Newbie: Robot steering bearing arrangement 1

[ColinDH]

Its a simple image but it shows the proposed arrangement for a 4 wheel agricultural robot. We want a simple design and thought 2 'thrust' type bearings 'squeezed' either side of a plate would be OK to give a study leg and the ability to steer (90-degree worm motor connected to the shaft at the top). Weight per wheel is around 40Kg, the rotation speed is 40 rpm and for steering, the terrain is soil, horizontal tube length to the centre of the robot is 1.2m and the height of the vertical tube is 350mm. Wheels are 400mm diameter and 150mm width. Vehicle speed is up to 10Km/hr.
This is a prototype and we just need to get it moving to brainstorm further ideas, prove concepts and raise funding.
Could anyone kindly suggest if the arrangement is OK for this purpose and what type of bearing (20mm ID on 20mm shaft, 40mmOD) would be appropriate?
Any help would be very gratefully received.
Thanks in advance.

Colin (out of date engineer)

 

[Tmoose]

I think you need to take advantage of the 80 mm OD tube (axle?) to get some bearing separation.

http://www.fixthatford.com/images/48-53 Front Axle.jpg

 

[ColinDH]

Yes, I see your point. I wondered if my approach would be sufficient for a prototype as it is a thousand times simpler than separate bearings, hence the proposal simple 20mm hole is only machining, no turned shaft, no turning of the tube for shoulders, etc.). What would be the greatest weakness of my proposal if I used tapered bearings top and bottom of the plate and I got the correct compression (these bearings rated up to 2.5-ton load)? Where would it break?

Thanks for the follow-up

Colin

 

[Tmoose]

At best the 350 mm long "stu(r)dy leg" will only as stiff as the horizontal leg of the 15 mm thick aluminum angle ( henceforth called Oscar).
The 20 mm (aluminium?) shaft will be trying its darnedest to wallow out the hole in Oscar when the 6 inch wide 100 lb wheel is in a tussle with the sandy terrain, and responding to effects of trail and whatever steering inputs are being sent down from the gear motor.
Depending on what the gear motor is anchored to, Oscar may not enjoy or be able to properly resist those inputs.
The wheel weight 40 kg. What does the rest of the chassis weigh? There may be times when the vertical load on Oscar is the full weight of the chassis and even a little more.

Are the brakes ever applied? Oscar will have to resist 100s of Nm of moment from that too.