Bumper Quick Release With AndyMark Chassis (AM14)

This year I’m looking for our team to use a bumper quick release system for switching bumper colors. This is our team’s 3rd year so we are planning on sticking with the AndyMark chassis. The past two year’s bumper brackets supplied by AndyMark have been time consuming to secure. Last year we almost got booted from a match due to delays in bumper attachment (officials were nice to us).

I’ve read several other posts about bumper quick release on CD and there is a lot of conversation on the hardware used as a quick release (pins, etc) but not on brackets. I’ve prototyped in OnShape using several of the AM brackets for bumpers for the past 3 AM chassis on Home - Mechanical - Building Materials - Bumpers & Accessories - AndyMark, Inc and also standard corner brackets: McMaster-Carr. The problem is really with the AM chassis side rails, the distance between screw holes and the frame perimeter is very narrow, .145in. All of the brackets seem to be supporting a distance of .365. Based on the rules, a gap must not be greater than ¼ in (R33).

The brackets I’ve chosen are technically within the 1/4in limit but too close for comfort. Plus, having a 1/4in gap will result in an unstable bumper anyways.

Pin: McMaster-Carr
Pin Receptical: McMaster-Carr
Bracket: 2018 AM14U3 Front & Corner Bumper Bracket - AndyMark, Inc

Any help or thoughts is appreciated!
Michael

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Primarily, I don’t see how this method constrains the bumpers vertically. That pin has quite a large ‘usable length’.

You’d want to use shorter pins or add a block. Both doable, but maybe not optimal.

@michaellee1019 Look on McMaster for “Toggle Clamps” and see if there’s something there that might help. You’ll want to do a full wrap-around bumper if you can, or at least large sections, but it’s not uncommon for teams to use those to hold their bumpers down, and use the corners of the frame for the rest of the stability.

You could also try putting bolts up through the frame, secure them somehow so they don’t fall out, and use wing nuts to hold the bumpers down.

I like using bolts and nuts that are riveted to the frame personally. Bumpers need to be fixed with some pre load in order to transfer impact forces without knocking around the mount in my opinion.

But if you want to use this design, I recommend you look at quick release pin “receptacles”, which are at least machined to an accurate length.
https://www.mcmaster.com/quick-release-pin-receptacles

[Edit - oops, nevermind. I see you have those in your original post. I was thrown off by the too-long pin.]

i recommend simply designing your own.
our team tends to use a piece of L bracket with a hole for the pin and the pin just goes right through the bracket and the chassis. then your only gap is the thickness of the material. if you do one on the bottom too it remains more stable.

edit; that wasnt meant to be a reply to you nuclear. just hit the wrong reply button

heres kinda what im talking about. obviously take your own dimensions and all. i just hastily threw this together. you can use one really long pin and then just use some hefty screws and attach the L brackets to the wood. we use countersunk bolts to reduce gap. this is roughly how we do it every year. some little things may change depending on yearly rules.

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Another option besides using pins is to use rivnuts. I was fortunate enough to talk to some members of 118 at AZ North and they told me they use rivnuts. Rivnuts would also be quite speedy and they would secure the bumper down harder than using pins. You would use similar brackets to what you show in your cad with the difference being a rivnut being installed in the frame.
Our team plans to use this method as it is quite fast and secures the bumpers quite well since you are essentially bolting them down.
I personally would advise against these pins as they have more play to them. You could use wingnuts but I personally am not a fan of those as they usually stick and out and depending on the game, could get caught on something.

If you would rather avoid the keyholes, the 4 attachment points you have should be plenty, but if you build this make sure you test it’s robustness before it goes into any matches.

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We used push nuts to keep keep our bolts in place a few years ago and it worked pretty well.

I advise against rivnuts for bumper mounts. Wish all those shock shear loads, the rivnuts have a tendency to loosen in the hole. A loose rivnut just hangs onto whatever you screw into it until you can get vise-grips or similar onto the blind side. Not fun at all when you’re changing the bumpers between matches. I haven’t tried PEM nuts yet, but that appears to be a more robust solution.

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We have used Dzus Slide-Snap latches on both the AM kitbot frame as well as on custom tube frames, both with good results. The bushing that the slide latches to mounts quite nicely on the narrow ledge of the AM frame. The slide latches themselves are mounted to a piece of angle attached to the bumper with a hole drilled through to accept the bushing. We use a minimum of two latches per side of the bot.
These latches are available through specialty auto racing sites such as https://www.pegasusautoracing.com/productdetails.asp?RecID=4660
and also through McMaster (for more $$) https://www.mcmaster.com/1872A71.
(Using a continuous wrap-around bumper also helps make this system more secure.)

https://www.chiefdelphi.com/t/exactly-which-type-of-rivets-should-we-be-using/342831/10

Gus, as noted in the above-referenced thread, your experience with rivnuts as a bumper fastener comprises a single installation in which you had 2 failures of the rivnut turning in the frame. Despite this relative lack of experience with rivnuts and their proper installation, you continue to advise against their use in this application. As a counterpoint to your advice, I would offer the following from the more than 10 year history of Team Tators use of rivnuts as a means of attaching bumpers: not one bumper failure.

With respect to PEM nuts, we have used these fasteners for many years as a means of attaching items to sheet metal belly pans etc. PEM nuts (with perhaps one exception) do not provide any clamping force to the materials to which they are installed and are intended for installation in thin sheet metal and other materials. I would not recommend the use of PEM nuts for bumper attachment.

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In 2018 we bolted small 1/4" plates to our frame. These plates then have a 10-32 locking Helicoil in the center. This gives a robust steel thread in a lightweight aluminum part and if the Helicoil strips out or loses its locking feature we can just replace it.

This year we riveted locking, floating nut-plates to the frame which allows for a little misalignment when attaching the bumpers

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I’m going to say that in what I’ve seen, I wouldn’t trust those latches to NOT release at a critical moment.

That said, there’s much to be said for using a lot of them and making sure they’re locked properly every time you take the field. Fewer chances for enough of them to get released to cause an issue.

i second this sentiment. i work for a company where we build custom radiators and oil coolers for racing as well as any other automotive application. and we quite commonly use ¼-20 nutserts (thats what we call them. i assume were referring to the same thing. nut that holds in like a rivet) and we never have issue with nutserts spinning in their hole if the hole is the correct size. and were all aluminum. we’ve had nascar teams dig their car nose first into a wall at 200mph and the whole assembly comes back still intact. utterly destroyed, warped, cracked all over, etc. but the nutserts are still holding strong

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Wow, thanks for all of the great advice! I’ve put together a summary of four ideas based on your feedback. The TLDR is that, in any of the options, neither the prefabricated holes on the sides of the AM chassis nor any of the available AM brackets will work. It will be a challenge for us this year, as we are not yet at the caliber of precise machining, but it is great timing because we are going to purchase a proper machine shop for fabrication. This is only our team’s 3rd season.

Here are the options that I’ve play around with in OnShape. The L brackets have a little bit of transparency to see the whole assembly from one angle.

Option 1: Side Snap Latch
Use a Slide-Snap Draw Latch and a 3/4in L bracket, on both top and bottom of the chassis. Assembly is shown in 2363’s video here.

Option 2: Quick Release Pin with Rectangle Receptacle
Use a Rectangle Receptacle in combination with a quick release pin and a 3/4in L bracket. Would mount on both top and bottom of chassis. As mentioned, there is risk of the pin coming out easily unless something like a locking quick release is used.

Option 3: Quick Release Pin with Threaded Receptacle
Similar to option 2 but uses a [Threaded Receptacle] (McMaster-Carr) instead of a rectangular one and requires a single threaded hole instead of a main bore and two securing screw holes. Uses a different pin too.

Option 4: Attach Rivet to the chassis and secure using screws
Use a rivet nut and secure the bumper brackets, which could be a 1/2 in bracket. And then we could use thumb screws or even knobs

So far, I’m thinking option 1 is best, it provides a true quick (no screws) release option that is easiest to make the bracket absolutely flush to the top of the chassis. It seems one of the more secure options that is quick release and also involves drilling the least into the AM chassis (one hole).

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As I implied earlier, most of the bumper pop-offs I’ve seen this last year were because a slide-latch released. No joke. The ones that weren’t were screws tearing out of the bumper plywood.

Easy ways to minimize the issues:
–use lots of the latches
–use latches pointing in multiple directions
–use 2-piece or 1-piece bumpers, and put slide latches on all sides of each bumper, minimum 1
–Match checklist item: ALL latches are LATCHED (and try to make it easy to see latched/unlatched–red markings visible when unlatched might work well). Check every match.

You’re right about Options 2 and 3, though–enough force and the pin will come out.

option 1 is also the cause of most in season bumpers falling off for me. Yet some teams have success with them.

Once upon a time I used a cotter pin with a zip tie to tie it down and prevent it form backing out.

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I would say that speed is important but having 10 second bumper switches isn’t going to be a game breaker. You usually have around 20 minutes at least between matches which is plenty of time to change your bumpers. It would be more worthwhile imo to use a more robust fastening solution at the cost of a little more time than to have your bumpers potentially fall off.
If doing rivet nuts, you could also just use socket head screws and use a drill or impact to tighten them further increasing the speed.

Here’s a cad mock-up of what 2227 has done for securing our bumpers to the kit bot the past 2 seasons.

We drill our the holes on the outside frame rail to 1/4", put 2 1/4-20 bolts sticking up and secure them with lock nuts, then machine a bracket from 1"x1"x1/8" angle stock to match, those then get mounted to the bumpers. The bumper goes over these bolts and gets secured with regular nuts.

The number of these brackets ranges on how many pieces our bumpers are and mainly by where they are convenient to place. This year’s robot was a 1 piece bumper and had 6 sets of them. We keep an impact driver with a 7/16th socket on our cart and in our pit for quick bumper switches, nuts are normally just spun on by hand then all tightened down with the driver. Can normally be done by a single person in about 2 minutes and in a minute or less with a team of 2. ( assuming adequate practice)

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