;17414 wrote:

Tim Harrigan; maybe you said somewhere how you obtained these numbers, but if so I missed it. I suspect that you are using a strain gauge of some sort. Could you briefly outline your methodology in making your measurements? SRR

I measured tension in the towing device for horse- and ox-drawn farm utility wagons loaded to 6100 lb. One wagon had 6.00-16 bias ply tires and the other had 5.5 inch wide steel tires. Each wagon was drawn with both a team of horses (16º hitch angle) or a team of oxen (8º hitch angle). The horse hitch consisted of a standard collar harness with stitched, inelastic leather/nylon traces. A North American-style ox yoke with a dropped hitch point was used with a team of Milking Shorthorn steers.

Pulling forces with the standard horse traces or towing chain (ox) were compared to the nylon towropes. The nylon towrope (3/4 inch diameter) consisted of woven nylon strands that formed a hollow shell. Within the shell was a 12 inch long hard rubber core. The nylon towrope stretched 4 inches at a constant rate of 1/2 inch per 225 lbs under an 1800 lb load.

Pulling force measurements were made with a hydraulic pull-meter with a pressure transducer on the discharge side of the cylinder. The pull meter was placed in the towing chain and the pulling forces were recorded at a frequency of 5 Hz with a monitor attached to the transducer. A sub-meter accuracy global positioning system receiver was used to record the position of the implement and match pulling forces with specific locations in the field.

[Tim Harrigan]

This graph shows the pulsing of the pulling forces of a sled as the team steps into the load. This graph showing the speed looks alot like the earlier one showing the pulling forces. The spikes in speed look a lot like the spikes in draft. Read the sled speed from the left axis, seconds on the bottom axis and pull on the right axis.

I changed the right axis on the ox drawn sled graph to the same range as the horse drawn wagon draft for ease of comparison. The horse drawn rubber tire wagon average draft was 492 lbf and the bounce was about 350 to 700 lbf. The average ox drawn sled draft was 476 lbf and the bounce was about 275 to 675. So those look pretty similar even though comparing a wagon to a sled is not the best.

Clearly there are differences in anatomy between horses and cattle. I am not so sure cattle movement is as choppy as you described. Where horses and cattle are similar is most of the power for draft comes from the hind quarters. The slight acceleration and deceleration that causes the pulsing is accentuated under greater resistance. The deceleration is the instance when one hind leg is extended forward ready to push and the opposite hind leg is extended back having just completed the push with that leg. The acceleration is when the forward leg begins pushing through. Both buffer the pulling reaction throughout their body.

Some of the things related to fluidity of movement could be evaluated but just measuring forces is going to leave a lot of unanswered questions. To get at what you suggest you would need video cameras to look at efficiency of movement, pressure sensors at the yoke or harness contact points, probably other things as well. I do not have any plans for that. It would be interesting.

[Tim Harrigan]

I agree that reducing the draft is something we should set as a goal. It is the practicality of it that is a concern. It seems for the most part there would be a bigger impact in most cases with a focus on proper fit and adjustment and conditioning. Draft buffers are more strategic. I will be interested to see what you come up with.

[Tim Harrigan]

Carl Russell;17310 wrote:

Why don’t you think that the ox yoke acts like an evener?

I would think that draft angle would have more effect than you seem to indicate.

For sure draft angle is important. A greater draft angle provides more lift and allows the team to get under the load and keep the line of draft through their center of gravity as they lean into the load. I understand competitive pullers often like taller animals such as the Chianina for just that reason. It is not hard to put a pencil to this question and calculate theoretically how draft angle can change the pulling forces. It is a question of the combination of horizontal forces and vertical forces. Over a certain range increasing the vertical lift with a greater draft angle allows the team to carry some of the load and reduce the horizontal pull requirement. One day I decided to test this and see how it actually played out on the ground.

I loaded my stoneboat to 1000 lbs with sand bags. I wanted to check pulling forces with draft angles of 0 degrees, 20 degrees and 30 degrees and also with the load distributed on the boat evenly front to back, front loaded on the front half of the boat, and back loaded on the back half of the boat. Of course that is not possible with a team so I used a tractor with the boat hooked to the front-end loader so I could set the height and hitch angle. After I measured all those I pulled the stoneboat with the Will and Abe shifting the load from front to even to back. The graph shows the results.

With the tractor pulling at 0 degree hitch angle the average forces were greatest and increased as the load shifted from the back (428 lbf) to even (491 lbf) to front (514 lbf). At 20 degrees, the pull in the chain was lower and progressed from 368 lbf back loaded, to 452 lbf evenly distributed to 513 lbf front loaded (same pull as at 0 degrees front loaded). At 30 degrees reaction in the chain was generally lowest progressing from 366 lbf back loaded (same pull as at 20 degrees) to 396 lbf front loaded. So angle of draft clearly made a difference but it depended on how the load was distributed when the tractor was doing the pulling.

When Will and Abe pulled the load the average draft was 400 lbf back loaded, 396 lbf evenly distributed and 400 front loaded. If you compare the even loaded 20 degree angle pull (452 lbf) with Will and Abe at 18 degree angle (396 lbf) you can see that load distribution did not make any difference.

I need to look at this in more detail at some point but it almost seems like Will and Abe were able to make some adjustment in their pulling technique to keep the pulling forces minimized as the load shifted from front to back. Now the tractor pull would clearly be a more steady pull with less pulsing than we see with drafts as they step into the load. That likely has something to do with it, but right now I am hard pressed to offer a convincing explanation. Carl earlier mentioned an intentional energy management on the part of the team, there may be something to that.

Carl, I do think the ox yoke acts like an evener, but I do not think it is as efficient as a horse hitch in buffering the forces that are absorbed by the team. And, hitch angle is important, but less so with a wagon than a log or boat because the angle is much lower because of the higher hitch point with the wagon. Also, the wagon offers less resistance that the log or boat and that has an impact on the dynamics of how the team respond to the load. It is not that I think those things are not important, just that I think they were somewhat minor factors in this situation.

[Tim Harrigan]

Here is a force frequency graph slicing the distribution of pulling forces into smaller 50 lbf increments comparing the horse hitch and the ox hitch drawing the steel-tired wagon. As I mentioned, there could be some small effects from the lower hitch angle with ox team, but the surface was quite hard and fairly even so it seems any advantage from a higher hitch angle would be small. But the buffering effects of the horse hitch are very clear. Look at the greater frequency of high-end forces on the right side of the graph for the oxen.

So what about draft buffers? Well designed and proper fitting horse harnesses are an advancement in draft animal technology compared to the ox hitch. The beauty of the North American ox hitch is in it’s simplicity and attention to animal comfort. I think there is value in draft buffers as equipment and animal protection from shock loading for both horses and oxen. From a practical standpoint, it does not seem necessary as a draft reduction tool for horses if their harness fits and they are conditioned to work. But that does not seem to be the case in many parts of the world.

As we look around the world we can find many cases of draft animals that are poorly fed and cared for with harness or yoking systems that are not attentive to animal comfort and productivity. Not out of malice, but for lack of resources, education and a cultural understanding that places little value on these things that we understand to be so important. For instance, it would not be uncommon to find folks clearing overgrown land for agricultural production with underfed oxen with poorly designed and fitting (by our standards) yokes with primitive plows catching on roots or obstructions every several feet. Any question why they might not demonstrate willingness? So perhaps buffering systems, including harness and yoke improvements offer a possibility of real improvement in many situations.

Closer to home, some type of buffer may offer more to oxen than horses. Some may promote the 3 pad ox collar but I do not know much about it, I have never used or tested one. Presumably, it could offer some of the same benefits as the horse collar. I would consider a compression spring buffer for some jobs for my team, but those would be higher draft tasks with an eye toward shock load protection. My understanding is the 3 pad collar may not be best for the high draft work. We always need to keep an open mind toward possible improvements in our hitching and harnessing systems.

[Tim Harrigan]

Carl Russell;17278 wrote:

I am also interested in knowing the dynamics associated with changing nature of the required draft power. My sense is that the animals already are the buffer. After-all they are not gear operated.

In this work measuring wagon draft we loaded a steel-tired wagon and a rubber-tired wagon to 6100 lbs. Pulling forces were measured with horses using standard traces and a nylon trace. We also used an ox team with a standard North American-style neck yoke with a tow chain or a nylon tow rope.

Because an average draft represents a composite of pulling forces, it does not reveal much about the nature of the forces transmitted to the team as it pulls the load. Is the load steady and predictable, or does it bounce between a wide range of high and low values? It seems that a steady and predictable pull would be more suitable and comfortable for the team. The graph below shows how much and how rapidly the pulling forces fluctuate. These were the pulling forces for the horse-drawn, rubber and steel-tired wagons with standard traces. The average draft for the rubber tired wagon was 282 lbf, 490 lbf for the steel tires. The forces were measured five times per second and bounced between 350 lbf to more than 1000 lbf for the steel tires and 350 lbf to 700 lbf for the rubber tires. This is largely the pulsing of forces from speeding up and slowing down as the team steps into resistance of the load.

There were big differences in draft between the steel and pneumatic tires. There were small differences between the standard traces or steel chain and the nylon traces. Probably the most interesting result of this work was the effect that the type of hitch had on the wagon draft. Hitch in this case refers to the team (horses or oxen) and the harnessing method (collar, standard tugs and evener for horses; neck yoke and steel chain for oxen). Compared to the horse hitch and rubber-tired wagon (average draft of 260 lbf), draft increased about 19% (to 309 lbf) when using an ox hitch. When using the steel-tired wagons the ox draft increased about 17% from 490 lbf with the horse hitch to 574 lbf with the ox hitch.

At least two things could have contributed to the lower drafts of the horse hitch. One is the greater angle of draft with the horse hitch. The hitch angle with the horse-drawn wagon was 16 degrees but only 8 degrees with the ox-drawn wagon. A low angle of draft provides a horizontal pull but little lift for clearing bumps and small obstructions. A greater angle of draft provides more lift which lessens draft on uneven ground.

The most likely cause for the improved efficiency of the horse hitch is in the nature of the hitch itself. There no reason to think that the wagons pull harder with the oxen. The difference is in the transmission of pulling forces to the team. The horse hitch reduced the high-end drafts compared to the ox hitch. The horse hitch redistributed the load through four traces and the two-horse evener and shared the load between two collars. The ox yoke transferred all the pulling force through a single towing chain. There was no redistribution or sharing of high-end drafts, and every surge and shock was transferred directly to the yoke beam and bows. The multi-component horse harness was an effective draft buffer.

So it is difficult to separate the animal from the hitching system from the load. Of course, the teams are responding to the resistance of the load so they perceive the magnitude of the fluctuating forces. They absorb the pulling forces transmitted from the load and through the hitch. This is why proper fit and maintenance of equipment is important. Conditioning is important so they maintain a working reserve of power to respond to the spikes in pulling forces, so they are not exhausted and uncertain from working near the edge of their ability.

[Tim Harrigan]

Carl Russell;17278 wrote:

This is what has been going through my mind.

First of all is the difference in pneumatic vs. steel a matter of elasticity of the tire, or a matter of the steel wheel getting “trigged” against the berm of soil formed in front of the depression?

In most cases it is a combination of both those things. I will comment on the animal-as-buffer later.

Draft is the pulling force (pounds-force, lbf) measured as tension in the towing chain needed to move an implement in the direction of travel. Draft for wagons and carts on level ground is largely the force needed to overcome the motion resistance of transport wheels. Motion resistance is the force needed to keep an implement moving at a constant speed while compressing or moving soil and overcoming wheel and axle bearing friction. Motion resistance is largely a function of the road surface. A hard surface offers little motion resistance while a soft surface offers considerable resistance.

Important design considerations affecting wagon draft are tire width, tire height, and whether the tires are pneumatic or steel. Pneumatic tires cushion the impact of stones and other obstructions and are particularly helpful on a gravel road. Pneumatic tires also deflect under a load. As the load increases, tire deflection increases the tire/soil contact area. This provides a larger bearing surface, improves flotation, reduces tire sinkage, and reduces motion resistance and draft. When a steel tire contacts an obstruction such as a stone on a hard surface it cannot deflect and easily roll over it. Instead, it acts as it would going up a steep incline, if only for the few inches it takes to get over the stone. Draft forces spike up in that short distance as it climbs over.

A wheel will sink into the ground until the resistance offered by the soil equals the pressure applied by the tire. Wheel sinkage increases a tire’s contact area and bearing surface. Tire sinkage increases the tire/soil contact area when steel tires are used because steel tires do not deflect under a load. Tire sinkage increases wagon motion resistance and draft.

A large tire bearing surface generally improves flotation, reduces sinkage and reduces motion resistance and draft. Tire bearing surface is directly related to wheel height. In other words, doubling wheel height doubles the tires contact area. In a uniform soil and under similar loads a 48-inch wheel will sink to only one-half the depth, but will have the same contact area as a 24-inch wheel.

In many cases, wagon design limits our ability to use taller wheels to improve flotation. And, taller wheels may be a hindrance when loading or unloading a wagon by hand because a higher reach is needed. Perhaps a better way to increase tire contact area is to increase tire width. Tire bearing area increases in direct proportion to tire width. In a uniform soil we expect a four-inch tire to sink to one-half the depth of a two-inch tire. Wider tires typically create less motion resistance and draft than narrower tires

[Tim Harrigan]

Yes, it is very interesting. My interest and motivation is to understand the nature of the pulling forces and how they are transmitted to the team. An understanding of those issues can reveal opportunities to improve animal comfort and productivity. I have to think the animals would appreciate damping out those 1200 to 1600 lbf sulky plow forces measured with the ox team.

[Tim Harrigan]

No, it is not a big difference but it is fairly consistent. It also occurs at the relatively low draft but there could be some benefit for young or small teams over the course of hours of pulling. It does demonstrate that the concept of a draft buffer is sound, the problem is that it is not practical unless you are doing repetitive and predictable work, perhaps like carriage driving. In general, for farming and logging, I really see the benefit as shock load protection. So if you have springs you rarely want to see them doing anything. My opinion.

Another interesting thing about these nylon traces, when we switched to the wagon with the steel tires the draft reduction advantage disappeared. Actually, the draft with the nylon traces was even a little higher.

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