Determining motor/pump size
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RJA.Ilex
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The deck you are using was probably designed for a blade tip speed of 13000ft/min (~65m/s), this is the max speed allowed under either UK or USA standards hence is the normal target speed.
If you are planning to cut thick wet grass or vegitation then I would suggest a target of atleast this.
From the picture of the deck you posted earlier I suspect that the limiting factor in the power you can use will be the belt drive. This can be calculated from the belt size and pulley contact angles I think, try a web search for full details. I would try and deliver the maximum torque that the belt can transmit to enable a fast acceleration of the cutters when started in the grass.
If you are planning to cut thick wet grass or vegitation then I would suggest a target of atleast this.
From the picture of the deck you posted earlier I suspect that the limiting factor in the power you can use will be the belt drive. This can be calculated from the belt size and pulley contact angles I think, try a web search for full details. I would try and deliver the maximum torque that the belt can transmit to enable a fast acceleration of the cutters when started in the grass.
J_J
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If the blade's are 25 in long, then the circumference is 78.5 in, x 1800 rpm = 141,300 in per min divided by 12 in = 11, 775 ft/min.
25 in would allow some overlap to give a 72 in cut. If they are 26 or 27, in, then the blade tip velocity will be greater.
25 in would allow some overlap to give a 72 in cut. If they are 26 or 27, in, then the blade tip velocity will be greater.
RJA.Ilex
New member
From J.J.'s calcs above then 1800rpm would work with 25 in blades but personally I would try for more, in my experience of cutting in UK conditions the extra blade speed makes a real difference in the cutting and discharge of the cut material.
If you want to judge the power available then put a pressure meter in the motor supply line and try cutting, there should be a reading for just turning the blades which will increase when cutting. The difference between the cutting and maximum will indicate the surplus power
If you want to judge the power available then put a pressure meter in the motor supply line and try cutting, there should be a reading for just turning the blades which will increase when cutting. The difference between the cutting and maximum will indicate the surplus power
Wow, there is getting to be way more math involved than I ever would have thought! I do plan on putting a flow control valve on line going to the motor so that I can adjust the rpm to the desired speed. Still waiting to hear back from the manufacturer about that big clutch pump I got. I would guess it should be sufficient, it has a 1 1/2" outlet on it.
J_J
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Although pump volume is a good thing when needed, all those excess GPM not being used is going to cause some design problems. Most manufactures only use a pump large enough to get the job done, and then they have to figure the cooling required for that much volume, and size of the reservoir, will a radciator be required. etc. So extra large is not good sometimes. Sure, you can install a flow control and vary the speed, but the size of the motor in cu in and GPM will determine the rpm of the motor. After everything is put together, how are you going to determine the speed of the hyd motor. Any fluid not used by the hyd motor, is a heat source.
I was going to control the speed on it with something like this Brand Hydraulics Side-Ported Adjustable Flow Control Valve — #12 SAE ports, 0–30 GPM, Model# PFCR51-12SAE | Adjustable Flow Valves | Northern Tool + Equipment . That way I can adjust it as needed. I have pretty much figured on having to run a hydraulic cooler of some kind as my tank will only hold 8 or 9 gallons tops and I don't have room for a bigger tank.
J_J
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dodge85rc,
On my Power-Trac, My engine turns four pumps that pump a total GPM of about 22.
My reservoir is 20 Gal of 10W-30 motor oil, which is used as hyd fluid. It also has a hyd cooling radiator, and fan. The sides of the reservoir still get plenty hot.
On my Power-Trac, My engine turns four pumps that pump a total GPM of about 22.
My reservoir is 20 Gal of 10W-30 motor oil, which is used as hyd fluid. It also has a hyd cooling radiator, and fan. The sides of the reservoir still get plenty hot.
RJA.Ilex
New member
Dodge85rc
I assume that you are planning to use the tractor with other machines in the longer term, so have you thought about using a single variable displacement pump. This would enable you to run the engine at a lower speed and still drive a high speed implement or run at full engine speed and not waste power pumping heat into the hydrualic oil.
Such pumps are often used on the land drive units of mowers or excavators.
I assume that you are planning to use the tractor with other machines in the longer term, so have you thought about using a single variable displacement pump. This would enable you to run the engine at a lower speed and still drive a high speed implement or run at full engine speed and not waste power pumping heat into the hydrualic oil.
Such pumps are often used on the land drive units of mowers or excavators.
J_J
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dodge85rc, said, This is for a home build custom tractor I am building.
So far he has only talked about the motor/pump combination to drive the deck. He has also said he is going to use about a 100 HP engine. Yes, he will have to come up with a way to drive his machine, either gear transmission, or hydrostatic transmission. It is not as simple as some might think, like how much does the machine weigh when finished. How much HP/torque is required to turn the wheels at a certain rpm to give a working speed of XX. Then you have the engine cooling, fan, hyd cooling /fan, hoses, valves, steering, size of the tires, width of tire. turf tread, or tractor tread, tire pressure. Is it being designed for a FEL, or 3pt system. How is he going to steer the machine, like a tractor, or swivel in the middle and steer with hyd cylinders, like a Power-Trac. How many valves will be necessary. Will hyd wheel motors be used.
Sometimes you can just throw things together, and it might work good, but in most cases, poor planning will cause one to grab this, grab that, slap it all together, and hope for the best.
A carefully thought out plan, financial considerations/budget, time factor, mechanical aptitude, electrical knowledge, welding ability, all have to be considered.
Any idea how much 20 gal of hyd fluid weigh, and how much oil can be filtered in an hour, What kind of hyd fluid will be used? Will it have a ROPS system?
Really, a lot of things to be considered. Patience, time, knowledge, and the financial
aspect will determine the successful conclusion of this endeavor.
So far he has only talked about the motor/pump combination to drive the deck. He has also said he is going to use about a 100 HP engine. Yes, he will have to come up with a way to drive his machine, either gear transmission, or hydrostatic transmission. It is not as simple as some might think, like how much does the machine weigh when finished. How much HP/torque is required to turn the wheels at a certain rpm to give a working speed of XX. Then you have the engine cooling, fan, hyd cooling /fan, hoses, valves, steering, size of the tires, width of tire. turf tread, or tractor tread, tire pressure. Is it being designed for a FEL, or 3pt system. How is he going to steer the machine, like a tractor, or swivel in the middle and steer with hyd cylinders, like a Power-Trac. How many valves will be necessary. Will hyd wheel motors be used.
Sometimes you can just throw things together, and it might work good, but in most cases, poor planning will cause one to grab this, grab that, slap it all together, and hope for the best.
A carefully thought out plan, financial considerations/budget, time factor, mechanical aptitude, electrical knowledge, welding ability, all have to be considered.
Any idea how much 20 gal of hyd fluid weigh, and how much oil can be filtered in an hour, What kind of hyd fluid will be used? Will it have a ROPS system?
Really, a lot of things to be considered. Patience, time, knowledge, and the financial
aspect will determine the successful conclusion of this endeavor.