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Discussion Starter #1
Guys,

I need to find a system that will actuate an arm with a large force (maybe 100+ lbs of linear force) and at high speed. I need something with a high response rate (< 1/10th second) and that can actuate at 2+ fps (feet per second). Doesn't have to be an electrical or hydraulic actuator, but must be able to retract and actuate indefinitely without "reloading" (e.g. a spring system).

Oh, light weight would be nice, too. Definitely can't weigh more than 50 lbs. And it can't require like a million amps of battery power to run it, either. It's gotta run off standard electrical systems that you could expect to find in a car. Maybe a 2nd battery would be acceptable, but no more.

Anyone know if anything like that exists?

Thanks! :)
 

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Kind of like a pitching machine??
 

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Doesn't a pitching machine use a spinning tire? That's based on momentum.
No, that's a football throwing machine with the tires.

Well, I do see tire-type pitching machines.....but I've seen the type where an arm comes overhead and flings the ball.
 

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Discussion Starter #6 (Edited)
Pneumatic would be fine if it can do what I need. But wouldn't that require a big, heavy air tank, or is there a small compressor I could use? Maybe a belt-driven air-compressor running off the engine block could pressurize an air tank?

Also, a high level of precision is required (Edit: not required... nice to have). I'm not sure if a pneumatic system would be capable of doing that?

I was thinking hydraulic, like a power steering system?
 

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without knowing more about the forces involved, how far, how long, which direction, repetition required etc its tough to say, but i'd think a small tank and cylinder would be lighter even with a tank, but that all depends on how much of the stored energy it requires for each actuation.

there are some small motors with ungodly amounts of torque but they're usually very expensive or very heavy.
 

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I'd check out the sites that sell stuff for "Lowriders" since they're all about hydraulics and actuators
 

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I know, I know, he's building the jumper legs from Speed racer!
 

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charliex has it nailed.
compressors are small, tanks are small and with a two-way valve you have a killer ap.
decide on forces needed, pressures and cylinder diameter and stroke will decide on pressure recovery time for the next actuation. (duty cycle).
horsepower required is computed from that.
electric actuators would require high peak current pulses and the time, 1/10 second is doubtful.
good luck. sounds like fun.
sam
 

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Discussion Starter #14
Could a pneumatic tank be pressurized by a pump that's driven by a belt attached to the engine? Does it have to run constantly, or can the pump be turned off when the tank is at max pressure? That would be a pretty cool setup, if it wasn't drawing HP from the car at all times.
 

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AP Racing's lightweight pneumatic air jacks are available in different size and stroke configurations to suit the widest possible range of vehicles and installation requirements. Dimensional information for standard and fast air jacks can be found on the following pages using the links below, pdf format installation drawings are also available to download. Exaust valve kits are also available from AP Racing. Safety Props are available to suit the most common Air Jacks.


Air Jacks
 

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Let's summarize:
Force=100lbf
High speed=2 ft/sec
Response rate = 100msec
Retract and actuate indefinitely
Light weight
Low power
High precision

Questions:
1) Assume response time is lag time from trigger to actual beginning of actuations, or time to get to peak velocity.
2) By indefinitely, are you simply implying this is not a one-time device a la an airbag, or that it will be repeating this motion immediately
3) How 'high' is high precision for you in this case
4) For any electrical actuator (direct or gear drive), power will be a function not so much of speed, but of the acceleration...so you may need to define that more fully.
5) Are you trying to generate a constant force, spec a needed force (may answer the accel question above), or are you referring to mass not force.
6) What is the most critical motion parameter: point A to point B as fast as possible, as accurate as possible, as smooth as possible OR distance travelled is only moderately important so long as accel, force, velocity, etc. are constant, etc.

Sorry, I know that's more questions than answers, but all of that will help narrow down what may or may not work.
 

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Discussion Starter #18 (Edited)
In thinking about it, 2fps isn't enough. Need more like 4 or 5fps max speed.
1) Assume response time is lag time from trigger to actual beginning of actuations, or time to get to peak velocity.
Yes, trigger to beginning of actuation. Obviously less than 100ms is preferable.
2) By indefinitely, are you simply implying this is not a one-time device a la an airbag, or that it will be repeating this motion immediately
Typical motion will be extend - sustain (for an indefinite period) - retract. The next actuation could be immediate.
3) How 'high' is high precision for you in this case
Precision isn't a necessity. It would be nice to be able to actuate 1/2 of the full extension. Would be amazing to be able to control it to within 1cm.
4) For any electrical actuator (direct or gear drive), power will be a function not so much of speed, but of the acceleration...so you may need to define that more fully.
Right. I think I'd like around 1G (32fps² ?)
5) Are you trying to generate a constant force, spec a needed force (may answer the accel question above), or are you referring to mass not force.
Well, the actuator will have to accelerate a 100lb (though realistically, maybe as much as 250lb) weight vertically, then sustain its position. In retrospect, 100 lbs of force will not accelerate it - it will only counteract gravity. Let's say 1000lb of force just to be safe.
6) What is the most critical motion parameter: point A to point B as fast as possible, as accurate as possible, as smooth as possible OR distance travelled is only moderately important so long as accel, force, velocity, etc. are constant, etc.
Fast as possible is the most important factor. Accuracy could be a benefit, though not a necessity. Smoothness isn't important. Distance traveled will be < 12".
 

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so 45kg lifted .3m in 2s

so 45x.3/2=67.5W

with a 100% efficient electric motor(doesnt exist) that means you will be pulling 5.625 amps from a 12V source. so realistically you will need to pull 7 amps assuming no loss in the wiring(again not possible) so depending on the Impedance of the motor and the impedance of the wiring you are probably looking at 8-10 Amps

something to consider if you go the electric motor route
 

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great discussion.
10 amps into a small air compressor will do a fair job of using any latency in the return stroke to refill the tank.
20 amps with the engine running is reasonable.
with a pressure switch to shut down the compressor it will use no power when idle.
using an old r-134 freon tank for the reservoir would give 100 psi capability.
i wouldn't exceed that in such a light tank, tho.
the next step up in pressure might be a 20# propane tank, maybe 200 psi max.
air tanks available at advance auto, etc.
sam
 
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