Falcons and Moving to West Coast Drive Questions

Good afternoon.

My team is currently looking at moving to a West Coast Drive system for the first time and would like to use our Falcon motors. Alternative would be NEO’s but we have none on hand and that would mean adding separate controllers which we didn’t have to do last year with the Falcons.

Since it’s our first time - we want to stay as standard as possible.

Looking at JVN, lowest standard gearing possible, Push Draw per motor is as follows:

2 Falcons High Gear 111 A, Low Gear 55 A
3 Falcons High Gear 74 A, Low gear 37 A

So if the target is to remain below 40 when pushing, it seams like we need to use 3 falcons per side.

Is is possible to use 2, have decent performance, and just limit current to 40A?

When you purchase the WCP DS boxes - can you mount with either 2 or 3 motors with the parts included?

Thanks!
Chris

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Most teams are gearing for a specific drivetrain free speed and generally don’t focus on the pushing amp draw. Going over 40A when pushing is standard, but also you really shouldn’t be getting into pushing matches in the first place.

Yes. In the age of BLDCs, current limiting is your friend, although I’m not sure most WCD teams are current limiting their drivetrain motors to exactly 40A.

Yes, if you are buying the 3 CIM version it will happily take 1, 2, or 3 motors.

I will say you might want to check out the Single Speed Flipped gearbox from WCP instead, it’s compact and a decent price. Shifting drivetrains have gone the way of the dodo:

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Thank you for the advice - I will definitely check those out.

I seems that the guides I have found to building WCD are getting a little out of date.

Is there a more current guide that I should be aware of that explains the flipped gearboxes?

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Hmm not sure, but the TL/DR is that BLDC motors like Falcons and NEOs are physically shorter and more powerful than the CIM, so you can get away with only 2 motors and can flip the motor over the drivetrain tube because it’s short enough to not conflict with the wheels. This compact design saves a ton of horizontal space inside your robot frame.

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That actually helps a lot - much appreciated.

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Here’s an example of what these gearboxes like look on our 2022 chassis (Note: these are custom gearboxes, but 100% copied from the WCP SS Flipped design).

We absolutely loved how compact they were!

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It is very likely that traction will be your limiting factor even with 2 motors, so little point in using 3.

We’ve run the flipped gear boxes for the last 3 years, there’s a snap ring we absolutely loathe that we’ve retrofitted to be a bolt on the end of the shaft. Other than that, glorious design.

OP, with a pair of falcons you can run a single speed drive. Supply side current limit around 50 or 55 amps should be fine, I’d just do drive practice until you’re seeing brownouts in the first 3 minutes of the session and then pull them back down a little.

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Great information from everyone - thanks!

Trying to strike balance between build the absolute most perfect and most powerful drive train vs something that is a little more simple to achieve with limited resources but still advancing our tech is a hard thing to do. Sooo many options out there.

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This setup is very impressive. I love all the open space.
I also found your open alliance post thanks for sharing.

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I believe this is mostly true, but even in a game like 2017 you wouldn’t have dual speed? I understand shifting is mostly negated by the extreme power of BLDC but it might still be helpful for the tight areas and then the large open field.

If I was running WCD in a year like 2017 but with modern BLDCs I wouldn’t run shifting, I’d probably gear slightly higher than normal based on the longer cycle time.

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Still not worth it.

In 2017 we ran a 2cim single speed 22fps free speed drive on a 55lb, 11" tall robot, and it cooked. Highest we’ve ever ranked. Related, that year we learned about current limiting with TalonSRX.

22fps is about a quarter step from uncontrollable, we had a software “mute button” that cut drive power in ~half for small maneuvers. We’ve never designed over 18FPS freespeed afterwards, it’s truly unnecessary. You’ll flip your own 'bot over on deceleration, with any “normal-size” superstructure. We’ve even faceplanted this year’s robot, at 80lbs, with 18fps free speed.

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That what we used last year and really liked them. I do have to say we did some things with them one has done before like 30t pulleys. They don’t fit without a lot of work and I would say if its your first time just use chain and save yourself the headache.

I know which one you’re talking about, had a few issues with one side this past year.

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We actually used 3 falcons per side on our WCD last year. We enjoyed the better power curve and efficiency for it and we didn’t slip around much at all using 4” custom 3D printed/1/8” plate wheels with 1.5” blue nitrile tread from TTB

We have a video series on WCD. It was made in 2018 when we didn’t have falcons buy I goes into a lot of what is needed. https://youtu.be/Paj8XRv0QX8

Hi EHutson - I started with your series about a month ago - that’s what gave us the confidence to attempt this. Thank you for your series - very much appreciated.

Interesting – were you using current limiting to prevent slip? It was apparently pretty common this past year for “super powered” drivetrains to burn right through the carpet in pushing/stall situations.

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Your welcome :hugs: