Weight Limit of Parallax Servos?

Oldbitcollector (Jeff)

Using Parallax Servos as drive wheels, (like the Boebot) what is
the max weight I can build before I risk damage to the servos?

Thanks
OBC

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
New to the Propeller?

Getting started with the Protoboard? - Propeller Cookbook 1.4
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
Got an SD card? - PropDOS
Need a part? Got spare electronics? - The Electronics Exchange

Mike Green

I don't really know, but think about the structure. You've got a lever arm in the form of the wheel. If there's direct force applied from the wheel shaft in the direction of the rim of the wheel, you will get increased wear in the "bearing" surface of the servo shaft which is nylon and relatively soft. If the wheels are at all splayed or out of alignment or on an uneven surface, the wheels will splay and the lever arm will tend to distort or break the nylon shaft of the servo. I wouldn't put more than a couple of pounds on them and there'd be increased wear with increased weight.

Oldbitcollector (Jeff)

Couple pounds?! Wow.. I was concerned about 1/2 -- 1pound...

I can't imagine them handling two pounds... Perhaps an "official" Parallax test is in order.

OBC

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
New to the Propeller?

Getting started with the Protoboard? - Propeller Cookbook 1.4
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
Got an SD card? - PropDOS
Need a part? Got spare electronics? - The Electronics Exchange

Mike Green

I was imagining a 2 pound box of sugar laid across my BoeBot. It wouldn't break the BoeBot, but it would slow it down and cause increased wear on the servos eventually damaging them.

erco

Depending on the load, the plastics (especially the servo shaft & coupling) can warp, take a set, and cause wheel wobble problems before wear becomes an issue, unless you store the robot on a cradle to take the load off the wheels & servos. A lot of materials (i.e., plastic, nylons, rubber) creep and get distorted while bearing long-term static loads.

Annoyingly, this includes the soft rubber tires on our Scooba floor washer. Unless we charge & store it in a raised position, the tires get flat spots that cause problems.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·"If you build it, they will come."

vampyre

is there a simple solution to take the stress off the servo? some kind of simple axle support or something?

MSDTech

What type of chassis are you using and what do you want to do with it? There are many ways to take the load off the servo drive shaft, but most of them will require you modify the system to allow additional space between the wheel and the servo.

You could install the wheel on a shaft of its own with its own bearing and use a coupling between the wheel shaft and the servo. With this type of arrangement, you might also be able to connect the wheel and servo with either a pully drive or gear drive. A pully or gear drive would allow you to also modify the wheel speed/torque to match the load you are expecting.

Another option, if you are using the BOE-Bot chassis is the Tank Tread Kit (#28106)·that Parallax sells. This bolts directly to the BOE-Bot chassis and takes the weight of the robot off the servos. The bogey wheels on the tread carry the load. The only load on the servo is the tension on the treads. Of course, this results in a much slower top speed for the system.

Without specifics of what you are using and what you wish to accomplish, it is difficult to come up with more specific possible solutions.

vampyre

MSDTech said...

could install the wheel on a shaft of its own with its own bearing and use a coupling between the wheel shaft and the servo

Thats pretty much my plan, i was just hoping for a cheapskate way of doing things that would be easier to implement. Like , maybe just using an eye bolt round the shaft of the servo to strengthen it. At the low speeds a servo turns at i think chain would be the best bet, just wanted something cheap and simple.

As for specifics, I'm planning to build a back-yard rover type bot from scratch, and at this point i'm pretty open to any design thats really really cheap. Thought someone might have a trick they use to add a lil extra weight to a direct wheel mount servo system.

iamdenteddisk

what is wrong with steping up/down with either direct drive sprocketts,or a cam and lever like a locomotive. dont forget the work of those who go before us. though I compleatly respect the solid axle to bear load I think the question was also pointed at moveing the load too. dont be constrained to just boxed or packaged kits, though it makes a prety bot like the last one I saw.
a solid axle will allow you to add a good payload but to move it uphill you might need to shift it into low gear with meshed sprockett's or even worm driven wheels . in short a solid steel axle thick enough to bare the weight of a horse can be used but unless you can move your bobot its a fine rollerskate for horsey, but with a R/C transmission setup you may just pull the bumper off that old horse. that is trail blazeing at its finest,it may require a chasis modification or even radical reworking but it end's with a more capable more powerfull bott "that is to be desired"......

iamdenteddisk

why not let the wheels spin freely on a axle,then direct drive them with meshed sprocketts this will allow payload and a step/up in tourqe without costing to much speed is there say 3/16 gap between wheel&frame?"room for 2 sprocketts to overlap"

or how about swaping the direct drive servos with wormdrive or I once made a realy cool bot useing the drive motor's & 100:1 transmission from a power wheels."it openly accepts a solid axle too".

happy building.