servo control help

[regstar123]

hello

i am planning on building an antweight bot but need some help. i will need to get some servos as my old futaba s148's take ages to do a full rotation. any tips on cheap but fast servos? also the main question. i have a spektrum dx3.0 rc car radio. if i use 2 servos as 2 independent motors controlled by the throttle is there a way when i turn the wheel one servo stops or reverses ? maybe like a variable resistor that when i turn it one way it cuts power to one side and the other side it cuts power to that one?

Many thanks

Reggie

[joey_picus]

Hiya Reggie, welcome to the world of robots

Fast but cheap servos...the vast majority of ants use geared motors and small speed controllers rather than servos now, if you're after servos (for simplicity) then I can reccommend the GWS HPXF or the Naro +F HP BB, the latter of which are available pre-modified from the RW101 shop - more info on gearmotors and speedos can be found on the RW101 forum with a bit of digging as that's where ant builders tend to congregate.
I can't help much regarding the second question as I've only ever used two stick transmitters, sorry :P

Hope that helps, what sort of ant do you have in mind to build?

[regstar123]

wow quick reply!

geared motors and esc's sound like a good idea but yeah i wanna use servos for simplicity. i plan on making a flipper robot out of either 1mm plywood or some 1mm lexan. if i can make a robot using my 3 channel spekkie then i will persuade my brother to make one aswell ans we both have 3 channel wheel radios

[banana_man]

Hi Reggie,
I have never used a 3ch radio set myself, but I guess the throttle and the wheel just take the form of two separate channels on the receiver. If so, you need to connect one servo to the throttle channel and the other to the wheel channel, and then enable some sort of V-tail mixing, be it using a plug in mixer, or on the transmitter (if the dx3 has V-tail mixing built in) This will mean that the throttle will control both servos for forward/backward movement, but the turning of the robot (reversing one or other servo) will be done by the wheel, ending up with control similar to an RC car on the same transmitter.
Hope this helps, although I may be spouting rubbish,
Alex

[daliad100]

The only problem I can forsee is that a lot of rc car controllers have 70/30 controls. You might be able to turn it off if on the transmitter or if you do eventually go to motors and speedo the sabertooth 5a has a setting for it.

The current issue is that if you center the potentiometer or replace with resistors in the normal fashion you will end up going forwards or backwards whilst the throttle is neutral because the neutral position of the servo will be 50/50.

[regstar123]

the spektrum system has 50/50 throttle. there is a channel mixer on the which i could use, but then i have no weapon control :/ would it just be easier to get a 3/4 channel stick system? like this one http://www.servoshop.co.uk/index.php...MBO&area=RADIO

[daliad100]

From their manual

2P = The 2P, or 2 position, Servo Travel function is designed to be used as a transmission gear shift channel. This feature is designed for use only with vehicles such as the Traxxas® T-Maxx. This function is accessible through the Grip Button C or Grip Dial A if Grip Button C is occupied by another function. In this function, the servo€™s travel can be selected to only three positions: left, center and right. The left and right travel values are determined by the End-Point Adjustment function, page 23.

Hence you can have a servo set up to go from full left to full right and be a flipper on channel 3.

http://www.spektrumrc.com/ProdInfo/F...30ManualHR.pdf see page 16.

[regstar123]

thanks for that. i am going to get a v tail mixer as previously suggested and will make a prototype chassis today and use my current equipment and if it fails miserably, which it probably will, i will have to get some better stuff. i like the idea of geared motors and small esc's. i might use that for the 2.0

[regstar123]

i used some old futaba servos and a old ps2 case for the chassis. i forgot how glitchy those old servos are! they were really hard to control. i have 4 of these coming http://cgi.ebay.co.uk/ws/eBayISAPI.d...EOIBSA:GB:1123 and a one of these http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=370409998848.
all i should have to do is mod the chassis slightly so the servos are back to back, the wheels i am using were outside the chassis because of the larger servos, but with smaller servos they should be inside the chassis