Inconsistent stopping

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shrewdPanther46
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Inconsistent stopping

Post by shrewdPanther46 » March 16th, 2018, 5:16 am

Hi guys,
I know I'm double posting, but I think its ok because its on a different thread lol

So our car has a unique issue. Our first run (obviously after sitting at impound for some time) goes about 20 cm under the second run witht he same windings. In other words, our car isn't "warmed up" prior to the first run and it falls about 20cm short of our expected distance every time. And then the second run, if we wind the same way, it goes within 5 cm of target distance.

This only happens during our first run of our practice session, or the first run at competition after our car sits at impound. Afterwards (at practice) our car behaves much more consistently. At states, we wound 20 cm over for the first run and wound up 6 cm slightly in front and far to the right. But that left us clueless for winding/predicting the second run.

We suspect one main issue which we fixed in our new design (which hasn't been properly tested as it skids wayyy too much). We currently stop our wingnut against a 3d printed stopper. The "forks" of the wingnut (NOT the flat side, the opposite side) make contact with the 3d printed part (in two unique spots), and it created holes in it (in two spots, which are hit every time). We filled the holes with CA glue, and thoroughly tested it assuming it was being compressed each time. We feel that the glue filling the holes more or less "expands" or returns to normal after a period of time, and then for our second run (and all future runs at practice) we think the glue is compressed (which is what we intended to happen the entire time) and our wingnut is hitting it and continuing for different distances. This is just our theory.

On our new design, we are braking the FLAT end of the wingnut against a 3d printed part of the same size, and we are hoping the part itself wont compress, and that there would be no holes that require filling.

Suggestions? Advice? Thoughts?


Thank You!!!!!!

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Re: Inconsistent stopping

Post by cheese » March 17th, 2018, 4:59 pm

Yes, I would definitely make sure that you are using the flat part of the wingnut. The pointed end can be very inconsistent depending on the size of your wheel.
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Re: Inconsistent stopping

Post by vb » March 19th, 2018, 4:56 am

shrewdPanther46 wrote:Hi guys,
I know I'm double posting, but I think its ok because its on a different thread lol

So our car has a unique issue. Our first run (obviously after sitting at impound for some time) goes about 20 cm under the second run witht he same windings. In other words, our car isn't "warmed up" prior to the first run and it falls about 20cm short of our expected distance every time. And then the second run, if we wind the same way, it goes within 5 cm of target distance.

This only happens during our first run of our practice session, or the first run at competition after our car sits at impound. Afterwards (at practice) our car behaves much more consistently. At states, we wound 20 cm over for the first run and wound up 6 cm slightly in front and far to the right. But that left us clueless for winding/predicting the second run.

We suspect one main issue which we fixed in our new design (which hasn't been properly tested as it skids wayyy too much). We currently stop our wingnut against a 3d printed stopper. The "forks" of the wingnut (NOT the flat side, the opposite side) make contact with the 3d printed part (in two unique spots), and it created holes in it (in two spots, which are hit every time). We filled the holes with CA glue, and thoroughly tested it assuming it was being compressed each time. We feel that the glue filling the holes more or less "expands" or returns to normal after a period of time, and then for our second run (and all future runs at practice) we think the glue is compressed (which is what we intended to happen the entire time) and our wingnut is hitting it and continuing for different distances. This is just our theory.

On our new design, we are braking the FLAT end of the wingnut against a 3d printed part of the same size, and we are hoping the part itself wont compress, and that there would be no holes that require filling.

Suggestions? Advice? Thoughts?


Thank You!!!!!!
What kind of motor is it?

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Re: Inconsistent stopping

Post by shrewdPanther46 » March 19th, 2018, 5:14 am

a normal brushed motor

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Re: Inconsistent stopping

Post by builder83 » March 19th, 2018, 9:47 am

I think if you gave up even a full second to get your accuracy down to 2 cm or less you would have a good chance at nationals. I suspect somebody will get a 1 cm or less run in. But I do not think it will be a car that runs under 2.5 seconds. I would run a car between 3 and 3.5 seconds and make sure its accurate. (And add the scope!)

Will see what kind of scores come in at state I suppose!

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Re: Inconsistent stopping

Post by shrewdPanther46 » March 19th, 2018, 12:34 pm

It is possible to get <5 cm consistently at very good speeds, but I definitely agree with you that it is best to reduce speed and work on accuracy (which is what my partner and I are doing prepping for nats, even though it kills us to do it)...

But I'm pretty sure there will be one or two cars putting up 1.5 cm or less at below 2.5 seconds....

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Re: Inconsistent stopping

Post by hippo9 » March 19th, 2018, 12:47 pm

Definitely would sacrifice speed for accuracy, but I don't think anything above 5 seconds would be able to be competitive at nats, even if it is <1cm away from the target.
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Re: Inconsistent stopping

Post by shrewdPanther46 » March 19th, 2018, 1:27 pm

Seriously??? A 5 second car which is on the dot puts up -15, which is a very, very, very good score...
It would probably put up double digit negatives which is impressive regardless. I doubt teams out of the top 10 or so would be in the double digit negative range.

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Re: Inconsistent stopping

Post by cheese » March 20th, 2018, 2:01 pm

yeah maybe the first place team will be in the negative teens, and that would probably be mostly luck, where the rest will be in the single digits and negatives
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Re: Inconsistent stopping

Post by windu34 » March 21st, 2018, 6:07 pm

cheese wrote:yeah maybe the first place team will be in the negative teens, and that would probably be mostly luck, where the rest will be in the single digits and negatives
Agreed. I suggest looking at 2016 Electric Vehicle scores as a reference. If getting <2cm at <2s was top 3, than I would predict <5cm and <3s to be top 3 in Battery Buggy. We had encoders and brushless motors and battery packs for EV while battery buggy has no electronics, brushed motors, and AA batteries. I would be surprised to see more than 3-4 double digit negatives.
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