Bot Drive speeds - Beetleweight

Hi Everyone!

For those who haven’t met me in person I am Sam Gad (Learn the hard way Robotics). I usually am in the Featherweight world with mediocre bot FeatherDozer.

As I am getting closer to finishing my new workshop, I hope to start building beetles. As this weight class is new to me, I have a question for all:

How fast are your beetles?

Thanks in advance for all replies

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Hey Sam! Love your feathers, would love to see you at beetles, here’s some massive generalisations and a few shameless plugs:

Average brushed drive bot running BBB 22mm / drive kit:

  • ~750rpm under load at 3S, ~1000rpm at 4S
  • 2.25", 2.5" or 2.75" wheels (57-70mm)
  • gives you a range of 5-8mph if i’m mathsing right at nominal voltages.

Average brushless drive bots 1806 2300kv, 22mm 19:1 reduction:

  • maybe 1500rpm under load at 4S?
  • slightly smaller wheels maybe 40-55mm?
  • gives you 7-10mph if i’m mathsing right at nominal voltages.

With brushless drive some people will do reduced Tx rates particularly for turning and also for bigger wheels. 4S LiHv for that extra 0.6V is becoming popular too :stuck_out_tongue:
Larger reductions are also an off the shelf option with mega sparks or repeat max’s

EDIT: our tip speed calculator is very useful for this stuff :slight_smile:
Hope this helps!

The most widly used arena in the UK is David’s.

It 2m X 2m.

A fast robot will cross it in under 0.5secs a slower one will do it in about 0.75secs at a guess.

My robot The Chilli Daddy at peak charge and not accounting for load and friction etc should be roughly 12mph.

2300kv motors @ 17.4v = 40,020rpm on motor
19:1 gear boxes take that down to: 2,106
I have another 1.3 reduction bringing it to 1620rpm

wheel circumfrence is 210mm

1620rpm x 210mm circumference = 341,039mm per minute

/1000 to get meters

x 60 to get hours

/1000 again to get kilometers - which comes out about 20.46 kph which is roughly like 12mph or probably more usefully like 5.6 meter per second.

Add load and friction etc and I’m probably loosing a bunch of speed, but I’m fairly confident that it’s crossing 2m in under 0.5secs.

The Chilli Daddy is a fast robot too, borderline too fast for David’s arena tbh.

If you’re over like 3.5 meters a sec you’re probably ok, can always slow it down on your mixing if too fast.

unlike Jack i can’t do maths so I just used the tip speed calculator on the BBB website and got 19mph for Bonbonbonbon (v1 and v2). This is ridiculous speed and I never use all of it in the arena, I limit all my rates and endpoints so it caps out a fair bit lower.

There is the Team Tentacle Drivetrain Calculator on the Team Run Amok/Ask Aaron website that you can use to work out torque, top speed, accelation and more for brushed and brushless bots.

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