Help with motor selection, skid steering, battery

[size=2][font=verdana, sans-serif]Hi All,

I am a total newbie to this and am committed to building a 5.44 Kg combat robot.

Basic design: It will be a four wheeler, with the 2 front wheels driving. Two motors with skid turning. Weapon is spinning wheel (vertical). Metal chassis with HCPE overlay. 6 channel R/C. Hopefully everything within the weight limit. Matches last 5 minutes.

So here goes:

**Motors
**
Can someone maybe suggest a suitable pair of 12 volt motors (I presume that 24 volts would be overkill for this weight class?). I need lightness and power because although I could have my robot be slow and strong, the organisers showed us videos of robots that practically flew across the ring so I guess they want to see violent action!I would prefer to have the motors with a right angle drive, by which I mean that I cannot mount the motors in line with the drive shaft because I do not have space enough for this. Well I could but I would need to cut away more of my chassis and it will weaken the structure.

**Wheels **

Motors apart, I would also need wheels; my design calls for a wedge shape which I want to achieve through using different front and rear wheels, so; 2 Large wheels at the back (12 cm diameter, solid rubber) and for the driving wheels at the front, 10 cm diameter wheels, also solid rubber. Not sure how these will attach to the motor shaft though!I was advised to use a material which has some slippage (or a pulley for the same reason, i.e. that in a stand off between two robots the motors do not burn out), so not sure about the wheels being rubber. Still I would prefer not to be pushed around the ring by everyone due to lack of grip!

ESC

Should I buy the ESC as a match for the motors (i.e. buy them together) or can any ESC be used?

Skid Steering

I do not understand how this works and my friends who are into R/C helicopters and planes have no idea either especially since the receiver does not feed into a servo (like with a plane or instance) but directly into the ESC. Can someone please explain how this effect is achieved and how many channels it will take up on my R/C? Do I need two ESCs? How do I wire it all together?

**Making it “Flippable” **

The idea is that the robot can be flipped by any other robot in the ring and will carry on driving even upside down. To do this I was thinking of using an Arduino Nano (for lightness) plus an accelerometer to sense the robot has been flipped. So far so good. But how do I then translate this to the ESC in such a way that “front” on the R/C remains “front”. if this works my robot will be very effective and there will be no confusion if I get flipped. Any ideas anyone?

Solenoids?

Has anyone out there used solenoids to make a robot hop away (sideways/backwards) etc if cornered or being pushed into a pit or whatever? All the ones I could find although light enough have a very short travel (typically 2 cm at most). I need 4 cm (if at front where wheels are 5 cm radius) and if at back 5 cm (maybe more because they would be at an angle, so even with an extension to their rod, its still not going to give me enough of a jump). I want to be able to HOP away… probably doable with 4 solenoids on a 5.44 Kg robot

Battery

We were advised to use LIPO. Does anyone have an idea as to what size of pack I would need for a 6 minute match (with some spare capacity for when i want to over boost the voltage?). Ideally it would power the motors and receiver plus arduino (its low consumption), plus (wishful thinking) the solenoids; although I could have separate 2 x 9 volt (so 18 volt) batteries for those to be sure I don’t drain the main one, especially as I won’t be hopping all the time!

Sorry if I overwhelmed people with my questions! Any suggestions by anyone on any of the above (not necessarily all) would be gratefully accepted, especially if (but not only) coming from people who have fought in this class before! It would be really great if people would ideally also point me to a specific model from the range available here (or elsewhere for that matter)!

Thanks all!

John[/font][/size]
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Motors
Unfortunately we don’t have a selection of right angle gear motors. Consider something like these:
robotshop.com/en/198rpm-1200 … motor.html
robotshop.com/en/planetary-g … hm-01.html
robotshop.com/en/pololu-12vd … motor.html

Wheels
If you choose a motor with a 6mm diameter shaft, you have some options. Banebots wheels are cheap and pretty durable:
Ex: robotshop.com/en/ban-135-green-wheel.html
with: robotshop.com/en/banebots-hex-hubs-s80.html

ESC
The motor controller / ESC needs to be able to provide the current which the motor will consume; in a pushing match, it can be close to stall, unless the wheels slip.
Be aware that most “ESCs” are associated with brushless motors as opposed to brushed motors like the ones suggested above.
Sabertooth series are quite popular:
robotshop.com/en/sabertooth- … river.html

Skid Steering
A dual channel DC motor controller is best, like the Sabertooth above. You need only two channels. One channel controls the motor on the left side, while the other channel controls the motor on the right side. The concept is like a tank.

Making it “Flippable”
If you plan to make it R/C, you really don’t need to implement anything electronically - when you see the robot has been flipped, realize that your left joystick controls the right side and vice-versa.

Solenoids?
Need to go through a bunch of robot combat videos… perhaps someone else has seen something.

Battery
The battery’s voltage should correspond to the motor’s nominal voltage, which will likely be 12V.LiPo can provide high current discharge which is great.If a LiPo is punctured, it’s gone… you should never charge it again. NiMh is a good option provided the current required by both motors and whatever other items you have does not exceed the battery’s maximum discharge.

Thank you! I will follow up on all links.

As regards the skid turning though, I would prefer to have a single control for left/right and one for forward/back.

Isn’t there any way of achieving this without having to control two motors through two joystcks?

regards,

John

To clarify, you’d need two axis; if that’s from one joystick up/down or the up & down from two joysticks, it’s up to you, so long as the controller can do it (“mixing”). Most R/C controllers can.

To clarify, you’d need two channels; if that’s from one joystick up/down or the up & down from two joysticks, it’s up to you, so long as the controller can do it (“mixing”). Most R/C motor controllers can, including the Sabertooth.