Is your frame tough enough for FIRST?
 

I was cadding up our last years frame up and a thought hit me. How many pounds of force actually hits your bot? Weak hits, medium hits and the hardest hit possible. So i need some help finding out the forces.

Thanks
CD

Re: Is your frame tough enough for first?
 

I would like to think so... and hard, harder, and hardest
mike d

Re: Is your frame tough enough for first?
 

The speed at which the collision occurs, as well as the angles and location of the hit, and how effective the bumpers are, etc will play a big part. For weight, figure 150 lbs to make it easy.

Some materials absorb impacts better than others...for example, fiberglass tends to bounce back, while some aluminum shapes get bent easily.

Re: Is your frame tough enough for first?
 

Thatz what i was figuring, but i wasn't sure. What do you think composite sides

Re: Is your frame tough enough for first?
 

I don't know the forces involved, but there are dents on the front of our robot that would be tough to make with a hammer.

Re: Is your frame tough enough for first?
 

Our hardest hits this year were when hybrid went awry. 15 ft/s into the wall is tough. Turns out the wall is a flexible member. Other than that, bumpers help a lot. We have some pretty vicious scars from years past.

As a little bit of how bad can it really get, I recently saw a vehicle go to 10 G's during a 5mph impact with a wall. 15 ft/s is almost 10mph. For a little math let's assume that your robot collides with a stiff wall at 3 m/s (approximately 10 ft/s). bumpers are about 3 inches thick or rough .1m Let's assume the bumpers are perfectly balanced and do an ideal deceleration.

Therefore d=V*t-1/2at^2 which is really d=V*t-1/2*V*t therefore d=1/2Vt
or t=2d/V=.2/3=1/15 second.
V=at therefore a=45m/s^2 or about 4.5 G's. This would be if the bumpers had perfect crush causing constant deceleration. If you assumed a linear rate of decel from 0 then the peak will get closer to 10G's. You can continue playing this game and second guessing it quite a bit. Overall having it survive a 10 G impact is probably pretty reasonable. You shouldn't see a lot of those, but you may likely see a couple a season.

Re: Is your frame tough enough for first?
 

I agree, those robots can take a beating! But, no matter how many numbers you run, your probably never come close to those freak incidents. So, always throw in a hefty safety factor.

Re: Is your frame tough enough for first?
 

We didn't use bumpers our 07 season and all the chassis aluminum is bent in.

Re: Is your frame tough enough for first?
 

One thing to keep in mind is that dents and dings aren't always a bad thing. They absorb impact energy that could go elsewhere. If your robot is still fuctional consider it good energy management. If your robot was incapacitated. Make it stronger.

Re: Is your frame tough enough for first?
 

we did our robot with an 80/20 frame this year.. the same chassis lasted from NJ to Chesapeake to atlanta. our hardest hit was in atlanta first elimination match our autonomous goes crazy and we hit the wall soo hard the entire wall is moved... the bumpers arent there our robot steering mechanism is toast... turns out the force angled one of the beams so the connecting point to the main chassis went from 90 degrees to say 65-70... neways our robot weighed 130 with bumpers and top speed which is what it hit the wall at was 25fps.

other than that the 80/20 frame has held up very well.

Re: Is your frame tough enough for first?
 

Squirrel from 1726 can attest to the toughness if 1662's frame. We were pretty busted up in 05 & 06. We totally redesigned the frame. We have ran it into a wall at full speed to test it. It passed. Pic is on CD

Re: Is your frame tough enough for FIRST?
 

I'm not sure about force, but at the Pittsburgh regional hitting another robot caused our 1/4 in plexi to shatter into 5 pieces.

Re: Is your frame tough enough for FIRST?
 

oooh, any pics?

Re: Is your frame tough enough for FIRST?
 

Was the "plexi" acrylic or polycabonate (Lexan)?

The reason I ask is that while they look similar, acrylic can shatter like glass, whereas polycarbonate is much stronger and normally it should never shatter (unless you spill Loctite on it). The only "downside" to polycarbonate is that it is more expensive than acrylic.

On both the teams that I mentor, acrylic is almost never used on a FIRST robot with only a few very limited exceptions, as polycarbonate is the preferred "plexi" material.

Re: Is your frame tough enough for FIRST?
 

For the good of the order (since I can't think of any such cases), what are those limited exceptions where acrylic is used? (1618 used it as side panels its rookie year, but wised up quickly following that.)