101 réponses à ce sujet

[OdorousWo1f]

absolute maximum speed i want is maybe 20mph
true, and you're probably right. I'd also like the satisfaction and 100% customization that comes with making your own thing/basing it off of someone else's design

[Mike118]

Ok I will not try anymore to change your mind about what you want to do. If you perfectly know why you want to do it this way this is fine .

[OdorousWo1f]

oh alright. i'm not trying to just instantly shut down your ideas. i think they're great ideas it's just this is what i'd like to try out and put together.
trx4 vigibots are pretty neat and i might make one in the future

[firened]

oh wow that's hefty,
this battery is 23.1 Lbs.

keep in mind that with a differential drive the wheels get actually dragged sideways across the ground when turning.
adding that much weight will result in a lot of forces on the frame, and if you plan on a suspension the forces on it will be high.

however, if you actually consider an SLA battery, then you can pay your local moto or car mechanics a visit and ask nicely if they have a leftover used battery you could have. i got some for free that way too. don't expect more than 50% capacity, but it will give you a way to try it out. if it's too heavy you can get a li-ion, li-po or LiFePO4

[OdorousWo1f]

o yeah you made a really good point on weight. never would have thought about that.
might stick with the lifepo then
although I've heard that lifepo ecosaver battery or whatever it was called has a terrible BMS in it.
i would have just done RC car type steering but idk how i would scale that up and make it work with suspension. just seems overly complicated for something like that.

[firened]

i think, to reach speeds of 20mph, with a lithium based battery, you'll need a total motor power of around 200W!
with the heavy SLA, around 300W.

20mph is 6 times as fast as icecream, if using the same motors (total power of 150W), the slow rpm precision is still going to be 6 times worse. that's one reference i based my thoughts on.
the other being the trx-4 that has a 190W to reach 21mph, while weighting only a couple pounds...
perhaps my estimates are even conservative.
anyway, it's possible, just needs power

ps: Brushless motors have better power, and less losses, but poor low rpm precision.

[OdorousWo1f]

might need some sort of lipo yeah. to me at this point good low rpm control is a loss, was just a nice to have. 200 watts of motors all together or per motor?

[firened]

yeah those 2 things are difficult to DIY

[OdorousWo1f]

i should probably find motors that are powerful and right first then find a good battery and BMS
the controller *shouldn't* explode

[firened]

200W all 4 motors together.

[OdorousWo1f]

alright so 50w per motor (idk why i had to think about that)

[firened]

jepp
ok from speed we can calculate rpm and wheel size proportions

[OdorousWo1f]

i mean
This is 50 watts but seems awfully small.

https://www.amazon.c...,aps,219&sr=8-6
isn't that the same kind of motor found in the TRX4?

[Mike118]

I was not that far with my 20 lbs estimation x)

[OdorousWo1f]

it says 23 pounds on the Amazon page
oh nevermind it's dual shaft

[Mike118]

With 50w motors and 200 rpm and 150mm wheels you can have a robot that weight easily around 20lbs in total including motors base wheel and battery.

[firened]

20mph = 8.888 m/s
= 533 m/min

533 m/min divided by (example) 500 rpm = 1.07m wheel circumference

1.07m / [U+03C0] = 34cm wheel diameter

that's the proportion: [U+2205] 34cm wheel at 500 rpm

if you double the rpm, the [U+2205] wheel halfes - and vise versa. it's inverse proportional.
that should help you find something suitable.
if you find a [U+2205] 20cm wheel you'll need 850rpm motors. makes sense?
i hope it's correct what i wrote.

[Mike118]

Where ? I did not find it.

[OdorousWo1f]

i have no idea if that's correct
in the description

[Mike118]

8m/s is very fast x)