My Pseudo9398 Crawler

[Hopey]

Hiya. I like the look of the 9398, but I don't have one. I do, however have an 8110 Unimog, an 8043 excavator and an 8109 flatbed. So I decided to see how close I could get.

Obviously there's quite a few significant parts that I was missing. For the tyres, obviously I used the Unimog tyres. And of course the colours are completely different.

No L motors, so I used two M motors on each axle. This meant widening the top of the structure a bit, but the shocks could still attach pretty much the same way. I also only had 2 of the 6L link, rather than the 4 required to prevent the axles moving sideways. I experimented with various solutions to this, including using universal joints or some bionicle parts I had lying around, but ended up just using panhard rods as in the unimog. Not great, but it does the job.

I also changed the gearing a bit, simply because I didn't think I had enough 12t and 20t double bevel gears (although maybe I did after all). I replaced the last 12:20 - 12:20 before the wheels with 16:16 and 8:24 (the latter in the portal hubs), changing this part of the gearing from 0.36:1 to 0.33:1. After watching Sariel's videos, I also decided to replace the diffs with knob wheels.

No servo motor for the steering, so I used a single M motor. I experimented with a return-to-centre steering system using rubber bands attached to a 3L crossblock on the steering axle(hence the extra space on the end of the axle in the above photo) but this really didn't work out. I also only had a 7L space in which to fit the motor and a gear on the end, which demostrates the problem with the placing of the pin holes on the M motor. It's held in place primarily by the two 2x2 plate-with-axle-hole underneath it, which are braced on the side by two 6L half-width beams. The axle joiners on either side are to prevent it moving sideways; note the bend in the axles on the one that is rotated so that grey pin-with-stud holds it in place. From above, the battery pack kind of holds it down. The second picture shows how the 2x2 plates are braced sideways (this was an earlier attempt with 7L half-beams, which I changed to 6L when I swapped the gears around)

The ubiquitous underside shot. The end that's cropped off is pretty much the same, as in the real one.

To be honest, I was more interesting in replicating the chassis than the body. My first attempt was to match the various panels and fairings as closely as I could, and I aimed for a colour scheme where it was yellow at the front, orange in the middle, and red at the back, but it looked hideous. I really didn't want it to be yellow, but didn't really have any other option. I got a bit creative with the doors and the sides of the bonnet, as I didn't have anything that remotely matched the fairings. I also got around the need for the new right-angled connector piece with some crossblocks. I also put some extra lights on to make it look pretty, although one of them got knocked over when I was testing it out just before I took the photos. It's still pretty ugly, but better than I expected it to look.

As for performance, well, It's pretty bad, although I'm fairly sure this is because of the crappy batteries that I'm using (prompting this thread). The steering seems very heavy, and the driving slows noticeably when the steering is applied. Trying to climb onto a 10cm or so tall cushion, which shouldn't be too difficult, it can get the front wheels up no problem, but stalls trying to get the back wheels up. Then it falls over, usually. There's no gears clicking though, so I think I've built it tough enough, and hopefully the lack of torque is because of the dud batteries, and not the crappiness of the M motors.

I'm also not sure if you're supposed to try and drive 5 M motors from a single battery pack and IR receiver, especially with 4 of them on one channel.

The next step is to try and gear it down a bit and see if it goes any better.

If anyone's interested, I can take some photos when I dismantle it to show how it's put together.

[DLuders]

I like how you used your available parts for your Pseudo 9398 Crawler. The Power Functions M-motors just do not have the required torque to get a large model like this over large obstacles. The extra set of M-motors adds to the weight (which affects performance). If you get your voltage up, it may help.

According to the answers to Frequently-Asked Questions on the official Power Functions (PF) website, it is not advised to run 5 ea. PF M-motors on one PF battery:

"1. How many Power Functions Motors can I drive from one Power Functions Battery Box?"

"As a rule of thumb, you can drive 2 Power Functions XL-Motors, 3 Power Functions Train Motors or 4 Power Functions M-Motors at the same time from one Power Functions Battery Box. If you wish to run a combination of motors, you can e.g. have 1 XL and 2 M running together. The XL-Motor requires about twice as much power as the M-Motor. The Battery Boxes and the IR Receiver have overload protection, so attempting to drive too many motors will not damage anything. The power a motor consumes depends on what function the motor is performing. Motors will operate best when driving a small load."

"11. What happens when the Power Functions overload protection kicks in?"

"Overload protection is activated when too much power is consumed from either a Power Functions Battery Box or the IR Receiver. This can happen when a motor is blocked or when too many motors are running at the same time. If overload protection is activated, the Battery Box or the IR Receiver will cut off power to the output until power consumption has dropped under the allowed value. To regain power, unblock the motor or disconnect motors from the output – then turn the Battery Box OFF and ON again. Under overload protection, the green light on the Power Functions Battery Box will still be ON."

Edited July 20, 2012 by DLuders

[Saberwing40k]

Well, you could always try adding another battery box and receiver. All you would need to do is turn the battery box so that is vertical rather than horizontal. From there, slide the other one in, hook up another receiver, set it to the same frequency as your existing one, and plug in two of the drive motors. That should hopefully improve performance, not sure by how much. Or, if you have some extra money and some serious patience, buy some XL or L motors.

Now that the suggestions are out of the way, let me say that this is very inventive and pretty spiffy. I would have just loved to see the red, orange and yellow one!

[Aussie BJ]

Very nice Crawler Hopey and VERY inspiring for me to have a go at one. Considering the parts you had I think it looks great yellow.

Brendan

[Hopey]

I'm not noticing the power cutting out, so I think it is the batteries. Will give it a go with 2 receivers & 2 battery packs.

I would have just loved to see the red, orange and yellow one!

Here you go; shield your eyes.

[Saberwing40k]

Here you go; shield your eyes.

Oh come on, it's not that bad. The hood, however, should be yellow or black, and the transitions need to be a little less abrupt. I've got to say, the gray chassis does wonders for the looks, over the red one the real one has.

[Hopey]

So I took it for a little test drive outside. It's using the 9.6V battery pack from this thread. The only difference from the standard gearing ratio is the portal axles have 8:24 instead of 12:20. I've also modified the steering a little bit; I moved the steering motor back 1L and using the space to brace it so that the gears don't skip, which meant removing a horizontal beam, but it still

seems pretty sturdy.

(Many apologies for the shaky camera; I was driving it and filming it at the same time, and i'm too uncoordinated to drive it with one hand.)

Without being scientific, it looks as though the performance is roughly equivalent to the videos I've seen of the real thing, so it appears that two M motors is roughly equivalent to a single L motor.

I'd be interested in seeing someone do an empirical test, though. E.g. get an L motor vs a pair of M motors, pushing in opposite directions on the same shaft, or something like that.

One last thing I want to try out before I pull it apart is to put the diffs back in. It seemed very strained when turning, particularly on a flat grippy surface (i.e. wooden floor), and you can noticeably hear it running more smoothly when it's going in a straight line.

Edited July 21, 2012 by Hopey