Tracked test bed in the house, Snow outside, what else could I do?

[Burf2000]

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Prototype at the moment but thought I would share. This thing is nearly a meter square!

Edited December 22, 2009 by Burf2000

[Milan]

That thing is enormous!

Is this part of your T1 project?

[Burf2000]

Yup however its becoming a T1 / Johnny 5 hybrid becuase T1 has no arms, lol. It lego is powerful enought it going to be big

[Milan]

You know, thats how the Skynet started, and we all know what happened next...

Really, do you have all the parts ready, or you are going to buy them as the projects rolls on?

I mean, just look how much empty space is there!

I do not know it those XL motors are going to be strong enough to overcome forces caused by weight and friction.

[Jetro]

Looking great. Held my breath when I saw those long leads nearly touch the snow though. Not sure how well the PF system would respond to it causing a short circuit...

[Burf2000]

Looking great. Held my breath when I saw those long leads nearly touch the snow though. Not sure how well the PF system would respond to it causing a short circuit...

All the stuff has been dried and the motors and PF stuff was kept away from it. But yeah see your point (doh!), you can tell it was the wiring was knocked up for the video

To answer the other questions

Some lovely Brickish members have been helping me out a little with pnematics, technic pins, liftarms, track etc. I also have quite a lego collection. I think the things I will be a little short of are technic beams (George the robot might have to be broken up) and large black plate.

However I am sure a solution will present its self

As for the PF XL motor, If 1 does not do it per side, then I put 2 per side and so on! Its not even geared yet!

[Jetro]

Just keep in mind that you cannot run more than 2 XL motors from a single battery box. If you run 2XL plus anything else the safety will kick in and the thing won't move.

[Burf2000]

I did not know that, even on the rechargable pack?

[Jetro]

The limitation is in the battery pack (but not in the RC battery pack) and in the PF IR-receivers.

[Burf2000]

Thanks mate, So I could run 2 recievers off the rechargable battery on the same channel and drive 4 xl motors for a short period

[DLuders]

The limitation is in the battery pack (but not in the RC battery pack) and in the PF IR-receivers.

Check out Philo's excellent Power Functions information at http://philohome.com/pf/pf.htm . He does not show the Power Functions RECHARGEABLE Battery Pack, but he has good information about the CURRENT DRAW of the various motors. I use 2450 mAH rechargeable AA batteries in my regular Power Functions battery box, and yes it seems that it's the PF RECEIVER that is the limiting factor. So, more motors --> more battery packs --> more weight (a vicious cycle).

[Burf2000]

Yeha I had seen that before but still cant see the bit where it says the Ir Reciever handles only 2 motors

I think I might have 2 of the new recievers too but not really worked out what I can do with the new functionality

[Fistach]

Yeha I had seen that before but still cant see the bit where it says the Ir Reciever handles only 2 motors

I think I might have 2 of the new recievers too but not really worked out what I can do with the new functionality

The problem is not with Infrared receivers but with maximum current allowed by battery box. The current is higher the more motors are used. But it also depends on load. The higher the load under which motors are used is the higher the current is. Rechargeable battery box has the top limit of current at which it interrupts the power to the electric circle (by switching itself off). So you may use 4, 6, 9 motors simultaneously or just one to exceed this limit.

Edited December 24, 2009 by Intact

[Brickthus]

The problem is not with Infrared receivers but with maximum current allowed by battery box. The current is higher the more motors are used. But it also depends on load. The higher the load under which motors are used is the higher the current is. Rechargeable battery box has the top limit of current at which it interrupts the power to the electric circle (by switching itself off). So you may use 4, 6, 9 motors simultaneously or just one to exceed this limit.

I exceeded the LiPo battery current limit with two 8866 train motors (though 9V train motors were fine with the same load)!

The battery box can supply about 800mA and an XL motor can draw as much as 1.5A. An IR receiver is limited to 1A.

Since the LiPo battery box is light, having one per motor would be OK for weight if you could afford it.

4x battery box, receiver and XL motor = £246!

AA battery boxes adding weight might not be a problem for a tracked chassis (more grip is good), unless you were driving it on an icy pond!

It would be possible to add a greater power system, still controlled by the IR receiver. I have used a circuit to read the motor output of a receiver and convert it to a sensor voltage for the WeDo system, so a similar a circuit could drive a power H-bridge instead of generating the sensor voltage, and could use a set of RC car NiCds (or NiMH or Li-ion cells) and a few RC car motors for serious power!

Mark

[CP5670]

It would be interesting to test the current limits of the various Lego power sources. I think the highest limits might have been on the 8475 RC buggy's receiver, as it uses two 5292 motors on one output that can each draw over 3A on load.

I recently found that the original 1990 control center has very strict current limits and can't even start up a single, unloaded XL motor. The later 1995 control center has higher limits and works well with a single XL or 5292 on each output. The RCX has a 500mA limit per output and reportedly has trouble with these motors, and we know that the PF battery box can handle two XLs on its single output. Not sure what the 9V speed regulator or the NXT are like.

Edited December 25, 2009 by CP5670

[Burf2000]

I was amazed to fine out Lego put cut off switches on these things in the first place

The rechargable battery seems to do fine with 2 xl motors. I was going to use the RC car base (the one that take 6 aa batteries and drives 2 5292 motors plus a stearing unit) however because it needed to drive 2 of the motors at the same time plus the stearing unit to make it turn (i wired up 4 Polarity switchs so that turning left and forward on the RC control would drive 2 XL motors in opposite directions, and just forward on the control would drive 2 motors forward) just lost sooo much power (not a suprise really). So I had to come back to PF. I now just got some bluetooth stuff going so it might be come a NXT/PF hybrid)

Merry Xmas