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  #16   Spotlight this post!  
Unread 02-22-2018, 04:44 PM
Daleolgren Daleolgren is offline
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Re: Brownouts , PDP and roborio

We are using 8 inch inch wheels with 4 to 1 direct drive planetary gear boxes on each of of our 4 cims .. so we have no chain or sprockets.... previously I miss stated the ratio and wheel size..... we do plan to order add on reduction to actually make it 8 to 1 ratio.... the wheels are softer rubber ( grey ) smooth
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Unread 02-22-2018, 05:04 PM
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Re: Brownouts , PDP and roborio

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Originally Posted by Daleolgren View Post
We are using 8 inch inch wheels with 4 to 1 direct drive planetary gear boxes on each of of our 4 cims .. so we have no chain or sprockets.... previously I miss stated the ratio and wheel size..... we do plan to order add on reduction to actually make it 8 to 1 ratio.... the wheels are softer rubber ( grey ) smooth
Yeah, it makes sense that you are browning out. That's 46.5 ft/sec free speed. Waaaaaayyyy too high for the CIMs, they don't have enough torque to handle that. Even 8:1 on 8inch wheels is pushing it if that's your only speed. You probably want to go for 12:1 or so.
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Unread 02-22-2018, 05:07 PM
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Re: Brownouts , PDP and roborio

4:1 with 8'' wheels will not move at all, with 6'' wheels is still almost guaranteed to cause constant brownouts, and with 4'' wheels it will likely do so while turning or accelerating at low speeds unless the drivetrain is exceptionally efficient or other precautions are taken.

I would not recommend gearing for above ~14 ft/sec (theoretical no-loss speed at 12v) unless you absolutely know what you are doing.
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Unread 02-22-2018, 05:16 PM
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Re: Brownouts , PDP and roborio

Direct drive to each wheel with 4 CIMs sounds like you're either running 4 wheel drive with sticky wheels or mecanum. Once you get the gear ratio down to something sane like 12:1, mecanums should turn fine no matter where the wheels are, unless you have them installed backwards. 4 sticky wheels will need a wide wheelbase to turn well, though.

Can you post a picture of the bottom side of your robot for us to look at? Don't open the bag, though. Even a picture through a bag will probably work since we just need the approximate wheelbase aspect ratio.
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Unread 02-22-2018, 07:50 PM
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Re: Brownouts , PDP and roborio

So we use 6"omni in each corner we have the versa clamping style gear boxes and we do 5.14:1 reduction so far we haven't browned out at all. But will we be seeing brownouts later in the season
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Unread 02-22-2018, 07:55 PM
Oblarg Oblarg is offline
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Re: Brownouts , PDP and roborio

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Originally Posted by RoboAlum View Post
So we use 6"omni in each corner we have the versa clamping style gear boxes and we do 5.14:1 reduction so far we haven't browned out at all. But will we be seeing brownouts later in the season
That gearing is quite a bit more aggressive than anything I would consider in a single-speed, and probably even in a shifting drive. Even if you don't have brownout problems (you almost certainly will if you try to go full forward to full reverse without some sort of ramping), you're going to be crippling your acceleration and moving more slowly than you want to.
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