[WIP] Greyhound - 4WD RC Buggy with BuWizz 2 - Redesigned wheel hubs

[Permo]

Ah thanks, I was just not shure what I was looking at.

[Didumos69]

10 hours ago, pagicence said:

20E for a shock absorber!!!!! They are insane!!!!! Even the PF motors are cheaper!

We have third party tires, we have third party RC, now we need thrid party shock absorbers! Or would it be illegal to make copies of original LEGO parts?

Edited June 6, 2018 by Didumos69

[agrof]

I am a bit involved in RC business lately, and I was always wondering about using RC shocks with LEGO, example:

https://www.ebay.com/itm/4pcs-70mm-aluminum-shock-absorber-Set-for-rc-rock-crawlers-CC01-D90-SCX10-/311703830304

In theory they could work, adjustable, for LEGO You don't even need to care about filling them with oil. I have 90 and 100 mm long shocks at home, maybe without the pivot balls (can be popped out) an axle would just fit through, I need to check.

Edited June 6, 2018 by agrof

[Ivan_M]

No need to be as extreme as that. I have bought only 3rd party springs and shocks with soft springs, in the end each was less than 1€ in total.

[agrof]

@Ivan_M Now that is a brilliant idea! Can you please share what parameters (length, diameter, strength) the spring should have, what we should ask for?

[Ivan_M]

You have to aim for similar dimmensions - length around 45mm, overal diameter around 10,5mm, wire thicness around 0,8-1mm and of course force. If I remember correctly the total travel of 9,5L spring is 10mm and extra hard spring need around 1-1,2 kg to be compressed fully. So you need spring with R~1N/mm.

[technic_addict]

To each their own but I am not a fan of RC parts, especially when Lego parts exist.

[pagicence]

Ok, this is clearly of topic, but, has anyone tried to use a spring from a ball point pen and put it over Lego axle (if it will fit) to make DIY shock absorber?

(I realize that this discussion might be more appropriate on General parts discussion topic)

Edited June 6, 2018 by pagicence

[Permo]

I did that in the late 70's when I was a kid

Yes it works, on small passive builds, but not on this beast.

 

[sirslayer]

not to long ago I was making my own shock absorber and out come from that is ... a its not Lego acceptable, balloon tires make up from the lack of using suspension and I believe the default shocks from Lego is enough to carry the weight of the PF devices till the use live non shocks suspension of larger models like the 42070 would be a common platform for future models, The Bugatti is just the example of crossing a big model and trying to implement a non live suspension and use shock absorber that failed due to the limits of the shocks Lego are using...I would believe Lego will have a updated solution soon, Last of making your own shocks is on how many times I got poke by that dang spring!! it hurts!!!!!  

[z3_2drive]

For heavy models, using a pneumatic cylinder in conjunction with a spring can provide the perfect damped suspension motion, avoiding excess sag and extra bounciness on bumps. You can combine them but it's kind of a non purist MOD unless you're very careful. It worked well for my previous projects: Link

Lego could learn from the RC world though. A great part I could see being developed is a line of proper plastic shocks - 3 choices of plastic shock bodies and metal shafts with the same or 2 sizes of diameter so the seals can be the same, with threaded shock caps/O-ring seal so the damping force is provided by air or a light oil. Doesn't have to be that beefy or take a lot of abuse, but it would be a great thing to have as models get bigger and heavier.

Edited June 7, 2018 by z3_2drive

[Bublehead]

@z3_2drive, can you attach a hose between all the pneumatic cylinders or is it better to just plug them and let them act on each wheel independently?

[z3_2drive]

@Bublehead I haven't tried that before, but from what I understand, having them disconnected (I snipped the inlets and made the holes slightly bigger so the damping wouldn't be too strong) allows air to flow in and out freely, so it adds a damping force during both compression and expansion. If they're plugged, it would be like having air-ride suspension, no spring needed, and might need to be reset if air escapes slowly over time. I've seen the latter used on very heavy Lego truck models with all cylinders connected to a single air tank/pump.

[AFOLegofan66]

so @Didumos69 It has been a while since you talked about instructions. I was wondering how you are coming along? 

[Didumos69]

After two month without LEGO I took my Greyhound for an indoor drive and had a lot of fun again. But there were also a few things that bothered me. First of all, the rear suspension feels a little too soft and while driving, the rear suspension arms show quite some unintended negative camber. Secondly, although I did not have much trouble with the front suspension, it is clear that the front wheel hubs remain to be the weakest point of the whole build. The problem is that the vertical thin levers from which the hubs are built, are not form-locked, they are only (heavily) friction locked.

So I took a look at what I could do about this, without making any consession to suspension travel and steering angle. Eventually, I managed to solve the issues by adding some silicon bands and belt wheel tires. Not very elegant, but it works. I also reinforced the front suspension arms a little. After making the adjustments, I made an indoor endurance test drive, during which I drove over all kinds of obstacles, like shoes and branches at high speed and low speed, over and over again. No problems occurred, nothing fall off or got displaced and the rear wheels don't show much camber anymore while driving. This is what I did:

The changes also lift the tail a little, which looks better imo.

I updated the digital files (LXF, LDR) to reflect the changes.

Edited August 30, 2018 by Didumos69

[Didumos69]

I didn't like the idea that the belt wheel tires played a role in the overall suspension hardness. So eventually this is what I did to avoid the unintended negative camber.

I once again updated the digital files (LXF, LDR) to reflect the changes.

[piece]

@Didumos69 

Thank you very much for your hard work.

Currently I'm building the chassis and I gotta say, it was pretty hard to figure out the order in which to put it all together. While building it, I'm also creating the instructions in stud.io.

Now that I've put together the front Axle part, I have some issues. First of all my servo's center position is not flat center. Don't know yet if this will be a problem later. But my bigger problem is that the steering does not allow the servo to use it's full range. Is that intended? Currently I have to restrict my Remote control to 80% range to left and right. I'm missing the last 2 steps of the servo. I don't think so, but maybe I build something wrong.

And I cannot find a way to build the rear swingarms without stressing any parts. 

 

Edited October 6, 2018 by piece

[Didumos69]

On 10/6/2018 at 8:08 PM, piece said:

@Didumos69 

Thank you very much for your hard work.

Currently I'm building the chassis and I gotta say, it was pretty hard to figure out the order in which to put it all together. While building it, I'm also creating the instructions in stud.io.

Now that I've put together the front Axle part, I have some issues. First of all my servo's center position is not flat center. Don't know yet if this will be a problem later. But my bigger problem is that the steering does not allow the servo to use it's full range. Is that intended? Currently I have to restrict my Remote control to 80% range to left and right. I'm missing the last 2 steps of the servo. I don't think so, but maybe I build something wrong.

And I cannot find a way to build the rear swingarms without stressing any parts.

I hope you are using this LXF-file. It has groups resembling reverse engineering steps. If you delete all (sub)groups from top to bottom (depth first) up until the last subgroup, and then restore them one by one with Undo (Shift-Ctrl-Z), then you will be able to follow the steps I used to build it. However, some steps are quite big, for example the front axles and the rear swing arms.

The Servo's center position should be flat center. It can happen that your Servo is not centered, you will have to use it to make sure it centers correctly. The whole steering setup allows for perfectly centered steering. The Servo output axle should have a zero degree orientation when the gearrack is perfectly centered. The steering setup does not allow for a complete 90-degree Servo-rotation, so it does not use the last steps of the Servo.

Building the rear swing arms without stressing parts is possible by using some rotational steps. I will show this in my photo instructions later.

Edited October 9, 2018 by Didumos69

[piece]

Yes, I used your latest lxf as my basis and imported that into stud.io. Then I made some changes to fit my needs.

For example attached is an image how i reinforced the swing arms and changed the gears. I'll iterate on this to get it somewhat cleaner. But for the moment this seems stable enough. The gears in your version broke within the first 10 seconds in my setup.

I use a proper RC remote and built a little circuit to control the motors smoothly. You can also see the center position of my servo. Maybe I should go to the lego store and demand a replacement. I bought it brand new recently.

I'm looking forward to find out how you put the swing arms together. I honestly have no idea how you've managed that. If you look closely at the image, you'll see that I have to put some pins through the lift arm into the motor from the outside. As a result, I have to push the wheels 1 stud further out. That's not optimal.

Edited October 9, 2018 by piece

[Didumos69]

@piece, it amazes me that your gears broke after 10 seconds. In my build I use the same gears and axles for over half a year now. Without any problems.

Did you use this part? 

Edited October 9, 2018 by Didumos69

[piece]

No, I had to remove the 48496. There was not enough room for that.

Driving with the small gears should be not much of a problem. But when I blocked a wheel for a fraction of a second, it immediately burst into small pieces. The double bevel gears do not break so fast when the wheel gets blocked.

After all i use a 11.1V battery which gets down to about 9.5v after the circuit stuff. It reacts a lot faster then any Lego or buwizz remote.

[Didumos69]

I reserved time to make photo sequence instructions in the first days of this week. However, things worked out a little differently. I found myself completely reworking the wheel hubs, both in the front and in the back. I've mentioned before that the front wheel hubs were the most vulnerable part of the model. They relied on (extensive) friction locking only. Eventually, I replaced the small turn-tables in the wheel hubs with large turn-tables. After a few iterations I found a setup that feels really strong and rigid: The inner side of the tyre is squeezed between the turn-table and the rim. The outer side of the tire connects to the rim normally. The rim is attached to two 5L axles with end-stop sticking out the turn-tables. The rims are locked as before; by squeezing rubber connectors that are slided over the axles with end-stop. That works very well and if the rim would slide over the axle while driving at all, it is very easy to re-secure it. You only need to squeeze the rim back on, while giving resistance to the turn-table. I installed these new wheel hubs on one side of the model and they perform really well. I will soon install the hubs on the other side and make a more abusive test-drive. I also plan to lubricate the turn-tables. Not decided whether I will do that with WD40 or with graphite.

The pros:

• Completely form-locked front wheel hubs
• Way less slack in the wheel hubs
• Tyres look less balloonish, because they are drawn to the inside of the rim by half a stud.
• Reduced chances of tyres running off the rims in fast turns (this happened only a few times with the old setup)
• No need for silicon bands to keep the front wheel hubs together
• No need for belt wheel tyres to reduce slack in the front wheel hubs
• No need for the rare shorter 5.5L axles with end-stop

The cons

• One stud wider track width, half a stud more width on each side.

Here is a temporary development version of the Stud.io file in case you would want to study this more closely.

Edited October 30, 2018 by Didumos69

[AFOLegofan66]

Wow this newer version is so worth the wait for me... thanks for the quality work you are doing!!

[AFOLegofan66]

Was the stud.io file for everyone? It is password protected...

[Didumos69]

I did not password-protect it. Maybe it's because I'm using Stud.io 2.0. I'm still making updates btw. One thing I had to do to make it foolproof was inserting Unimog tires inside the CLAAS tires. The CLAAS tires attach to the outer ridges of the rims and the Unimog tires attach to the inner ridges. That way the CLAAS tires can be nicely squeezed against the turntables. It works very well and it looks very cool too, because of the flat flanks of the tires, but it adds quite some weight too. After some abuse nothing got displaced.

Edited October 31, 2018 by Didumos69