couple of questions regarding drills

[ady]

building my daughter a simple push bot for any whiteboards at the robochallenge event, 4 x drills 12volt, do you think i should use 2 x 8.4v or 2 x 9.6v packs. Also are the gears in most cheap cordless drills mostly the same? i seem to have a few broken motors that i want to try and make a few good ones out of for spares.

thanks

[ady]

Re: couple of questions regarding drills

can anyone also tell me how i work out a rought guide of amps for a 12v drill at different voltages, on 75mm wheels.

[psycho_fling]

Re: couple of questions regarding drills

i would go for the lower voltage packs, mine get warm on that but still nippy

from my expierence if its the same voltage the gears either metal or plastic will fit in other gear boxes obviously the metal ones are better

not sure what you mean with the second post?????

[cuddles]

Re: couple of questions regarding drills

http://architeuthis-dux.org/torquecalc.asp

That calculator will let you see approximate values for Amps and AmpHours for different voltages. Use the Harbour Freight drills on the drop down box.

[RogueTwoRobots]

Re: couple of questions regarding drills

If you're using 75mm wheels, I would opt for using 2 x 9.6V packs giving 19.2V total. This would run your drills at about 880rpm and with that wheel size you'd be looking at 7.5mph. Might not sound fast but in an arena, especially the Robo Challenge one, it will be perfectly nippy (enough for ramming or darting away from danger) while still being controllable.

For cheap cordless drills I believe the gear teeth numbers and ratios etc to be the same. Therefore you can chop and change gears from different motors/gearboxes for spares or repairs. The cheap drill gearboxes have one stage of metal gears and one stage of plastic gears; if you've got enough surplus metal gears, I'd advise you fit them in place of the plastic gears to make your gearboxes all-metal - helps to eliminate a point of failure in your robot.

I'm assuming your second post referring to the drill amps is to know what current-rated speed controllers you'd need for running your drills over-volted? I'm not sure exactly how to calculate it as I think drill motors are more 'eccentric' (for lack of a better word) in terms of their performance in relation to standard 550-size motors. By that I mean their performance is not as predictable and so some people tend to buy an over-spec speed controller to give them a margin of error.

I've run 4WD over-volted drill motors before and everytime I used the Electronize 30A escs with external relay mods, and they've never been put under much strain driving the four motors.

Hope that helps

[ady]

Re: couple of questions regarding drills

cheers for that people, so will go with 9.6v i think, sounds suitable for me, wasnt sure with it being 4x12v drills whether it would last the fight time for my daughter if i went with the 8.4v's,
I'm assuming your second post referring to the drill amps is to know what current-rated speed controllers you'd need for running your drills over-volted?

yeah thats what i meant, basically didnt want to blow up a 25x2 sabertooth, i have also got some fc15? i think??
they are electronize speedos with external relays.
isnt it that if you have 2 drills on one side it draws halfs the amps? say 1 motor draws 10 amps or something, 2 motors draw 5 amps each not twenty? im not too hot on that side of things, too technical.

[RogueTwoRobots]

Re: couple of questions regarding drills

The voltage you run at doesn't affect the fight time you get from the robot, that side of things is to do with the 'Ah' or 'mAh' rating of your batteries. My packs are 3700mAh and they ran a 2WD setup for about an hour at one of the Haven park shows last year. When I had the same setup running with the drum at the UK champs they didn't last as long but that's understandable with the additional current drawn from the weapon motors.

The motors drawing 10A with one motor, 5A with two motors etc only applies if they motors are wired in series. For your purpose, they'll be wired in parallel and so it'll be double the load and therefore double the current that the speed controller(s) will have to deal with. I've not worked with a Sabretooth 25A or FX15s in a 4WD setup so I couldn't say for sure how well they'd handle. I wouldn't expect the Electronizes to cope, and I'd be a bit wary of the Sabretooth blowing but I could be wrong with the latter, as my experience using them is zero/null/nada/non-existant

[ady]

Re: couple of questions regarding drills

i ran 4 x 9.6v drills with the electronizes at fw champs 2007 in the old Prodigy, but cant remember what voltage i ran them at, i think it was 2 x 7.2v or 8.4v packs..

[RogueTwoRobots]

Re: couple of questions regarding drills

If you have both 8.4V and 9.6V packs to hand, then you could always run the 4WD setup with the two 8.4V packs and if the speed controllers seem to handle it okay, move up to the two 9.6V packs, and do some moderate to rugged testing to see how they handle. If they're still going fine, you should be alright to use them.

[craig_colliass]

Re: couple of questions regarding drills

I have used the sabertooth 25A controller on a 4 drill motor setup in Tron, it did all kinds of weird stuff so I never used that setup in the arena. The sabertooth is now in Seraphim and works very well that€™s with 2 12v Como drill motors running at 14.4v this is to be increased to 16.8v soon.
In Tron which has 4 9.6V drill motors running at 14.4V I now use a Sidwinder this grabs the motors by the scruff of the neck and throws Tron around the arena with no fuss at all. I agree with the rule with 4 drill motors in a feather the bigger the speed controller the better.

[woody]

Re: couple of questions regarding drills

I have used the sabertooth 25A controller on a 4 drill motor setup in Tron, it did all kinds of weird stuff so I never used that setup in the arena. The sabertooth is now in Seraphim and works very well that€™s with 2 12v Como drill motors running at 14.4v this is to be increased to 16.8v soon.
In Tron which has 4 9.6V drill motors running at 14.4V I now use a Sidwinder this grabs the motors by the scruff of the neck and throws Tron around the arena with no fuss at all. I agree with the rule with 4 drill motors in a feather the bigger the speed controller the better.

GENERALISATION.

A featherweight bot geared for 8 mph with 18v drill motors could ...under normal fighting conditions... pull 24 amps total....[ 4 motors = 6 amps each 2 motors = 12 amps each ]
with 12v motors 32 amps total
with 9.6v motors 44 amps total

gearing for 4 mph will halve the amps required......gear for 12mph and you would increase the amps required by 50%.

Speed Controllers with built in current limiters could / will current limit continiously if your bot is overgeared.

Note that stall amps per motor can be also excessive.

http://www.mabuchi-motor.co.jp/cgi-bin/search/e_use.cgi

[ady]

Re: couple of questions regarding drills

cheers woody, so if i have 12 volt drills x 4, with 75mm wheels how can i get a indication of what amps it would draw (tried the calculator link as above but struggled.
i still need to decide 100% on what voltage to use.

[woody]

Re: couple of questions regarding drills

OK.

http://architeuthis-dux.org/torquecalc.asp

Choose the 12v harbourfrieght , 3 inch wheels , 30lb bot , 2 motors per side & 1:1 gearing.

You'll need a value for the RPM/volt ...So YOUR drills rpm divided by 12.

Let's say 500rpm as an EXAMPLE ....so 500/12 = 41.66

Read the amps values etc output by the calc.


Torque (per motor) to spin wheels 162 oz-in
Amps (per motor) to spin wheels 4.9922 Amps
Theoretical Top Speed 4.4617 MPH
Total Peak Amps 19.969 Amps
Amp Hours Required - 3 Min 0.6989 AH
Amp Hours Required - 5 Min 1.1648 AH

[woody]

Re: couple of questions regarding drills

Seems the mabuchi search link didn't work........
Here's another.

http://www.mabuchi-motor.co.jp/en_US/pr ... _0305.html

Home Appliances & Cordless Power Tools

Drill
Screwdriver
Garden Tool

RS-380PH
RS-540RH/SH
RS-550PC/VC
RS-755VC/WC
RS-775WC
RT-8B7WA


Gives an idea of the possible motor specs.

[ady]

Re: couple of questions regarding drills

ok cheers.