Rotary Horsepower Units
Rotary Horsepower Units
A 5-sweep rotary horsepower unit powering a circle sawmill at the Old Threshers Reunion on Labor Day weekend, 2022.

Rotary Horsepower Units

by Khoke and Ida Livingston of Davis City, IA

Living off grid is a fascinating way of life that captivates large audiences with varying degrees of reservation. Here in Southern Iowa, Khoke and I carve out a life on the land that omits many modern amenities that electricity in any form is counted among.

A couple of the most common concerns people ask about include, how we manage without refrigeration, and how we do laundry. To say we do laundry with horses only begets more questions. Setting aside the mental image of horses treading washtubs full of laundry, our laundry house consists of more than one wringer washer powered by an old cast iron single sweep rotary horse power unit that Khoke rebuilt.

There are horse power units beyond what a motor is measured by. The two primary types of horsepower units are treadmill and rotary. Among the rotary units are two primary categories, the old cast units and the modern gearbox units.

Rotary Horsepower Units
Looking at the underside of a cast rotary unit waiting to be set up for use.

Standard Cast Rotary Horsepower

The original rotary horsepower units were an assembly of cast iron gears. You can sometimes find the remains of these at old auctions. They may or may not be assembled. If you know what you are looking at and can put it together, pieces that are worn out can be rebuilt with body putty and sent to a foundry to be recast. Technically, you can take an old rotary unit apart and have as many duplicates recast as you want.

Most rotary units have a large horizontal gear called the bull gear with usually three smaller gears inside it. These three gears are turning a vertical shaft that are engaging the vertical/horizontal converter gears. Another common rotary design has the bull gear running two small gears that run a shaft with a vertical/ horizontal converter. Either way, this converter turns the tumble rod that powers the shop.

Most of these horsepower units are sized by how many sweeps they have. A sweep is a tongue attached to the bull gear. A single sweep unit has one tongue and it can have a single or double tree on it to be run by one or two horses depending on how much torque you need. A double sweep has two tongues, a triple sweep has three and so on. The largest cast rotary unit I have seen in action was William Livingston’s 7-sweep unit used to power a thresher with 14 horses in motion.

Rotary Horsepower Units
Horsepower units need to be well anchored.

Set Up

So suppose you bought a rotary horsepower unit at an auction, brought it home, assembled it, greased it up and got it ready to go. Now what? How does it get set up?

Usually these are set up outside a building that holds the machinery you want to power. Enough space is needed between the building and unit to fit a tongue length and the circular horsepower track that the horse walks on. The tongues should be 14-15 feet long depending on the size of unit you have and the rpm/torque ratio that you need. Larger tongues generate more torque with greater ease for the horses but they also generate lower rpms which then requires more step up. Longer tongues tend to also be much easier for the horses. It’s like the difference between pivoting something with a five foot bar versus pivoting the same thing with a three foot bar.

The tongue is bolted to the bull gear. On the opposite side of the bull gear is a cast hook where a pull rod can be attached. One end of this pull rod is bolted to the bull gear and the other end is attached to the end of the tongue. This pull rod is actually what is designed to take the pull strain, not the tongue. If you put sideways pressure on the tongue it can split and break. This pull rod needs to be adjusted tight enough to keep the tongue from flexing.

Once you select a level site for the unit to reside near your building, you will want to anchor it securely. Khoke recommends digging 2-3 post holes to fill with cement (and reinforced with rebar), each with a heavy metal loop to anchor the unit to.

From here you will buy a 1.25 inch steel rod from your nearest welding or metal fabricating supply company. This steel rod makes the shafts you need. You will also need to buy knuckles, pillow bearings, pulleys and V-belts. If you use any flat belts you can find flat belt pulleys in old thresher graveyards where retired threshers were parked.

Knuckles are used to join two rod ends. They can be used to join two short rods or to allow this jointed shaft to continue spinning even when it needs an elbow. Pillow bearings anchor the shaft(s) to stabilize them. Pulleys are used to step up or step down the rpm and offer a seat for the belt powering the machinery. V-belts offer the most belt grip and slip resistance.

Rotary Unit Ease

How can you tell if your rotary is working well enough or if it is too hard on the horses? When your horsepower unit is fully set up but no belts are adding resistance to the shaft, a strong healthy person should be able to lay hold of an evener and be able to pull the tongue in a full circle with the unit turning the tumble rod. It may not be easy but a person should be able to turn it. If you cannot budge the tongue when it has no belt resistance then it might be adjusted too tight or not oiled/greased well enough.

Not all units work equally. We have a single sweep unit that pulls harder than our 3-sweep unit. Khoke can pull our 3-sweep unit in a full circle with ease and the single sweep with difficulty. They are made slightly differently and the 3-sweep happens to have a much more efficient design.

Using only two horses on one of the sweeps on our 3-sweep, Khoke can run two flour grinders, a large 24 inch roller corn cracker, and a large table bandsaw used for cutting wood, simultaneously. They activate all this with ease.

Rotary Horsepower Units
A modern 5-sweep unit used to power the Hoover Mill in Scottsville, KY.

Modern Homemade Rotary Units

Having visited several communities with various types of horsepower units, it has been interesting to see what has developed in the face of a shortage of cast units. Most if not all of these homemade units are taking gearboxes used for something else entirely and repurposing them as horsepower units.

A highly sought after gearbox is one that comes out of the backend of a Mack truck. Other popular gearboxes come from a Massey Ferguson Baler and the cement truck gearbox that turns the mixer. These all have gears that will convert a shaft from vertical to horizontal. This is important because on a horsepower unit, the horses will always be turning a vertical shaft and your machinery is running on a horizontal shaft.

The cement truck gearbox is one of the most sought after gearboxes because it is already built to have this horizontal to vertical conversion. The Mack truck gearbox converts a line shaft coming from the motor under the hood that runs back to turn the shaft running the wheels. So this backend gearbox converts the shaft 90 degrees so that the line shaft coming from the motor engages the shaft perpendicular to it to turn the wheels. This repurposed gearbox is then turned 90 degrees to have one of the now vertical wheel shafts cut off and the other will be engaged by the sweeps.

Likewise the Massey Ferguson baler gearbox has a horizontal shaft coming into it and it too has a shaft running also horizontal but at 90 degrees to run a flywheel. This is taken out and this right angled shaft conversion is flipped to make it a vertical/horizontal 90 degrees. Other balers have a different design that doesn’t include this 90 degree shaft converter.

Roy Schrock at the Scottsville, KY, Hoover Mill converted a factory winch into a horsepower unit. This winch was originally powered on one end by a high rpm motor, a heavy duty gearbox reduced the rpm and raised the torque so that very heavy machinery could be moved slowly. Roy used the gearbox in reverse, meaning by making a horsepower unit out of it the horses were engaging the slow end to gear up and power much higher rpm equipment.

This gearbox did not have the horizontal/vertical conversion so he had to buy another gearbox to make this conversion. The conversion gearbox is not nearly as heavy duty as the winch gearbox and doesn’t hold up as well so it needs replaced every so many years.

The weak point with most of these homemade rotary gearbox units is that the gearboxes are not really built for the torque that multiple sweeps can require. If you had three or less sweeps on any of these, you probably couldn’t wear it out. The four to six sweeps usually put on these units apply torque they were not originally built for and will wear them out quicker. The bearings and drive chains in particular. However they do work and can often do regular work for several years. But if you run too large of equipment on too small of a tractor, you will spend more time repairing the tractor.

One of the things that has amazed me as I have looked at some of these modern homemade horsepower units is the innovation used to reinvent uses for machinery/gears that was created outside of a box and looking at it from a different angle.

The old cast rotary units can generally handle more torque because they were built specifically for that job. But the new rotaries work well and are a great alternative. The old cast rotaries can be hard to find, often they need a lot of work or recasting which can be expensive, and they can also break teeth when set incorrectly.

Rotary Horsepower Units
Marty and Stanley engaging this single-sweep rotary unit to operate a laundry house.

The Track

When looking for a site for a horsepower track, you want it as near as possible to whatever you are powering. You also want the site as level as possible. First of all, you do not want the horses to have the extra resistance of pulling uphill. If your unit track is not very level then you will also have your tongue too near the ground on one end of the track and too high at the other. This can cause the tongue to have too much flex which does not bode well with its longevity.

It helps to have the track under a roof but this is not always possible. When the track is out in the weather then when it rains the track can get soupy which can be slippery for the horses. Often an outdoor track will either be concrete or gravel. You can either let the horses wear the dirt track down a little making a groove where they walk so the gravel stays where it belongs better or you can dig it down just a little otherwise the applied gravel drifts outside of the walkway.

Rotary Horsepower Units
Khoke hooking Willow and Susie to the 7-sweep rotary horsepower unit.

Hooking Horses to the Rotary Unit

Stepping the horses up to the horse power track, always clip the horse to the guide rod before hooking the horse(s) to the evener. The guide rod is a metal or wooden rod chained to the tongue near the bull gear. The other end of the guide rod is a metal or wooden rod chained to the tongue near the bull gear. The other end of the guide rod has a clip for the halter of the inside horse. This guide rod keeps the horse(s) from walking off the track. To forget the guide rod hook up can result in the horse walking off the track and pulling the unit apart.

If two horses are attached to the sweep, the outer horse will need a leadrope clipped to its halter and tied to the halter of the horse beside it to keep them spaced correctly and together. A short guide rod with clips on both ends can be made for this as well.

When hooking the tug links to the eveners, the inside tug needs to be just a little shorter than the outer. The inside horse will also need to be hooked up just a little shorter overall than the outer horse.

Rotary Horsepower Units
Zach Miller with Stanley and Sidney.

Bikini Harness

It doesn’t take much harness to operate the rotary unit. All you actually need is a collar, hames and tugs. We call this a bikini harness. We put the bridle on the horse mostly as a formality, but the bit lets them know it is a time to work and the bridle blinders are key in a way I’ll explain later. Our horses are also expected to operate the unit independent of lines.

The guide rod is clipped to the halter, not the bridle. No hold-backs are needed as they only pull and don’t back on a rotary track. Obviously if you have a full harness that you usually use on your horses, this works perfectly fine. All the extra strapping on it, however, is not required to operate a rotary track.

Rotary Horsepower Units

The Horses

A well set up rotary horsepower unit is not usually particularly hard work for a horse(s). Sure it can be, if not geared correctly, or if the tongues aren’t long enough, or the unit doesn’t have enough horses for the machinery it is trying to power. But most of the things we use our rotary units for is light, mind-numbing work. I think some of our horses would prefer hard plowing over light rotary work.

With rotary work the horses walk around and around a track with no cues to signal when the job is done. At least with plowing, the furrow row has an end and maybe a break waiting on them there. Nothing takes the ginger out of a horse quite like rotary work.

Roy Schrock, owner of the Hoover Feed Mill in Scottsville, KY, said he likes to buy runaway horses that most people will sell really cheap to use on his 5-sweep rotary that powers his mill. There is nowhere to run away to or from on that circular track. Walking around and around a track behind a tail that you never catch up to will turn about any high strung horse into a plug.

Khoke has a young team named Stanley and Marty that he started working on the rotary when he needed to do shopwork. Stanley had spent a couple of years as an active stallion before being gelded and is easily the strongest horse we have. The rotary work was not very hard and Stanley kept taking the notion to trot around the track. The shop tools were geared for walking pace and the trotting was a little much. So Khoke looped a chain from the tongue to around Stanley’s evener. As long as Stanley walked, the double tree evener worked like normal, sharing the load equally with Marty. But when he decided to trot, the chain caught the evener to allow it to pull only so far before Stanley got to pull the full load. As long as he behaved, everything worked like normal. He quickly decided that trotting with the full load was no fun and he settled down pretty quickly.

When you hook up a team to the rotary unit, always put the slower horse on the inside track. The faster horse is put on the outside as they usually try to set the pace and the outside circle has more steps.

Training Horses to Operate a Rotary Unit

Most of us do not have the luxury of having someone to drive a team of horses around the rotary track while we work in a shop. One cannot also be driving a team and using a tablesaw at the same time. How is the rotary then practical and workable?

It helps to have two people working to train the horse(s) to steadily engage the rotary unit independent of a driver. We hook the team (wearing blinders) up to the unit and then either tie the lines back to the tongue or loop them over the hames as they are not needed. Then person A goes into the shop and gives a verbal start up command. If the horses do not engage, then person B will lighly tap them with a stick but must never say anything out loud. It is very important that all verbal commands come only from the person in the shop. Person B is there to enforce the commands but is invisible behind the blinders to the horses.

In the horses’ minds, every time they get a verbal command from the shop that they try to ignore, the command is silently reinforced by the person obviously behind them but whose voice comes from the shop. If person B says anything then the horses realize persons A&B are not one and the same and only care about the one behind them and learn to disregard person A in the shop. But if they think persons A&B are the same, they will learn to respond to person A’s vocal commands and person B is no longer needed as silent backup.

When I am working in our shop or laundry house alone I have trained horses getting bored or lazy on me – getting too slow and not responding well to my verbal commands. Then when they make a pass on the swing away from the shop I will duck out the door and follow them for a few laps, lightly tapping them when they slow down. Then I duck back into the shop as we pass it while I am invisible by the blinders. I never utter a sound out loud while on the track. This way they don’t know when I am there and when I am not. Talking to them while on the track is the surest way to keep them from obeying the voice in the shop.

Rotary Horsepower Units

Pulley Eveners

Watching the multi-sweep rotary horsepower units in motion, anyone more observant than me will note that each tongue has a pulley evener of some kind. This is not necessary for a single sweep but to ensure that multiple teams are pulling evenly, a pulley evener of some kind must be set up.

Eveners in general are used to balance the work load between all harnessed parties relatively equally. Two horses hitched to a wagon without an evener would make it very easy for one horse to slack off even ever so slightly and leave 100% of the load for the other horse to pull. Without an evener, both horses have to pull exactly evenly to pull their share. But with the evener, even if one of the horses walks just slightly (or even a lot) faster than the other, the evener allows them to still pull equally. When one horse hangs so far back that their side tops the evener to knock it against the pin holding it, then the evener ceases to work because it can no longer move and the faster horse carries the load.

The same principle applies to a multi-sweep horsepower unit. Without some sort of pulley evener all the horses would have to pull exactly evenly to pull their share and any slacking whatsoever would cause the others to carry the slackers full share. If you had too many horses hang back, the pulling horses couldn’t even pull it.

Here’s where the pulley eveners come to the rescue. Most of the multi-sweep units we have seen and/or used have had a floating ring that all the eveners are attached to. A 5-sweep would have five rod lengths, one between each tongue, with a pulley at each point. As the horses all pull, they pull against this floating ring which moves back and forth between the more and less ambitious horses to equalize the pull among them.

Where this can fail is when you have a horse who learns that it can slack enough to let their evener be pulled back against the tongue and disables the pulley action for that sweep. In the Vernon Community, the sweeps in motion that we saw there, clipped a lead rope from the halter of the horse to the tongue of the sweep in front of it just enough to make it impossible for the horse to step back enough to disable its evener pulley. Tying them this way will pace the horse. One would not be able to tie a head puller in this way. Some horses pull against a lead rope at any unrelenting pressure and cannot be tied to certain things.

Knoke also noted that at Vernon they used a different pulley evener system than the ones he was familiar with. Instead of a floating ring, they used a rope pulley system. In the V-point between each tongue there was a pulley and near the end of each tongue was another. A continuous rope connected all these pulleys. The mid-tongue pulley had a loop through which was threaded a rope and fed to the pulley at the tongue-end. To this last pulley the evener was attached. This rope evener essentially worked the same as the floating evener system, it just looked different.


In our shop we have an override slip clutch attached to the drive shaft. The shop has a lot of equipment and when the horsepower engages the shaft there is a lot of momentum built for the machinery with a flywheel. But a saw doesn’t stop spinning the second the horses are called to stop. If there is no override slip clutch, the machinery that was still spinning (but now losing momentum) is still turning that drive shaft. That drive shaft is connected to the horsepower unit and the unit could turn the tongues forward, hitting the back legs of the horses who are supposed to be stopped. So the override slip clutch allows the slowing drive shaft to keep turning without engaging the horsepower unit.

Rotary Horsepower Units
Mary and Dora pulling only one of the tongues on the 3-sweep unit. They are not engaging enough machinery to require more horses. The far unit is covered. The near unit is an uncovered but operating unit.


Most cast rotary horsepower units should be greased/oiled very regularly. Regularly means touched up with grease and/or oil with every use or at least every other time. This helps the gears and bearings to run smoother and wear less. The teeth on the cast gears need to be greased and the bushings that the gears run on need oiled.

On a modern chain and sprocket horsepower unit the oiling is reversed. With these, the bearings need grease (unless they are sealed bearings), and the chains need oiled. The gearbox type of horsepower just stays full of oil.

The chains and sprocket units need to have the chains checked regularly. When these chains break you can find yourself with several horses who all of a sudden have nothing to pull against, and are running away on a circular track only stopping if they want to.

Trouble Shooting Cast Rotary Units

Most of our experience with rotary horsepower units center around the old cast gear units. Here are a few common problems that can arise.


Bushings are basically just a rod that rotates in a hole. Over the time these rods wear out, the less they are oiled, the faster this happens. As the rod wears, you begin to get slop room as the rod can now wiggle or slide back and forth in the hole that was once snug. This slop can cause gears to quit meshing or it messes up the timing and teeth can be broken.

We had a unit with a worn out rod that had too much slop room to be able to use. Khoke cut some tin and bent it to wrap the rod and pounded it in. This is a temporary fix as the tin will wear out too but it got rid of the slop room for now. The only way to truly fix this is to recast the gears, building up the worn places with body putty first.

Tongue and Unit

You need to make sure the unit is well anchored. If the unit wrenches loose even a little, it can twist the tumble rod and the power shaft comes off.

If the tongue is too low this can cause it to flex as the horses pull and will eventually break the tongue. If the pull rods are not adjusted correctly then the sideways pressure on the tongue will eventually break it too.


Cast rotary unit teeth can wear out. Whether it is from insufficient greasing or from mechanical mortality, these teeth will wear over time. Blocky gear teeth that once fit together well will sharpen from wear, creating slop in the gears which will eventually begin to slip.

Ultimately the only way to really fix worn out gears is to take them apart, build up the worn places with body putty and recast them.

Treadmill vs. Rotary

Typically a treadmill horsepower unit is geared to have much higher rpms than a rotary unit. The Scottsville treadmills generate 250 rpm right off the treadmill and this gears up to a higher rpm easily. Our 3-sweep cast rotary horsepower only generates 80-90 rpm on the shaft coming up to whatever the necessary rpm are.

The benefit of the rotary unit is that it can generate a lot more torque. The horses pull to initiate the gear action but when the machinery tries to bog the unit down, the horses can lean into the pull to increase the necessary power. A treadmill unit only produces as much torque as the weight of the horses walking on an incline can generate. When the machinery requires more torque than the treadmill is putting out, the treadmill platform can slow or even fully stop. The horses are pulling nothing but their own weight and cannot work harder to add torque.

A treadmill is more compact so it is easier to put under a roof and out of the weather. The rotary track has to be as level as possible and should be maintained with gravel. If used too much in wet weather the track can become slippery and/ or soupy. You may have to consider putting the rotary unit and track under roof but this would take a large building.

Working Together

We have many old cast rotary units set up to power equipment on our farm. The woodworking shop and the machine shop are each powered by a 3-sweep. These units run smooth enough that they rarely ever had more than one team necessary for the machinery in use. Our laundry house has a single sweep unit anchored by its side to power the machines in the building.

These rotary units have helped enable us to live the life we choose with equipment that is powered by draft horses. These horses are more than a harnessed power source. How can I not love Mary, a large draft Belgian who will reach into the bridle and bite the bit as it is lifted. There is a heart and soul there who loves and feels loved. And we get to work together.

Rotary Horsepower Units