Will this circuit work?

We are working on a control system for the minibot. Would this work? We think we can get enough parts that meet the voltage and amp requirements cheap. Is this a sound concept? Do we need a motor controller in this arrangement?

I don’t see diodes or resistors on the list of allowed components in <R92>.

Will it work? That depends on what you want it to do.

What do you want it to do?

It also depends on what some of the components you’re showing are. The Zener diodes I’m familiar with only have two terminals. Motor controllers usually need a specific kind of signal in order to work.

The more immediate question is not whether it will work, but whether it will be legal. As Joe points out, you’re overstepping the bounds of permitted components.

I am not sure what logic you are trying to implement with the 2 limit switches as input and the 2 motors as output, but you might be able to implement it with just the 2 common house light switches allowed in <R92>.

The motor controller is only necessary if you are going to use the NXT brick to control the motors.

Please, please be careful with the advice you are trying to give rookie teams!!

That entire post is wrong, the Original Poster clearly stated they are working on the minibot which is completely different.

Joe, Alan and Brian are right on the money. Explain what you are trying to do and we’ll see if we can come up with a simpler legal circuit to help you do it.

We are trying to create a minibot with three function modes; off, 100% on and 5% on. We are trying to avoid the need for the motor controllers and the NXT brick for weight reasons. It looks like avoiding the motor controllers is not legal. But we are optimistic that we can create a legal circuit that could help us avoid the use of the NXT brick.

The plan our team is thinking about involves the three modes above.
The off mode would be how the minibot operates for the majority of the 2 minutes.

The 100% mode would turn on as soon as the first limit switch hits the pole. This mode would be the mode that is used to get the minibot to climb the pole.

The 5% mode, our guess at the percentage of power that would need to go to the motors to have zero acceleration thus zero velocity so it can just hold still once it hit the top of the minibot pole. We also talk about a 1 second delay on this mode after the second limit switch comes in contact with the top of pole plate. This would allow us to remove our minibot by hitting a third limit switch not shown here that would put the circuit back to off mode so that we can catch it when it falls.

Thanks for the help


The simple answer is no. Zener diodes have some specific requirements for implementation. Motor operation is one of the biggest areas of confusion on the robot. While voltage is discussed in terms of motor speed, it is the current that is actually making things happen. A a voltage regulator, the zener diodes would need to dissipate huge amounts of power when the motor is not running. As a hint for your team to consider, the minibot does not meed to stay at the top of the post. It merely must hit the target with enough force to trigger the goal, once is enough. Then it can return to earth. I like that your rookies are thinking. Keep asking, this is one of the more interesting questions so far.

Just from reading this, I have a question…

You HAVE to use some sort of motor controller on the minibot?


Lets throw out your first circuit things like diodes and logic circuits are not allowed on the minibot per rule R92

My first question is why are you trying to even have a 5% mode. I gather you think it is required to keep the minibot at the top after you make contact with the scoring disc. This is not a requirement.
Or does this 5% mode keep the robot on the pole like you are using one of the motors to grasp around the pole?? However if I am inferring correctly I dont think this is the case. So I really believe you can throw this 5% mode out the “design window”.

In this case here is my reccomendation. Limit switch in series with the battery and circuit. It is in its normally open position. When the minibot makes contact with the pole it closes the switch initiating your entire circuit.

Additionally you have a normal light switch somewhere at the top of the minibot with a little plate or finger of some sort pointing up. This switch is in its normal on/closed position and is in series with your motors.

As your robot climbs the pole this finger makes contact with plate setting of the scoring system and simutaneously moving the switch to the off position. This cuts the power to your motors. If you are worrying about the minibot not coming back down and not being able to get at it. I would recommend hooking the switches’ off position in such a manner as to shunt the motors. This should get them to back drive when power is cut and the robot will “coast” back to the ground.

NO NXT or speed controllers.

If you use the NXT brick then you must use the motor controller since the brick does not control Tetrix motors directly.

Does any one know if 3-way light switches are legal for Minibot use? They seem common (ubiquitous) to me. Could be a good Q&A.

If 3-way switches are legal and you still want the minibot to hold at the top of the pole, there is a way (think about speed controller “Brake Mode”).

My question is where do you find a limit switch that carries 14 amps of current?

Light switches were defined by the Q&A
"For the purposes of the 2011 competition, a common household light switch is any electrical switch that would normally be mounted in a wall outlet box with household wiring, typically available at a home supply center (e.g. Lowes or Home Depot).

Minor modifications of the switch (e.g. removing the mounting tabs) are permitted, as long as the basic structural integrity and overall safety of the switch are not compromised. "

Three way and four way switches would fit this description.


Grainger-they sell all types and flavors that can handle much more then your required 14 amp. Where is that number coming from btw? Our motors are not approaching anywhere near that much current.

I saw in one post the stall current of one motor was 7 amps. Since both on start would be stalled . The switch would have to handle that much if it was to survive long I think. Of course how many times does it have to climb the pole. Then again if you make it to the finals that could be a bummer if it failed that last time.::ouch::

Thanks agian for the knowledge folks

Here is our updated plan. Lets see if we understood the feedback correctly.

If the devices you are using are in compliance with <R92>, you should be all set. That being said, I’m not sure that they are…

That looks good to me.

Switch one is normally open

Switch two is normally closed

I think that will work well. Motors in Parallel??? I mean sure why not harder to physically wire but sure…for this application series will be work just fine

That’s not correct at all. Motors in series would get approximately half the voltage and spin half as fast. In a Minibot race you really don’t want to do that (for the way up at least).

Yes the voltage drop across them would be cut in half…Yes right DUH…Sometimes I loss my head