Why not make use of the linear actuator we've got? It's designed to output loads of torque, and you wouldn't have to worry about stopping the motor as it's got the micro switches built in. I don't know quite how you'd use it to power a 4 bar lifter but think Bio Hazard used an actuator successfully so it's got to be possible.
You could use it either to power a crank connected to the axle of the front bar (which is how Biohazard and Griffon did it, both using two actuators) or just have the actuator act on the front bar (a la Flick, Suren Balendran's pneumatic 4 bar flipper thing from a while ago). You could probably use both of those on the rear bar too but more torque would be needed I think?
I don't think the actuator will be quick enough, I could most likely use it to make a lifter but I want more speed.
Biohazard used 2 x 12v actuators overvolted to 24v pushing a bell crank which lifted the front arms.
The system worked well and satisfied his design to keep the robot on a very low profile but the amount of stress acting on that bell crank is well beyond anything I could engineer.
Making 2 pivot points and having an actuator acting on one of the upright bars does seem the simplest option though.
As for rear bar vs front I don't know which I better. I just assumed rear was since you're acting on the shorter bar, meaning a greater lever advantage, but I would be wrong. Plus I wanted as much weight at the back of the machine so that when full extended the rear of the robot doesn't lift up.
You could do a really simple real-world test, whereby you stick a length of something onto your motor's shaft and see how much it can lift at the tip of it. From there it's easy to roughly calculate the ratio you'll need, knowing what it could lift and the length of the bar you put on. That's how we designed Tormenta 2's ratios (in about 10 minutes with the drill itself and a 7" allenkey stuck in the chuck), and it has easily enough speed and power to leave the ground when selfrighting.
I'd work backwards from RPM figures anyway, not torque figures. Work out how fast the tip of the lifter must move to launch a robot a realistic amount (obviously not so it theoretically goes 50 feet) and calculate the ratio you need from the motor from that. At 4:1 I very much doubt the motor will have enough power to be satisfying. Depending on its RPM I'd expect more like 15 or 20:1. In a perfect world 4:1 would result in a ballistic flipper, but in reality such a huge mechanical disadvantage for the motor will make it turn slowly, and so it'll probably struggle to even lift a target, even if the torque figures say it should.
Interestingly in pneumatic flippers people tend to go with huge amounts of power (like more than half a tonne of force to flip a fw) which will make the flipper slower as it takes longer to fill up.
I assume there is a good reason for this which I can't really explain, but clearly you need lots of power rather than just a high speed.
in pneumatic flippers a lot of "power" is used because you need the flipper arm to move a long distance in a short time, the best way to do it is a large force close as possible to the fulcrum of the flipper arm. The large force is required as the closer the force applied is to the hinge point, the larger the mechanical disadvantage becomes.
lots of power alone is useless, take for example a flipper using a hydraulic system. You can easily get 3000psi on a ram with an equivalent force of in excess of 3 tons, but it will just lift the load not make it fly as the hydraulic ram will not extend as quickly as a pneumatic ram....
I was rereading the topic, and I itch to add a bit about drive.
Satanix is bloody fast, but does it with a single stage gearing.
The Z12 mod 1 steel gear is welded to the axle of the Speed 900 and drives a Z72 aluminium gear inside a 130mm wheel.
Simplicity has its advantages.
Last edited by maddox10; 21st April 2013 at 03:02.
I'm all up for simplicity!
I figured aiming for 100rpm output speed after reductions would be a good speed. So that's more like a 5:1 after the drill gearbox of 36:1.
As for power transfer I figured the simplest way would be to attach a gear to the centre of the rear arm pivot point and put a 2nd gear on the output shaft of the drill motor gearbox.
It would work, just that big question mark over whether the average argos drill gearbox would last. Why have you moved away from the car fan motor? In the right setup, that really could be ballistic.
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