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  #1   IP: 5.254.163.144
Old 17-09-2017, 02:44 PM
doobin doobin is offline
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Default Motor calculations- help please

Afternoon all.

I currently have a little flail mower for our two wheel tractor in the workshop. Needs new bearings all round. I'm contemplating replacing the bevel drive gearbox with a small hydraulic motor, and trying it on the mini digger.

I'm thinking a flail speed of around 2100RPM would be about right.
The input shaft from the sideways output of the bevel gearbox leads to a cog, which drives the shaft via a chain. It's geared up 1.55. So my input shaft would need to spin at around 1350 RPM.

Apparently my digger has a pump setup of 18.8x2 plus 13.7 (l/min). 51l/min total. Do you folks reckon 35lpm min going thru the flail motor would allow enough for slewing and a bit of arm movement? No tracking obviously.

According to this calulator- http://www.hydraproducts.co.uk/hydra...tor-speed.aspx - a motor of 22cc/rev would provide approx 1350RPM at 35l/min (and 0.85 efficiency).

A motor is only 100 ish so it's worth a punt. Can anyone spot any glaring flaws in my workings?

Also, is a cross-line relief all I would need for motor protection? My digger has a thing you twist to set it to one-way flow.

Thanks
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  #2   IP: 5.254.163.144
Old 17-09-2017, 04:18 PM
doobin doobin is offline
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Default Re: Motor calculations- help please

I think I've been looking at the wrong kind of motors

If I get a normal gear motor (which should be high speed low torque) and run it direct on the shaft, it'll be more efficient and a 16cc motor should be about right I reckon.

Damn this stuff is complicated.
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Old 17-09-2017, 06:18 PM
grahams grahams is offline
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Default Re: Motor calculations- help please

Glad you understand it - way beyond me.
Graham
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Old 17-09-2017, 07:53 PM
grifferr grifferr is online now
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Default Re: Motor calculations- help please

I'm not sure just adding the pump outputs together is the right thing. I would look in the specs for aux output. Also think about heat buildup as pumping flat out soon warms things up.
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Old 17-09-2017, 09:28 PM
quattromike quattromike is offline
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Default Re: Motor calculations- help please

Call Whitehouse hydraulic products and tell them what you are doing and the specs you have and they will sort you out with what you need.
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Old 18-09-2017, 08:55 AM
doobin doobin is offline
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Default Re: Motor calculations- help please

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Originally Posted by grifferr View Post
I'm not sure just adding the pump outputs together is the right thing. I would look in the specs for aux output. Also think about heat buildup as pumping flat out soon warms things up.
The work is intermittent, but I could always fit a radiator.

Can't find specs for aux output. I assumed that being a variable pump you'd just add the two together, then allow a little less for stick functions.
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Old 18-09-2017, 10:53 AM
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cps140 cps140 is offline
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Default Re: Motor calculations- help please

Quote:
Originally Posted by doobin View Post
Afternoon all.

I currently have a little flail mower for our two wheel tractor in the workshop. Needs new bearings all round. I'm contemplating replacing the bevel drive gearbox with a small hydraulic motor, and trying it on the mini digger.

I'm thinking a flail speed of around 2100RPM would be about right.
The input shaft from the sideways output of the bevel gearbox leads to a cog, which drives the shaft via a chain. It's geared up 1.55. So my input shaft would need to spin at around 1350 RPM.

Apparently my digger has a pump setup of 18.8x2 plus 13.7 (l/min). 51l/min total. Do you folks reckon 35lpm min going thru the flail motor would allow enough for slewing and a bit of arm movement? No tracking obviously.

According to this calulator- http://www.hydraproducts.co.uk/hydra...tor-speed.aspx - a motor of 22cc/rev would provide approx 1350RPM at 35l/min (and 0.85 efficiency).

A motor is only 100 ish so it's worth a punt. Can anyone spot any glaring flaws in my workings?

Also, is a cross-line relief all I would need for motor protection? My digger has a thing you twist to set it to one-way flow.

Thanks
You Wont get 35L from your machines aux! More likely 18-20lpm, That said, you wont need 35lpm to run the flail!
I have a femec flail to suit 2-5 ton machines and it runs perfectly well on a 3 tonner!

I will try and get you a picture of the motor and valve today if i can.

As for slewing etc, it just depends on the machines setup, if the aux is run on the same pump as the slew, then it will die when slewing.
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Old 18-09-2017, 12:35 PM
doobin doobin is offline
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Default Re: Motor calculations- help please

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Originally Posted by cps140 View Post
You Wont get 35L from your machines aux! More likely 18-20lpm, That said, you wont need 35lpm to run the flail!
I have a femec flail to suit 2-5 ton machines and it runs perfectly well on a 3 tonner!

I will try and get you a picture of the motor and valve today if i can.

As for slewing etc, it just depends on the machines setup, if the aux is run on the same pump as the slew, then it will die when slewing.
Well my old mini was supposed to do 32l/min, so I thought 35l/min from a new machine with a variable pump was a fair assumption.
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Old 30-09-2017, 08:36 AM
doobin doobin is offline
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Default Re: Motor calculations- help please

Well it's all together and mounted on the digger, just waiting for the pipes to turn up.

Nobody seems to know the flow rate but as far as I can work out this machine has 11.3 lpm auxillary from the third pump plus flow sharing from the main 2x18.9lpm. When you feather the tracks on tickover it creeps along, but then goes full chat if you engage the aux.

A TB016 has 33l/min aux flow, so this should be slightly more with slightly bigger pumps and more HP. A 22cc motor put me in the ballpark for flows from 30-36lpm so that's what I bought and will change this or the cogs if need be.

Any suggestions on what the cross line relief should be set to?
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Old 30-09-2017, 11:25 AM
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Shovelhands Shovelhands is offline
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Default Re: Motor calculations- help please

Set the cross line relief up as you go, so it's just capable of doing what you require it to do, crude but it's the best way of doing it yourself, you can work things out all you like, but you never quite know until you've got something working.
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