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Alex P. HASD Bots
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PostSubject: beater speed   Mon Apr 04, 2011 4:45 pm

I am working on our bots weaon drive train system and had a few questions. We are using a beater for a weapon with a 5 mm pitch belt. Our front pulley attatched to the weapon is two inch and our back pulley is .815 inch, and our weapon motor is going at46200 rpm. after doing some calculations i found that our overall weapon speed is roughly 19815 rpm. To me this seems like a good weapon speed for a beater, however my teammate believes that we need to be at least going 25000 rpm for our weapon to be considered affective. I understand the theory that the faster weapon head to head will most likely win, However i also feel that there is a point where fast is to fast and an almost impenitrible wall is formed where you end up not get any bite what so ever. what is your opinion on an effective beater speed. Very Happy
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Cody
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PostSubject: Re: beater speed   Mon Apr 04, 2011 5:37 pm

After drag and friction and blah blah blah your probably only at 12-15k tops.
Another important part is the weight of the beater. You can spin something to the moon but it doesnt mean it'll be effective
We've tacked our weapons, although they all use different rated motors the average somewhere between 18k-22k rpm with Atomic Shock and Shocker being exceptions

Personally I just look at it all as numbers that dont mean anything, its the hits that it puts out that you should look at compared to what you would like

O and dont forget your gyro forces
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Mon Apr 04, 2011 6:09 pm

So basically if your trying to make the weapon spin really really fast, chances are your not going to have any butt behind your hit, where as if your going a little slower your weapon will be able to expend its stored up energy quicker and better than high speed. For example i was looking in rio botz and found that their weapon for their mini class is only going 13,000 rpm and yet they are putting up some osm hits. overall do you think we should stick with the speed we have or try to pump it up to about 23000 rpm Laughing
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Mon Apr 04, 2011 6:10 pm

Theoretically not pratically
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Don Doerfler
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PostSubject: Re: beater speed   Mon Apr 04, 2011 7:05 pm

1 what is the Kv rating on your weapon motor
2 how many volts r in your bot
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Mon Apr 04, 2011 7:16 pm

3500 kv and 13.2 into that motor with about a 3.5 to 4 lb beater
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PostSubject: Re: beater speed   Mon Apr 04, 2011 8:55 pm

dont think you had to call him a noob alex. although hes right if its too fast youll just be brushing other bots back instead of making contact.
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PostSubject: Re: beater speed   Mon Apr 04, 2011 10:15 pm

gear it down to 12k. lets face it this on paper numbers look good, in the real world you only going to hit about 14k with perfect conditions with a beater even if you numbers say 25. so if you gear for 12 you will be putting very little stress on the motor and your spin-up will be instant and should have enough torque to spin even agents a wall. where as if you aimed for 25 your spin up will be horrendous and your weapon will have so little torque that that any well built wedge will bring it to a dead stop without even having to take you to a wall.

what it comes down to is a peak efficient equation and the curve just about dead stops at 12k

-Kyle
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Mon Apr 04, 2011 10:27 pm

Thanks for all the input. ill be sure to put it into effect
As far as being a noob- Im learnin and thats why im on here
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PostSubject: Re: beater speed   Tue Apr 05, 2011 8:05 am

Gearing a 4 pound beater to run that fast might cause the motor to draw a LOT of amps...perhaps more than your battery pack can supply....

What motor, esc and battery pack are you using? It sounds a bit ambitious....perhaps

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Alex P. HASD Bots
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PostSubject: Re: beater speed   Tue Apr 05, 2011 3:00 pm

Velineon 3500 kv- traxxas , jeti 70 amp speed control, and 13.2 volt a123 battery 1100 mamh
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Cody
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PostSubject: Re: beater speed   Tue Apr 05, 2011 3:45 pm

hard hitter wrote:
Velineon 3500 kv- traxxas , jeti 70 amp speed control, and 13.2 volt a123 battery 1100 mamh

Yeahhhhh your batteries definitly aren't going to last 3 minutes. I had a 15lb wedge design that used the A123 18650 cells. Even 2.3 Ah is hardly enough for a weaponed bot
Thats actually a pretty small motor to be using in a 15lb bot. I'm honestly suprised it spins your weapon, how long is your spin up time
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Tue Apr 05, 2011 5:24 pm

about 3.5 to 4 seconds
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Tue Apr 05, 2011 5:27 pm

instead what battery would you recommend because i know more of the mechanical aspect and less of the electronic aspect, and can you explain what the 1100 mamh means and what all of that stuff about batteries means
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PostSubject: Re: beater speed   Tue Apr 05, 2011 5:55 pm

... im going to assume that by mamh you mean MAH which stands for milliamp hour

that means your batteries has the ability to supply a current of 1100 milliamperes(or 1.1 amps) for an hour
this number can be played around with, depending on the discharge rating you battery could supply a current of 66amperes for a single minute this may or may not be enough power both the weapon and the drive.

My beater has a similar problem, so we tend not to use the drive motors while spinning up

so far the best battery's I have seen in terms of weight and capacity are the larger 123 cells found in dewalt drills.



Last edited by jeeves_m_d on Tue Apr 05, 2011 6:04 pm; edited 1 time in total
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Cody
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PostSubject: Re: beater speed   Tue Apr 05, 2011 6:00 pm

Right now your using the a123 18650 cell. These are the same battery I was planning on using in my wedge that I started to build because of the smaller size. But with the smaller size comes a lesser capacity (1.1 Ah)
A better cell to use is the a123 26650 cell. This cell has the same voltage as the 18650 (3.3v) but its capacity is 2.3 Ah. Unfortunatly these a fair bit bigger then the 18650 cell.
Ah stands for Amp Hours which is the storage capacity of the battery (amount of time to drain the battery). The tentacle torque-amp calculator is a great tool when it comes to figuring this out.
Using that you can find out how much your drive should use on its on.
To figure out how many Ah your weapon uses is a little tricky but you can multiply your average amperage drawn by the motor times how long it'll be drawn, for example 65 amps x 3 minutes(.05 hours) is about 3.8 Ah

I think lol
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Alex P. HASD Bots
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PostSubject: Re: beater speed   Tue Apr 05, 2011 7:47 pm

Thanks that clears some stuff up afro
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