Warning: Long post ahead!

I just want to say that I wrote this post in peices so it does go on for a bit, some parts include questions and some parts are just minor notes. Also where I say bot, I mean design. It's far from becoming a reality, but the more I learn the better it'll be. I want to thank those who've replied and appreciate any helpful suggestions. Some design features may seem foolish to you, so feel free to point them out (even the use of skirts again).

I drew about half of it (inner frame, motors, gearbox, wheels, cells) in Rhino 3D and I realised I wasn't able to fit everything in the width I had originally set aside, so to try and minimise width and avoid making it look like a square I changed the battery packs to be flat, 3 rows of 4 cells end to end. This gives them some space top and bottom (previously they were a valley style brick). This also made the bot longer, and it's now approx 400mm by 320mm + width of the side armour.


(Lifter arms are wrong, I just made them that size to see what was the largest length that would fit.)

I mentioned to Glen on Saturday that the best way to have a linear actuator fit would be if it was straight (unlike actuators which have the motors running parallel or at right angles with the cylinder). In the current design there's about a 300mm by 40mm by 40mm space for it. The actuator will need to be hinged around where the gearbox for the motor is. An advantage for having it this long is that the motor (which would be the largest part if I use a RS550) would pivot only 1/5 of the height of what the end of the actuator pivots. This essencially stops it from hitting the top and bottom.

Actuator construction I'm still in the dark about, I don't know what's required in terms of bearings, switches, cylinder thicknesses etc. I would also like to know if the following is possible, and bear with me as I know little about electronics: I want to have one of the AUX outputs extend the actuator until it reaches point B, where a switch is triggered and the actuator stops extending. If there is no AUX current flowing the actuator retracts until point A where a switch is triggered and the actuator won't retract further.

I'm guessing that the actuators will probably be the main roadblock in this design.

Prior to drawing the bot I realised that the left side and the right are only connected by the rear armour, the base and the lifting mechanism so I'll need to use something tough for the base or the bot will end up very warped after a good knock. First thought was 1.8 mm Titanium for the base which admittedly would be very expensive.

Another thing I picked up from the event on Saturday was that polycarbonate will suffice for the top so I'll use 3mm for that.

I'll need to source some gears for the dual gearboxes, I'll need 6 spur gears with a pitch circle diameter >= 19.5mm. Looking in my HPC gears catalogue I have from a few years back getting the gears from them will cost about $80 + postage... So if I can get something like that locally that would be good.

I need to enquire about the possibility of having the wheels made from aluminium tube, welding a disc inside for the axle, and gluing rubber on the outside. This of course leads to the question of whether there are good suppliers of aluminium tube around (hmm seems http://www.performancemetalsaustralia.com.au/ has some), I need one with an outer diameter of about 1.75 inches (44.45mm). If you're wondering why I have imperial measurements it's because I've been using international sources to find out what fits.

Do people buy their pulleys and belts from somewhere or make them themselves? I'd like to look into the option of using belts however The pulleys need to be under 35mm diameter, preferably the smaller the better to leave some space for wires to fit around in those tight spaces. Also how wide/long would pulleys that small need to be? I wouldn't want to go much more than 10mm if at all.

Battery Cells are currently designed as 3600 MAH NiMH.

I've decided to design the inner walls with 5mm aluminium. Mostly just to save weight as I'm unsure how much some components will weigh at the moment. Hopefully the juicy soft gooey insides of my design will be protected by a thick candy shell which I have yet to decide on.

Outer walls will almost defiantly be steel as I don't think I can use too much Titanium at this stage. Thickness depends on how much weight I'll have to spare, but for drawing reasons, I'll just go with 5 mm steel for now to match the thickness of the inner walls, and adjust accordingly later on.

I still want to use skirts; Jolts skirts impressed me even though they don't really hinge much by design. I figure if I do end up building this bot and do use titanium for the base, I could just buy a larger piece and cut some skirts from the same sheet (How hard would it be to cut 1.8 mm Titanium anyway?)

Lifting mechanism I haven't put much thought into but I think I'll need to use steel for all of it. The arms could maybe be the same thickness as the outside walls to save money? I'll probably need to go box section steel for the lifting bar also. I'm not sure what are common sizes and how available they are but I'll need something about 1.5 inches high (38.1 mm). Rectangle section would be even better if it's available and if I could get 1.5 inches (38.1 mm) by 0.75 inches (19.05 mm) that would be ideal. The rods/axles would also probably need to be steel but I don't know about the thickness, something like 5 or 6 mm would probably be good but I'm not sure if that's thick enough to support the lifting mechanism. Anything much larger would look a little bulky as the bot isn't very tall.

Um, I've probably missed something along here somewhere but any comments would be appreciated.

Sounds like a lightweight? Do you expect to fit this under 13.6Kg? If you do it looks like it's going to cost you a lot of money in fancy materials(titanium etc).
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Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
Albert Einstein.

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Originally posted by assassin:
Sounds like a lightweight? Do you expect to fit this under 13.6Kg? If you do it looks like it's going to cost you a lot of money in fancy materials(titanium etc).

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I have some thick wall ali tube in 40mm diameter; could you use thicker tread? From my experiences with a four wheel bot with 50mm wide treads, your wheels are probably wider than they need to be. My bot did NOT like turning and basically hopped from wheel to wheel as it skid-steered. that wastes a heap of battery power and is harder on your gearboxes. For a 4 wheel design, I would go 25 to 35mm wide tread, unles the tread is hard & slippery.

I'm still not quite sure how the actuator fits in the design - can you write a bit more about that? Is it a four bar lifter mechanism? You can probably get by with aluminuim for most of the lifter and just use steel at the end for bash protection - the flippers in QLD use aluminium arms and have no problems.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Sorry I don't know but is this your first bot? Are you confident you can design and build this to meet NSW standards? The reason I ask is, I wouldn't like to see you spend so much time and money and then meet you first spinner and this happens: http://www.youtube.com/watch?v=ifBLBYwxe2Q or would I thats a good vid!

Its a real neat bot, build what you want to build but be realistic too. This may only come with experience, which might be why your asking the questions. So are you sure you can build this underweight and reliable?
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Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
Albert Einstein.

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Originally posted by Nick:
I have some thick wall ali tube in 40mm diameter; could you use thicker tread?

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Originally posted by Nick:
From my experiences with a four wheel bot with 50mm wide treads, your wheels are probably wider than they need to be. My bot did NOT like turning and basically hopped from wheel to wheel as it skid-steered. that wastes a heap of battery power and is harder on your gearboxes. For a 4 wheel design, I would go 25 to 35mm wide tread, unles the tread is hard & slippery.

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Originally posted by Nick:
I'm still not quite sure how the actuator fits in the design - can you write a bit more about that? Is it a four bar lifter mechanism? You can probably get by with aluminuim for most of the lifter and just use steel at the end for bash protection - the flippers in QLD use aluminium arms and have no problems.

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Originally posted by assassin:
Sorry I don't know but is this your first bot? Are you confident you can design and build this to meet NSW standards? The reason I ask is, I wouldn't like to see you spend so much time and money and then meet you first spinner and this happens: http://www.youtube.com/watch?v=ifBLBYwxe2Q or would I thats a good vid!

Its a real neat bot, build what you want to build but be realistic too. This may only come with experience, which might be why your asking the questions. So are you sure you can build this underweight and reliable?

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at a glance the wheels are much too wide for the sort of motors behind them. my drill powered robots get away nicely with about 25mm of tread on two wheels so that with 4 would be fine.

about the connection between the sides of the frames you could always keep the shaft solid on the lifter and use that as a main connection point.

with the actuator unless you want to buy something you could always just use a length of threaded rod but instead of having it so long use a piece of tube with a pair of nuts welded into each ends and use that as part of the actuator. that way it will effectively be half length when retracted. andrew uses that method on sproing. works good for keeping things compact.

or you could try something like a scissor jack in a car they pack down fairly flat. (the diamond shaped ones).

about the belts you can buy timing belts in really small diameters, cant recall were but jeffs in late are a good example. smallparts.com?

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(How hard would it be to cut 1.8 mm Titanium anyway?)

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The 1Kg estimate for the batteries is good; the cells themselves would be about 820 grams.

The two wheels on Jolt are 25mm wide by 60mm diameter and they allowed me to push Ya Mum and Broken around with ease. Jolt is absolutely NOT a pushy bot, so 4 x 35mm wide wheels with a soft tread should do the trick for you. You might ask Russel aboutthe conveyor belt material he has, or about casting urethane tyres. I really like smal diameter wheels - they are harder to hit. light and fit into designs easily

For the actuator, i would look at a Banebots gearbox (like you said) and add an exta bearing housing on the end to take the thrust loads. you can use a ball screw for efficiency like Biohazzard :



or ACME threaded rod to save money:



The threaded rod loses around 40% of the motor's power in friction; you can see why Carlo went for Ball threads in Biohazzard! A 3 foot length of 1" acme thread is under $20 US. Either way, you would have to get the end of the rod machined to couple it to the motor and run in a bearing.

If that sounds too hard to make, I have an easier but heavier option. If you are interested, I can draw it out; its hard to put into words
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

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Originally posted by Glen:
about the connection between the sides of the frames you could always keep the shaft solid on the lifter and use that as a main connection point.

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quote:

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Originally posted by Glen:
with the actuator unless you want to buy something you could always just use a length of threaded rod but instead of having it so long use a piece of tube with a pair of nuts welded into each ends and use that as part of the actuator. that way it will effectively be half length when retracted. andrew uses that method on sproing. works good for keeping things compact.

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Originally posted by Glen:
or you could try something like a scissor jack in a car they pack down fairly flat. (the diamond shaped ones).

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Originally posted by Glen:
wrt the lifter if you expect it to take any hit it needs some ability to twist and go back to its original shape (rubber mounts or some such) or at least be able to get bent and still work. if aaron still has pics of his axe robot he can probably put some pics up, the axe on that thing could bend a huge amount side to side.

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Originally posted by Nick:
The threaded rod loses around 40% of the motor's power in friction; you can see why Carlo went for Ball threads in Biohazzard! A 3 foot length of 1" acme thread is under $20 US. Either way, you would have to get the end of the rod machined to couple it to the motor and run in a bearing.

If that sounds too hard to make, I have an easier but heavier option. If you are interested, I can draw it out; its hard to put into words

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Biohazzard used a four bar linkage on the lifter arm - very cool and effective!

I would atill make the end of the lifter from steel and / or titanium - anything that might be hit needs to be tough.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

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Originally posted by Karmond:
I would also like to know if the following is possible, and bear with me as I know little about electronics: I want to have one of the AUX outputs extend the actuator until it reaches point B, where a switch is triggered and the actuator stops extending. If there is no AUX current flowing the actuator retracts until point A where a switch is triggered and the actuator won't retract further.

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Was bored:


I also noticed that if I do go with the dual motor gearbox setup I could just not get a banebots gearmotor and just go for spur gears. This will save space, a small amount of money, and since I needed a reduction like 9:1 because the wheels are so small, I'd need a special order from banebots anyway or I would have had to order a 27:1 and 16:1 setup and combine the two. However going with spur gears would probably be harder and might be more unreliable.

Hi
I just looked over your drawing ,it looks like you are going to go 4 wheel drive .With the set up you have drawn, haveing the wheels spaced so far apart it will have great dificulty turning and require a lot of power do to so .I cant realy make any sugestions apart fromtrying to redisghn it with both sets of wheels spaced closer together or go 2 wheel drive with castors.

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Originally posted by Totaly_Recycled:
Hi
I just looked over your drawing ,it looks like you are going to go 4 wheel drive .With the set up you have drawn, haveing the wheels spaced so far apart it will have great dificulty turning and require a lot of power do to so .I cant realy make any sugestions apart fromtrying to redisghn it with both sets of wheels spaced closer together or go 2 wheel drive with castors.

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You can always start building your design and find out how it handles. Some builders have made prototypes from MDF and the like. This will allow you to test your theories and find if you are happy with the result without spending lots of money on purchasing specialized materials, cutting and welding.

Good luck.
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