Didumos69

[WIP] RC Off-roader w/ Dual Diagonal Drive - First results

Recommended Posts

You can't really compare the two drivetrains.

The Greyhound had a dedicated L motor per wheel and was built for speed and efficiency.

I believe the challenge with this model is to have a powerful drivetrain with a gearbox and locking diffs that won't suffer from gears skipping even under high torque and/or sudden gear shifts.

Share this post


Link to post
Share on other sites

is it a powerful drivetrain??  I guess we will find out?? even with a dozen drive trains of this type can't match the drivetrain on last year model would be more powerful due to its simplicity of a motor per wheel  

Share this post


Link to post
Share on other sites

In terms of pure power and ignoring friction, two geared-down XLs easily overpower four ungeared Ls.

Share this post


Link to post
Share on other sites
5 hours ago, suffocation said:

You can't really compare the two drivetrains.

The Greyhound had a dedicated L motor per wheel and was built for speed and efficiency.

I believe the challenge with this model is to have a powerful drivetrain with a gearbox and locking diffs that won't suffer from gears skipping even under high torque and/or sudden gear shifts.

That's exactly what it is. And the dual diagonal drive is 1) to divide torque over two separate drive trains while 2) preserving the advantage of having open differentials when cornering and 3) to pass this kind of tests at the same time, even without the differential lock engaged.

Edited by Didumos69

Share this post


Link to post
Share on other sites

well the video is great and I've been designing AWD moc for a while and a trick i've learn is how I drive my model,outside and  I see a ramp or incline and I learned how to approach in such a way that I never high centered. that video did show an advantage on its d mode drive vs ....     but I still believe they could of gone up those inclines if they approach it in a certain angle on any mode..  that how I've been handling and learning how to control my Lego "RC" and maintain the looking cool part and minimized getting stuck since I've only been building small scaled (49.5mm to 67.8mm) size tires..  The 49.5mm is almost as tall of my garden hose yet I can always go over them on those small tires is  because how I drive the model and approach into it at certain angles even on AWD center based diff.. !!  I see your idea now and thank you for that video.. ive learn something today..   Note:(since most of my models have posi-traction.. designing an anti-ackermann steering does help out on your turns if you ride on locked diffs all the time!!..   

Edited by sirslayer

Share this post


Link to post
Share on other sites
8 hours ago, gregorski904 said:

built this according to your file and is very rigid ,might even try it on Greyhound

If your RC-tires fit, it could indeed be a nice option for the Greyhound. I saw you don't use the inner tires, so the wheels on your Greyhound must be a bit sloppy now. This would solve that. Can you let me know if the RC tires fit the Porsche rims?

Another option would be to put the CLAAS tires on the Porsche rims, but then your tires will probably stretch and will no longer be usable on the CLAAS rims.

Btw, I updated the design of these hubs in the mean time, you can find the ldd file here and the stud.io file here. Here you see a cutaway:

800x450.jpg

Edited by Didumos69

Share this post


Link to post
Share on other sites
2 hours ago, Didumos69 said:

If your RC-tires fit, it could indeed be a nice option for the Greyhound. I saw you don't use the inner tires, so the wheels on your Greyhound must be a bit sloppy now. This would solve that. Can you let me know if the RC tires fit the Porsche rims?

Another option would be to put the CLAAS tires on the Porsche rims, but then your tires will probably stretch and will no longer be usable on the CLAAS rims.

Btw, I updated the design of these hubs in the mean time, you can find the ldd file here and the stud.io file here. Here you see a cutaway:

800x450.jpg

will try it later and will post picture with both tyres on ..rc tyres have foam inserts inside

Share this post


Link to post
Share on other sites
17 hours ago, gregorski904 said:

but RC tyre is a bit stretched :)

That does not look cool. I suppose this approach requires wider tires.

Share this post


Link to post
Share on other sites

I went ahead and started to build a simple chassis based on Didumos69 drive and looking forward to see its enhance traction control. Would be it be safe to design it with one L motor to observe the output??   It will have no hi/lo gear and simple as is. I know its similar to some tanks or tracked vehicles which can require 2 or more motors to do the left and right but this chassis is just for my learning and maybe to add tires latter..   

lego technic

 

Share this post


Link to post
Share on other sites
5 hours ago, sirslayer said:

I went ahead and started to build a simple chassis based on Didumos69 drive and looking forward to see its enhance traction control. Would be it be safe to design it with one L motor to observe the output??   It will have no hi/lo gear and simple as is. I know its similar to some tanks or tracked vehicles which can require 2 or more motors to do the left and right but this chassis is just for my learning and maybe to add tires latter.. 

I appreciate you are trying to experiment with the dd-drive yourself. That's the best way to value it.

5 hours ago, AFOLegofan66 said:

@Didumos69I really like where this moc is going. I thought that the Greyhound was your best work but this might be over the top!! That gear box is awesome!!

Thanks @AFOLegofan66! I hope I can live up to the expectations. At this stage I'm actually quite unhappy with the fact that I can't get shifting back from 4th to 3rd gear to work reliably. Still have some ideas to improve things though.

Share this post


Link to post
Share on other sites

This is the strongest rendition of my shifter so far, also with the best reach: The shifter now completes a full 90 degree shift, the 90 degree limiter is only necessary for allowing the shifter to return prperly. I hope this will allow me to shift back from 4th to 3rd gear.

Share this post


Link to post
Share on other sites
18 minutes ago, Didumos69 said:

 I hope this will allow me to shift back from 4th to 3rd gear.

When it is in 4th gear -being the quickest- puts the drivetrain under the highest torque. When I say drivetrain, I mean the "ring-clutchgear connection". So when these two are forced against each other, it takes more muscle for the changing mechanism to pull it out. I suppose your shifter is just around that limit with it's strenght to accomplish the task. If you take the throttle off in the time of that gearchange and it goes well, it's a sign of this phenomena.

Edit: I'm talking about the former, failing shifter, not the newly posted. Idon't know that yet. :sweet: 

Edited by Attika

Share this post


Link to post
Share on other sites
3 hours ago, Attika said:

When it is in 4th gear -being the quickest- puts the drivetrain under the highest torque. When I say drivetrain, I mean the "ring-clutchgear connection". So when these two are forced against each other, it takes more muscle for the changing mechanism to pull it out. I suppose your shifter is just around that limit with it's strenght to accomplish the task. If you take the throttle off in the time of that gearchange and it goes well, it's a sign of this phenomena.

This is exactly what is going on @Attika. I thought I could make things work by skipping 4th gear in combination with not gearing down the outputs towards the wheels to compensate for the lost max speed. But in that setup the extra torque in 3rd gear gives the exact same problem when shifting back from 3rd to 2nd gear. That confirms your explanation: High torque makes it hard to pull the driving rings out of the clutch gear.

Even the setup above, which is really strong, cannot pull the driving ring out of the clutch gear under high torque. The only setup that works, is when I drop 4th gear and hold on to gearing down the outputs towards the wheels, but that drops max speed significantly. In that setup I can reliably shift from 1st to 3rd gear and back.

Perhaps lubricating the 'teeth' of the driving rings will make them disengage under high torque more easily?

Edited by Didumos69

Share this post


Link to post
Share on other sites
36 minutes ago, Didumos69 said:

Perhaps lubricating the 'teeth' of the driving rings will make them disengage under high torque more easily?

I'm not a fan of that idea. Once it is messy, or it becomes that  in short time. Second, the same friction that causes the problem- by definition- helps to keep the engagement stable under higher torque. And that is where the problem becomes layered:

Without lubrication the engagement kept in more-less by the friction between the ring and the c.gear. If you lubricate it, this friction is eliminated so your ring wanna slide out from the c.gear and the ring will get forced against the orange rotary catch. As it is a stationary part, it will create friction on the rotating ring and this friction grows by the torque applied on this system. So lubrication is a trade-off in my view. Just release the throttle for a fraction of a second at the gearchange and it is sorted. Just like in real cars. 

Disclaimer: It takes a while to master which fraction of that second is when you take the gas off. :grin:

Edited by Attika

Share this post


Link to post
Share on other sites
9 hours ago, Attika said:

Without lubrication the engagement kept in more-less by the friction between the ring and the c.gear. If you lubricate it, this friction is eliminated so your ring wanna slide out from the c.gear and the ring will get forced against the orange rotary catch. As it is a stationary part, it will create friction on the rotating ring and this friction grows by the torque applied on this system. So lubrication is a trade-off in my view. Just release the throttle for a fraction of a second at the gearchange and it is sorted. Just like in real cars. 

But the 'teeth' of the d-rings and c-gears are straight, so I don't see why they would want to slide out when the friction between d-rings and c-gears is eliminated.

I still agree lubrication would not be the most elegant solution.

Releasing the throttle for a fraction is undoable. It halts almost immediately.

Edited by Didumos69

Share this post


Link to post
Share on other sites

@Attika, perhaps it's also good to know the ratios the transmission currently has. The input (directly from the XL-motors) output ratios of the transmission are 0.55, 1.00, 1.65 and 3.00. This is geared down by 0.60 in the toggle joints that are part of the front and rear axles. As you can see, 4th gear is 5.4 times faster than 1st gear, which makes a huge difference. By changing a few gear meshes, I can change the ratios to 0.55, 0.92, 1.00 and 1.65. That would work reliably with the shifter I have now, but the difference between 2nd and 3rd gear would be really small.

Guess I have to make up my mind about what's more important; max speed or being able to shift gears at speed? So far I think the latter is more important.

Edited by Didumos69

Share this post


Link to post
Share on other sites

Since the motors are strong enough for the 4th gear, why not raise all gear ratios?
So the gears go from 1.00 to 3.00?

In the end i guess you'll mostly use the first and last gear, so the gear jumps in between only help smoothen the transition.

Share this post


Link to post
Share on other sites
35 minutes ago, schraubedrin said:

Since the motors are strong enough for the 4th gear, why not raise all gear ratios?
So the gears go from 1.00 to 3.00?

In the end i guess you'll mostly use the first and last gear, so the gear jumps in between only help smoothen the transition.

The motors can indeed handle the 3.00 ratio and I could obtain ratios running from 1.00 to 3.00 by skipping the down-gearing in the toggle joints that are part of the front and rear axles. But the problem is that the shifter cannot shift at speed when the ratio comes above 2.2.

Share this post


Link to post
Share on other sites

This will hurt the efficiency a bit, but have you tried running the complete gearbox at higher speeds to reduce the torque?

Share this post


Link to post
Share on other sites
9 minutes ago, schraubedrin said:

This will hurt the efficiency a bit, but have you tried running the complete gearbox at higher speeds to reduce the torque?

High spin and low torque, that actually summarizes my strategy towards the whole drive-train, it is also my approach to avoiding slipping gears inside the differentials.

Currently I use the output of the XL motors to provide two inputs for the gearboxes: One input is geared up by 3:1 and the other input is geared up by 5:3. The outputs of the gearboxes are then geared down by 3:5. So I already have the gearboxes running with relatively high spin / low torque. If I want to have even higher spin and lower torque, I will need to introduce more gear meshes to gear up the XL-motor outputs and also more gear meshes to gear down the transmission outputs. That would make the whole setup much less efficient I fear.

Share this post


Link to post
Share on other sites

I should have guessed that you already optimised this drivetrain to death :laugh:

Another idea to reduce the torque on the shifter rings would be to double them. But this would be a huge step-up in complexity with questionable outcome.

Whatever you do, i'll follow this thread closely :wink:

Share this post


Link to post
Share on other sites
On 2/7/2019 at 7:35 AM, Didumos69 said:

But the 'teeth' of the d-rings and c-gears are straight, so I don't see why they would want to slide out when the friction between d-rings and c-gears is eliminated.

Yes, the teeth are straight, but due to the torque there is a minor "deformation" that makes a slight angle between the two parts. If it wasn't there we wouldn't have the problem of disengagement under torque in the first place. But it is plastic, not metal so we have it.

On 2/7/2019 at 7:35 AM, Didumos69 said:

Releasing the throttle for a fraction is undoable. It halts almost immediately.

Too bad. It was working on my (unpublished) 4 speed sequential "supercar". Although I have to admit it was equipped with 2 buggy motors and those have different caracteristic from the PF XL. So it is a fair point. Taking your priorities in consideration you may be right to gear it down.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.