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Thread: Barróg - Featherweight Lifter Build Diary

  1. #11
    mrsam's Avatar
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    Sam Price
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    You only need it ground scraping at the front, the arena floor is very rarely flat.

    Also you want to account for the extra weight of a robot on top so you don't just ground out when you pick something up

  2. #12
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    I like this design, it's looking really interesting. I especially like the sort of 'reverse-clamper' style you've got, where the spikes stay still but the wedge presses the opponent up against them. Do you have any plans for protecting your insides while the lifter is open? I'm just wary of the situation where you've just self-righted, and something like oddbot tries to jab his spike into your batteries.

  3. #13
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    Hmm, I didn't really think much of spikebots, but now that you mention them, that could indeed be a problem. I suppose the best thing to do would be to put a piece of HDPE along the front at about motor height, although I'll need to account for that in the weight. Shouldn't be too much more though.

    Also, does anyone know where would be the best place to get the 30A BotBitz speed controllers? I've heard ranglebox but they seem to have been out of stock for a while, and ordering them directly from BotBitz could take a long time.

  4. #14
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    Alright, so quick update. I've gotten most of the components delivered now: the actuator, HDPE, Battery etc. The only parts I still need are the motor mounts (which are en route, I'm told) and the ESC's (which are currently out of stock). I just have a few questions I'd like to rattle out there.

    1. What guage of screw would you recommend for 10mm HDPE? The only barrel nuts I could get locally were ones for 6mm screws, and I've been led to believe that barrel nuts are the best for holding HDPE pieces together, but I worry that they won't leave enough space when going lengthwise though the 10mm. As a side note, what are some recommended lengths for the screws as well?

    2. Does a linear actuator require an ESC, or can a simpler method be used to control it? It's not like I'd need to control the speed it travels at, but just in terms of interfacing with the battery and receiver, what is the best way to go about it.

    3. What would you consider good ground clearance. The wheels I'm looking at now (Banebots 3-7/8") I'm estimating would give me 10mm clearance all around, bar the front. Should I aim to reduce or increase that?

    4. Will just having the tip of the front of the machine be made of 12mm HDPE be OK, or should I attach some metal to the front. If so, how far up should the metal go, and what are some ways of securing it while keeping the face as flush as possible?

    Cheers for reading.

  5. #15
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    1. I use M6 countersunk hex bolts, some use M5. Either is fine really. Assuming you're going into the side of 10mm HDPE, I'd say probably use M5s. Get the nuts off eBay if you need to. Alternatively, self-tapping wood screws hold things together excellently, but you don't really want to be using them for something you'll be opening up regularly, since the head goes bald and the hole you've put the screw into will get chewed up gradually every time you reinsert it. They're very space-efficient, though, so that's perhaps something to consider.

    2. Short answer: no. If you're running your linac with the stock motor, it'll be brushed, so you could technically just switch it on and off with two RC switches (one for each direction). However, it's probably better to just get an ESC, because it means you can have forward and reverse on the same channel. You could use a double-pole switch on one channel and basically make it retract when it's not activated, but that means you can't really stop it halfway up. So yeah, I'd use an ESC.

    3. 10mm is a bit steep. I'd aim to reduce it to 5mm or below if you can. That said, the arena floor is never as smooth as you want it to be, and it's not going to be the end of you if you're not going full-limpet. You just have to put more effort into pointing your wedge at the opponent.

    4. Since you're relying on your wedge entirely for your weapon, I'd put a steel edge on it. It'll get chowdered after a few fights otherwise. You only need a few centimetres up the wedge I'd say. The point is just that the tip stays sharp. I'm no expert in this kind of thing, but let's say you have a 5mm thick steel (perhaps hardox?) edge. I'd cut a 5mm-deep indent into the edge of the HDPE, overlay the steel, then bolt through with countersunk bolts. See below:

    Flipper Edge.png
    There are other ways obviously, like using thinner steel and bending it over the edge of the flipper in two halves, but this was the best solution I could think of.

  6. #16
    RogueTwoRobots's Avatar
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    On point number 2, the easiest way would just be to use a servo to turn on a couple of microswitches, one for each direction. It allows you to control forward and back from one radio channel and the stock actuator motor will have a low enough current draw to not require any additional relays etc. Here's a setup in its simplest form; I usually tend to just hot glue the switches onto the sides of the servo and wrap a cable tie around them, but you may prefer a more robust/maintainable/aesthetically pleasing alternative

    DSC_2215.jpg
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  7. #17
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    Thanks for all of the advice, especially the diagram. I've ordered some m5 barrel nuts, and will see if I can source the steel locally.

  8. #18
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    Right, so quick question. I'm planning on getting the Banebots T81 3 7/8 wheels, and I see that you need a custom hub for them as opposed to a simple hexnut. The only thing that has me worried is that the shafts are not threaded, whereas the drill gearbox is. Would I be able to use a 3/8 T81 hub on a 3/8 threaded drill shaft, or should I look for another solution, such as different wheels?

  9. #19
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    you could use those hubs and tap them to use the tread, but is there any reason you for 3 3/8 wheels, as you can get the 2-7/8 wheels in the t40 format which you can use with standard 3/8 unf JOINER nut, also you can get them in the uk http://www.robotshop.com/uk/rb-ban-94-orange-wheel.html.

  10. #20
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    Cheers for the link to the UK store. The main reason I was going for the 3 3/8th is because the mounts I'll be using combined with the 10mm HDPE base puts the centre of the shaft 37mm off the ground, which leaves the 2 7/8ths just too small to make contact with the ground (radius is approx 36.5mm). I would prefer a hex mount, but it seems that Banebots don't do any hex wheels above 2 7/8. Are there any other options for someone who doesn't have the equipment to make some?

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