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Author Topic: Mounting Wheels on Servos for Medium Weight Bot  (Read 1640 times)

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Offline CalamariDudeManTopic starter

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Mounting Wheels on Servos for Medium Weight Bot
« on: September 12, 2010, 04:04:33 PM »
Are there any guidelines on how much weight a servo can take?  I don't mean before it stalls, rather, how much downward force can there be before bad things happen to the gears/motor/case/mounting hardware?

I'm going to be using some lead acids batts, a laptop, sensor accouterments, and a three-tier lexan/aluminum chassis, which seems to me like its going to have some significant weight.  My servos will hopefully be four HS-625MG 's from servocity. 

Bottom line is, will they be fine with omniwheels directly mounted to the horns, or will an axle and bearing be necessary?

Thanks

Offline Razor Concepts

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Re: Mounting Wheels on Servos for Medium Weight Bot
« Reply #1 on: September 12, 2010, 09:01:30 PM »
For that much weight, I would recommend gearmotors instead of servos. Sure, using axle/gears with the servo is fine, but with the weight you are planning, the servos will struggle to move everything.

Offline Soeren

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Re: Mounting Wheels on Servos for Medium Weight Bot
« Reply #2 on: September 12, 2010, 09:02:49 PM »
Hi,

Servos are made in various build qualities. Some have a ball bearing (and some have two) on the axle at the business end and they can take a good bit more than those with just a brass (or even plastic) bushing of course, but most come in a plastic house, so even with bearings, there is a limit to what it will stand.
I don't think there's any guides about that, since it's an unconventional use of a servo, but if you know all the data (about bearing/bushing and housing), it can be calculated, but I guess it will be really hard to come by the needed data.

Lead/acid batteries comes in a lot of different sizes as well, so instead of us guessing, tell us the total maximum weight.
Even without knowing the precise weight, I think it sounds like you'd be destroying your servos (if they can drag all that weight around at all).

When lead/acid is involved, a DC motor and axles  of (at least ~6mm) in diameter sounds more useable.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline CalamariDudeManTopic starter

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Re: Mounting Wheels on Servos for Medium Weight Bot
« Reply #3 on: September 13, 2010, 11:35:54 AM »
I haven't actually started building anything yet, but my plan is to have two of the small batteries from UPS's.  I apologize for being pretty theoretical, but I need to come up with $600 first >.<

The robot will be indoors only on level carpeting, so there won't be a need for insane amounts of torque scaling an incline.

I used the SoR servo calculator and by its measurements I should be fine with a 25 kg cm  servo.  On that note, does anyone know if the Tower Pro 9805MG is modable for continuous rotation?  Otherwise I'll bite the bullet and get the $40 Hitec 805 from servocity </off topic>

Would it be better to not spend as much on servos and buy a different type of battery?  I freecycled the lead acid ones which is why I would like to use them.
« Last Edit: September 13, 2010, 11:39:08 AM by CalamariDudeMan »

Offline Soeren

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Re: Mounting Wheels on Servos for Medium Weight Bot
« Reply #4 on: September 13, 2010, 01:14:46 PM »
Hi,

Well, don't take our word for it then. Buy servos and learn from your mistake instead ;)
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Alfa_Zulu

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Re: Mounting Wheels on Servos for Medium Weight Bot
« Reply #5 on: September 16, 2010, 03:02:12 AM »
you really should just use geared brushed motors rather than a servo, as far as im aware some motor drivers let you control the motors with PWN similar to a servo if you'd wish. i honestly doubt a servo will be able to hold that much weight without eventually breaking

 


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