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Hydrostatic Drives


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mudguard



Joined: 01 Feb 2008
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Hydrostatic Drives

I want to get a hydrostatic drive together. I'm thinking power steering pump from a car and someone mentioned some sort of auomotive fan unit for a motor? I don't need high speeds , but good torque.

Anyone doing something like this?

Post Fri Feb 01, 2008 11:19 am 
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Glen
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possible but going to be quite insanely heavy for any of the classes we run. i havent seen any small hydraulic motors that would fit inside 12kg or maybe even 25kg.

then you need the hydraulic valves which need to be radio controlled.

and a pump motor for 3000psi hydraulic pressure probably needs to be at least 2hp size.

let me know how you go though. im putting parts together for a hydraulic crusher myself with an ETEK (15hp) pump motor which should make for 3000psi and completely insane flow rate.
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Post Fri Feb 01, 2008 11:45 am 
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Knightrous
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Speak to Andrew (Totaly Recycled) He explored this path heavily as an option for Vertex. We ended up going for the electric drives instead Razz
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Post Fri Feb 01, 2008 12:31 pm 
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mudguard



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??

How can i contact andrew?

Post Fri Feb 01, 2008 1:10 pm 
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Knightrous
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Private Message "Totaly_Recycled" He should respond in a day or two.
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Post Fri Feb 01, 2008 1:13 pm 
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maddox



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The lightest hydraulic motors I know off are 400 grams, and the lightest pump/motor combination is about a kilo. That will deliver about 300W total to the drive. With a Hydraulic Drive you will waste up to 65% of power input from the batteries in losses everywere.


Maybe an option if you have a fairly light and powerfull IC engine driving the pump, then you can use the hydraulics to power drive and weapon.

Post Fri Feb 01, 2008 3:56 pm 
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Totaly_Recycled
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A power steering pump will not give you hydrostatic drive -- it will give you hydraulic drive which will have to be controlled by valves for speed and direction usually a pressure dump for speed and a slide or rotary valve for direction.


Hydro static drives use pumps with variable displacement but also full displacement in the system to the motor so basically all of the torque from the prime mover ( engine - electric motor) is available ie if your system is running at 3000 psi and 5 liters a minute with an ordinary pump -hydro- motor system and you want a slower speed you dump some of the pressure and flow from the system through a valve so the motor only gets say 1200 psi at 2.5 liters a minute for half speed this significantly reduces the motor torque available to the drives and if the drive gets an extra load ( like pushing another bot)then the extra pressure build up will only get dumped and you will get reduced pushing power to the wheels.

But in a hydrostatic drive the displacement of the pistons in the pump is reduced to half so with a similar system as above the motor would receive only 2.5 liters a minute of oil but still at 3000 psi thats assuming the motor is holding back with torque to allow this pressure to be achieved
with hydrostatic drives the displacement can be varied from 0 to full flow over the whole range of the pumps capacity pressure.,so basically shaft torque from the motor is constant at all rpm ( this is using an ideal pump- motor combination and not allowing for friction and pump slip and motor slip losses ) (so if you are moving at half speed and encounter another bot and start pushing it at the same speed you will still get full prime mover power ( torque ) on your drive wheels ( prime mover denoted what is actually powering the pump be it an electric or i/c motor)so basically your prime mover can be running at full speed torque range over all of the out put hydraulic motor speeds

Post Fri Feb 01, 2008 10:51 pm 
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