8 wheel Drive Train

[Yannick B]

As a pre-season project, a friend and I took on the challenge to design a versatile drive train our team could use and modify for future years.

It was decided the drive train would have to meet certain requirements, including 8 wheels, a direct drive custom two speed gearbox, belts and versatile.

The outcome of these decisions produced a drive train that looked like this:



The specification of the drive train is as follows:
• 8 wheel drive
• Pneumatic wheels
• Two speed Custom shifting Gearbox
• Belt drive
• 0.064 in thick aluminium frame
• Mountings for other components
• Interchangeable wheels and shafts
• Width: 26.25 in, Length: 28.13
• Weight: 54 lbs
• Perimeter: 108.76 in
• Speeds: low gear: 7.3 ft/s, high gear: 16.7 ft/s

The frame was designed using Solidworks, and a Mastersketch was used as a base to allow us to modify the frame with ease.

The custom gearbox was designed so the two centre wheels would be directly driven, meaning if the belts or the chains on the frame broke, it would always have 4 wheel drive.



The gearbox was made from a VexPro ball shifter modified to fit our needs.

If you have any questions, please feel free to ask and I will try my best to answer all of them!

Yannick,
Co-Captain, Team 2994

[Bryce Paputa]

Very nice, looks (and is) heavy though.

[julianpowell]

Why pneumatic wheels?

[OWilliamson]

Just out of curiosity, how much does that gearbox weigh?

[Deke]

It looks like a very nice design!

Two comments on the gearbox plates:
-If machining, you will need some internal fillets on the corners for the mill. Even if you are using a water jet, fillets will reduce the Kt of the stress concentrations in the plates.
-The thickness around the bearings may need to be increased for press fit, otherwise the press load could tear the metal/material.

I really like the gearbox incorporation into center 4 wheels. The Enginerds (2337) did a similar approach last year and had a very robust drivetrain.

[Yannick B]

Bryce Paputa, yes it is a heavy frame at the moment, but 54 pounds does include motor controllers, PD board, CRIO, router and a basic pneumatic system (not shown in the picture). We will be looking for ways to reduce the weight in the future.

julianpowell, we decided to use pneumatic wheels for two reasons, tractions and bounce. We are experimenting with the pressure in each wheel to give the robot the best traction (so far, the best result is centre wheels at 40 psi, outer wheels at 25 psi). Pneumatic wheels also give a pseudo suspension to the frame.

OWilliamson, a single gearbox that includes both cim motors weighs 8.15 pounds. It is heavier than a ball shifter by 1.29 pounds. However, it is much lighter than a AndyMark super shifter.

Infinity2718, you are probably right about the fillets, we had the plates manufactured for us, so I am not sure what procedure they used.
The drivetrain is extremely robust with its inter-lapping plates and the gearbox, it also has a very low centre of gravity and is quite manoeuvrable. We are extremely pleased with it.

[Bryce Paputa]

Oh, I didn't know that the 54 number included electronics, it's fine with that in mind. How will/did bumpers attach?

[Yannick B]

The bumper mounting mechanism we designed is quite simple. Outer plates you see on the frame will be part of the bumper (staying under the 20 pound bumper weight limit). Rivet nuts will be placed on the frame at set locations and we will mount the bumpers using fasteners (also included as part of the bumper). If needed we will have an l-bracket attached on the top of the frame.

[lewislongbottom]

So what are the benefits and fallbacks on an 8WD Drive Train? I just wanted a quick generalization of bullets for our team to go off of.

[EricH]

Originally Posted by lewislongbottom

So what are the benefits and fallbacks on an 8WD Drive Train? I just wanted a quick generalization of bullets for our team to go off of.

If I might make a suggestion...

There may be one already on the site. The search feature is near the middle of the orange bar at the top of the page.

There are a number of benefits and drawbacks to ANY drivetrain design. Weight, cost, chances of a failure and chances that any given failure will cripple half the drivetrain can be some drawbacks or some benefits.