Robo-Cross B

[UQOnyx]

Woo-hoo, Finally!
Something cool that I have discovered that I wanted to share.
Legos are perfect housing units for servos! Simply lay the servo on its side on a flat lego x x 2 strip, and build around the servo, and make a small box around the servo. For permanency, just glue each lego piece down to the one under it. There you have it, a virtually free servo housing. I will try uploading pictures if I can to help clarify.

[transcience]

Can you use lego mindstorm for Robo Cross.
I have using lego mindstorm for FLL which is like this event where you score mission and it will be cool if i could use lego mindstorm on both competition at the same time,

[mrburrito]

Can you use lego mindstorm for Robo Cross?

As long as there is at least one functional modification, you may.

[UQOnyx]

Need help with a problem I having,
I was building a robot arm, as sort of a preliminary sort of thing to making the robo-cross device, and I love robotics. My problem is that my first servo, the one taking the most weight was moving sluggishly, or not at all, because there was not enough voltage being supplied from the reciever.
Is there a way to add an extra or seperate voltage supply, just for that servo motor? I was thinking that I could simply break the power wire for that specific servo, and just add another battery, but I am pretty sure that would damage the circuit or something else. Any solution?

[iwonder]

Get a bigger battery for the entire system? Or what might be the easier way is to somehow counterbalance the servo so it doesn't have to work as hard. I've used steel weights in the past and they worked pretty well.

[UQOnyx]

I would use a bigger battery, but I am afraid that it would fry my reciever piece because it says it can only take 9.2 volts, and I am already supplying 9 volts.

A counter-balance is a good idea. I think I can use steel springs as counterweights. Maybe when I am actually doing this event, I will buy more powerful servos. Thanks for the advice! Lol, it seems like you always have the answers to my questions, iWonder

[iwonder]

Oh, not larger as in more voltage, larger as in more current (mAh). Be careful to not overvoltage the servos. And more powerful servos are honestly a lot of money and not super useful I've got 2 titanium geared top of the line hitec servos that are insanely powerful, and cost about $100 (if I recall right) and work pretty well, but when I added counterweights, I could use the $40 metal geared and get the same results. Same thing with the big geared down servo I found that has 1700 oz-in of torque to it, with a counterweight a less powerful servo can do the same job. Just keep in mind that if you add weights you need to move everything with slow accel/decel because it's all so heavy and any servos with plastic gears could snap.

[harryk]

Like iWonder said, voltage is not important since the servos have specified voltage that they'll operate with. What's important is current/amperage which, in a simplified view, is a measure of how quickly the battery is discharging its energy. Servos have a maximum current draw which should be stated in the specs of the servo. If your battery cannot meet that limit then your servos will not be functioning at their maximum strength. Though unless your using some monster servos, any decent sized Nimh battery should be plenty.

If you are using larger servos that are drawing many amps of current, then you'll want to use a Y-Harness to protect the receiver. Essentially a Y-Harness is a way to connect the servos directly to the battery to allow high current flow without routing it through the receiver.
Diagram of a Y-Harness

[UQOnyx]

Wait, how would you increase current without increasing voltage?
Currently, my 'battery' is actually a 9V DC Adapter that plugs into a wall, and using all cheap $10 Hitec servos, so I think I might have a problem. How would I increase current, and/or measure current in the servo?

[iwonder]

Well, firstly measure the voltage to the servos when they're running. Major problems with a small current supply are a voltage sag when the servos are under load, so I would check the voltage when you're using the arm and see if it's really 9v. Small wall supplies are typically low current. Also, we're not talking about more current through the servos, we're talking about supplies rated for more current.