2GodBDGlory

General RC Motorcycle Discussion

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Largely because of piterx's work on self-centering, RC motorcycles, there has been a fair bit of interest in these concepts lately, with a lot of discussion going on in the threads for his models. Because of this, it seemed like a good idea to start up a dedicated thread for discussion of all sorts of RC motorcycles, rather than cluttering up preexisting threads about particular models. Hopefully this thread will enable us to discuss different bikes being built, and the techniques behind them!

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To kick off some discussion, I'd like to show my heavily modified Ducati set. It has a buggy motor for drive, with various gearings (1:1 from the fast output at present), a servo motor to move the PF rechargeable battery side to side, and a revised steering pivot.

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It never does seem to self balance, though.

I guess this is because of:

A. The center of gravity is too high (the bike is tall!)

B. The imbalanced buggy motor makes it lose balance.

C. The steering forks have too much slack

D. It isn't fast enough.

I'm going to try working on C now, but I'd appreciate advice!

 

 

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Even with the buggy motor centred in the Fast Bike from piterx, it tends to wander just a little to the side the gears sit on. Even that much imbalance makes a difference, so if your whole motor is off centre, that'll be a main reason it's not working.

You could try putting the battery a stud over to the other side, see if it helps? I didn't test this idea yet but it seems sensible.

I found it useful to try this stuff with it freewheeling. Then you can try it at a slower speed just by pushing it.

Slack in the headset doesn't help stability but shouldn't completely stop it balancing.

I also see your buggy motor is mounted across an axle, and the shock bottom eye is across an axle. At high speeds, this much slack really matters. My modded version of the Fast Bike has minimal slack anywhere, everything is pin and axle into matching holes. It's way stiffer, and it doesn't get head shakes anything like as much as the original version.

Part of that is using CaDA pins 'with friction' in the headset. They have almost no friction, but also almost no play, whereas Lego non friction pins have a lot of slack. I'll post more on that thread when I've got a video of it driving.

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Thanks a lot!

I have since added a weighted brick opposite the buggy motor, which should help a lot with weight distribution. I also completely registered the forks, sacrificing the suspension in favor of stiffness, and I increased the castor angle to nearly 45 degrees. It seems better, but my steering mechanism is jamming up now.

I'll see how I can make things stiffer, and try freewheeling tests, to hopefully get this working. Motorcycles seem to require a lot more trial and error than other Technic models!

 

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4 minutes ago, Scoar Sonander said:

Probably add some roller wheels on the side! I know this is kinda cheating, but...

Well, I have some wheels to help it get started and steer, but they are meant to be disengaged when driving straight. If I got them more involved than that, I would give up too much challenge!

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8 hours ago, Scoar Sonander said:

Probably add some roller wheels on the side! I know this is kinda cheating, but...

I see why you'd suggest it, but this is exactly what this topic isn't about. We don't want this...

kawasaki-zx-6r-with-.jpg

We want proper, self-balancing motorcycles. Made of Lego. It sounds mental, but it's really possible as shown by @piterx's Fastest Bike and Baja Bike.

I've built both of those and driven the Fast Bike (still waiting for tyres for Baja Bike) and can confirm it works. Download the stud.io files I've uploaded, and try for yourself!

As far as I can tell, the main tricks are sufficient trail for it to track true, even balance down the centre line, and a stiff chassis for stability.

9 hours ago, 2GodBDGlory said:

sacrificing the suspension

Not sure about this one, at least not if you want to drive it outside.

Having previously said I doubted the suspension would even move, I've now driven the fast bike and the suspension definitely does eat up bumps. I think the frame stiffening I did helps, because the front of the frame now forces the fork to eat impacts, rather than making the frame flex.

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Posted (edited)

Hey guys! Awesome to see that you're having fun as much as i do with bikes :)
I've got more bikes coming in a while, still need to do tweaks here and there but what i can tell you if you wanna start experimenting with big wheels you can go with an XL motor, it's better centered than the others and it has enough torque to make the bike run.
On these two i'm using a chain that goes from the large gear to the second smallest one (sorry i have no idea on how many teeth they have)

3701e03e-a138-4294-a3b0-9d6f1016704f.jpg

 

Edited by piterx

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Amazing how few pieces you have on that dirt bike. I'd have to take something apart for an XL motor but if you're willing to share the model, ofc I'll build it.

The XL will be a MouldKing motor, they're not as strong as CaDA Pro but still a lot stronger than Lego.

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I've been doing a lot of freewheeling testing while moving weight bricks around, and I think it is better balanced now. It's a rainy day, though, so I can't test outside for now.

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Do you guys think it is reasonable to assume that the higher the weight of the model, the faster it will need to move to stay balanced, or would weight and minimum speed be unrelated?

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33 minutes ago, 2GodBDGlory said:

Do you guys think it is reasonable to assume that the higher the weight of the model, the faster it will need to move to stay balanced, or would weight and minimum speed be unrelated?

Seems reasonable there would be a connection. A wheel with a fixed weight will give a certain amount of gyroscopic effect, which needs to be enough to overcome the tendency of the bike to just fall over. In real bikes, it's often said that you don't feel the weight of a large bike (Pan European for example) once you get it moving. The inverse being true - at slow speeds, it's a pig to keep them upright.

The higher up the CoG is, the more you're going to need to force the bike to change direction. This holds true in real bikes, too.

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Posted (edited)

Hmm. My modified Ducati had both high weight and a high CoG. I'm starting to feel like giving up on it and starting with a fresh design, but I'll try some more things before that. 

That comment about the weight of the tires has me wondering if adding weights inside the tires could increase stability. I've added marbles in the tires of off road vehicles to aid traction and lower the CoG, and maybe it could work here too?

EDIT: marbles don't fit in motorcycle tires, but I could potentially see it helping with bikes made with balloon tires.

Edited by 2GodBDGlory

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I think you'll be better off starting with something simple, and light. You can always greeble it up later.

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Yeah, most of the successful designs out there are small and light. I do have my balloon tire one working fairly well, but I'd like to get some more speed and refinement. A buggy motor or two would help, but it's tricky to power multiple ones without a Buwizz. Perhaps I'll try some thing like piterx's "The fastest bike," but with a PF battery and my balloon tires, or go big and use both buggy motors and my larger motorcycle tires.

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I think two buggy motors is overkill. You can already get a lot of speed with one, doubling up isn't going to help anything. Especially since PF batteries can't supply nearly enough power to spin two of them.

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Posted (edited)

I just took my original balloon tire bike out with marble-stuffed tires, and the difference is quite dramatic! Where it would previously start violent shakes, particularly when speed dropped on modest uphills, it now proceeds with smooth composure, never once getting that kind of shake!

The trade-off, of course, seems to be speed, because of the weight increase, but it is not accompanied by the loss of stability motorcycles typically exhibit at low speeds.

This trick may be a mere bandage of sorts for poorly designed bikes, but the dramatic difference may make it worth considering. I'll also test adding weight to the tires via original Lego parts, such as axles.

EDIT: Filling it with Lego parts looks like it may require more patience than I have, so I may just stick to marbles.

4 minutes ago, amorti said:

I think two buggy motors is overkill. You can already get a lot of speed with one, doubling up isn't going to help anything. Especially since PF batteries can't supply nearly enough power to spin two of them.

If I were going for two, I would definitely have to use either two batteries or my high-output 9.6V pack. My only fear with using just one of that a lack of Buwizz power may reduce speed critically, but you're probably right that it is best not to overcomplicate things.

Edited by 2GodBDGlory

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my advice would be: focus only on the geometry and weight distribution of the model. Once you get something that can go at slow speed without falling down you start adding features.

c141e307-85a4-40c9-977c-858d275bd508.jpg

take this as an example, it only has the basic angle and pivot offset and it is really stable at slow speeds, you litterally push it gently and it will keep going straight.
Try finding the right angle and wheelbase that gives the bike the behaviour you're looking for and then you add all the rest on top of that trying to keep the same setup as much as you can.

Of course trying to keep the bike as specular on its forward axis is quite relevant for the weight distribution but the lower down you got differences the leatest impact they will have on the bike.
Take the Baja bike as an example, it goes straight even tho the servo and the L motor have different weights, but they are placed at the bottom of the chassis where it doesn't affect the balance too much.

 

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@2GodBDGlory I did just try shifting the buwizz half a stud away from the buggy motor's gearing. It really helped the bike run straight at free-pushing speeds, so I'm going to roll with it.

As an added benefit, it's going to make it much easier to charge the buwizz while in the model.

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Good!

I'm going to start on a single buggy motor-powered, balloon tired bike now.

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9 minutes ago, 2GodBDGlory said:

balloon tired bike

I reckon you'll have to deal with quite a bit of asymmetry on that build to get it balanced! Maybe even look at fixing the servo off-centre to help that, or put a weight brick in the mix?

Should work well if you can balance it though, those tyres have a lot of curvature.

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Yeah, the wide tires will keep the buggy motor offset, but it should be possible to get it balanced right.

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1 hour ago, 2GodBDGlory said:

Yeah, the wide tires will keep the buggy motor offset, but it should be possible to get it balanced right.

how about something like this?
cheap and easy to integrate :P

3b6d70cc-27c4-4e33-b6e8-0de11efb0f44.jpg

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19 minutes ago, piterx said:

how about something like this?
cheap and easy to integrate :P

That would be a good strong solution, but seems like it would be rather slow.

I've had a productive morning, and my new bike is nearly done! All I really can think of to do is to add a stud to the front suspension to raise ground clearance enough for tighter steering.

The balance is actually quite good with the PF rechargeable battery offset by one stud, and the sliding weights offset by one tooth of the gear rack.

Hopefully I'll have something to show you soon!

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Posted (edited)

Here it is! It appears very stable in indoor tests, but my only worry is that the turning circle will be too large. Unfortunately, it is still raining outside, so more thorough testing will have to wait.

EDIT: I got outside for tests, and they went well, with the only issue being that the sliding weights jammed up from time to time. I'm pretty sure this is due to grit from the road, so I'll have to see if the problem persists on drier road.

Thanks for all the advice and inspiration!

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Edited by 2GodBDGlory

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