|
|
|
|
|
|
|
|
|
|
|
|
|
maddox
Joined: 21 Dec 2006
Posts: 786
Location: Belgium
|
Pity I can't post any pictures yet (they on my dead hard disk), but recently I did do a bit on hydraulics for a UK roboteer.
Main issue with commercial hydraulics is the weight. A small valve like shown here can weight 2 kg, A ram with 50mm bore and 150 mm stroke of 10 kg isn't a big surprise either.
Basic information to remember is that the Robot wars rules (or Battlebots) impose a maximum pressure limit, and that is what we want to use. Because with high pressure we can reach high force from a small diameter ram.
The simplest, lightest and cheapest pumps are the gearpumps. These are found on lorry loading hatches and small (or cheap)forklifts.
These have a "normal" upper limit of 3000-4000 psi (depending on brand) that is why this is the current limit for the FRA on Hydraulic pressure.
Now, basic formula for hydraulic and the needed power is flow(liters/min)*pressure(bar)/500=power needed in Kilowatts.
A normal sized lorry pump is 4 CC/rev. with a top rev of 3000 rpm (standard commercial electric motor rev),This gives us 12L/min at top speed.
4000psi is 260 bar
12*260/500= 6.24Kw needed. Now, the pumps used in lorries aren't loaded so high, with good reasons. So the most of them will run on a 3 KW series wound motor.
So, reduce the pressure or the flow to get the best out of the motor/pump combination available, or match the pumpsize to the motor.
A bosch GPA 750 on 24V can drive a pump delivering 1.4L/min @260 bar. At 75% efficiency. This means you can drive this pump on 1 24V 3600mAh NiMH pack of a good brand.
Now, the size is 1.4L/min /3300 rpm. So a .42 CC pump is in order.
if this is not available, working with a gearing is an option.
Have fun with this information.
|
Sat Dec 23, 2006 4:00 pm |
|
|
|
|