[FW] Tracked 4WD Lifter: Aegis

[harry hills]

The thread is 3/8" UNF.

[overkill]

The thread on the drill shaft is very unlikely to be M9; after M5, metric thread diameters are all even numbers. Almost all Chinese drill threads are good old imperial (also known as UNF) 3/8 - 24 threads, which should be fairly easy to find.

[R9000]

Thought you'd ordered a track setup...

Well, I did, but it turned out the sprockets were nowhere near large enough for what I need. I'm gonna end up selling the Heng Long treads, but I'm still making tracks that will fit around the wheels, though the robot will run without them. You'll see when I make the final CAD. Sorry for the confusion.

The thread is 3/8" UNF.

The thread on the drill shaft is very unlikely to be M9; after M5, metric thread diameters are all even numbers. Almost all Chinese drill threads are good old imperial (also known as UNF) 3/8 - 24 threads, which should be fairly easy to find.

Thanks guys, I didn't realize imperial measured thread was that commonly used. Nice one.

-EDIT- Ok, after a good amount of searching, (while I did find the nuts) it looks like it'll be cheaper and less bother to just get some better wheels that are thinner and have a hole I can just drill out to screw onto the shaft. I've found some, but I'm gonna make the CAD before I order them, just in case anything needs changing. I feel stupid that this is the third time I'm buying locomotion for this thing, but I guess I had to make at least some noob mistakes. The current wheels I bought were only £6 for all 4 anyway. They're gonna have to hang around until I figure out what to do with them. :P Next time, I'm making my own wheels, or following this guide if I have a drill press: http://www.windisch.co.uk/robots/archives/170

[R9000]

Alright, we're on CAD revision what, 50 now? xD Anyway, I spent a good amount of time on this one, so hopefully I've thought everything through. Everything I've modelled is either from measurements of components or material I'm going to cut to size and shape. I've got just about all of the electronics together now, and some of the other bits. The linac I'm using shouldn't be too hard to modify with the Turnigy SK3 brushless I've got, but I'll have to work out the exact placement for gears etc by eye when I get round to building it. For the lifting arm, I'm looking at getting some 10mm and 5mm steel pieces cut, which I can countersink, hacksaw or drill as needed. I'm planning for the scoop to be 4mm steel, but I really don't know if it'll be too heavy. Titanium's as possibility I guess, but I don't know if I can get a piece big enough, and I don't really want to go importing anything if I can help it. The linac can shift 300N as it is, so hopefully I'll have plenty of power and speed with the new motor. The scoop might need more than the four screws I've shown here. Also, I realize when fully extended, the linac motor hits the rear lifter axle, I might move the axle back a bit more to fix it, otherwise I'll just have to not push it back that far, or add some kind of limiter switch. The motor and the top of the lifter will have additional thin steel/HDPE armour too, but I'll look at just adding that on later.

The axles for the shovel mech are all 10mm diameter, and I'll be using nylock nuts and washers to keep everything nicely in place. The sides should be about 3mm steel too, but I think I'll go thicker if I've got the weight to play with. The rest will be 20mm HDPE (main frame) and 10mm HDPE (top and bottom). The top isn't really transparent, I just did that so the components are visible. On that note, as you can see, the LiPo is in one of the sides. It's about 500g, so I'm hoping it won't drag the centre of mass too far off, but I'll put something in the other side to compensate if it really becomes a problem. The side compartment was the only place it'd really sit comfortably, because I obviously want to get some foam padding in there too. You can see I'm sort of making the drive motor mounts integral to the chassis, which should hopefully screw together nicely with some barrel nuts. With regard to the wheels; they seem to fit well enough, and give enough clearance from the body to propel the robot without tracks, but I'm adding some tracks made out of some light bike chains I have with 3mm HDPE plates screwed on. The plates will have adhesive neoprene pads stuck on to give extra traction, and I might modify the wheels slightly to help them grip the tracks, but that remains to be seen, since the robot will run fine without them. You can see a breakdown of a section of track in the pictures, but I was too lazy to model it really intricately, much less bend it round the wheels in CAD. Long story short, the chains and screws will sit either side of the wheels, with the connecting plates contacting the outer face of the rubber tyres.

One thing I'm still a little unsure about is how easily the side armour will get chewed off by horizontal spinners. I can't support it through the wheel hubs because the screws won't reach, so it's just attached by two big HDPE blocks in the middle. Should I aim to make it thicker, or try and curve it back round to screw onto the front and back of the body? This'd be tricky with the tracks, but if it's necessary, I should be able to find a way to do it. Anyway, I'll be setting up the electronics tomorrow, getting all the connectors soldered on and testing everything, etc, so at least I'm making some progress. :P

FRONT:


BACK:


TOP:


SIDE:


ISOMETRIC-ISH VIEW:

[overkill]

I would definitely try to attach the side armour at the back & front - it will get damaged or ripped off if it is just attached with four screws in the middle. The rest of the CAD design look great.

[R9000]

I would definitely try to attach the side armour at the back & front - it will get damaged or ripped off if it is just attached with four screws in the middle. The rest of the CAD design look great.

Thanks. Yeah I'll try and bend the armour round the front of the tracks there. Should be possible.

[overkill]

Just a thought - if you add an extension to those plastic spacers between the wheels, it will help to keep the treads on and improve grip.

[R9000]

I actually have some little 40mm castors which I might add to help track tension. They should hopefully offer lower rolling resistance.

[R9000]

Just changed the shape of the steel lifter mounting bracket (shown on its own in the top right) to move the lifter axle well clear of the brushless motor at full extension. Should be fine now.

[overkill]

Moving the pivot pion that far back makes it vulnerable to vertical disk spinners - it might be safer to limit the movement of the arm.

[R9000]

Moving the pivot pion that far back makes it vulnerable to vertical disk spinners - it might be safer to limit the movement of the arm.

How about moving it forward again slightly? How close to the edge is too close? That bracket should be 5mm steel btw.

[overkill]

Most vertical spinner disks are 16" or less in diameter, so draw a circle that diameter in your CAD and see if it touches any lifter parts before it touches the armour - it could be that you don't have to move anything.

[R9000]

Ok, sorry though, what are the " marks for? Surely you don't mean 16 inches.

[overkill]

I think the largest vertical disk I ever saw was about 16 inches in diameter. Nowadays builders are using smaller, thicker disks so if a 16" disk misses you lifter, you will be safe from the smaller ones too - its always good to plan for the worst case scenario.

[R9000]

I've moved the axle 7mm back in, and a 16" circle just hits the protruding lifter arms before hitting the edge of the armour. Can't really hit the main axle though. I might just end up armouring the back end a little more if I can't get the mech any closer in. I don't want to have to mess about with the limiter switches inside the barrel of the linac.