Homemade towable chipper - some advice needed

[ruxu]

As I every year cut down trees to make about 12 cubic meters of firewood I also get a lot of tree branches laying around on the premises.

That is why I started to build a towable chipper from a old trailer, a 16HP cast iron Briggs & Stratton and a lot of scrap metal.



After many months I ended up with this "Wallenstein influenced" construction. I have just tested it and it chips fine up to 4" but there is one problem - the self-feed is almost non-existent!



I guess that the only way to get it feeding is to remake the feed chute to one with hydraulic feed. Basically I know the construction of a hydraulic feeder but the dimensioning of the hydraulic components is not my strong area - here I would appreciate some advice and help. I have not been able to find any viable information from smaller commercial chippers with hydraulic feeder.

The chipper disc dia is 20" with two knives and spinning about 1 300 rpm.

Questions:

1. What size pump is needed - flow and pressure?
2. What size should the feed motors be?
3. What should the maximum feed drum rpm be?

Any help greatly appreciated - bying wrong size hydraulic components hits the wallet HARD!

 

[franklin2]

I am lacking in hydraulic sizing myself. But I was wondering how you are planing to drive the new pump? I see you have a guard on your unit, is it a belt or chain underneath? I supposed you will add another pulley onto the engine to run the pump? You may want to take the guard off and take a picture. You would probably have lots of opportunities to "fix" any design flaws with pulley/sprocket ratios. As least this will put your post back to the top.

P.S. I was looking at the surplus center pumps, and some say not rated for side loads. Can't use a pulley on those.

 

[ruxu]

I am lacking in hydraulic sizing myself. But I was wondering how you are planing to drive the new pump? I see you have a guard on your unit, is it a belt or chain underneath? I supposed you will add another pulley onto the engine to run the pump? You may want to take the guard off and take a picture. You would probably have lots of opportunities to "fix" any design flaws with pulley/sprocket ratios. As least this will put your post back to the top.

P.S. I was looking at the surplus center pumps, and some say not rated for side loads. Can't use a pulley on those.

Fortunately I made the chipper disc axle pulley end about 1" too long so I still have the possibility to add a single V-belt pulley to drive the hydraulic pump. The 16HP cast iron Briggs&Stratton should be able to deliver the additional power for the pump. I have been able to find a number of exploded views of commercial chippers with hydraulic feed. Surprisingly also for me they do not have a separate bearing unit in front of the pump to take up the side load. Unfortunately no technical data of components available in the manuals. When I a couple of years ago put a hydraulic pump on my Suzuki Samurai "Multipurpose Utility Vehicle" I also did put in a bearing unit.

As I mentioned I am familiar with the hydraulic feeder function and flow circuit - it is just the sizing of the components that I am struggling with. So far I have been able to find small pieces of information here and there,

• hydraulic fluid tank size about 2 - 3 gallons
• hydraulic motor size about 300 c.i.d
• hydraulic motor max. feeding speed aroud 60'
• the spring loaded upper feed roll presses down with about 110 lbs

So far I do not have any feeling for how strongly the feed rollers should push in the branches towards the chipper disc. That would again give the feed motor tongue needed. Then I would again get the needed oil flow and pressure to size the pump. I just need to be sure about correct sizing as hydraulic components tend to be expensive.

 

[dfkrug]

When I a couple of years ago put a hydraulic pump on my Suzuki Samurai "Multipurpose
Utility Vehicle" I also did put in a bearing unit.

Saw your Sami pix, RUXU. Looks great!

Did you use a power steering pump for hyd power? Or a trochoid pump as you would see on
tractors?

Either way, you will want to work backwards from the speed you want to turn your drive roller.
I would think that 60 RPM or so is fine. For that slow speed, you will probably NOT want
direct drive from your hyd motor because you would need a very large displacement, even
with a small pump of 0.25 cubic inches or so. There are plenty of hyd calculators online
to convert motor RPM, pump displacement, and motor size to roller RPM.
Surplus Center

To use a smaller motor (less money!), you will need to gear down the speed with
a chain or belt drive. The roller will need a pinching mechanism to grab the branches, too.

Motor torque will be more than adequate from inexpensive motors, even with relief valves set
as low as 1000psi.

 

[ruxu]

To answer your Sami question - here is a picture from under the hood...

The pump is a series 2 pump with a support bearing. It is driven from the crankshaft with a 6PK poly belt.

Thank you for your comments - they confirm that I am slowly going in the right direction. Meanwhile I have gathered bits of information here and there and made some own calculations.

My chipper rotor runs at 1 300 rpm and is fitted with two blades. I theoretically calculated that if the feed rolls with about 5" dia would feed in as much wood that can theoretically be chipped the feed roll speed would be about 50 RPM - very close to your 60 RPM as max. value. In reality you have to run slower.

I looked into gerotor motors - Bauer has a BMP selection of nine sizes between 3,2 to 24 cu in in the price range 180 to 215 Euros, about the same in USD. So I guess i could go with for instance 12 cu in. So at 50 RPM the needed flow would be 600 cu in. Then the hydraulic pump driven from the rotor shaft with a belt would be 600 cu in / 1300 = 0,46 cu in per rev.

I intend to put the two motors in series. Doesn't that mean that each motor puts out only half of a single motor torque? But there is still plenty of torque for this application as you noted with the 1000 psi pressure. Does my thoughts seem reasonable to you?

 

[franklin2]

Do the rollers slip on the branches when they overfeed the chipper? Or do they use some sort of clutch system to regulate the feed to the chipper? If a hydraulic expert comes along, maybe they have some sort of hydraulic regulator you could adjust to limit the feeding power of the inlet system to regulate it.

In the electrical world, we use adjustable current relays for this. We had a ct donut that monitored the current of the electric grinding motor(50hp) and that turned the feed belt on and off as the grinder started to get overwhelmed with wood.

 

[ruxu]

Do the rollers slip on the branches when they overfeed the chipper? Or do they use some sort of clutch system to regulate the feed to the chipper? .....

At some point they might slip but the upper roller is generally forced against the branches with a spring load of about 100-150lbs. So it is mandatory to be able two regulate the feed to a level where the rotor is able to chip everything that comes in.

I have found out that there is two ways I can do this - by using a set value flow regulator to run the feed motors at a speed that is slightly lower than the maximum speed the chipper rotor can cope with. This is the simpliest way but lowers the chipping capacity at lower loading and doesn't sense possible unforseen intermittent feed blockages.

The other way is to monitor the chipping rotor rpm and stop the feed rollers if the rpm drops below a set level and then start them again when the rpm has increased. In an other project of mine where I am making a digital readout to my old Myford lathe I also read out the spindle rpm with a small IR circuit. I guess I could slightly modify this IR circuit to monitor the chipper disc rpm and accordingly control a solenoid valve that cuts and opens the flow to the roller motors. The benefits of this approach is that you can run at a optimum feed rate all the time and unforseen intermittent feed blockages are also handled.