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Ogre - RG2013 lightweight
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Knightrous
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Joined: 15 Jun 2004
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Location: NSW


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Demon's wheels don't touch the floor when toppled, Catastrophe's does.
Catastrophe's disc also acts as a pivot point due to it being set further back in the robot.
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Post Fri May 11, 2012 1:02 pm 
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dyrodium
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Catastrophe could self right without the disk spinning, the wheels afforded enough grip and the disk was close enough to the fulcrum to self right, alternatively it could drive the disk towards a wall and self-right that way. Smile

Post Fri May 11, 2012 1:07 pm 
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Glen
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^^ yep, that's why i think that wheels at the back is the best way to do it if it can drive as well (which wouldn't be that hard)
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Post Fri May 11, 2012 1:10 pm 
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Nick
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First lightweight parts

The wheels arrived and I spent the evening turning them down from 50 to 42mm wide:



That 5C collet chuck doesn't get used often, but it sure is useful on special occasions! Now the wheels are done, its back out to the workshop to finish the hubs. I also had a an idea to make the weapon bearings and hub virtually unbreakable - once I have the dimensions finalised I wiil post that up for review.

Post Sat May 12, 2012 10:16 pm 
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Nick
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Axle and bearing design

Here is a cross section of the weapon hub, showing what I think is a near un-bendable axle:



Notes:

* The dual roller bearings have a combined radial load bearing of over 16,000 lbs and are rated to take heavy shock loads.

* The main axle is a massive 35mm, stepping down to 25mm inside the bearings.

* everything is held together with one M14 screw, so changes and repairs should be quick.

* The pulley has extra deep sides to prevent the belt coming off.

Post Sun May 13, 2012 9:27 pm 
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dyrodium
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Looks pretty bulletproof to me! It should also have some thrust bearings either side of the disk to help lock it in position and prevent any wobble in impacts against horizontal spinners. Smile
EDIT: Looking closer because of the way the shafts are stepped you probably wouldn't need them... Laughing

Post Sun May 13, 2012 11:12 pm 
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Nick
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Fitting in thrust bearings was difficult and bulky! The plan for horizontal spinners is to have a lighter vertical bar with different bearings; possibly two deep groove ball bearings and needle roller thrust bearings to take side impacts. Having a lighter bar should allow some extra front armour to be bolted on.

Post Sun May 13, 2012 11:35 pm 
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MikeNCR



Joined: 05 Jan 2012
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You're probably already planning on it to a degree, but make sure you've got at least some radius to the steps, otherwise it'll become a major stress concentration point.

Post Mon May 14, 2012 4:47 am 
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Nick
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Yeah, I learned that lesson the hard way a few years ago! I will put the largest possible radius on the stepped shaft and not get it hardened to much, so it will take impacts without failing.

Post Mon May 14, 2012 8:50 am 
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Nick
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Here is a rough plan view of Ogre showing the main components:



The main part of the frame is short front-to-back to help with self-righting and wide to help counter gyro forces. There is still some wasted space at the front, so I will probably camfer the front corners for extra strength and lower weight. The front wedge is fixed and has an angle of 30 Deg; it could go lower but would be harder to weld.

The external panels are 8mm; I just picked a random number to start the drawing without having any idea about what's needed to resist other lightweights. Any ideas on the required armour thickness?

Post Wed May 16, 2012 5:41 am 
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Knightrous
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If your trying to copy how Catastrophe self rights, you need the wheels sticking out the back, the whole short front to back thing is only part of the equation. Swap the drive and the battery position and I reckon you will have it Smile
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Post Wed May 16, 2012 9:08 am 
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Daniel
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6mm would easily be enough for armour. Most of the americans use 6mm on their heavy weight wedges, so they'd be impressed seeing in on a light weight.

Post Wed May 16, 2012 10:07 am 
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Nick
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Thanks Daniel, excellent tip! I was worried about the weight of 8mm steel plate so its all 6mm now. If there is some spare weight later on, I will make some of the wedge & corner parts 8mm again. I won't have the tools to fix dents or broken welds, so its best to be a bit cautious.

@ Aaron; I just can't bring myself to have exposed wheels at the back, at least not without a test model. My thinking about the current wheel position is that there will be high friction from the fixed wedge scraping on the floor; to make the bot fast & controllable, its better to have more weight over the wheels and less weight over the wedge. With the current wheel position, there is probably still about 2/3 of the weight on the wedge, enough to stop it lifting under acceleration.

If the wheels were right at the back the side armour would be poorly supported at the corners and the wheels would be open to attack - the Touro Light guys would go straight for them!

I like Glen's solution better. It needs an extra radio channel and uses up weight, but it doesn't give up other advantages. I plan to make a test frame from plywood and concrete for weight; if wheels at the back work out on the model, then I will change the design.

General
The CAD for the disk is finalised, it was almost balanced from my first 'eyeball' attempt and a little tweaking got the centre of gravity a tiny bit on the side of the counterweight. once the disk is cut out, it will be easy to drill or grind down the counterweight side for a perfect balance. Its not even very noticeable that the disk even has a counterweight; the rim segment opposite the tooth is just 6.3mm thicker than the rest of the rim Smile.

The frame design has plenty of room for larger batteries; weight permitting, Ogre could run on 44 volts (ie two 6S packs). That would give the weapon motor more torque and RPM as well as more driving speed. The Dewalts will need some stress testing to see how they cope with an extra 7 volts abut its not a large percentage jump so they will likely be OK.

Post Wed May 16, 2012 12:16 pm 
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Nick
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I camfered the front corners of the frame- it looks meaner like this for some reason and there is a slight weight reduction. The base plate has been extensively lightened; there is a 1.5Kg reduction between the pictured 6mm part and a solid 5mm plate (the thinnest Bisalloy available).

Post Thu May 17, 2012 12:17 pm 
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Nick
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Parts arriving

A large & expensive box arrived today; time to get fabricating! The bearing for the disk is interesting:



The dual spherical rollers can take over 8,000 pounds of radial load each and as they can run off-axis, there is no problem if the axle flexes a bit.

The aluminium for the disk pulley also arrived, there is no way my small lathe's 4" chuck can ever hold this 5" x 3" round but as always there is a sneaky plan Twisted Evil.



The aluminium will be drilled and bored out to final size on the mill and then mounted in the lathe with the pictured 5C expanding collet. This allows me to turn the pulley and the bearing pocket but parting the pulley off will be impossible - I can either take it to the R2 builder's workshop or try to part off on the band-saw and then clean the face up on my own lathe.

A bunch of less interesting bits arrived, including screws for the P80 gearbox mounts and outboard bearings for the wheels - its hard to know where to begin!

Post Fri May 18, 2012 7:30 pm 
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