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?

Re: Homemade resitor
 

#1
02-16-2011, 07:38 PM
2011FRC0292
Junior Member

Join Date: Dec 2010
Posts: 2
Mini Bot Resistor
May we use an electrical resistor on the mini bot? It would be in line with a switch?

#2
02-21-2011, 09:43 PM
GDC
Game Design Committee

Join Date: Jan 2006
Posts: 2,770
Re: Mini Bot Resistor
Resistors are not permitted per Rule <R92>.

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.

Re: Homemade resitor
 

There's no need for a resistor on the minibot. It just makes it heavier and adds no value.

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.

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.

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.

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.

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.

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.

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.

Re: Homemade resitor
 

We are plaaning on using it to slow the robot down for the decent. not for the ride up.

Re: Homemade resitor
 

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.

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.

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.

Re: Homemade resitor
 

I would agree. Any wire, 6 inches or 10' has some resistance. So, I cannot see how a 10' piece could be disqualified. But your point is taken on being up to the the event inspectors. In 2009, our front bumpers failed inspection at the championship, because the plywood backing inside was a half inch shorter than the minimum, even though the bumpers themselves were technically the correct length, and they had previously passed inspection at the regional. In the end it came down the the inspector's interpretation of the rules, even though there was no rule that specifically said the internal backing material had to be a specific length.

Re: Homemade resitor
 

Well that explains why you were heating the motors up, I'm surprised you didn't burn them up back driving a powered motor.

Re: Homemade resitor
 

I would agree. Any wire, 6 inches or 10' has some resistance. So, I cannot see how a 10' piece could be disqualified. But your point is taken on being up to the the event inspectors. In 2009, our front bumpers failed inspection at the championship, because the plywood backing inside was a half inch shorter than the minimum, even though the bumpers themselves were technically the correct length, and they had previously passed inspection at the regional. In the end it came down the the inspector's interpretation of the rules, even though there was no rule that specifically said the internal backing material had to be a specific length.

Re: Homemade resitor
 

What type of 4 way switch are you using? Is it a light switch? I took the term "Standard Light Switch" to mean a single pole single throw switch. Does a 2-way or 3-way switch qualify as a standard light switch?

Re: Homemade resitor
 

In that anecdote, it didn't come down to some inspector's arbitrary interpretation. That was the rule as originally written, immediately clarified by the GDC in the Q&A (below), and reemphasized in Team Update #2

Re: Homemade resitor
 

Well our robot does back drive so we aren't using a 4 way. Unfortunately the rules changed a couple of times so there is lots of confusion over this issue. So they do allow pretty much any sw designed for wall box mounting to 2-way, the most common sw, as well as 3 and 4-way switches are legal.
To cloud things even more household wiring sw terminology is different from other types of wiring terminology. Basicallly in household switches the # before the -way refers to the number of terminals.


To wire it to provide "reverse" to one motor and brake to the other:

A 4-way switch has 2 black color and 2 brass color terminals, so we'll call them bl1, bl2, br1, and br2. Connect B+ to bl1 and B- to bl2. Connect forward + for motor a and b to br1 connect motor forward - for motor a to br 2 and motor forward - to bl2.

In sw position 1 terminal bl1 is connected to br1 and bl2 is connected to br2. Flip the sw to position 2 and bl1 connects to br2 and bl2 connects to br1. So in 1 position both motors are powered forward and in the other position motor a is powered reversed and both motor b leads are connected together which just so happens to be also connected to battery - which plays no part in that circuit. both of the brake motor leads could just as well be connected to battery +, and it would still work the same.

However to have a minibot that doesn't back drive it needs to have a high effective gear reduction and be very light.

Re: Homemade resitor
 

Chuck,
Now I see. Interesting idea. I haven't heard of anyone doing that so I was having a hard time understanding your description.

Re: Homemade resitor
 

What does your minibot weigh? :) :)

Re: Homemade resitor
 

~3.1 lbs