Counting Rotations

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MadCow2357
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Re: Counting Rotations

Post by MadCow2357 » March 9th, 2019, 12:59 pm

mtownley wrote: It was a rotary counter with a max of 350rpm. I'm curious why a 350 wouldn't work for counting since when you are winding the wheel, you are not rotating it at 1030rpm. As it unwinds, it obviously can't keep up with 1030rpm, but it wouldn't matter b/c the counter doesn't have anything to do with stopping the motor. We just reset the counter to 0 after each run and rewind. Maybe there's something I'm missing? Our season is over. My son's car got first in Regionals, but he won't be going to State in the event.
I'd like to use a mechanical counter, but because the motor and braking system are on the same axle, the only way I can wind is by reversing the motor current the opposite way. Like, I have to turn the motor on to wind for braking. I don't think I would mount the counter on my vehicle either, since it would add significant width to my vehicle. And kudos to your son for getting first!
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Re: Counting Rotations

Post by shrewdPanther46 » March 9th, 2019, 4:31 pm

MadCow2357 wrote:
mtownley wrote: It was a rotary counter with a max of 350rpm. I'm curious why a 350 wouldn't work for counting since when you are winding the wheel, you are not rotating it at 1030rpm. As it unwinds, it obviously can't keep up with 1030rpm, but it wouldn't matter b/c the counter doesn't have anything to do with stopping the motor. We just reset the counter to 0 after each run and rewind. Maybe there's something I'm missing? Our season is over. My son's car got first in Regionals, but he won't be going to State in the event.
I'd like to use a mechanical counter, but because the motor and braking system are on the same axle, the only way I can wind is by reversing the motor current the opposite way. Like, I have to turn the motor on to wind for braking. I don't think I would mount the counter on my vehicle either, since it would add significant width to my vehicle. And kudos to your son for getting first!
why is that the only way you can wind what stops you from just turning the wheel mechanically

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Re: Counting Rotations

Post by MadCow2357 » March 9th, 2019, 6:27 pm

shrewdPanther46 wrote: why is that the only way you can wind what stops you from just turning the wheel mechanically
Because of the motor's internal electromagnets (I think that's what they are referred to), it makes turning the wheel much harder - in fact, this was very important in my buggy's braking last year (regenerative braking?). While turning the wheels manually is possible, it would:
1. Be a pain, and my hands would fall off after continued testing.
2. The duration of the time needed to wind it manually could possibly make us go over the 8 minutes of run time, which would definitely not be a good thing.
Sad thing is, I cannot even put the motor on my other axle to allow for manual winding, at least in this current configuration.
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Re: Counting Rotations

Post by Tendan » March 9th, 2019, 8:07 pm

MadCow2357 wrote: Because of the motor's internal electromagnets (I think that's what they are referred to), it makes turning the wheel much harder - in fact, this was very important in my buggy's braking last year (regenerative braking?). While turning the wheels manually is possible, it would:
1. Be a pain, and my hands would fall off after continued testing.
2. The duration of the time needed to wind it manually could possibly make us go over the 8 minutes of run time, which would definitely not be a good thing.
Sad thing is, I cannot even put the motor on my other axle to allow for manual winding, at least in this current configuration.
If the motor is restisting rotation because of the electromagnets, it is probably being short circuited. This could be caused by the braking system you were referring to (an eddy current brake). If you are using an eddy brake again, disengaging the brake should be all you have to do to get it to rotate pretty freely.
If the motor isn’t being shorted, the problem is more likely high inertia and/or high friction in the motor or other parts of the buggy. You could try and fix this in a few ways, including:
1. Replacing the problem part(s). If the part you replace is the motor, your buggy might be able to accelerate faster, since the motor won’t have to overcome as much inertia before moving.
2. Disconnect the motor from the axle. If you are using a coupler with set screws, you could loosen the set screws and make you distance setting with the motor disconnected. Then retighten the set screws before the run. This might not work, depending on your configuration.
I hope this helped. Good luck with your buggy!
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Re: Counting Rotations

Post by shrewdPanther46 » March 9th, 2019, 8:36 pm

Tendan wrote:
MadCow2357 wrote: Because of the motor's internal electromagnets (I think that's what they are referred to), it makes turning the wheel much harder - in fact, this was very important in my buggy's braking last year (regenerative braking?). While turning the wheels manually is possible, it would:
1. Be a pain, and my hands would fall off after continued testing.
2. The duration of the time needed to wind it manually could possibly make us go over the 8 minutes of run time, which would definitely not be a good thing.
Sad thing is, I cannot even put the motor on my other axle to allow for manual winding, at least in this current configuration.
If the motor is restisting rotation because of the electromagnets, it is probably being short circuited. This could be caused by the braking system you were referring to (an eddy current brake). If you are using an eddy brake again, disengaging the brake should be all you have to do to get it to rotate pretty freely.
If the motor isn’t being shorted, the problem is more likely high inertia and/or high friction in the motor or other parts of the buggy. You could try and fix this in a few ways, including:
1. Replacing the problem part(s). If the part you replace is the motor, your buggy might be able to accelerate faster, since the motor won’t have to overcome as much inertia before moving.
2. Disconnect the motor from the axle. If you are using a coupler with set screws, you could loosen the set screws and make you distance setting with the motor disconnected. Then retighten the set screws before the run. This might not work, depending on your configuration.
I hope this helped. Good luck with your buggy!
Your brakes should only engage when your limit switch is closed... there is no reason for turning the wheel to become more difficult. you are probably wiring incorrectly or something as Tendan mentioned if you really are having issues turning the wheel...

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Re: Counting Rotations

Post by MadCow2357 » March 9th, 2019, 8:51 pm

Tendan wrote: If the motor is restisting rotation because of the electromagnets, it is probably being short circuited. This could be caused by the braking system you were referring to (an eddy current brake). If you are using an eddy brake again, disengaging the brake should be all you have to do to get it to rotate pretty freely.
If the motor isn’t being shorted, the problem is more likely high inertia and/or high friction in the motor or other parts of the buggy. You could try and fix this in a few ways, including:
1. Replacing the problem part(s). If the part you replace is the motor, your buggy might be able to accelerate faster, since the motor won’t have to overcome as much inertia before moving.
2. Disconnect the motor from the axle. If you are using a coupler with set screws, you could loosen the set screws and make you distance setting with the motor disconnected. Then retighten the set screws before the run. This might not work, depending on your configuration.
I hope this helped. Good luck with your buggy!
I don't think it's an issue of short circuiting or problematic parts - I believe my motor was made that way. According to the website, it has a stall torque of 44 ounces per inch. I'm guessing that it is the reason why I cannot rotate my motor freely. I'll look into motors that have less stall torque, which should function you as described - rotating easily and freely.

The latter of your suggestions won't work in my current configruation, lol.
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Re: Counting Rotations

Post by MadCow2357 » March 9th, 2019, 8:53 pm

(double post - mods please delete)
Last edited by MadCow2357 on March 13th, 2019, 2:00 pm, edited 1 time in total.
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Re: Counting Rotations

Post by invisiblebanana » March 13th, 2019, 12:42 pm

Has anyone calculated the distance that the vehicle would travel for each of the possible target distances?
Or do you just roll the vehicle over the arc during testing and count the rotations then?
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Re: Counting Rotations

Post by MadCow2357 » March 13th, 2019, 1:58 pm

invisiblebanana wrote:Has anyone calculated the distance that the vehicle would travel for each of the possible target distances?
Or do you just roll the vehicle over the arc during testing and count the rotations then?
I would advise against trying to use those distances to calculate your brake setting, since the other factors that can affect your run are numerous and sometimes impossible to predict without extensive testing. It would be easier to test a lot, and base your wheel setting on previous data than use an equation to find the optimal brake setting for every distance.
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Re: Counting Rotations

Post by LittleMissNyan » March 13th, 2019, 2:55 pm

MadCow2357 wrote:
invisiblebanana wrote:Has anyone calculated the distance that the vehicle would travel for each of the possible target distances?
Or do you just roll the vehicle over the arc during testing and count the rotations then?
I would advise against trying to use those distances to calculate your brake setting, since the other factors that can affect your run are numerous and sometimes impossible to predict without extensive testing. It would be easier to test a lot, and base your wheel setting on previous data than use an equation to find the optimal brake setting for every distance.
So I don't know if your Battery Buggies will work like this, but what we do is we set the Battery Buggy at where we want to finish, put a piece of tape on the wheel, and roll the Battery Buggy backwards to the starting line we have, counting the rotations of tape. It makes for a pretty good estimate.
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