Percussive Cushion Massage Machine

My goal for this project is to bring comfort to people at a very low cost compared to commercial devices. I hope that this massage machine can give you relief from your symptoms for may years to come.

The massager is intended to assist with

• Loosen lung build-up sputum / mucus. This occurs in people with lung disease, COPD, cystic fibrosis and in some cancer patients.
• Muscle soreness. Cramps. Injury recovery.

I was asked by a family member to design a massage system to help loosen lung mucus. The person's doctor recommended them to pay $20,000 for a commercial massage vest. They couldn't afford a purchase like this, as I'm sure nor can many, many other people. The commercial unit was a percussive / vibrating massage device. My machine needed to be a MUCH cheaper alternative to commercial medical devices.

Typical alternatives to buying a professional massage unit are to have massage performed by a masseuse, a physiotherapist or by a trained family member. Paying people for massage can become very expensive over time and usually would not be performed every day.

I was able to design what seems to be an effective machine that is comparable to the cost of three or four professional massage sessions. This machine is variable speed, adjustable force and also has adjustable firmness of the massage cushion. The massage pulses are reasonably powerful and are very useable strength. I designed the machine to be as simple to build as possible. Anyone with a little mechanical know-how will have no problem with this project.

The one disadvantage from using readily-available components that I am aware of: The compressor used for the machine is designed for outdoor use and, for a medical device, it makes a bit of noise. I wouldn't call the machine quiet, but you can comfortably listen to the TV while the machine is running.

I can't make any claims how effective this machine will be for your health condition. I can say that this machine has assisted two of my family members get rid of mucus build-up and breathe more comfortably. Medical professionals have confirmed that the machine is assisting to relieve their discomfort and increase their blood oxygen levels.

I have not tested this machine for treatment of muscle conditions because neither I nor my family / friends have any significant issues. I have however attached the machine to my arms and legs and the massage seems strong and effective to me.

Sorry to be a downer, but I need to say the following to protect myself and to help you think through whether this machine is suitable for you.

• I am not a medical professional and I cannot recommend this machine for any particular condition.
• I am not able to assess the risks for you and there may be risks of which I am not aware.
• The decision to use this machine is yours alone and I cannot be held responsible for any injuries that may result in using this machine.
• If you have a serious medical condition, please do your homework and be aware of risks, potential problems and contraindications. If you are concerned, please consult a medical professional prior to use.
• If you experience any problems, cease using the machine and, if necessary, seek professional medical help.
• Do not assume that this machine will be an effective alternative for other treatments that your doctor recommends. Don't stop other treatments unless you are are sure that the machine is working for you.

Hardware needed

The links here are examples of suitable equipment. You don't necessarily need to buy the particular item on that link. I don't make any money if you choose to buy from the link.

Air compressor. You need a mid-sized 12V DC tyre inflator compressor. Compressors are generally sized in "free air delivery". Choose a compressor with around 70 litres per minute (2.5CFM) capacity. The pressure rating isn't important. The compressor only needs to deliver low pressures. These are usually sold as suitable for 4WD / off road use.

During development, I tried a compressor with 160l/min capacity. It worked, but it was too big. It was very heavy and it required a much bigger (read, more expensive) power supply. In the end, it did not put out any more force either, so it's a waste of money.

All auto shops and many hardware stores sell a range of compressors. I recommend reading the reviews as some cheap ones have issues with reliability. Your compressor will be running for much longer periods than tyre inflators normally would, so try not to skimp on quality.

Example of a suitable compressor

Manual blood pressure measuring set. Get a cheap manual blood pressure measuring set, perhaps from eBay or Amazon. Don't get a motorised unit or just a cuff by itself. You will need the inflation bulb that is only found on the manual sets.

Select a cuff size depending on what you want to use it for. For airway / chest use, a regular adult cuff works well. If you want to massage muscles, you may want to get a cuff suitable for thighs or large arms.

I recommend you get a set that includes a stethoscope. I was able to use the stethoscope tubing to extend the air lines. It's good to have the compressor a few extra feet away from the cuff.

Example of a suitable blood pressure set

Power supply. A 12V (nominal) DC power supply. Supplies that are intended to replace a car battery are often described as 13.8V. These are ideal. The power supply needs 20A capacity or greater. You may be able to get away with a slightly smaller supply depending on your compressor. I used a 15A supply for one of my machines.

Most people will want to use a purpose-built mains voltage to 12V supply. A nice solution is to use a basic "bench" style supply available online or through an electronics supplier. You could also use a 12V car battery, except that these are usually very heavy and so not very portable.

Some car battery chargers have a "power supply" mode that is also suitable. Beware though, most of these chargers will revert back to battery charging mode when turned off. You will have to select "power supply" mode over again every time you power on, which is a pain.

Example of a suitable power supply

Speed controller. Any basic DC speed controller that handles 12VDC and at least 20A. These are generally quite low cost.

Example of a DC speed controller

Air fittings. To connect the tube to your compressor, you need a C type (Nitto) SF20 with 1/4" NPT female thread. These are a common type of fitting found at hardware and auto parts stores.

Example of a Nitto coupler

To connect the blood pressure cuff tube, you need an Industrial connector. These may be described as Milton M-style, type D or I/M style. You need a coupler plug with 1/4" NPT male thread. Tip must be 6.25mm (1/4") diameter to allow the hose to slide over and fit firmly.

Example of an industrial air coupler

M6x5mm grub screws (probably). Grub screws or bolts to block the air intake holes within the compressor. For my project, M5 were perfect. Your mileage may vary. Read on through the "Reed valves" section for details.

Tools

Fairly simple tools are all that is required for this project

• Screwdrivers
• Wrenches
• Hex keys
• Tap and tap wrench
• Drill and drill bits
• Wire cutters and crimpers

Air compressors pump air through in one direction, air inlet to air outlet. There are valves inside the compressor that ensure the airflow always goes in this direction. Check the diagram "compressor normal operation" to see how this works.

The massage effect happens when air is pumped into the cuff and then sucked back out of the cuff repeatedly and with force. We need to modify the air compressor to cycle air back and forward to the cuff. The second diagram shows the configuration of the compressor modified for massage duties.

Test your compressor before modifying it. If you need to make a warranty claim, now is the time. Warranty will be void after these modifications.

Over the course of this project, I modified three compressors of different brands and sizes. They were all surprisingly similar in their basic construction and were all easy to disassemble.

Unbolt the handle silver bracket and the cover on the electrical end of the compressor. Remove the bracket. Slide the metal motor cover towards the electrical end to expose the nuts at the piston end. Unbolt the silver handle bracket from the piston end.

Unbolt the cylinder head and remove it from the compressor. The lower part of the head will be a plate with holes and valves. This plate is usually square, so I highly recommend marking which way up and around it goes to avoid confusion during reassembly.

The valves in the compressor are "reed" type valves. These are simply a thin piece of metal that flexes away from a seal when pressure is applied on the correct side. The reeds are either screwed or riveted inside the compressor. We need to remove all reed valves from the compressor. If the reeds are held in with screws, remove the screws and the reeds. If the reeds are riveted in place, just break the reed off. The reeds are very thin and snap off quite easily. There is no need to remove the rivet.

On one of my compressors the inlet valves were located in the piston. This makes no difference. The valves must be removed.

Next, we need to identify which valves are the air inlet. These holes must be blocked to prevent new air from entering the system. I recommend using grub screws to block the holes. You might also use rivets or bolts screws depending on your situation. The main thing to be careful of here is that the blocking materials do not intrude into the cylinder. Make sure the piston can't contact the bolts when it is at the top of the stroke.

The first photos show me using M8 bolts to block inlet holes on a larger (blue) compressor. A second set of photos shows a smaller (red) compressor that has inlet holes and valves built into the piston itself. The location of the inlet valves does not matter. They still need to be removed and blocked off.

To modify the piston valves, first remove cylinder body and cylinder liner. They simply lift out. Remove the reed valves from piston by lifting them up and snapping them off. I used M6x5mm grub screws to block the holes. I couldn't use bolts here. The bolt heads hit the cylinder head when the piston rose up to the top. Ask me how I know this. ;)

Make sure you use thread locking compound on any bolts or screws you install. These fasteners must not come loose and rattle around in the cylinder head.

Reassemble the cylinder head and everything on the piston end of the compressor.

Most air compressors have a relay in the electrical input end. The main reason the manufacturer adds the relay is so that an expensive, high-current switch can be replaced with a small one and the cheap relay does the high-current switching instead.

The speed controller works by turning the DC current on and off very fast. The relay cannot handle this high speed switching. The relay must be removed from the compressor. All other devices such as switches, over-current and over-temperature devices will be redundant and should also be removed. The power supply and speed controller now perform over-current protection. The compressor will be running at much lower power than it normally would and there is no chance that the motor will overheat.

If you are lucky and your compressor doesn't have a relay or thermal protection, you can skip this step. If your compressor has a fuse for over-current protection, it can stay in place. It won't interfere with massage operation.

Your compressor needs to end up with only two wires coming out of the motor. The cover on the electrical end of the compressor should still be unattached, so let's get started.

First, remove the relay, the overload and the switch from the compressor. See the pictures to help you identify which device is what. If you need to cut wires, make sure the wires staying in the compressor are as long as possible.

There are three wires coming out of the motor on this large (blue) compressor. The two thicker ones are the positive and negative power. The thin wire is used for thermal overload. The thin wire is no longer needed.

Once the relay is removed, it is likely that you will need to join the power input wires to the motor power wires. I used insulated crimp connectors for this job. Soldering and heatshrink or tape is also fine. The current here is quite high and there is a lot of vibration, so I would avoid using wire nut connectors.

Now you are ready to replace the electrical cover and reassemble the compressor.

This step is optional. Please read this step through and decide for yourself.

Please, if you are not fully confident and/or competent to modify the internal power supply wiring, leave the the power supply as it is and use the terminals on the front. As a bonus, you won't void your warranty by modifying the power supply.

Danger: When the power supply unit is plugged in, there are very dangerous voltages inside. Never open the case of the power supply unless it is unplugged from the mains.

We are going to modify the power supply to bring the 12V power output out on wires instead of terminals. This step is optional, but I did this step myself for two reasons: First, leaving the output on terminals is less robust. If the wiring gets disconnected and is re-connected backwards, the speed controller will be destroyed. Second, it looks nicer.

Remove the output cabling from the back of the terminal block. Both of the wires on my unit were red, so I clearly marked the negative wire with black sharpie before I disconnected it. Remove the remaining nuts and remove the terminal block from the front panel.

Find the battery clips at the end of the compressor cable. Mark the positive wire with some red tape or similar. Cut the battery clips off the cable. Cut an extra piece at least 200mm (8") long from both wires. We will use these pieces to extend the power supply output wires.

Cut off any lugs that are on the end of the power supply output wires. Join on the 200mm cut pieces. Now you should be able to route the wires to just about anywhere on the case and bring them out into your speed controller.

Open the lid of the speed controller. My controller had a piece of white foam in the top of the lid. This foam is for packing purposes and it will restrict airflow. Remove and discard the foam.

Break off the locating tab from the potentiometer as shown in the photograph. The tab prevents the potentiometer from seating firmly against the inner wall of the case. Screw the potentiometer nut on so that the circuit board sits in the correct location inside the case.

If you have modified the power supply do these steps:

Work out where on the power supply you want to mount your speed controller. I mounted mine on the top right of the power supply. Drill the four screw holes using the circuit board as the template. I used 4G x 1/2" screws, so I used a 2.5mm drill bit for the screw holes. Drill all four holes and screw the speed controller temporarily onto the case.

Locate the two terminals on the speed controller for power supply input. Drill two holes adjacent to these terminals, one for the positive wire and one for the negative. Size these holes so that the wires are a snug fit. Drill the holes through the speed controller housing and through the power supply case.

Unscrew the speed controller and detach it from the power supply case. Choose a drill bit two sizes bigger than the one you used for the wires. Use this drill bit to enlarge the holes for the wires in the power supply case only. These larger holes ensure that the wires do not rub on the metal case of the power supply and damage the insulation.

Caution: Make sure you are connecting to the correct terminals on the speed controller. Reversed connections are likely to destroy the controller.

Run the power supply wires through the power supply case and into the speed controller. Connect the wires to the speed controller power input terminals.

Connect the compressor motor cables to the speed controller motor terminals. Screw the speed controller down onto the power supply case and tidy the wiring. I used a zip tie on the inside of the case to help relieve strain on the motor cable terminals. Put the lid on the speed controller case, tighten the nut on the potentiometer and push the knob onto the pot.

If you have NOT modified the power supply do these steps:

Drill holes in the speed controller case to accommodate the power supply wires and the compressor wires.

Find the battery clips at the end of the compressor cable. Mark the positive wire with some red tape or similar. Cut the battery clips off the cable. Cut an extra piece at least 200mm (8") long from both wires. Connect these wires from the power supply output terminals to the power input terminals of the speed controller.

Caution: Make sure you are connecting to the correct terminals on the speed controller. Reversed connections are likely to destroy the controller.

Connect the compressor motor cables to the speed controller motor terminals. I used a zip tie on the inside of the case to help relieve strain on the motor cable terminals. Put the lid on the speed controller case, tighten the nut on the potentiometer and push the knob onto the pot.

Everybody does this:

You're now ready to power up the compressor and try out the speed control. Does it all work properly? Good!

In this step we assemble the blood pressure cuff so that it can be connected to the compressor.

Screw the Nitto fitting onto the Industrial fitting. Use thread tape on the connection and tighten firmly. (The photos show the fittings I used which both had female pipe thread ends. I needed to use a 1/4" coupler in between to join the two.)

The blood pressure cuff has two tubes attached. These tubes function identically, so it doesn't matter which you choose. Attach the inflation bulb to one of the tubes.

The remaining tube goes to the compressor. This tube is quite short, however. It is best to extend the tube if possible. My blood pressure set included a stethoscope. The stethoscope tube was exactly the same inside diameter as the blood pressure cuff tube. I hope this is the case for your set too.

Cut the "Y" section off the stethoscope tube. To build a joiner, I removed one of the metal stethoscope earpiece tubes and cut off the bent section with a hacksaw. After cleaning up the cut end with a file, I used this straight tube to join the blood pressure tube to the stethoscope tube.

All that remains is to push the final open tube end onto the Industrial air pressure fitting. This is a nice firm fit and I have found that there is no need for glue or clamps to prevent the tube from falling off.

Connect the air fitting to the compressor and give it a try. You can adjust the firmness of the cuff "cushion" using the bulb. Squeeze the bulb to inflate and expand the cushion. The silver screw is a tiny valve that allows you to release air from the cuff by opening the valve and squeezing the cuff. When the firmness of the cushion is to your liking, close the valve. The cushion will retain its shape without inflating or deflating during operation.

Speed adjustment

You will notice that the strength of the pulsing changes with speed. It starts at low strength at low speed. The strength increases until you get to about half speed on the speed controller. The strength decreases again as speed approaches full speed. For best effect, tune the speed to maximise the strength of the pulses.

To loosen mucus

Sit on a chair or lie on a bed. Place the cushion behind your back and locate the cushion in your preferred location. You adjust the force of the massage by pressing back onto the massage cushion as hard or soft as you like. The machine can put out high pressures, so feel free to press as hard as you want. The harder you press, the stronger the pulses will be.

Some expensive commercial equipment uses massaging vests. I have had the idea that the cushion could be placed inside a boat lifejacket. The lifejacket straps can be tightened very firmly to hold the massage cushion against your back or your chest. This may work similarly to the commercial units. I have not tried this, but it would not be an expensive exercise to give it a go. My family members are satisfied using the machine while sitting in a chair.

Websites that describe percussive massage for COPD / cystic fibrosis say that treatment sessions should last no longer than 20 minutes on each lung. Please read up or ask your doctor what treatment regime will be most useful and the safest for you.

For muscles

Apply the cushion to the treatment area any way you like. Lean on it, hold it with your hand, use the Velcro cuff to strap it on. Whatever works best for you. There are a few different cuff sizes available that may work better for you. There are small paediatric ones for little kids and they go right up to adult thigh-sized models. The larger the cuff, though, the less strong the pulses will be. This is because the air itself is spongy. The larger the volume of air in the system the more of the force will be dissipated by the springiness. Again, the machine is capable of putting out very high pressures, so don't be afraid of pressing hard into the cushion if you want to. The harder you press, the stronger the pulses will be.

Minimising noise and heat

These tire inflator compressors are designed for outdoor use and can be a little noisy. Turning down the speed control helps the noise greatly, but also reduces the strength of the massage pulses. Experiment and find the best compromise for you. I think it would be fairly safe to place a blanket or similar near the compressor to reduce the noise, but be careful of the compressor getting hot.

When used for inflating car tires, these compressors get too hot to touch. For this massage machine, the compressor is not working very hard at all and runs much cooler. At worst I have found that the compressor cylinder head gets warm. But please be careful as your compressor may run at a higher temperature than mine.