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-   -   Pushing down the bridge (http://www.chiefdelphi.com/forums/showthread.php?t=104210)

jimwick 08-03-2012 18:26
Re: Pushing down the bridge
 
we used a FP/motor and transmission, then geared that down 4 to 1 using a chain drive with #25 chain.

it worked well at the Granite State Regional

matteo2171 08-03-2012 19:03
Re: Pushing down the bridge
 
Our team is using a wedge that is raised and lowerd by a window motor, when it drives the bridge down the bridge pushes back on it straight back when the bumper is there tto keep it rigid. We don't have to worry about the motor nat being strong enough because it only puts the wedge in place, however it will back drive if we hit the bridge to hard.

metainf 08-03-2012 22:47
Re: Pushing down the bridge
 
Quote:
Originally Posted by Bruceb (Post 1140637)
From watching several competitions now I have to say that those of you trying to use the drivers depth perception and an arm to lower the bridge have 2 problems. 1. getting the bot at just the right distance from the opposite side of the bridge to allow your arm to lower the bridge is difficult at best.
2. developing enough torque with a motor and coordinating its lowering with your forward motion is a trick in itself.
Solution. just lower a wedge shaped arm at the front of your bot using an over center link(motor or pneumatic) and just drive up the bridge to lower it. see our bot here.

http://i1121.photobucket.com/albums/...2/100_0011.jpg
Another way to solve this problem is to have two posts that stop the robot from going too far into the bridge, and then just back up a small bit to deploy an arm. Our team has done this, and it should only take a maximum of 30 minutes, and a few feet of angle.
We are also using a 550 banebot with a 251:1 reduction. We have pushed our entire robot onto two wheels with it :D

PAR_WIG1350 08-03-2012 22:57
Re: Pushing down the bridge
 
Quote:
Originally Posted by matteo2171 (Post 1141165)
Our team is using a wedge that is raised and lowerd by a window motor, when it drives the bridge down the bridge pushes back on it straight back when the bumper is there tto keep it rigid. We don't have to worry about the motor nat being strong enough because it only puts the wedge in place, however it will back drive if we hit the bridge to hard.
Be careful, the widow motor in the kit, and probably many others, use plastic worm gears. The danger here is that if you get hit hard enough, or after many hits, the teeth will shear off of the gear. Removing the locking pins helps (and it sounds like you already have), but have a spare motor handy if you are using one with plastic gears.

V_Chip 08-03-2012 23:02
Re: Pushing down the bridge
 
Quote:
Originally Posted by PAR_WIG1350 (Post 1141234)
Be careful, the widow motor in the kit, and probably many others, use plastic worm gears. The danger here is that if you get hit hard enough, or after many hits, the teeth will shear off of the gear. Removing the locking pins helps (and it sounds like you already have), but have a spare motor handy if you are using one with plastic gears.
^This.

We've already sheared one window motor and have a couple on hand ICE.

Bruceb 09-03-2012 09:21
Re: Pushing down the bridge
 
Pneumatics

sandiegodan 09-03-2012 14:32
Re: Pushing down the bridge
 
I would ask a different question. I wouldn't worry about how much force it takes to push the bridge down, I would look at how much force it takes to lift up your bot, and size to that. You may even want to intentionally limit it so you don't tip yourself over. It's really the weight of the bot that lowers the bridge, not your mechanism.

What I observe in competition is that tipping an empty bridge is only one of several scenarios. Often you need to tip the bridge with a robot already on or you need to squish a ball (or 2) underneath the bridge far enough to let you climb up. If you can't go over the bump because of low clearance you've got the dual problem of needing to lower the bridge nearly to the floor and pushing past any balls that are stuck underneath. In most cases it will take the full weight of your bot and a partner to lower the bridge far enough to get on. The arm should allow the bot to bring it's full weight into play. Big advantage to the wedge designs here as they are mostly based on this idea anyway.

We are also seeing that if the arm is too ridgid and engaged on the bridge, the bridge can flip the bot back over in short order.

Just my observations.


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