[Andy Carson]

When I had been thinking about this at the beginning, I had been thinking of two smaller extention springs, mostly based on the Pinney springs and as in Tim’s experiments. As I started to put pen to paper and see what spring constants would be useful, it became clear that no one spring would be useful for heavy jobs without some sort of preload. That lead me to compression springs as the system to compress would possibly be more simple. Another advantage of a compression spring is that when they are overloaded, they simply bottom out. An extension spring can be stretched beyond the point of return by a rock or other “immovable” object, and would require another mechanism to make sure this didn’t occure. I doubt this is a problem for Pinney-type overload springs, as thier spring constants are probably very very high, but for these types of drafts buffers it might be. When looking into the range of preloads that the spring must experience, and the speeds they must respond to, it came out that a longer spring was needed. The short springs can store just as much energy, but it would probably be released in one big “pop” as opposed to a long steady “push.” If we want to target 1/5-2/5 of a second response and release time, a spring of at least 8 inches in length is needed and a 10-12 inch spring is probably better. Dividing up the load between the traces does mean the diameter of the wire (and the resulting weight) used to make each spring could be smaller, but the time of response (and the length of the spring) would need to remain the same. Also, if a 12 inch spring had a diameter of much less than 4 inches, I start to worry about the potential of the spring bending sideways or “buckling” instead of compressing evenly. So, you still end up with a spring of approximately the same size, but just two instead of one. Also, one would have to make sure the springs are adjusted to the same preload, which seemed like more fuss than required… 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?

[Andy Carson]

Compression spring. I order it from McMasters and it’s not here yet, so I still have to play with how to rig it up. It’s probably going to resemble a beefed up drawbar spring (like a porch swing spring) and will probably use a long threaded rod or bolt through the middle to preload the spring. Turning the screw in or out to adjust preload will be a little annoying in this mock-up, but I think investing time in a better mechanism is probably a little premature right now. Any ideas on how I might set up an objective test of it’s efficacy? I don’t have Tim’s measuring equipment, but if I was thinking if I made a close up video of the spring in action, I could possibly determine the max draft force by the length of the movement of the spring… Maybe I could then preload the spring to a much greater degree (such that only very high draft could compress it) and take another video over the same course. If the spring is sometimes compressed at the high preload, but never obtains that same level of compression with moderate preload, I think this demonstrates a reduction in maximum draft forces… Not as good as Tim’s system, but it could be a decent “first pass” using equipment I have and might help me tweek things if needed. Any thoughts?

[Andy Carson]

@Tim Harrigan 17440 wrote:

Generally they are going to be effective over a small range of pulls and you work your range over a wide range of pulls.

This became abundantly clear when I started to do some of the math to figure out the rate of the spring, the length of the spring, the reduction in forward speed, and the preload. The one I am attempting to design may be useful in buffering average loads of around 300-500 pounds, and the user would need to adjust the preload on the spring within that 300-500 range. It would be a simple thing, but it would need to be done. The spring won’t kick in until the force exceeds 25% of the average, and will lose it’s ability to buffer (bottoms out) if the load exceeds 1000 lbs. It is designed for one horse, and geared around back calculations of force from my stoneboat work. If someone wanted to use the system for two horses, I suppose they might want to make two of these things, or they could make one bigger one. The bigger one would require a different spring though, not just a different preload on the “one horse” spring. 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. Because there is an adjustment in preload that would need to be performed for each different job, and the system fails if the maximum loads are very high, it might be less useful for a logger than a farmer.

[Andy Carson]

Carl and Geoff, I do think you lay out a good argument about how draft buffers would never work in theory and I do appreciate the discussion. If it weren’t for Tim’s carefully laid out experiment demonstrating that buffers (in the form of nylon tugs) actually do reduce the draft required for a job, I probably wouldn’t be as interested in this idea. Look back at the wagon example at the start of this thread, same load and distance, but less draft with a buffer. To me, this directly demonstrates that determining the effort (either purely mechanical of physiological) required to do a job is not simply a matter of determining the average draft and multiplying by the distance. My fluctuating load example, as well as the bicycle example, provide “real world” examples that demonstrate how two different work conditions with the same average draft and distance can be very different in the effort required by the animal or person. I think that also like the multispeed bicycle example, this spring concept is going to need to be demonstrated before anyone seriously conciders the concept due to the Power = Average draft x Velocity argument… I suspect that people are open minded enough to consider this IF it can demonstrate a reduction in average draft (like tim’s nylon tugs) or a reduction in max draft forces. It might fail to do this, but I think it’s worth a test. I’ve ordered a spring and the rest should be pretty easy to put together… We’ll see.

[Andy Carson]

Tim’s experiments show that with a correctly tailored buffer (such as a nylon traces on the wagon) can not only decrease the frequency of high draft forces, but also reduce the average draft. In my mind, it is hard to not see how a reduction in the average draft would not help an animal complete the job. Honestly, I had expected that the buffers would act more to “even out” the loads, redistributing areas of high draft to areas of low draft. Even though this may keep the average draft the same, the system might still be very useful. To give a concrete example, I condition my horse with a sled on a half-hour long trail loop. I usually warm up with an empty trip at 500 pounds (me and the sled), then load up with cinderblocks to give her a workout. If I load up the sled to 1800 pounds, she can make it around once with only a couple short breaks, but she’s pretty pooped when we finish. For the two trips together, that would be an average load of 1150 pounds ((500+1800)/2). Now if I load up 1150 pounds and do not fluctuate the load, she can pull it for a very long time and is not nearly as taxed in the process. This is a pretty extreme example, but these examples demonstrate how two work conditions with the same average draft (but very different maximum loads) can be very different in how taxing they are. So, redistributing the work load such that the power required is as constant as possible can be extremely effective. In theory, one might think that since animals do not have gears and can pull very heavy loads slower, they could learn to regulate their power expenditure so as to not overexert themselves on heavy loads. I am sure this helps, but I am not convinced this is the most efficient way to even out loads if there are other options available. In theory, humans (as we do not have gears either) should also be able to do the same thing, but how good are we at it? I think a bicycle is a great example, anyone who has ridden a bike up a hill in a tall gear knows that it is possible to stand up and push through the hill using slow powerful strokes. Try shifting down and you’ll see you get up that hill much faster with less exertion. The human body is simply more efficient with repeated light loads compared to a few heavy loads, even though it is the same overall amount of weight that must be elevated the same distance. It is interesting that when multiple bicycle speeds were first introduced and promoted around the turn of the century, many established racers said that these multiple speeds are “unnecessary” as a “healthy young man” can adjust to hills by pedaling with slow powerful strokes. Many were convinced by the argument and it was such a controversy that in 1902, The Touring Club de France organized a 200 km race between a professional racer on a single speed bicycle and a young woman on a three speed. You can guess who won. The beaten professional, wrote this after his loss: “I applaud this test, but I still feel that variable gears are only for people over 45. Isn’t it better to triumph by the strength of your muscles than by the artifice of a derailleur? We are getting soft. Come on fellows. Let’s say that the test was a fine demonstration – for our grandparents!” It took another 30 years for multispeed bikes to not be seen as “tools of the weak,” but once allowed, they quickly made jokes of nearly every racing record made on a single speed bike. Now, I doubt the use of a draft buffer will be as dramatic as the use of multiple speeds on bikes, and there are many differences between the two cases, but it is interesting to hear some of the same arguments that were mentioned 100 years ago… I really believe the concept of the draft buffer is sound, I am more concerned about the practicality of the system.

[Andy Carson]

I might make a mock-up of the design I have in my head and see what happens. I think I can test it out on my spring tooth, as I have some work to do with it anyway. Unfortunately, unless anyone can think of anything better, I will only be able to make a very subjective judgement of it’s effectiveness… Maybe if it looks like it has potential and the “bugs” are worked out, I’ll take some pictures and others can give it a try too. It would definately be useful to me if it works.

[Andy Carson]

Tim, again fascinating work! It is interesting and encouraging to see that a buffer can be effective in some applications. And, in my mind, an 18% reduction in draft accompanied by a virtual eliminiation of any draft forces over 500 lbf is a big deal! It does make sense that the spring constant would need to be tailered to the draft forces for each individual job. Perhaps the nylon traces are too “stretchy” to be effective in the case of the 1900 lb log or the wagon with steel wheels. Looking roughly at the pneumatic wheel example, it looks like the traces would be extended only about 10% of the time (I added up the frequencies of the high draft areas where the nylon traces are significantly less common than when using standard traces). Replacing springs for different jobs would be a pain in the butt, but it would be pretty easy to adjust the preload on one spring even while in the field. It might be similar to the system used to adjust the preload on the springs on a motorcycle (necessary for different sized riders). This could provide a quick and easy way to use a buffer that will only be in action about 10% of the time. Based on Tim’s pneumatic wheel study, I think a spring that is in use only about 10% of the time seems to have potential for reducing draft. Also, using a steel spring would probably address any concerns over the speed of response. Just thoughts…

[Andy Carson]

Maybe there might be a use for springs to equalize the required power is some instances, but Tim’s field chart on his second post convinces me that plowing is probably not one of them. The fact that areas of high draft often boarder other areas of high draft means the spring is going to do just as Mitch suggested, extend for long periods of time and the draft will be the same as with no spring. If the draft for a particular application fluctuated widely over the span of inches, the spring could extend and slow progress through these tough spots, which would in turn, reduce the power (force x velocity) required to go through this area. This would then be followed by the return of the spring in a lower draft area which would increase the power required in these low draft areas (as compared to no spring) and might serve to equalize the power required. When the load is sped up following an area of high draft, some work must be done to overcome innertia. If the load is heavy, or if it completely stops in the area of heavy draft, you would probably loose a lot of efficiency. Perhaps this is why the average draft is higher with the nylon rope compared to the standard traces? I am not sure I can think of an application where the power required might fluctate wildly over the course of a few inches, but logs hitting roots and plows hitting rocks would be a pretty good guess. Oh well, another intellectual exercise to confirm what others already knew… Maybe these thoughts are helpful to others who might have innitially thought in the same vein as I did.

[Andy Carson]

Tim, this is a fascinating and extremely useful chart… I noticed that the chart plots everything above 700 lbf as one event. I am curious what the maximum force you recorded in this run or other runs… In the same vein, it seems that a spring hitch (like the ones used on some of the pioneer sulky plows) could “smooth out” some of those higher draft spots. I am interested in hearing opinions about the use of these springs and if they help much in the real world…

[Andy Carson]

Bradbury, I couldn’t agree more with you. I would like to add that it also seems to depend on the particular job. I never had any rubbing using this basic nylon harness with my current horse before I started doing jobs that require alot of tight turns. I had another horse before this that never had any rubbing no matter what job I was doing with a basic nylon harness. I really love the nylon for how cheap, light, strong and easy to repair it is in general. This leather lining is still working, by the way, and was a cheap and relatively easy fix to the problem. The leather I was using did have a little nap to it, but after a couple times using it, it had been rubbed smooth. Just as another side note, I have had to tighten the lacing a couple times, particurly when the leather got wet. Not a big deal, and the stretched and dried leather seemed to get a little harder and smoother.

[Andy Carson]

I am envisioning a system where support structures could either be hauled into rough county with horses or prepared on site using pole sized trees. These structures might be as simple as two 12 foot poles attached to the cable support apparatus and staked to the ground at the base on each pole to make an inverted V and ought to be easily erected by hand. A 3/8 inch cable could also be strung by hand, and the whole cableway could then be tensioned by a hand powered cable come-along. You would probably need some way to keep the tension from exceeding some safety limit, but I am sure this could be figured out if there is interest… Once the cableway is set up, logs could either by skidded to the cableway with horses and/or winched into place using a small winch. The logs would then be winched up onto the log carriage and carried by gravity through the very rough terrain to the bottom of the hill, where I assume there is better access. I would think that you would want to have a rope to control decent and possibly another “trip rope” that you could pull the release the log from the carriage at the bottom or the trip. The carriage could then be hauled back up the hill by hand using the same rope that controlled decent. It seems to me that the limiting factor in this system is placing and erecting these support structures… There would need to be 25 placed for a 1000 foot trip. I would think this would be useful in situations where skidding for the full trip is not an option due to the terrain and the competing technology is either building a road or using a helicopter. As the initial costs for this system are tiny, it might even be competative in some situations where small operators might have been tempeted to hire a yarder. Hopefully the loggers out there can tell me whether the system I am envisioning would be helpful even IF the details can be ironed out. It might work out that the “details” are limiting to the system, but there is no sense thinking about these details if there is no interest in the concept…

[Andy Carson]

More musings… If the log travelling downhill on the cableway was suspended above the ground by a 20 foot long support beam (with pulleys on either end), then the cable does not have to be near as strong. Putting a beam on the cable also allows for more deflection in the cable line without requiring steep slopes to overcome the sag prior to encountering a support… Using this kind of setup would allow a 2 ton log to travel on one 3/8 inch cable with support structures roughly 40 feet apart (4 foot maximum deflection). That’s with roughly a 1:3 safety factor, I am not sure what kind of safety factor is normal for logging applications. I would think the support structures would need to swing back and forth slightly to equalize tension as the log travels downhill. Maybe simple inverted “V’s” staked to the ground at the base. Sorry again if I am bugging people with my musings. I really don’t know much about logging, I just think designing is fun…

[Andy Carson]

Thanks Scott, I had somehow thought the limitation of ziplining logs was the destructive energy released by a big log flying down the mountain… I did a little math and it is very clear to me (as you seem to know) that the major limitation is the strength of the cables and the tensioning of the cable line to elevate the logs. It is amazing to me just how huge those cables have to be and how much power is required to tension them!!! The heavy machines needed to handle them seem out of reach to people doing this on a small scale… So I was thinking of other ways to zipline big logs down a slope. I hope I am not bugging people with my amateur musings… At any rate, based purely on mathmatical modelling, it seems a 2 ton log could be ziplined down a slope using two 3/8 inch cables tensioned at 4 tons each (as with a hand come-along) IF the cables are supported every 25 feet or so (at 8 feet off the ground). This would require erecting some sort of temporary support structure every 25 feet for the length of the line. Tho whole system might look something line a ski lift. Putting up the support structures might be annoying, but it seems to my amateur mind less annoying and destructive than building a road.

[Andy Carson]

I know next to nothing about logging, but I am fascinated by the mental image of zip lining logs. Is it possible to rig up some sort of braking system on these zip lines to make for a more controlled decent?

[Andy Carson]

I think the point is that it is possible to make money rather than loose money by working horses. Because this may be challenging, I try to approach every decision, including how to shoe my horse, as a buisness decision. If I had to pay $200 a pop to get even one horse shoed, that’s $1800 a year and seriously cuts into the bottom line! I am glad I shopped around and found a cheaper guy who does a great job at 1/3 this price. Even with my current guy, I would be tempted to learn if I had a team. If I had more than two heavy horses, or if the only farriers I could find charged $200+, I have a hard time seeing how hiring a farrier is the best buisness decision…

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