Is 4 neos enough for a west coat drive?

Technical Technical Discussion
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I am designing a 6 wheel drop center west coast drive for my team. Would 4 neos be enough for this drivetrain? It seems like all the teams I see online use 6 motors, what is the benefit of this over 4, it seems like 4 should be plenty powerful.

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4 is definitely plenty powerful for a wcd but teams that go for 6 neos do it mainly for the extra pushing power. It’s more about having more power than other robots. Also 6 neos will put less stress on each motor.

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4 NEOs is rather powerful all things considering, and in most brushless drivetrains (4 or 6) the tractive ability to put power to the floor is the limitation. 6 miniCIMs in the pre-brushless era is mostly an artifact of PDP port current limits via the breaker.

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Yes.

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Many robots have been built with 4 NEO drivetrains, and move. 2 will also probably make the drivetrain move. Really you only need 1 if you don’t care about turning. A wise man once said ‘moving sideways is a waste of time’

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“Turning is a waste of time” - Thaddeus 2020

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image

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4 NEOs is plenty unless you have a specific need for 6. If you end up on the 6 NEO train though, be careful with current draw as that could easily trip your main breaker/cause brownouts if you arent careful with current limiting.

I would suggest using the Ilite drivetrain simulator for gear ratios and current limits. it is very nice.

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2 CIM’s were enough to win events in 2018, probably could of gotten more with NEOs…

dont do 2 any motor drivetrain please

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You really only need two. Not sure where they’d fit beyond one in each pocket.

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When we used to only have CIMs, the majority of teams used just 4 motors. Some started using 6 to get an extra little bit of power into the drivetrain. When miniCIMs were introduced this became more popular, as a 6 miniCIM drivetrain could perform marginally better than a 4 CIM drivetrain without all of the weight of 6 CIMs.

With the newer brushless motors, you really only need 4. The battery will only feed you so much current.

You have probably seen so many 6 motor drivetrains because they are neat and people like to post neat things here. The boring 4 CIM drivetrain has been the normal drivetrain for the vast majority of teams, but they aren’t very exciting to post about. If you went by CD posts you’d think 75% of FRC teams had a swerve drivetrain.

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Note that in most cases, this is not true. Your max pushing power is your robot’s weight time your coefficient of friction on the carpet. Most FRC drivetrains can push more than this, which we call a “traction-limited” drivetrain. The case for 6 NEOs is higher acceleration because you can push more current into each one, and the robot will be able to deliver enough torque to stay traction-limited for a longer stretch of your acceleration path. They’ll also handle heat better because you can dissipate your heat heat over a larger number of motors.

Edit: yes, 4 NEOs is enough for a WCD.

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We used 4. It was plenty. Especially as a tall bot, the field layout definitely limited your need for ludicrous acceleration.

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I mean… sometimes yeah… Dark FRC, show me your secrets

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My answer is to examine the comparative response of the two systems.

Motor Qty Weight G/R Amps Max speed Time to 10 ft/sec Speed at 2.5 ft/sec Time to 25 ft
NEO 4 145 7.56 45 18.52 ft/sec 0.53 sec 9.67 ft/sec 1.949 sec
NEO 6 145 7.56 30 18.75 ft/sec 0.5115 sec 9.92 ft/sec 1.9035 sec

Both simulations use 6 inch wheels
The current limit values are tuned to avoid wheel slip under acceleration.
The bottom line is that I expect the 4 NEO solution to be slightly slower than the 6 NEO solution.
I am not sure that the difference is noticeable.

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It would be pretty cool if someone actually did some testing to see at what robot weight 6 neos become no more useful than 4 neos in a pushing match due to slipping, while varying wheels as well. In my eyes though, 6 neos is only worth it if you have nothing else to use your motor slots for. Pushing matches are usually a waste of match time anyway and 4 neos still provide plenty of acceleration.

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This (and traction of different wheels in general) is probably one of the most requested experiments of all time and I think a search on this forum may yield some people’s findings. Notably, I think there’s some CIM vs Neo pushing tests from when the Neo just came out, which would more or less be the same test as what you’re proposing in that it’s the same chassis just more power.

A possible thing that people overlook sometimes is that while the total friction force is given by F = N*mu where mu is the coefficient of friction, mu is not always constant. We normally assume that mu = 0.9-1.1 is a constant value (this is usually the case for static coefficient of friction), however in reality dynamic coefficient of friction mu_k is often a function of the speed between the two surfaces, which would be the amount of wheel slip. Thus, the more wheelslip, the greater the amount of traction.

tldr: this is a very technical way of explaining what you’re suggesting and why it’s often overlooked in robot design

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Yes. We ran a 4 neo WCD in 2019 and it took us to semis in our world champs division.

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IMO the best WCD of 2019 was build by 1796. It uses six 6" Colsons and two 6" dual omnis in an 8WD west coast set up, and is powered by four Neos + two miniCIMs.

Hands down the best acceleration of any robot in the Carson division (Detroit). First overall draft pick.

Without the need for clearance, due to high centering risk at the corners of HAB level 1, 6" wheels would not have been required and 1796 could have been just as zippy without the miniCIMs.

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