Design Dilemma

[Gabe01]

Re: Design Dilemma

It was always called thin gas pipe armour by the commentator, I never bothered correcting them, it was an inch thick, the tubing I have just purchased is only 10mm however .

[jonny]

Re: Design Dilemma

Can we change the topic name to design diarrhoea please?

[Ellis]

Re: Design Dilemma

I had the problem of invertability (I hope that's a word) when designing/making my robot. Instead of trying to fit a srimech of some sort, I simply exposed the back wheels through the top armour. This means that when I'm upside down the wheels clear the top plate and I still get 2wd, plenty of control to keep the rules at bay. Sure, it's not as good as something that rights you, but it allows you to stay in the game until a friendly enemy machine decides to flip you again! Just a thought if you want to have 4 motors but don't have the weight for a srimech if you do.

Really liking this by the way, my approach to building was rough drawing on paper then start hacking at plastics, this is the complete opposite way of doing things and despite being longer winded, I like it.

[Eventorizon]

Re: Design Dilemma

Well I now have about 6 different possibilities to be going on with!

2WD with Disc, and Lifter/Shrimech is probably the root I will look at first.

Though here is a point... I have 2 7.2V racing packs as power both weighing around 550g each and wired to give me 14.4V but they have a total capacity of 10200mAh (10.2Ah) which I think is just overkill but I don't know. Of course it all depends on what combination of parts you are running but what do other people run?

my approach to building was rough drawing on paper then start hacking at plastics, this is the complete opposite way of doing things and despite being longer winded, I like it.

And I would be doing that if I could afford the plastics, but I cant. with CAD though I can get it wrong as many times as I like and it cost me nothing

[Mouldy]

Re: Design Dilemma

Id double check your battery spec... 10.2amps for a race pack?

Id also suggest something like this would be well suited 3.3ah lipo; http://www.flightpower.eu/global/index. ... cts_id=178

[Eventorizon]

Re: Design Dilemma

Each pack has a capacity of 5100mAh, giving a total of 10200mAh (sorry should have been clearer)

Could I get away with a single 14.8V Lipol Pack at say 4000mAh Like this...

http://www.electricwingman.com/volton-3 ... ttery.aspx

And what does the C mean?

[Ellis]

Re: Design Dilemma

If you have your packs in series (must have if you're getting the combination of voltages) then you don't have double the capacity as well. Unless this is some sort setup I don't understand/recognise. Series = double voltage, same capacity, parallel = same voltage, double capacity.

So, you have a capacity of 5100mah which is about standard, if anything quite high I think.

As for the C rating, I believe that you multiply the C number by the capacity of the pack and you get the maximum you can discharge from the LiPo. So, the higher the better.

[MikeNCR]

Re: Design Dilemma

Each pack has a capacity of 5100mAh, giving a total of 10200mAh (sorry should have been clearer)

Could I get away with a single 14.8V Lipol Pack at say 4000mAh Like this...

http://www.electricwingman.com/volton-3 ... ttery.aspx

And what does the C mean?

To give an idea, my Featherweight bar spinner Moros uses 1 5 cell 2300mAh A123 pack for the drive and 1 6 cell pack for the weapon and I've yet to have battery issues. I'm also working on a new feather that will use a single 6 cell pack as it doesn't have a massive spinning weapon.

If you want a rough idea of your power needs you can use this site to figure out how much your drive will want based on motors, gear reduction and wheel size- http://www.killerbotics.com/kbtools/TentacleTools/

[Eventorizon]

Re: Design Dilemma

And that is why I got a D at A Level Physics... you are right it will be 14.4V and 5100mAh capacity. So if I went LiPol I could have the came voltage and capacitance at half the weight

[ewan]

Re: Design Dilemma

If I were you I'd go for an 18.5V li-po and a relatively cheap pack would deliver current as well as a more expensive pack if you go for one with a slightly larger capacity (meaning each individual cell is under less strain to output the same power) e.g. http://www.hobbyking.com/hobbyking/stor ... _Pack.html

Btw if you want an approximation of the GR01's with the tentacle calculator select the Johnson ('Small' RMP) motor and a gear ratio of 36:1 then,

for 9.6V motor- Voltage Constant 1890rpm/Volt, 0.50oz-in/A
for 14.4V motor- Voltage Constant 1430rpm/Volt, 0.68oz-in/A

Be aware it's an approximation but it should give you some indication of speed/current draw. Friction coefficients are very likely to be below the 0.9 calculator default btw in an arena environment and it appears to assume the full robot mass is over the driven wheels.

[typhoon_driver]

Re: Design Dilemma

You can measurebate all you want but you won't use much more than the capacity from a 3Ah pack. I've run a few high powered discs and never used much more than 2 to 2.5Ah from a pack and that's running it non stop for an entire 3 minutes

[Eventorizon]

Re: Design Dilemma

Ewan, you mentioned using Nylon as a chassis material. Where would you advise getting it from an do you know what the density is. Solidworks is giving me 2 options, one with a density of 1400kg/m^3 called Nylon 6/10 and another at 1150kg/m^3 called Nylon 101?

At 10mm thick for all parts the chassis weighs 2Kg in 6/10... which given as I have cut the back off seems a little strange...?

[Ellis]

Re: Design Dilemma

Here you can buy sheets of Nylon 6. http://www.directplasticsonline.co.uk/N ... Sheet.html

I believe many people use that site for HDPE and such as well.

[Eventorizon]

Re: Design Dilemma

I found this site...

http://www.nyltek.com/pdf/SAFETY.pdf

in an attempt to find the density of Nylon 6 and it has given me...

Specific Gravity / Density: 1.0840g/cm3

and this one for Nylon 66

http://www.theplasticshop.co.uk/plastic ... _sheet.pdf

which says 1.14 g/cm3

Does anyone think that these are wrong or unreliable?

[ewan]

Re: Design Dilemma

The link that Ellis gave (http://www.directplasticsonline.co.uk/N ... Sheet.html) is a good source and where I get mine. Here's the datasheet for the natural (white) Nylon 6 they stock http://www.directplasticsonline.co.uk/p ... t_Cast.pdf with a density of 1.15g/cm^3

A 2kg chassis seems reasonable for a feather- where's the remainder of your weight going if it's still too much?