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Unread 28-03-2011, 17:24
Ian McShane Ian McShane is offline
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Homemade resitor

We made a homemade resitor that is basically a wad of 18 gague wire. i am assuming that is legal on the minibot. Is it?
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Unread 28-03-2011, 17:49
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Re: Homemade resitor

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02-16-2011, 07:38 PM
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Mini Bot Resistor
May we use an electrical resistor on the mini bot? It would be in line with a switch?

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02-21-2011, 09:43 PM
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Re: Mini Bot Resistor
Resistors are not permitted per Rule <R92>.
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Unread 28-03-2011, 17:53
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Re: Homemade resitor

c-parent, it's made of a lot of wire and nothing else. Wire is legal, per <R92-O>.

I'm torn on this--it would depend a lot on how the wire was configured. I also can't give an official answer (nobody on here can, except maybe one or two). I'm going to say that the inspectors at your event will tell you whether it is legal or not.

What are you using it for? There may be other options.
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Unread 28-03-2011, 17:54
Jim Wilks Jim Wilks is offline
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Re: Homemade resitor

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Originally Posted by Ian McShane View Post
We made a homemade resitor that is basically a wad of 18 gague wire. i am assuming that is legal on the minibot. Is it?
There's no need for a resistor on the minibot. It just makes it heavier and adds no value.
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Unread 28-03-2011, 17:57
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Re: Homemade resitor

I hear you Eric, but the answer was so cut and dry, I would be concerned about being snagged on it at a competition. Just my opinion. I guess posing the homemade resistor on Q&A would be worthwhile.
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Unread 28-03-2011, 17:59
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Re: Homemade resitor

The resistor if I am interpreting R92 right would be banned. The usage of the term electrical hook-up wire implies wire may only be used for this purpose.
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Unread 28-03-2011, 18:07
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Re: Homemade resitor

I could argue that point.

I have a 6" connection. I connect the two points with 10' of wire. Is it still being connected? Absolutely. Is there a lot more resistance than if I only used 6" of wire? Yep.

<R92> does not say that you can't make some other part out of the stuff in it. For example, I could use the rubber bands and surgical tubing to make a nice powerful torsion spring to store energy for latching on to the pole. Is it legal, despite springs not being on the list? Yep. (Now, if I powered vertical motion with it, then I'm illegal under a different rule.)

So, if I can take the 18-gauge wire, connect one end to one connection, connect the other end to the other connection, and bundle the rest safely in the middle (using legal material for the bundling), I just made a resistor out of 100% legal material. The resistor should be legal.

However, again, I am not a source of official answers. The Q&A is, and the inspectors at your event are. If you would like to say what the resistor is used for, then there may be other ways to do that that are clearer with respect to the rules.
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Unread 28-03-2011, 23:31
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Re: Homemade resitor

It is likely that it would pass inspection. But again the question is why you want a resistor on the minibot? It serves no purpose other than to slow you down with the additional weight and I can't believe you have enough resistance in your wad of 18ga wire to make a significant difference.

As has been discussed here many times putting the motor in "brake" mode via shunting it's terminals together is very effective. If your minibot doesn't back drive after it's collision with the trigger then a 4 way switch can be used to put one motor in "brake" mode while having the other drive reverse.
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Unread 29-03-2011, 00:29
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Re: Homemade resitor

About two weeks ago we experimented with switching a 4 ohm resistance in series with the two motors in parallel. A lamp switch was in parallel with the resisitor. When the switch hit the top plate of the tower it opened and placed the resistance in the circuit. The minbot came back down the tower better than with back emf. Because of all the hub bub about light switches and resistors, we opted to use limit switches and back emf.
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Unread 29-03-2011, 07:50
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Re: Homemade resitor

Ian,
Hookup wire is legal for use on the minibot just as in the robot in unlimited quantity. As long as it not used to modify the motors to gain an advantage in the upward vertical movement of the minibot, there is no rule that prevents it. I would pass it as a legal minibot.
Nov8r, I can't see how a 4 ohm resistor would give better control than just a short on the motors. Realistically, it would/should descend much faster with the resistor.
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Unread 29-03-2011, 17:20
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Re: Homemade resitor

Al, with the 4 ohm resistor in the circuit the motors no longer had enough power to climb the pole. We initially tested the concept with a variable resistor. Values as high as 10 ohms resulted in decents almost like free fall. Values less than 4 ohms really decented very slowly but would over heat the motors. Btw, we had a switch that shut off all power when the minibot hit the base. It was an interesting experiment but all of our current minis use back emf.
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Unread 29-03-2011, 17:47
Ian McShane Ian McShane is offline
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Re: Homemade resitor

We are plaaning on using it to slow the robot down for the decent. not for the ride up.
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Unread 29-03-2011, 22:07
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Re: Homemade resitor

Quote:
Originally Posted by Ian McShane View Post
We are plaaning on using it to slow the robot down for the decent. not for the ride up.
Are you powering down? If so then yes a resistor will slow your decent. If you are using dynamic braking ie shorting the motor leads together then adding a resistor to the circuit will speed you up as noted in the post above if put high enough resistance in the circuit it will be the same as free fall.
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Unread 29-03-2011, 22:23
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Re: Homemade resitor

Chuck,
So you were inserting the 4 ohms into the power leads of the motors after you reversed the voltage? The braking action of the motors unpowered is sufficient to get the minibot to descend without damage.
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Unread 29-03-2011, 23:45
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Re: Homemade resitor

Al, we never reversed the voltage to the motors. We simply added additional resistance in the circuit to reduce power. The reduced power wasn't enough for the minibot to maintain position on the pole and it would decend. Yes, shorting the motor leads (what we are now doing) is working well also.
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