Servo Suitability

[thechipmunk]

May I ask if this servo (The Protech B305) would be suitable for a small biped? The main material would be aluminium.

I’m thinking of buying tomorrow morning (GMT), so a speedy reply (anything!) would be really helpful!

Thanks in advance,

theChipmunk

[italian_guy299]

From my calculations 3.5 kg-cm is equal to 48.5 oz-inch. Assuming you are making a pretty standard Biped I dont think these will be sufficient unless your making a BRAT or BRAT jr…or assuming my calculations are incorrect they may very well work

…but I doubt that

[skarim]

Ehh you’re using aluminum, my 48 oz/in servos can barely lift a small hand made of legos, I doubt that servo will be useful.

If you need cheap servos for testing, look into GWS and TOWERPRO. Tell me if you need a link. GWS offers 111 oz/in for really cheap and TOWERPRO 208 oz/in for $7.55 (5.6 euros), they arent the best in reliability but you get a ton of power if you need to mess around.

[icra]

@S. Karim

Ehh you’re using aluminum, my 48 oz/in servos can barely lift a small hand made of legos, I doubt that servo will be useful.

If you need cheap servos for testing, look into GWS and TOWERPRO. Tell me if you need a link. GWS offers 111 oz/in for really cheap and TOWERPRO 208 oz/in for $7.55 (5.6 euros), they arent the best in reliability but you get a ton of power if you need to mess around.

I’m intrested in the link too.

Thanks

[skarim]

unitedhobbies.com/UNITEDHOB … dProduct=2

beware, these servos are exactly how much you pay for. some will arrive dead on arrival, some will self destruct in 5 minutes, others will give poor feedback. they’re perfect for testing, so dont overload these sumbiatches, buy a ton of then incase one breaks.

i hear unitedhobbies is the best place for towerpro servos, because they ensure they send you ones that work. cant verify that, because before i dumed 100 bucks into 10 of these, i found out they’re not what im looking for, especially in bipeds.

you’ve been warned.

[thechipmunk]

Thanks for the replies. I’ll stay away from those, then. By the way, how exactly is it that you guys calculate how much power is going to be needed to move a limb of a 'bot?

(I’ll check those links as well, thanks!)

theChipmunk

[italian_guy299]

Formula for calculating oz-in to Kg-cm…divide oz-in by 16 to get pounds, then divide again by 2.2 to get Kilograms
then multiply by 2.54 to get Kg-cm. Reverse the calcs for conversion in the other direction.

[icra]

offtopic S. Karim I dont understand you first you tell that you can give a link with cheap servos than you tell that we have to beware.

[italian_guy299]

@icra

offtopic S. Karim I dont understand you first you tell that you can give a link with cheap servos than you tell that we have to beware.

He mentioned them as (pardone my french) “crap servos” and that they can be used to mess around with. They aren’t realiable equipment, they’re bassically used to test things by us, I would never use those in any kind of robot.

[thechipmunk]

@Italian_guy299

Formula for calculating oz-in to Kg-cm…divide oz-in by 16 to get pounds, then divide again by 2.2 to get Kilograms
then multiply by 2.54 to get Kg-cm. Reverse the calcs for conversion in the other direction.

Thanks, but I meant, if you have a certain length of limb that weighs a certain amount and so on, how do you calculate the power of servo needed?

Or maybe there’s no real way?

theChipmunk

[italian_guy299]

@theChipmunk

@Italian_guy299

Formula for calculating oz-in to Kg-cm…divide oz-in by 16 to get pounds, then divide again by 2.2 to get Kilograms
then multiply by 2.54 to get Kg-cm. Reverse the calcs for conversion in the other direction.

Thanks, but I meant, if you have a certain length of limb that weighs a certain amount and so on, how do you calculate the power of servo needed?

Or maybe there’s no real way?

theChipmunk

There most likely is, but Its most likely a somewhat difficult formula (not a standard equation).

[skarim]

@icra

offtopic S. Karim I dont understand you first you tell that you can give a link with cheap servos than you tell that we have to beware.

exactly, i said ill link you to cheap servos. its not fair for me to link you to them and not tell you what you’re messing with. you wanted cheap, you have it, we never said anything about quality here. just trying to help you out.

thechipmunk: look on societyofrobots.com robot tutorials, they have equations and everything of calculating required torque (given you know how long your limbs are and how heavy they are).

[thechipmunk]

@S. Karim

thechipmunk: look on societyofrobots.com robot tutorials, they have equations and everything of calculating required torque (given you know how long your limbs are and how heavy they are).

Thanks very much. Now to see if my GCSE Ad/Higher/Mech Maths is any good…

theChipmunk

[icra]

@S. Karim

@icra

offtopic S. Karim I dont understand you first you tell that you can give a link with cheap servos than you tell that we have to beware.

exactly, i said ill link you to cheap servos. its not fair for me to link you to them and not tell you what you’re messing with. you wanted cheap, you have it, we never said anything about quality here. just trying to help you out.

thechipmunk: look on societyofrobots.com robot tutorials, they have equations and everything of calculating required torque (given you know how long your limbs are and how heavy they are).

Yes sorry, my mistake.