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Thread: Designing my first robot - Advice Needed

  1. #1
    Noisy's Avatar
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    Ruairidh Thomson
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    Hello everyone. I am designing my first featherweight robot, a lifter called Pancake. Pancake is designed to be simple to build and repair while still being competent in battle.

    So far I have designed the base and bulkheads, drive system, armour and I have started on the weapon. The base and armour will be made from 3mm hardox and the bulkheads from 25mm HDPE. The drive is 2x Ranglebox RB-775 motors with Saturn-16 gearboxes connected by chain to the front and back wheels. Speed controllers are Botzbitz 85a v2. The weapon is a lifting wedge powered by an electric motor designed to go both ways so it can lift, push over opponents and self right. I currently have another RB-775 with Saturn-16 which will then be chain driven to another gearbox but this is still to be designed and I don't know if this is enough or too much.

    My questions are:

    1) What should I do to for the lifter? Should I use the RB-775 or are there alternatives that would be better? If I stick with the RB-775, does it need the second gearbox and what should I do/avoid when designing that or is the Saturn-16 enough?
    2) What batteries and receiver should I use and where do I get them?
    3) Is there anything I have missed or could improve so far? This is my first engineering project so any advice will be helpful.

    Thanks
    - Ruairidh
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    Albear's Avatar
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    hey mate and welcome! Looks good! The googly eyes being a particular highlight Love the design, haven't seen anything like this. Only thing I can point out is an inability to self right. Lots of flippers and pushers that could take advantage of that.

  3. #3
    Noisy's Avatar
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    Thanks. The theory on how Pancake self rights is similar to how Sewer Snake self rights. Pancake's lifter can go 140° so when its on its back it can flip its self over back onto the wheels. It may not self right if the weight distribution is too far back or if the top wedge is too short and it rests on it's back armour.

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    1) What should I do to for the lifter? Should I use the RB-775 or are there alternatives that would be better? If I stick with the RB-775, does it need the second gearbox and what should I do/avoid when designing that or is the Saturn-16 enough?

    For a flipper the Saturn's should be fine. No second gearbox. Aim for around 100mm diameter wheels
    Looking at the design they seem much smaller which effectively gears down the motor meaning your bot will be slower

    2) What batteries and receiver should I use and where do I get them?

    Optipower or HobbyKing. You should go for LiPo but you will need a LiPo charger and dont forget the LiPo bag when charging
    Probably a 2200mA 5 cell should be ok, maybe push up to 3000mAh - I'm sure there will be lots of opinions

    The Botbitz have a BEC in them so no separate battery for the receiver


    3) Is there anything I have missed or could improve so far? This is my first engineering project so any advice will be helpful

    Electric flippers are more like electric lifters. You wont get the explosive speed that CO2 gives

    Read the build diaries carefully!
    Last edited by shakesc; 2nd January 2017 at 09:04.

  5. #5
    maddox10's Avatar
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    Why use 25mm HDPE bulkheads?
    Those are about as heavy as the 3.2mm Hardox. 15mm HDPE has a real weight advantage and will do the job as bulkhead too.

    Weaponpower with the Saturns. I suggest to look at Ellis's Tormenta's.
    He used a secundary gearing with a timing belt and the original torque limiter of a big batterydrill.

    Batteries. Depending on budget, but Lead, NiCd or NiMH are rather outdated now.
    Even if you're really strapped for budget, the older batteries will cost as much or more, and eat away the weight you have.

    Reciever, just use a standard RX/TX set, ain't that expensive anymore, and would last you a few years.

  6. #6
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    Ellis will be able to advise better on the suitability of the Saturn 16s but I would expect you to need another gearbox or a high reduction between the motor and the weapon. It may be better to use a belt and timing pulleys on the weapon instead as it will allow for some slip and transmit less shock through to the motor. You can also get larger reductions for smaller diameter pulleys compared to sprockets.
    Jamie McHarg
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    With great power, comes great reliability.

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    For the weapon a DeWalt or a big Makita with secondary gearing would be the way to go

  8. #8
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    Ruairidh Thomson
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    Thanks for the feedback everyone. The design has evolved in the past week but I am at a bit of a crossroads. I added the battery and finished the weapon's gearbox. The reduction is 81:1 and is chain driven to the lifter. After this I decided to weigh the main parts and get an estimate on how much the robot weighs and costs. This came out at 7.3kg so I decided to try a redesign with 100mm diameter wheels. The current ones are 50mm and as Shakeesc pointed out, they would make me slower. So I would need to design another gearbox for the drive or reconfigure the robot to fit the bigger wheels. I have started by placing the motors at the far rear at the robot. The bulkheads have had to be raised and lengthened and the armour will have to be redesigned. I'm reluctant to continue with the redesign as I don't think it is as efficient and the motors might be more vulnerable from a spinner hitting the rear than the side. Thoughts?
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  9. #9
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    It looks like you are using a set of bevel gears to transfer power to the chains which drive the wheels, could you not include a 2:1 ratio at this stage to double the speed of the wheels? That way your robot will be the 'normal' speed but can keep the 50mm wheels

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