All of my robot orientated questions go here!

[Ellis]

Hi guys!

I am looking into building a chassis with HDPE or a similar plastic (what do you guys recommend? I know there are several plastics that are used). My question is, for a chassis, what kind of mm am I looking at? Would 12 be a little measly?

Thanks, I'll post any questions (sorry! ) I have to do with robots in here.

Ellis

[harry hills]

Re: All of my robot orientated questions go here!

12mm would be good (if youve got the money go 20mm)

[Ellis]

Re: All of my robot orientated questions go here!

Hm. How about 15mm? Compromise! I plan to have the walls as low as possible, in the region of 5cm, so I'm not sure if 20 is really necessary, since the weight and strength baring sides are small and therefore will flex less, right?

[Laser]

Re: All of my robot orientated questions go here!

I use 15mm at 60mm high and works fine

[Ellis]

Re: All of my robot orientated questions go here!

Well I've just downloaded Google Sketchup. I see everyone making really good CAD stuff and I have always thought it must be super difficult. For a first project I made a to-scale (within half or less of a mm) drill motor!
http://storage.darkdemon.org/16909/1303225355.png
http://storage.darkdemon.org/16909/1303225490.png

Quite proud for a first try! The program is so intuitive.

This means I'll hopefully be able to represent a basic idea for my robot. I think I'll go with 15mm, 20 mm seems like overkill imo.

[Ellis]

Re: All of my robot orientated questions go here!

More messing around with CAD, a few hours and I have this. It's all 100% to scale. Wheels are very small, about 5cm. This doesn't bother me, in fact it gives the bot a lot of push due to gearing. Plus, I'd most likely over volt somewhat, as at 550rpm or so this thing will only just pass 3mph. Volting to 24 I get around 7mph and more torque.

Right?



Was extremely fun making these CAD things, one afternoon and I thought this thing took weeks to learn how to use.

[RogueTwoRobots]

Re: All of my robot orientated questions go here!

Are you sure you'll have enough ground clearance with 50mm wheels? From memory, the outermost part of a drill motor gearbox is close to 50mm in diameter which, by the time you add on a few extra mm top and bottom for a baseplate/top armour, means you could suffer grounding issues on arena floors.
Why not go for some 75mm wheels with nut inserts from Robo Challenge? They're still relatively small which maintains some torque yet are less likely to cause grounding issues due to increased clearance, plus you'd get a little extra speed too. They also do 63mm wheels if I remember rightly (although not sure if they come with a nut insert - could probably be made up though) if 75mm is a bit too big for your liking.

[Anttazz]

Re: All of my robot orientated questions go here!

Overvolting a 12v drill motor to 24v might cause it to burn out. I think people tend to recommend overvolting to 1.5x as a general rule. I'm on 19.2v on 12v drills, but at the uk champs I only moved for about 10seconds

[PJ-27]

Re: All of my robot orientated questions go here!

I would advise against exposed wheels too.

Nice Sketch Up work, I've been playing around with it for a while now, but I really struggle to get any of my 3D models made up of components symmetrical.

[harry hills]

Re: All of my robot orientated questions go here!

i dont think i ever measured or planed anything

[jonny]

Re: All of my robot orientated questions go here!

i still can't use sketchup. tried, didn't understand it, gave up. maybe it was just because my mind is used to working with prodesktop

[Ellis]

Re: All of my robot orientated questions go here!

I have looked at my drill motors and they're at their fattest point about 460mm (without filing down unnecessary plastic). So say that gives me 5mm to play with.

I know that isn't enough for any substantial top armour or a very thick base plate, so what I hope to do is say use 6 or 8mm HDPE for top and bottom, and cut out small sections, so that any pointy bits on the drills can have more space. In reality the side plates, and the whole chassis, would be flatter still. Just enough to poke the head of the drill through and keep strength. Right now in the CADs there is far more space than necessary in the sides to accommodate the drills. I could gain a whole cm right there. If I went the cutting gaps for clearance route, as the img suggests a thin metal plate of a mm or two would be bolted on top.

I am not too fussed about speed if it means more torque. I'd prefer have more control over the bot and someone else's than go skidding around doing more damage to myself than anything.

We'll see how it all goes. I'm not quite sure why more feathers aren't made less tall, 10cm wheels is pretty big... so count this as an experiment, lol! If it fails and is impossible I'll let you know!

Also, I may never find a suitable set of ~5cm wheels, so all of this could be down the drain from the word go. :P

Thanks for the reply.

------

On another note, as you can see, there is a lot of space in the centre of the robot. I am sure lots of this will get eaten up by bits and pieces but; if I were ever to fit a 4 bar lifter, do you think it would be possible? And make that whole centre piece of top plate the lifter. Just a thought!

Oh and for anyone wondering, the chassis is 350x350, meaning it could be a hell of a lot smaller if I gave up the idea of a space for a weapon, allowing for more sturdy armour. The thicker stuff shown is 15mm, and the plates are 4mm, excluding the metal plate (flat grey thing on the top) of a mm.

(I may be getting way ahead of myself here, I'm excited I guess)

Edit: WOW! More replies!

I see. I knew the risk of overvolting them was there... I thought that since they were geared so leniently the motors would have to work less hard to push the thing. Now that I think of it, I see about 189 flaws with that idea. Thanks for letting me know it's a bad idea.

I was fretting over the wheels for quite a while. I was trying to allow more space inside for... robot stuff. I think I might make a new CAD following the idea of just being a rambot at heart (with the wheels inside). Thanks for the reply!

@Harry: I don't normally either. It's just we got this fancy electronic calliper and I'm measuring everything.

Phew - long post.

Ellis.

[ewan]

Re: All of my robot orientated questions go here!

I'd definitely recommend you go for 75mm wheels, or at the very least 63mm which I seem to remember is another, though rarer standard 'blue' wheel (or similar rubber type) size. You'd definitely save yourself considerable time and money. This is from the experience of building several four wheel drive drill motor machines a few years ago!

[ewan]

Re: All of my robot orientated questions go here!

Examples (all built to a 50mm chassis height, base & top plates are additional to this)







And a four bar (can be done but pretty tricky especially for a first time)



Additionally don't worry about torque, the limiting factor is grip not motor power with drill motors & small wheels.

[Ellis]

Re: All of my robot orientated questions go here!

Wow! Thanks for the pics!

I'll look into further designs. I could stretch (lol) to the 63mm I guess. I may be able to source wheels locally however, I'll look into that before making any decisions. If the local wheels are too small or will be hard to mount
to a drill then I'll have a look at these 6.3cm jobbies (just had a quick look around, can only find castors ). Any links to such wheels would be much appreciated!

Also, I have an electric window motor from a Fiat Panda (don't be fooled!), it's 12v, torque'a'plenty and has a nice mechanism that with some fiddling could become an actuator of sorts? Interesting stuffs.

Again thanks for the replies.

Ellis