Crazy 8 wheel 4WD idea

I’m not looking to argue either. I should have clarified in the beginning of the post, each tandem mount will have its own motor. So the inside and outside wheels will be able to turn at independent RPMs. It’s the front/back that will be turning at the same RPM (forced by the belt). Since each front/back wheel should follow roughly the same path, I believe it would be a fair assumption to say the RPMs would be the same.

As an engineering student, I am always looking to learn more. I think a fun test would be to make an 8 wheel pusher board, and put some form of paint or powder on the wheels so it draws a line. If they trace the same line, it is fair to say the wheel RPM will be the same, since they follow the same path. If not, then your hypothesis will be proven correct.

The tandem truck design (non-motorized) is a pretty non-ideal design in it of itself (as is the regular 2 wheel truck, since it is not ackerman), since the angle between the group of 4 wheels is fixed. Ideally, they should be able to turn to different angles, like this lego model below. However, that hasn’t stopped anyone from making them. I’m excited to test out the 8 wheel setup on a non-powered board to see how it handles.

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eventually one of you crazy people are going to make something like a Stair Rover


great photos. nothing more to say than get my two cents in and say …thats a crazy catipilar lookalike vehicle upside down bug

That’s crazy. You’ll never make it work. Just give up now…

…is what some people would say, but not me! That looks just crazy enough to work. And if I might help steer this crazy train directly into the sun, don’t tread lightly on his project. Go all out, man! And btw, tanks for the idea. :joy:


@Mobutusan Thanks, I’ve already ordered some tandem mounts for a non-powered board, going to test the waters and see if I like it. My thinking is that it will make going over bumps and cracks much easier!

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Good luck making this work man. It will be cool if you pull it off. Maybe it will be cool even if you dont.
The problem I see is that as the two wheels pivot around the main axle the geometry of the pulleys changes so the belt length changes. Also idle pulleys aren’t really meant to go on the drive side of a belt or chain which since you’ve shown it between the two wheels it would have to be. The pulley would need to be as solidly mounted and have the same quality bushings as the wheels themselves since it would be under the same strain. A solution to both these problems would be if you could somehow put the driving pulley on the same axis as the main axle. That way the geometry stays the same the wheels pivot. If you had a jackshaft extending out from the end of the axle with a drive pulley on it, you could drive the jack shafts with your motor. If the top of the drive pulley were below a line tangent to the top of the driven pulleys (which it would not be unless the wheel geometry was changed from your drawing) then you could route the chain/belt around the top of your drive pulley like the idle pulley in your drawing and have tons of belt engagement on all three pulleys. Of course, this will only work with chain, unless they make belts that are toothed on both sides. Sheesh, it’s starting to seem kinda complicated! Btw, I do think the tires would scrub a tiny bit on the turns but not enough to even notice. Anyway, good luck dude. I’ll check in tomorrow and see what’s up.

I see what you did there @Mobutusan


@Pstrap Thanks for the kind words. I don’t really see how the geometry of the pulleys would change relative to each other, however. I didn’t draw the actual plate that they would both be mounted to, so I can see the confusion with that.

The wheels and motor would all be fixed in position to the same plate that pivots around the main axle. So, the geometry between them should be fixed.

I am also a bit confused about what you said about idler pulleys. In this design the idler (or tensioner) is on the non-toothed side of the belt, which I think is a pretty normal configuration, at least with car engines. Could you clarify a bit?

hahaaa! funny! just hours ago I stubled over my bookmarks on Egay with this setup. I will give it a try after back from holiday. looks like they ship from HK or China.

I will go for 4 hubmotors in the back and a normal truck in the front. (6 wheels with 4wd)

Oh you are going to mount the motor off the yoke piece that joins the wheels to the axle. Well, that makes sense. I thought the motor would be mounted the the axle. Yeah, I get it now. Yeah, the back of the belt can wrap around the idle pulley. That’s fine. My point about the idle pulley was this: When one pulley drives another via belt or chain, the length of belt transmitting the force is under great tension, while the other length of belt that returns to the drive pulley from the driven pulleys is more or less slack. This allows you to use a very light weight bearing for an idle pulley on the slack side. That is how bicycle derailleurs work. You can put an idle pulley on the drive side, it just has to be much more sturdy, as study as the wheel and motor in your case. Also, since the belt transmits force in the opposite direction when braking or in reverse, there is no part of your belt that will always be “slack”. Anyway, to sum up, just make your idle pulley sturdy enough to take the strain. But you probably already knew that. I hope you do make this. Good luck mate.

@Pstrap Your tension/slack concept is something that I have not considered until now, but it totally makes sense now that I think of it. Thanks for the useful information. From that, I think I’ll place it somewhere that will have equal stress between throttle/braking.

The position you showed in your drawing might be good. You could fabricate a yoke piece that had a stub shafts coming off it to mount the idle pulley. You need to look for an appropriately sized pulley with a bearing inside it, I guess. Your design is good. Build it!!!

please build that.

Unfortunately these things are for kids and I exceed the weight limit by quite a bit. Otherwise…

I just tried out my new electric build using some tandem mounts just in the front. The board is definitely slightly heavier. The handling seems a little less snappy, which I think is a good thing, since it felt a little too snappy for my liking. It’s mellowed out the board in all the best ways without sacrificing overall hadling ability.

The biggest difference I see with the 6 wheel board vs a regular 4 wheel board is a remarkable increase in ride quality. Every bump I go over feels less pronounced, even though the wheels are smaller (70s in the front 83s in the back).

At this point I am sold an 8 wheeler is going to make an awesome project, and have full intentions of moving forward with coming up with a viable design.

Will post a picture of the current setup soon.


How’s the project going?

On hold at the moment. I’m heading to Copenhagen for a few months for a big project I am doing with my University. I have full intentions on picking the project back up when I return in mid May.

Have fun man!