Deathly Hallows - FW - Alligrater

[Maxamuslead]

I was told I'd need to glue them in. Any particular product I should look for - something special a thermal adhesive epoxy or good old super glue?

Epoxy, i used THIS stuff and it has worked fine (no loose magnets yet) and depending on how they magnets are held in it depends on how you glue them. If you look at Blacksmith Build log the last page shows you the two version i have found.

I found a suitable sprocket on Robotshop, 48T and 0.25" so should work fine. 10:48 will give me 2750/4.8 = 573 rpm

Still rather nippy but it will be manageable with a tweak to the TX settings I think. It's important I get the drive sorted quickly so I can work on the other systems. If it's a rolling wedge at least I can push stuff, and at 30kph (if my rough maths is right) I could push quite quickly.

Looking at this sprocket it will go around the fixed axle no problem, fixing it to the heel is another question. Needs to be dead center, probably need to make a tool to ensure I fix it right. Was thinking I would bolt it through the wheel hub. No appropriate mounting holes so I'd make those, and a plate or spacers to keep the plate off the wheel.

I think a belt tensioner will be essential. Found a few options mostly for dirt bikes.

Depending on what tools you have and what you are going to use for wheels depends on how you are going to mount it. If you using HDPE i would suggest drill holes through the wheel and bolting to too the wheel, about getting it true, i can see three methods:

1 Eyeballing it, quick dirty and with the help of a ruler can be accurate enough that it shouldn't wobble too much.

2 Use a 1” hole in your wheel and a 1in shaft, should be fairly accurate, what i used on my axe mechanism it worked well enough.

3 Model it in CAD and find a model or make a model of the sprocket us that to make a wheel design and get it cut out.

Also need to do the calculation for the battery.

Can anyone tell me how much time is there between rounds typically? Do you get time to top up charge or should I plan for a massive 6S battery or a couple of smaller ones?

ermm I would look at 2700mah + battery what voltage is up to you. I fully drained a 2200mah battery using 550 motors x2 for drive and a MY1016 for an axe (so not contain draw) in 4 mins ish. Michael did you take part in the Featherweight play time at Manchester, if so do you remember how long that match was ?

[Ocracoke]

ermm I would look at 2700mah + battery what voltage is up to you. I fully drained a 2200mah battery using 550 motors x2 for drive and a MY1016 for an axe (so not contain draw) in 4 mins ish. Michael did you take part in the Featherweight play time at Manchester, if so do you remember how long that match was ?

I didn't have a active weapon (much to my annoyance) but I ran separate batteries in The Honey Badger 2 for the drive and weapon for this reason. My 775 motors will go the distance on 2100maH batteries (2x 2S1P LiFePo4 batteries in series) which worked perfectly well... ish.

I did take part but I wasn't in there for the full amount of time, my batteries packed up about halfway though (wheel was binding on the bodywork causing a major drawdown on the batteries). I think the whole thing was at least 6 minutes from what I recall.

[Deathly Hallows]

The sprockets if ordered turned up. Perfect fit - thank goodness.

Now to mount them...

The wheel profile does not have an obvious option. My idea was to make a custom mount out of HDPE that spread the load over the premoulded spokes then bolt the sprocket to this and the mount fix by glue or bolt to the wheels.

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Above you see the outside and inside profile.

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The sprocket is perfect, almost matching the hub.

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The finished mount...or so I thought

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So it fit snuggly over the 6 spokes and the hub shaft, so I thought I would give it a tap with a hammer to see how tight it was. (Above picture does not show finished mount but for illustration)

BANG - it shattered into three pieces!

So I made another, this time with wider slots. This is not going to grip the spokes tight.
I will glue it in place with the fine two part araldite mentioned above.

But before I do that I want to fix into it bolts to hold the sprocket in place. I will use the heated and countersunk method, allowing me to fix the nuts on the outside also with some thread glue to stop them moving.

I also realize that the depth of the mount is too shallow as the revised version sits flat to the end of the raised hub. This gives very little clearance for the chain, perhaps only 3-5 mm, which would be enough if there was no flexing or movement but I think to big a risk, so I need to build a bigger block.

EDIT: While walking the dog I concluded I will stick with it and buy some 20mm HDPE, perhaps a piece of 30mm too.

[Deathly Hallows]

While I wait for my thicker HDPE to arrive, I ordered a 79mm core cutter so the hub will be bigger and more solid. Should give more fixing options.

Going to start on a wooden prototype to make sure I don't waste the HDPE sheets. I'm not yet sure about the layout of the motors and wheels. I want quite a compact design to allow flexibility in weapon and ensure the wedge is not too steep and the size (and therefore mass) of the body is not too large.

[Deathly Hallows]

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Just quick update on the chassis mock up. Using 12mm ply as it's similar size to the HDPE I have but a fair bit lighter.

[Maxamuslead]

Gosh that gonna be a big Feather.....

[Deathly Hallows]

Yep. Hence the trial with ply. Gonna have to be careful of the weight. Doing it this way if I need to narrow it it I can work out the space.

The height of the back panel and length of the ramp is constrained by the size of the motors and wheels. So really the only thing I can change is the width. This design is 600mm wide, I could drop it down to 500mm without any issues. I'd like it wide as I want other robots to get on top so any weapon can do it's thing.

Speaking of the weapon I want to be able to swap out depending on arena. But first I need a working rolling chassis.

My plan is as follows:

1 Rolling chassis
1.1 fix wheel hubs and sprockets to wheels
1.2 sort out chains and tensioner
2 first wire up and fuse
3 Self righter
4 weapon
5 rebuild chassis
6 final wire and safety switch
7 cosmetics

[Ocracoke]

600mm is as wide as the baseplate on Kaizen... you are indeed going to have a trial getting this under the weight limit. That being said, I think it is possible if you are careful with the shell and weapon components. However, the danger is that the armour becomes too thin to realistically stand up to the competition in the arena.

What is the expected overall size of Alligrator?

[Deathly Hallows]

Let's assume I narrow it to 500mm, length will be 550mm, height 270mm including wheel clearance.

In theory I could reduce the width further but it will limit my weapon options and I want stuff to end upon top.
The height is pretty fixed, and the length of ramp is constrained by the big motors and the necessary angle to cover them.

I have some nice Alligrator green 12.7mm HDPE but the floor can be aluminium. Will have to do some sums.

This is exactly why I wanted to build a full size ply version to see how it all comes together.

[Maxamuslead]

you can reduce the high, those motors can sit fine in a 110mm frame and have the wheels poking through the top ? also if you can shorten you could have the wheels sticking out the back a little as well.

[Deathly Hallows]

you can reduce the high, those motors can sit fine in a 110mm frame and have the wheels poking through the top ? also if you can shorten you could have the wheels sticking out the back a little as well.

Thats a good idea, could help if I land on my rear to self right but would expose the wheels to rear attacks. I'll get my saw out tonight.

[Maxamuslead]

you will always have a weak point, to be honest it a lot of wedges using that idea, look at the heavyweight flippers

[Deathly Hallows]

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I didn't start cutting but drew what could be a layout. I could go steeper but that makes the gap to the motor very small. I drew a fainter pencil line to show that angle. The darker sharpy lines show a possible new design. The length of base is near enough 500mm the height goes down to 220mm. I also looked at reducing the width, from 600mm to 400mm. This would reduce the materials needed for the outer body by around 40% I think. I'll need a spreadsheet to really work it out.

[Deathly Hallows]

I managed to fit up one side of the drive system in the ply mock up. I narrowed the chassis to 400mm but that maybe too narrow for the final build.
Never broke and shortened a chain before, so bought a good tool for the job which made the task a doddle. I cut slots out the back to move the wheel further back as advised by Mark.
The HDPE hubs I made worked well. Though the design of the wheel with 6 spokes one side (the side I fit the hub and sprocket) and 3 the other,limit the number of bolt options. I have one going through the sprocket, hub, and wheel clamping it all together. A second bolt locks just the sprocket to the hub. With the hub sitting over the 6 spokes there is no way this is moving. For final build I will glue it on.
Bolted the motors to the floor, and span it up.
..
Vvvrrrrrmmmm
..
The chain drive makes a different sound to a direct electric drive. Very satisfying.

No photo or video until I get it a bit tidier.

Second chain on order, some new bolts of optimal length, and various bits.
Weapon and self righter still to go.

Also have to decide if I get the aluminium floor professionally warer cut or attempt it myself.

[Deathly Hallows]

Think all the postie's and parcel men wanted to get home to watch the wedding! The bits I ordered on eBay came also the clamps I ordered from http://www.simplybearings.co.uk items look good and cheaper than eBay or Amazon paid under £8 for 10x shaft collars!

I managed to crafg the second hub and assemble another wheel, but I seem to have lost an oilite bush. Also started to cut the HDPE, which is a risk when I haven't got the linear actuator yet to know how it will fit.

Triedmto do some soldering and just got frustrated. I just can't get the hang of it. Bought some flux which appears to be helping the solder stick to the connectors but, can't get wire, connector and solder all in right at same time, despite having a spare hand clamp.